Adsorption-based processes play a crucial role in reducing environmental pollution and eliminating harmful substances. Common filter media materials, like activated carbon, zeolites, and metal-organic frameworks, are used to effectively purify fluids and gases for applications ranging from water treatment to air purification. A way to measure and classify the quality of adsorption filter media is to look at breakthrough curves. A breakthrough curve shows the concentration of the adsorbate in the filtrate behind the filter media, and breakthrough occurs in the moment when adsorbate shows up in the filtrate.

In carbon capture, adsorption is vital to trap and store CO₂ emissions from industrial activities and power generation, preventing their release into the atmosphere. The CO₂ may be stored or used in processes like enhanced oil recovery or synthetic fuel production. However, determining breakthrough curves for a specific contaminant often requires time-consuming and costly experimental procedures.

In this context, the use of simulations allows to precisely control experimental parameters such as temperature, pressure, and surface properties to investigate their effects on adsorption behavior – gaining important insights into the microstructure to develop next-generation filter media.

In this study, we introduce the efficient simulation of adsorption on the filter media scale using GeoDict, a powerful tool for digital material development and prototyping. The approach is to calculate the molecular movement of particles and to solve for the adsorption equilibrium step by step using Langmuir and Toth adsorption isotherms. The simulation delivers breakthrough curves for arbitrary contaminants. The method is validated against experimental data from Coker and Knox, 2014 [1].

Future developments seek to include additional adsorption isotherms and improve simulation speed. Overall, these new simulation features provide new capabilities for product development in the field of adsorption-based filtration applications.

Filtration solutions are often deployed without accurately understanding the contamination challenges of the environment to be protected. This is usually done to either implement a solution as quickly as possible, or to minimize cost by using pre-defined and readily available off-the-shelf solutions. However, this approach neither assures an efficient contaminant removal nor does it optimize cost of ownership. An inexpensive filter changed out often may be more expensive than getting a tailored, more expensive solution that lasts much longer.

The approach promoted here is the See it. Control it. paradigm, where “seeing” means measuring the contamination first in order to characterize the environment, and “controlling” means implementing a filter solution that is tailored to that specific environment. Instead of formulating a filter solution that provides equal amounts of adsorbents for different contaminant classes, we suggest adjusting the adsor­­bents such that they match the actual environmental challenge, as determined by accurate measure­ments (Figure).

Contamination control concepts detailed in this paper are specifically for filters removing gas-phase air contami­na­tion and particles, but apply equally to any other type of filtration, such as the purification of liquids, solids or slurries.

To arrive at the best characterization of the environments to be protected, an accurate and specific measurement technique needs to be applied. For gas-phase evaluation, qualitative or semi-quantitative methods are unsuitable to do so (e.g., corrosion strips or micro balances).

To measure actual concentrations as well as contaminant identification, ISO 17025 accredited lab services should be used, which are found competent for specific analyses of spe­cific environments for specified concentration ranges. Such gas-phase contaminant concentrations can range from 100s of parts per million in odor problems to single digit parts per trillion in cleanroom environments as per ISO standard 14644-8. For particle contamination, the ...

INTRODUCTION

A wide variety of process conditions and parameters influence the design of high-performance gas phase contamination control solutions such as filters to remove airborne molecular contamination (AMC). AMC filters play a pivotal role in removing harmful contaminants from air streams in commercial operations, to protect humans, products and processes. Proper filter pleat designs maximize lifetime of the filter and provide lower costs of ownership. However, it is difficult to obtain filter performance experimentally at very low contaminant concentrations due to long test times, high experimental cost and technical limitations.

Virtual prototyping using computational fluid dynamics (CFD) can minimize these limitations. The link between AMC filter performance and a predictive, numerical model is validation through testing. A numerical model is only as good as its verified performance. Physical measurements are essential to provide a sound basis, to which the model can be tuned, before it is able to extrapolate the physical measurements to calculated data.

This study will demonstrate an approach that involves validation and prediction of the removal efficiencies of AMC filters at low contaminant levels required in many industrial applications such as SEMI cleanrooms. The application introduces ...

MATERIALS AND METHODS:

In our test setups, the AMC filter is positioned in a laminar air flow zone inside a wind tunnel. The pollutant test gas is introduced in the upstream airflow. The filter is then challenged with the test gas at controlled concentrations, flow rates & test conditions. The test gas is measured in both upstream and downstream locations to measure the filter performance. Fig. 1a is a sketch of the test set up, Fig. 1b shows the model of a single layer pleated filter.

Activated carbon was chosen as the adsorbent and toluene was chosen as proxy organic contaminant with initial upstream concentration of 1 ppm. A 2D representative transient CFD model was developed with a goal to predict AMC removal at low parts per billion (10^-9, ppb) level, as the ability to measure AMC at those test levels is important to understand behavior in ...

RESULTS & VALIDATION

An unsteady 2D CFD pleated filter model was developed by ANSYS Fluent for a specific air flow rate with toluene as the contaminant. The flow was laminar and the model was based on gas adsorption processes in a porous adsorbent bed. Modeling pressure compared well with experimental values. Moreover, the flow profile offered spatial and temporal resolution of the flow which is critical in assessing local flow uniformity profiles of filter systems. The models were able to predict and validate filter adsorption capacity. Figures 2 captured the transient contaminant mass fraction progress at three different time stamps (5, 111 and 236 hours), respectively. Red and blue indicate the saturated and unused parts of the media...

CONCLUSIONS

The design of high-performance gas filtration and purification products critically rely on the sensitivity of adsorption performance to a variety of process parameters, which are often difficult to know in advance of product design. Due to the constraints of conducting experiments, a CFD methodology was developed to predict adsorption behavior and filter capacity of specific AMC pleated filters. Results indicated that ...

In recent years, there has been an increasing demand for HVAC filters with adsorptive effect resulting in the standardization of a test method for these filters and filter media in ISO 10121, Parts 1 and 2. In 2022, Part 3 of ISO 10121 also introduced a classification system for adsorptive HVAC filters. This classification of adsorptive filters is based on the results of breakthrough tests with 9 ppm toluene, SO₂, NO₂ or 3 ppm ozone on the test filters. The filters are classified according to how long the filter separates the supplied test gas with an efficiency of at least 50 %. Following the evaluation of parts 1 and 2 of ISO 10121 in previous research projects, the project reported here focuses on the third part of the standard.

An overview is provided how the results of the standard breakthrough tests are used to determine the classification result. The individual classification parameters, performance class or duty level, integrated removal efficiency, initial removal efficiency and retention capacity are presented and the practical significance of the classification parameters is explained for various filter designs (compact filters, pocket filters, filter cartridges). In addition, the challenges involved in the practical implementation of the classification tests are shown with several examples.

One of the main challenges turned out to be the practical implementation of the tests with ozone. The provision of 3 ppm ozone with air flow rates of typically up to 3400 m³/h requires high-performance ozone generators. Another difficulty is the long test duration for ozone tests which is caused by the following reason: To obtain the performance class, the filtration efficiency for the specified test gas is considered as a function of the amount of test gas added (dose) per cross section of the filter. In this way, also filters with different nominal volume flow rates and installation cross-sections can be compared with each other. The performance class is determined by the dose at which the filter efficiency falls below 50 % during the breakthrough test. ISO 10121-3 specifies dose limits that classify the filter as Light Duty (LD), Medium Duty (MD) or Heavy Duty (HD). The molar dose limits are the same for all four test substances. Since the standard specifies a three times lower test gas concentration for ozone as for the other test gases the duration of the filter test with ozone is correspondingly longer. The test times for filters with a high ozone separation efficiency and/or low volume flow rates can by far exceed one working day, which is difficult to realize due to the special safety requirements for handling ozone.

In summary, the evaluation of the pure realization of the classification procedure and the basic practicability of the tests according to ISO 10121-3 has led to a positive result. The benefits of the classification are unquestioned; for the first time it is possible to compare the performance of adsorptive filters with different geometries and nominal volume flow rates. However, the test procedure on filters is quite complex and expensive because of the required test facility dimensions, large air volumes which have to be conditioned and large quantities of test substances that have to be provided. For this reason, it was also investigated to what extent and under what conditions the tests on media samples from filters lead to comparable classifications as the tests on filter elements. The results on the significance of determining the flow rate through the media sample during the test and the reference area for calculating the area-specific dose are discussed.

As part of the health protection of employees, occupational exposure limits are set for hazardous substances, which must be complied with by the operators of plants and companies. These regulations can be achieved by a near-source capture of the emissions and a separation of the hazardous substances by industrial vacuum cleaners and dust extractors that are equipped with filter elements made of highly efficient filter materials. These materials must be tested regarding their penetration rate in accordance with IEC 60335-2-69 annex AA. The test method described within this standard uses a photometer or a suitable measuring system to determine the concentrations used to evaluate the separation efficiency. The traceability of a photometer within the scope of accreditation is difficult to implement. For this reason, a test stand using a gravimetric measuring method was established at the Institut für Luft- und Kältetechnik in Dresden. Investigations into the limit of quantification have shown, that this measuring method is sensitive enough to reliably determine the dust classes “L” and “M”. Difficulties, limitations and new developments concerning the essential filter material test will be discussed.

We have studied the effect of ageing on the efficiency of fine fiber Melt Blown.

Two grades have been selected for this study: One grade ePM1 75% and another one use in masks with BFE efficiency 98%.

These grades have been stored during 3 years in different shapes (rolls and A4 sheets) in different environments. The two environments are standard conditions (heated warehouse) and extreme conditions (in a trailer protected from weather but exposed to a large span of temperature and relative humidity).

Temperature and relative humidity have been recorded during the study. Mechanical properties and filtration properties have been measured regularly during the ageing. Whatever the conditions of storage and the shape of the samples, level of efficiency remains close to its initial value and remain well above the minimum efficiency obtained when exposing the samples to Isopropyl Alcohol vapor for 24 hours (discharge method used in ISO 16890).

This stability can be explained by....

Gas phase filtration has gained much attention due to increased pollution level, growing public awareness and issued guidelines by regulatory bodies on global air quality¹. In the cabin air segment, OEMs and filter element manufacturers demand higher removal efficiency of VOCs and harmful toxic gases, in addition to high particulate filtration targets, dust holding capacity and lower pressure drop. To address these challenges, we will describe an innovative media, that combines high-quality adsorbent layer and next-generation particulate filter layers for improved performance. This data will be supported by computational modeling.

In this study, we illustrated the media developing workflow through a case study to meet element performance and VOC removal requirements. An alternative carbon composition was engineered based on the model. Its performance was further confirmed via in-house flat sheet media testing. Finally, the optimized solution was validated through complete filter element testing.

The semi-analytical model developed in this work has demonstrated the capability to predict the adsorption performance of flat sheet carbon media and pleated filter elements for multiple application environments involving different flow rates, various upstream concentration levels, and a wide range of carbon add-on in the media.

Sorption material in gas cleaning units that serve occupational health and safety must be changed at an appropriate early stage. The instructions from the professional associations stipulate that driver's cabs must have an appropriately equipped ventilation system when used in contaminated areas. However, the standards for the sorption filter specified in the document only contain the type of filter test and no recommendations for the duration of use. The research project at the ILK Dresden aims to develop a sensor system for the safe monitoring of the operating status of a sorption device for the separation of gaseous substances from air. The sensor we develop will convert the loading status of the sorption agent into an electrical signal so that a warning message can be issued to the user or the system control when a threshold value is reached. The measurement is carried out via the electrical capacitance at a frequency and a specific measuring voltage. Capacitance/voltage converters are used, which enable a simple evaluation to be carried out. Such ICs (interdigital circuits) cost between 10 and 30 €. The evaluation unit includes the sensor unit, so they are reusable. The price also allows several sensor elements to be queried in the filter element, which means that the resolution of the adsorption front can be mapped more precisely. It is essential to record the moisture, as the water retention dominates the loading of the sorbent. This observation is confirmed by measurements carried out at the ILK Dresden on pollutant filters actually used. The filter elements used were exposed to 70% humidity and the test gas cyclohexane at the nominal volume flow. One filter element showed an immediate breakthrough with the simultaneous release of moisture into the clean gas. The sorbent is evidently saturated with water. Therefore, sensor elements for temperature and humidity are placed up and downstream of the filter. We prefer printed electronics for these sensors. Results will be discussed...

The WHO has recognized air pollution as an invisible health threat responsible for about 7 million premature deaths per year, of which 3,8 million are attributed to indoor air quality. Due to the associated link between air quality and health, the general concern about improving air quality has been significantly increased in the past years. Various air treatment technologies have gained interest, including physicochemical technologies (e.g.: filtration (HEPA), adsorption, UV-photocatalytic oxidation, ozone generator, plasma, ultraviolet disinfection and ionization) and biological technologies (e.g., plant purification methods and microalgae-based methods).

Although their performance is well defined and very efficient in specific areas, there are several limitations to consider. One of the most common problems from these technologies is that they do not cover the simultaneous removal of all pollutant types, including microorganisms, gaseous contaminants and particles. Most of these technologies do not remove any of the harmful gaseous indoor contaminants (VOCs, formaldehyde, NOx, SO₂…) and sometimes, they emit more dangerous pollutants than those they can remove. For example, the release of toxic byproducts (such as ozone) by all kinds of UV or plasma purifiers should be carefully controlled and efficiently removed. Other technologies focus on the removal of microorganisms and do not focus on eliminating gas pollutants at all. To ensure a fully effective indoor air purification, the optimal solution appears to be the combination of different technologies. Some purifiers contain activated carbon foams as a mean of removal of volatile organic compounds generated indoor or the ozone generated from the purifiers. However, the adsorption capacity and gas type selectivity of these activated carbon foams is very limited, not reaching its purpose.

For the appropriate removal of most indoor gaseous pollutants, a blend of at least two different types of absorbent media is needed. A high surface area active carbon should be used for efficient physisorption of ozone and high molecular weight volatile organic compounds (VOCs), and a different type of adsorbent, including some chemically active ingredient, such as potassium permanganate, favoring the chemisorption of formaldehyde, ketones, aldehydes, alcohols NOx, SO₂, among others, is required. Other types of adsorbents can also contribute to the removal of amines and ammonia, which when generated indoor can cause health effects associated with strong odors.

In this work, we critically review and address the limitations of the most commonly used air filtration technologies through the implementation of a novel, holistic combination of air purification systems, air conditioning systems, and physical and chemical gas adsorption systems. Laboratory test have been performed with adsorbent media with promising results in the adsorption of NOx, SO₂, and formaldehyde. This integrated approach leverages the strengths of each technology, providing a comprehensive solution that ensures both comfort and healthy indoor air.

Personal cyclone samplers have been widely used to measure the respirable mass of particles in occupational and ambient environments. In respirable dust sampling, it is essential that the cyclone cut-off characteristics be known and constant, and that each cyclone be operated at a flow rate, which produces the desired cut-off. The personal sampling methods used today comprise air flows up to 10 l/min. This work aims to develop a 20 l/min sampling cyclone that meets the sampling efficiency curve, determined by respirable convention EN481.

Based on the previous numerical study, the cyclone of the GK design showed the lowest deviation compared to the respirable convention and therefore was used for further investigation. The GK cyclone with an internal diameter of 6.27 cm was manufactured in two versions, one from steel and another from plastic by 3D-printing.

The following experimental setup was developed. Solid glass spheres Ballotini 3000 with a 2.5 g/cm³ density were dispersed into an open aerosol box by the generator RBG 1000. The generated aerosol was drawn through the cyclone sampler, then through the filter located downstream to deposit non-collected in a cyclone sampler aerosol particles, and finally through the flow meter TSI4040 and flow control valve by the usage of a vacuum pump. Particle concentration of different sizes upstream and downstream of the cyclone was measured by the aerodynamic particle sizer APS 3321. The penetration curves were calculated based on the particle concentration upstream and downstream of the cyclone sampler.

Two cyclones were tested at a flow rate of 20 l/min and the measurements were performed at two different sampling flow rates, 1 l/min and 5 l/min to reveal its effect on the results of measurement.

Compressed air filters are often a combination of different layers of filter materials. Thus the behaviour of single layers as well as different combinations of filter materials is of interest in the development of new filters.

The test of compressed air filters is described in 2 Standards, ISO 8573-1 to 9 “Compressed air –….. “ describes test methods for the classification of the compressed air quality on site. ISO 12500-1 to 4 “Filters for compressed air – test methods” describes how to characterise the filters regarding their oil mass efficiency under defined conditions in the steady state in part 1) and with regard to their fractional separation efficiency in part 3.

Looking closer into ISO 12500 itself and also the conditions of testing we find the following critical points:

• Standard conditions as e.g testing at a temperature of 20°C (@7 bar overpressure) will give a good comparison for the elements. But these filters are often used at Temperatures up to 100°C what influences the viscosity of separated oil droplets and the pressure drop curve during loading.
• A flat sheet media holder to simulate different layers of media is not given.
• The detection of particle size distribution directly in overpressure is difficult. Most of the optical particle counters cannot work directly in overpressure and a pressure reduction may lead to a change of the particle size distribution.

In this presentation we will outline the construction of a filter test bench with regard to ISO 12500-3 with direct measurement of the particle size distribution in overpressure up to 10 bar and also heatable up to 80°C.

Special care is taken in determining fractional efficiency directly in overpressure and with a pressure reduce in the sampling line. Clearly visible is a significant change of the particle size distribution

A specially constructed filter holder implemented in the bench, designed to perform different forces on the packing of flat sheet media layers to simulate a complete filter element will be discussed. Changes in the filtration behavior due to standard temperature and a temperature of 80°C are also in the focus.

The European Commission is currently discussing the importance of introducing new limit values for the exposure of employees and a limit value for welding fumes. What is being examined here is whether a general limit value for welding fumes in the Directive on Carcinogenic, Mutagenic, and Reproductively Toxic Substances (CMRD) 2004/37/EC is included in Annex I of the CMRD list. However, there are already difficulties in complying with existing limit values. The WELDOX project by DGUV still includes accurate information about welding fume concentration levels. That means concentrations in the workplace are often in the limit range of the AGW (1.25 mg/m³), but the AGW for manganese (0.02 mg/m³) is often significantly exceeded. Our measurements also confirmed this in metal companies in Saxony. What makes matters worse is that there is no test procedure to determine the separation effect of industrial vacuum cleaners for manganese. However, VDI 2262 requires this to allow clean air to return. Specifically, the clean air concentration must be a factor of 0.2 (4 mg Mn/m³) below the AGW. A verification procedure for testing welding fume separators is currently being developed at ILK Dresden.

Some applications in gas particle separation processes run at low absolute pressures, for example the cleaning of the vapour stream during vacuum drying. Surface filter media are used in this application to allow the recovery of the mostly high-quality products. So far, not much is known about the operating behaviour of filters at low system pressures. Previous studies have been limited to depth filters. The dimensioning of the filters is thus based on data for filtration at ambient pressure. This often leads to incorrectly dimensioned filter sizes. To prevent this, a fundamental understanding of the filtration processes with surface filters at low system pressures is required.

An essential parameter in gas filtration is the pressure drop of unladen surface filter media. In this work, the differential pressure of unladen surface filter media was measured for two different types of filter media with a widely differing structure at two filter face velocities as a function of the absolute pressure. The system pressure was varied in a range of 1 - 1000 mbar. Furthermore, a semi-empirical model was developed that allows the differential pressure of surface filter media to be calculated as a function of the system pressure for the entire Kn-number range...

Two new Eskom Power Stations have a total of 12 boiler units of the same design by the same Original Equipment Manufacturer (OEM). All the commercially operating boiler units make use of a Pulse Jet Fabric Filter Plant (PJFF) for particulate emissions abatement. However, the high differential pressure issues, coupled with excessive erosion began to be experienced during the first year of operation and have not yet been corrected at these sites.

This has resulted in filter bag failures and consequently unit outages for bag replacements as well as high emissions. The installed PJFF bags were expected to remain operational for 36 000 hours before needing replacement. The effect is that the filter bags fail to reach the three to four years’ expected bag life and are currently averaging a bag life of about 12 months. Full generation load is frequently unattainable due to the PJFFs and the fabric filter bags are failing with unusual frequency. This poses insecurity in production and power supply resulting in financial loss and environmental risk.

Mechanical wear and abrasion of fabric is a kind of wear experienced by fabric filters during utilization. Abrasion is the eroding away of fabric fibers or fiber surface material through moving contact between the fiber and dust particles or adjacent fibers. There are mainly two forms of abrasion, the two body or three-body abrasion. Fiber-to-fiber rubbing or fiber-to-particle collision are two-body systems.

As a measure to investigate possible improvement of plant performance, fabric filter materials that are not traditionally used within the Eskom fabric filter fleet are being considered for trials. A project has been initiated to identify high wear resistant trial bag materials to provide interim operational relief by reducing bag failures. The objective is to establish whether alternative bag options may provide operational relief. This urgent research undertaking is required to fast track the process of obtaining a solution to the high erosion condition experienced in the PJFFs.

Eskom utilises high temperature fabric with the base fibre being Polyphenylene Sulphide (PPS) while other units utilise low temperature fabric with the base fibre being Polyacrylonitrile (PAN). The potential high wear resistant material that are being tested include Para-Aramid Needle Felt Fabric, Novates^® Fabric Treatment On Needle Felt Fabric, Resiltes^® Fabric Treatment On Needle Felt Fabric and Pyroguard^® Fabric Treatment On Needle Felt Fabric.

The intention of the test is not on filtration performance but rather proving abrasion resistance; the overall air-to-cloth ratio is expected to be influenced negatively. Each alternative trial bag type is to be tested in one compartment in the first two rows of the Cells to assess performance in the highest wear zones and to limit potential impact on the air-to-cloth ratio. Trial fabric filter bags are to be installed and experimental data collected over a period of a minimum of one year; sampled every three months or up to bag failure.

All trial bag types are to be installed in different Cells during the same period to ensure that the same operational environment is experienced by all bag types. To provide reliable trial results, the PJFF plant will need to be appropriately operated and maintained in accordance with the relevant procedures during the trial. It is anticipated that the benefit of possible longer filter bag life will outweigh the potential marginal increase in differential pressure introduced by the trial filter big materials being observed.

Although the test work is still in early stages, the first batch of results are expected by the end of July 2024 and the testing will be concluded at the end of 2025.

The pulse jet method stands as a firmly established means for cleansing fabric filters. It leverages the mechanical force of a compressed air jet, generating a pressure wave that traverses the bag filter, dislodging
dust accumulation from its surface. Preceding this, an initial step entails employing Computational Fluid Dynamics (CFD) techniques to simulate airflow. With the continuous advancements in computing power and
simulation software capabilities, CFD finds application across diverse engineering domains involving fluid dynamics. Notably, CFD offers extensive data distribution, relatively economical implementation, and the
virtual capacity to simulate any flow process irrespective of complexity or scale. However, a primary challenge highlighted in prior research lies in the considerable computational demands, encompassing both processing time and memory requirements. Particularly in scenarios involving turbulent flows, the fundamental fluid flow equations derived from mass, momentum, and energy conservation principles necessitate mathematical manipulation and subsequent numerical approximation for computational handling. This process yields coefficients, parameters, and closure equations, often empirical and poorly characterized, compelling users to make subjective decisions and introducing uncertainty into simulation outcomes. Consequently, the focal challenge for CFD practitioners lies not merely in solving equations, but rather in configuring settings such as sub-models and parameters—to ensure dependable numerical forecasts. To address this, a specific parameter set and sensitivity analysis have been conducted and found to be the most accurate possible tradeoff among time and cost.

This study highlights the potential of CFD in fabric filter pulse jet cleaning. While previous research has explored CFD's role in simulating this process, it has mainly been limited to pioneering or recent investigations
of the entire cleaning operation. In contrast, this study aims to evaluate CFD's practical effectiveness as an engineering tool, focusing on accuracy, robustness, and computational efficiency...

The biggest challenge when developing filtering face pieces (FFP) is to guarantee the required level of protection while keeping breathing resistance as low as possible. For instance, the FFP2 classification according to the DIN EN 149 standard requires that at an air flow rate of 95 l/min, particle penetration must not exceed 6% and breathing resistance must not exceed 2.4 mbar [1].

The aim of the research project SULA (“Sicherer und leichter atmen”, engl.: ‘safer and easier breathing’) is to significantly reduce both penetration and breathing resistance by improving the manufacture and processing of the nonwoven fabric. Expertise from industry (Reifenhäuser Reicofil, IMSTec) and application-oriented research (Fraunhofer ITWM) is being pooled to investigate the interaction of the individual processes and their effects on the product.

For a meltblown nonwoven to meet the specifications, the fibers are electrostatically charged. In this project, the focus is on the hydrocharging technology, which is applied already during fiber production and thus promises an even distribution of the electric charge in the nonwoven.

In Part 1 of the contribution, we aim to analyze the impact of various process parameters on the charging characteristics of nonwovens, particularly focusing on the differences between electrostatic charging and hydrocharging, as this is the main driver to reduce the pressure drop resulting in lower breathing resistance for the face mask.

To increase the productivity of the filter layer the Multi-Row process is in favor to the well-established Single-Row process. Nonwovens produced by these methods exhibit distinct permeabilities and charges, affecting the quality of FFP2 masks.

Our goal is to enhance our understanding of the positive effect of hydrocharging in comparison with electrostatic charging through simulation and to adapt the superior performance of the hydrocharged single row process to the multi row process with increased productivity.

The entire meltblown process, including hydrocharging, is complex. Therefore, we are starting with modeling and validating individual aspects of the process. Initially, the water nozzle was modeled in a static airflow, simulated, and its performance validated against the nozzle manufacturer's measurements. The simulation results closely matched the actual measurements, both in terms of droplet diameter distributions and velocities. Subsequently, we modeled the high-turbulence airflow without considering hydrocharging effects and validated this model using measurements of Reifenhäuser Reicofil. Later, we incorporated the interaction between water droplets and the airflow into the model and conducted further validations. We measured water quantities at various positions of the water nozzles behind the air jet and compared these with our simulation results.

In the next steps we want to include all the effects of Meltblown process to get insight into hydrocharging process. With this knowledge we want to optimize ...

The biggest challenge when developing filtering face pieces (FFP) is to guarantee the required level of protection while keeping breathing resistance as low as possible. For instance, the FFP2 classification according to the DIN EN 149 standard requires that at an air flow rate of 95 l/min, particle penetration must not exceed 6% and breathing resistance must not exceed 2.4 mbar [1].

The aim of the research project SULA (“Sicherer und leichter atmen”, engl.: ‘safer and easier breathing’) is to significantly reduce both penetration and breathing resistance by improving the manufacture and processing of the nonwoven fabric. Expertise from industry (Reifenhäuser Reicofil, IMSTec) and application-oriented research (Fraunhofer ITWM) is being pooled to investigate the interaction of the individual processes and their effects on the product.

For a meltblown nonwoven to meet the specifications, the fibers are electrostatically charged. In this project, the focus is on the hydrocharging technology, which is applied already during fiber production and thus promises an even distribution of the electric charge in the nonwoven. The corresponding experimental investigations and the associated modeling and simulations are presented in Part 1 of the contribution [2].

This second part is dedicated to the characterization of the electret media produced and the model-based prediction of their protective effect and breathing resistance. The characterization includes basic properties such as thickness and surface weight. In addition, a workflow is being developed for the automatic detection of the nonwoven’s fiber diameter distribution, based on suitable sets of SEM images. In terms of performance, air permeability measurements as well as standard tests for the filter efficiency are performed for both flat sheet samples and mask prototypes. These experimental investigations are carried out for different aerosols (paraffin oil, sodium chloride) and volumetric air flow rates. The influence of the charging is studied by comparing the filtration efficiency for discharged samples of the filter materials with the charged counterparts. To quantify the effectiveness of the charging process, electrostatic fieldmeter measurements are performed on both sides of the flat sheet samples.

These data form the basis for the identification and calibration of models for the prediction of air flow resistance and fractional efficiency of the materials. The modeling allows for

Biobased, biodegradable, and environmentally friendly materials have shown potential to substitute fossil fuel-based polymers in production of professional grade face masks. Although there is a good chance to alleviate the stress on the environment, the biobased medical face masks need to fulfill the same approval procedures as the current synthetic products. At the same time, the manufacturer needs to be aware of quality characteristics that may relate to the biobased origin.

The aim of the study is to establish a concept for a “chain of quality” for biobased facemask manufacturing that covers the steps from in-house checks to product approval and the use and dispose of the product.

The proposed quality control concept includes checks for raw material, nonwoven, prototype, product, shelf life, use, and disposal/recycling (Table 1). The quality checks are grouped in three categories: primary and secondary checks and product approval tests. Primary checks are conducted mainly in-house by the manufacturer utilizing quick standard or alternative tests. More detailed secondary checks are conducted mainly by a 3rd party with applicable resources such as microbiology laboratory. Product approval tests are conducted by an accredited test laboratory utilizing appropriate standards like EN 14683, ASTM F2100 or YY 0469-2011 depending on the target market.

The focus of the concept is on key technical parameters that affect the manufacturability and performance of the product. Criterion for manufacturability includes processability, mechanical strength, chemical properties, and market availability. Concerning product performance, the focus is on quick, reliable, and comparable evaluation of the main parameters for protection, that is, filtration efficiency and breathability, starting from early material and prototype development phases. The key hardware is a filtration efficiency measurement system for flat sheet materials that has been successfully adopted for rapid alternative measurements of face masks and mask materials. With this approach the R&D cycle of a mask can be speeded up and a deeper understanding of features affecting filtration performance studied in a lean manner.

Various bio-based materials are available for use in medical face mask production. After careful evaluation of different options, the quality concept is demonstrated with nonwoven materials and mask prototypes made of polylactic acid (PLA) polymer.

Despite a sustained decline in pollutant emissions in Europe in recent decades, legal limits are still being exceeded, particularly in urban areas where around 90% of European city dwellers are exposed to dangerous levels of particulate matter. This exposure leads to serious respiratory diseases, lung cancer, strokes and premature mortality and shortens life expectancy in the EU by more than eight months. The average city dweller spends 90% of their life indoors, where hazards arise from emissions from building materials, furniture, textiles, mould spores and daily activities such as cooking and heating. Energy-efficient buildings exacerbate the problem as they reduce natural air exchange to minimise heat loss. Therefore, the demand for efficient and less energy-intensive methods of air treatment is growing.

One way to optimise the energy efficiency of air filtration is to use an electric ioniser to charge the particles. This charging has the great advantage that electrically charged particles improve the separation efficiency of downstream mechanical filters (electret filters) or electrical filters (electrostatic precipitators). In this way, significantly lower pressure losses and therefore energy-efficient filter systems can be realised. However, until now such electrostatically enhanced filter systems can only be used to a limited extent due to the power-dependent ozone emission and the long-term decreasing stability of the corona discharge (due to wear and contamination of the high-voltage electrodes). The wear behaviour of the electrode is the result of a complex combination of physical and plasma-chemical phenomena. These phenomena include oxidation reactions of the atomic oxygen and the emitted ozone with the electrode surface as well as ion- and electron-induced sputtering, in which high-energy particles collide with the electrode surface. These wear phenomena are also superimposed by deposits and soiling on the electrode. During prolonged operation, these effects can significantly change the electrode geometry and therefore...

AeroSolfd is an EU co-funded innovation action developing retrofit filtration solutions as a fast track to cleaner urban air. A particular focus is on developing, installing, and testing filtration devices for improving air quality at metro stations. Per day more than 100 million people are commuting by metro. Metro networks are the backbone of the economy in bigger cities and contribute to reducing inequality by affordable transport options. However, the semi-closed environment of a metro station, in particular underground, is usually not primarily designed considering air quality and studies confirm it by demonstrating that concentrations of respirable particles in metros and their stations are high, and usually higher than those in the ambient environment (e.g., Martins et al., 2015). Providing good air quality, both inside trains and at the stations, is a key and challenging objective of metro operators. Primary local sources of particle emissions are brakes and rails. But there are many other factors influencing the air quality (e.g., the design of station, ventilation systems, trains’ frequency, etc.). Studies show that each station is different. Nevertheless, a flexible, scalable filtration solution to be installed as ‘retrofit’ at the platform would be a promising option for improving air at existing and new stations.

The 3-year innovation action AeroSolfd started in May 2022. First results can now be reported: The design of the air purifiers has been updated for use at metro stations. Emissions of metro brakes have been analyzed to find a good tracer. Air purifiers have been installed at a metro station in Lisbon. We are going to report on the progress, present and discuss the setup at the metro station in Lisbon as well as results on air quality measurements.

Indoor air pollution is a complex issue involving a wide diversity and variability of pollutants that threaten human health. For creating a healthy indoor environment, it is important to start with the control of indoor pollution sources. Most of the time it is impossible to control the pollutant sources, making it necessary to use filtration technologies. These technologies consume a considerable amount of energy to provide a comfortable indoor climate. This review presents a general overview of existing filtration technology, evaluating, their effectiveness in improving air quality while considering energy efficiency and economic factors. Additionally, the review provides insights into how diverse filtration techniques use energy conversion to mitigate various indoor air pollution, showcasing their advantages and limitations, and paving the way for future solutions that prioritize energy efficiency and optimal indoor environments.

The study explores the intricate relationship between filtration efficiency, pressure drops, and energy consumption in heating, ventilation, and air-conditioning (HVAC) systems. The findings reveal that while...

Ventilation plays a critical role in mitigating the airborne transmission of exhaled virus-laden aerosol particles in indoor environments, particularly underscored by the recent COVID-19 pandemic. Strategies such as more frequent natural ventilation, higher fresh air ratios in mechanical ventilation systems, or decentralized air purification technologies have proven effective in reducing the indirect risk of infection indoors. However, when maintaining thermal comfort, these strategies also lead to higher energy consumption for heating, cooling, and air circulation. This presents a challenge, as the effort to eliminate potentially infectious airborne particles indoors conflicts with the objective of increasing energy efficiency within buildings.

To address this problem, novel approaches are required that take into account not only air quality based on CO₂ concentration and thermal comfort, but also the risk of indirect infection by virus-laden aerosol particles and energy expenditure, when designing ventilation concepts for occupied spaces. In this context, we present an analytical model that can be used to assess both the spatiotemporal probability of infection based on a Wells-Riley approach and the spatiotemporal air quality based on the analytical CO₂ concentration in indoor spaces. Experiments and flow simulations using a representative test aerosol that mimics infectious exhaled particles inform this model.

By combining different ventilation measures, including natural ventilation, stationary ventilation systems, and mobile filtering air purifiers, we aim to reduce the concentration of airborne pollutants in occupants' breathing zones while partially substituting fresh air with purified recirculated supply air. This approach minimizes ventilation heat transfer and mechanical energy demand while allowing for compliance with thresholds for air quality, thermal comfort, and infection probability. We vary operating conditions of ventilation measures, such as employed filter classes, air purifier locations or volume flow ratios, to assess their impact.

To correlate the impact of operating conditions on energy expenditure, we determine the analytical energy demand in a steady energy balance, assuming optimal operative temperatures for maintaining thermal comfort. By partially substituting fresh air from an HVAC system with filtered recirculated air from a mobile air purifier, significant ...

Post SARS-COVID-19 pandemic, higher MERV-rated filters are increasingly used to capture airborne contaminants, but their integration into existing HVAC systems often results in elevated airflow resistance, complex installations, and increased maintenance requirements. These factors contribute to higher capital investments and operational costs, posing challenges to widespread adoption.

This study introduces the economic impact on energy usage in a typical office building using a patented silver-graphene oxide (AgGO) coated MERV-A 9-A (M9AZG) versus a regular MERV-A 9-A (M9A). Such estimations are derived using the particle filtration and viral filtration efficiency (VFE) results of M9AZG and M9A.

Experimental analysis using Phi6 as a surrogate virus demonstrates that M9AZG filters achieve an average increase in viral filtration efficiency of 57.7% over six months under typical dust loading conditions, compared to equivalent uncoated filters. Notably, the VFE improves with progressive dust loading, M9AZG filters achieving an efficiency of 83.6% versus 55.2% in control filters after six months. This indicates the coating's sustained effectiveness despite particulate matter accumulation on the filter surface. Through the particle filtration efficiency testing, it was confirmed that the coating did not clog the filter and the pressure drops exhibited by these filters were the same as the uncoated filters.

While the mechanism of action is still not fully understood, AgGO is perceived to be enhancing the mechanical filtration phenomenon, along with enhanced attraction from positively charged silver particles. In terms of mechanical filtration: impaction, interception, and diffusion, we believe the latter two are more pronounced as the coating forms rough microstructures and increases the surface area of the filter fibres. This dense porous-like matrix could then be increasing...

Heating, Ventilation and Air Conditioning (HVAC) units utilize a significant amount of energy in our buildings, hence improving energy efficiency and reducing the cost of ownership is particularly important. The importance of energy savings is reflected globally. For example, the European Union has agreed on a set of measures to make Europe a carbon neutral continent by 2050 (1). As 40 % of the annual energy-consumption in Europe is generated in the building sector (2), it is no surprise that one set of initiatives of the European Green Deal is built around energy efficient buildings. In an HVAC system, savings can come from better fans, better heat exchange or energy efficient air filtration. In this paper, we will address solutions to improve the energy efficiency of the filtration media using novel nonwoven solutions.

Traditionally, single layer and dual layer media have been used to achieve efficiency and capacity of pocket filter media. However, for energy savings, pressure drop of the filter is the key parameter. Hence, 3D composites using waved media have been developed to reduce pressure drop and increase capacity. An example from our data analysis showed that waved 3D filter media can achieve up to 4 times higher Dust Holding Capacity (Lifetime) at 250 Pa filter element pressure drop compared to traditional pocket filter media. In summary...

The gravity-driven drainage behavior of coalesced oil has been extensively characterized in fine porous coalescence materials, showing that oil drains in a (partially) closed film at the rear side, whereas intraporous drainage is negligible in such materials. In industrial applications, a structural support structure and a drainage layer (a.k.a. entrainment barrier) are often placed behind the coalescence material.

These components introduce additional interfaces that can alter drainage behavior, potentially leading to interfacial drainage paths along the gaps of the interface. Furthermore, contrary to fine-porous coalescers, the open porous structure of the drainage material can present an intraporous drainage path. This research aims to obtain a fundamental understanding of the drainage behavior of coalescing filters in real applications.

A novel filter chamber will be designed with partitions to distinguish between and measure the intraporous, interfacial film, and rear-side surface film drainage streams. The filter chamber requires oil outlets at different and precise positions to measure the various drainage rates. This study will investigate how the drainage behavior is influenced by the properties of the drainage material (e.g., mean pore size, thickness) and the support structure, along with process parameters (e.g., face velocities, oil delivery rate)...

This work presents a novel demister which combines the principle of a swirl or cyclone separator with the micro-impaction principle, i.e., inertial impaction on the micro-scale. The latter was already investigated by Kaiser (2020) for planar droplet-laden flows through woven wire meshes with weft and warp wires aligned perpendicularly and parallel to the flow direction, respectively.

Kaiser’s work showed, that separation performance of wire meshes can be significantly increased by a shallow inflow angle with respect to the wire-mesh plane, while at the same time only moderately increasing pressure drop across the mesh. The present work aims to synergetically combine the prescribed separation effect with that exploited in cyclone separators, i.e., centrifugal separation in swirling flows (Dwars and Mehring (2024)).

To that extend, numerical flow simulations were carried out for a 7.7 degree periodic sector of a cylindrical flow cell with prescribed swirl in the incoming axial flow, as shown in Figure 1 (left). The droplet-laden swirling gas stream is allowed to flow radially outward through a cylindrical square wire-mesh along the height of the flow cell. At its outer radius, the flow cell is limited by a wall diverting the flow in axial direction.

Simulations are based on the steady-state incompressible RANS equations with SST k-ω turbulence model (including curvature correction) and Lagrangian description of the disperse phase using a random-walk model for turbulent dispersion. Numerical solutions were computed using the - ANSYS Fluent Version 2022R1. A contour plot of the calculated velocity magnitude in a q=const. plane is shown in Figure 1 (right).

Numerical simulations show that, depending on flow cell geometry and operating parameters, low flow angles through the wire mesh can be maintained and the benefit of inertial droplet impaction can be preserved even at through-flow directions not aligned with weft or warp wires.

Experimental comparison of pressure drop and separation efficiency for a properly tuned modified separator geometry (consisting of the flow cell with an integrated swirler) and a unidirectional cyclone (with identical swirler-blading but different swirler-core and a downstream cylindrical section) were carried out. A white-light aerosol spectrometer (Palas WELAS digital 3000) was used to determine particle size distributions in the upstream and downstream flows. Information on the geometry of the two separators is summarized in Table 1. Experimental results for a mean axial inflow velocity of 16 m/s are illustrated in Figure 2. The cut size diameter x50 of the new separator is found to be 40% lower than that of the unidirectional cyclone, while at the same time yielding a pressure drop reduction of nearly 50%. In addition, the new mesh-type swirl separator is 50% shorter than the comparable typical axial flow cyclone design.

Biomass pyrolysis can produce charcoal for several applications. For example, the “Biomet” project studies how to transform the wood waste of the furniture industry into a renewable carbon-rich char for metallurgical use.

Along with char, biomass pyrolysis produces a gas (syngas, formed by hydrogen, carbon monoxide, methane, and other incondensable) and a condensable liquid. Upon cooling, the latter yields an ultrafine aerosol whose separation is required to obtain a clean gas, reduce environmental pollution, and turn it into a resource whenever possible. The liquid obtained from slow pyrolysis (also called wood vinegar) can be considered a high-value by-product in the preparation of biochar by biomass pyrolysis. As a natural fungicide, wood vinegar has great potential to control plant disease, achieve more sustainable agriculture, and avoid the massive use of pesticides.

We present some experimental results obtained employing a slow pyrolyzer operating with a closed-loop principle to produce metallurgical char and slow pyrolysis luquid and relatively clean syngas. The FumeCatch reactor adopts an innovative cooling-down principle and a cyclone to maximize the separation of condensed vapors. It cools down suddenly the pyrolysis fumes, mixing the hot flow with a recirculated cold fraction. This way, we can study the effect of the cooling and cyclone collection efficiency on yield and composition in the pyrolysis liquid. Aerosol collection efficiency was quantified, showing cyclone geometry’s and operating parameters’ important effect on the collection efficiency.

Quantifying and analyzing this new technology’s prototype output showed some promising results. The biochar yield ...

Water constitutes most bio-oil, accounting for 67% by mass; the remaining 33% comprises various chemicals (acetic acid, levoglucosan). According to the results...

A continuous filtration process that starts with a new, particle-free filter medium usually goes through the following phases: The initial depth filtration in the given filter medium, the clogging phase in the given filter medium and the cake-forming filtration on the surface of the filter medium. Until now, these phases have been described using different modelling concepts, which make a holistic view of the entire filtration process difficult.

In a new holistic view of the entire filtration process, the traditionally distinct phases are to be described with the aid of a coherent model. According to this model, particle separation takes place during the entire filtration process in two coexisting filtering systems: In the case of a fiber layer as a filter medium, a fiber packing represents the one filtering system. All particles deposited in and on the fiber packing are regarded as the other coexisting filtering system, in which all these particles can be described together in the form of a granular-bed.

Model calculations can be carried out on this basis. An important aspect of this modelling approach is the investigation and corresponding description of the particle quantities separated by the two filtering systems. These assigned quantities of the separated particles by the respective filtering systems change with the filtration time both in their absolute quantities and in the form of a ratio.

Suitable experimental investigations are carried out to verify the corresponding model calculations. In microscopic in-situ investigations, serial images of the continuous loading process in real filter media are taken, which are used to document the changes in the loading status in small steps. The desired information is to be obtained by subsequent image analysis. The first results...

Numerical simulations can aid in the development of more efficient air filters, not only by increasing separation efficiency and reducing air-flow pressure drop but also by enhancing filter loading capacity thereby increasing resource efficiency. However, in order to correctly determine time-varying performance parameters, an accurate representation of the filter media structure and a sufficiently accurate physical numerical model are required.

In the present work, particle deposition on a single filter fiber (representing the smallest unit of a fibrous filter media) is investigated. A two-step simulation process is used based on the coupled CFD-DEM approach; the latter employing OpenFOAM-8 as flow solver and well-established DEM contact models, which include adhesive/cohesive force interactions and a suitable set of DEM model parameters for the investigated particle/fiber system. In the first step, the flow field around the fiber and deposited particles is solved in a resolved fashion using the immersed-boundary (IB) method.

From this, the force and moment vector acting on each deposited particle due to aerodynamic interaction is computed by integrating viscous stresses and pressure over the particle surface. This information is used in the second step in which the deposition of particles (newly admitted to the flow field) on the existing fiber/particle structure is computed. The particles are propagated within the already computed flow field (via one-way coupling) while taking into account contact forces between all particles (free or deposited) and between particles and fiber. Aerodynamic forces acting on the free particles are computed using a simple drag-model whereas aerodynamic forces (and moments) acting on deposited particles are retained from the previous step. Particle-particle and particle-fiber interactions are solved directly by the employed DEM algorithm. Subsequently, the first step is repeated including now the newly deposited particles.

Using the prescribed two-step procedure, the deposition of polystyrene particles on a single filter fiber is investigated at various Stokes numbers in the inertia and interception regimes. Considered is a straight fiber under cross-flow conditions with particles being admitted to the gas stream at low volumetric concentration.

The present investigation shows that, depending on the Stokes number different morphologies of particle deposits result. Predictions are found to be in good agreement with experimental observations. More importantly, the present numerical results provide important insights into the dynamics of deposition formation not captured by other simplified approaches such as the frequently employed “stick on first contact” model for particle/particle and particle/fiber interaction. For example, simulation results for the case in which particle dendrites are formed reveal the ...

Nanofiber media have shown great potential as a filtration material, both for surface and depth filtration, outperforming traditional fibers in energy efficiency and filtration performance. Due to their large specific surface area by volume, nanofibers significantly increase the chances for smallest aerosol particles to adhere to the fiber surfaces, thereby achieving high filtration efficiency for particles of the Most Penetrating Particle Size (MPPS) at minimal pressure loss.

The deposition behavior of submicron particles on nanofiber structures remains an active area of research. Understanding this phenomenon is crucial for optimizing the performance of nanofiber filter media, such as enhancing their dust holding capacity while minimizing pressure loss across the filter.

In previous numerical studies, numerous authors modelled particle deposition on nanofibers based on the assumption that a particle predicted to collide with a fiber or an already deposited particle will adhere to the fiber/particle (so called "stick-on-first contact" model). For submicron-size particles, this assumption, i.e., no particle rebound upon initial contact might be acceptable. However, the assumption of "frozen deposition", which neglects the movement, dynamics and interaction of the deposited particles, is not able to accurately predict the formation of particle dendrites or agglomerates [1][2].

Once a sufficient number of particles has been deposited, detachment of particulate aggregates or agglomerates can occur, even in the case of submicron-size particles [1][3][4]. While this phenomenon is difficult to observe experimentally, it can be studied by means of numerical simulations using a calibrated set of DEM model parameters while resolving the flowfield around each particle.

Accordingly, the present investigation employs a four-way coupled and fully resolved CFD-DEM simulation methodology based on the Immersed-Boundary (IB) method, to investigate the deposition of submicron-size particles on a representative nanofiber structure while allowing for detachment and re-entrainment of particles and particle agglomerates. Figure 1 depicts initial simulation results reveal different phases of the deposition process, i.e., initial deposition of particles on bare fiber (Fig. 1A), formation of particles agglomerates (Fig. 1B), and bridging between these agglomerates (Fig. 1C), eventually leading to clogging of the filter medium...

Crossing of the nanofibers plays a crucial role in the observed “bridging” phenomena between deposited particle structures. The particle bridges act similarly to individual nanofibers by providing additional surface area for further particle deposition. This phenomenon can significantly influence ...

The aim of optimising the operating behaviour of surface filtration is to maximise the filtration time for dust separation. This is achieved by a slow increase in pressure drop during filtration and a low residual pressure drop after regeneration. These parameters can be specifically influenced by raw gas conditioning. The effect is improved energy efficiency and longevity of the filter system.

A positive influence on the operating behaviour is possible, for example, by increasing the cohesion in the cake layer for improved regeneration. The influence of gas humidity on cohesion and regeneration is known from the literature. However, the complexity of the influence of gas humidity on particle bindings and regeneration only allows targeted influencing to a limited extent. Reinforced bindings between the particles in the cake layer with increasing humidity can be considered favourable. A concomitant increase in the adhesion of the cake layer to the filter medium, on the other hand, is to be categorised as disadvantageous. The concept presented here utilises the deliquescence and efflorescence properties of salt particles to increase cohesion without necessarily increasing adhesion.

As part of the study, the influence of hygroscopic salt particles in the dust cake on the operating behaviour of surface filters was analysed using a filter test rig in accordance with VDI 3926-1. The test rig allows each filter medium to be subjected to a defined mass concentration of a dispersible powder. Furthermore, it is possible to additionally filter airborn dry salt particles and to influence the raw gas humidity by modifying the test rig.

The aim of the investigation is to determine whether the operating behaviour of surface filters is actually improved over a longer process duration when this conditioning concept is used. Based on screening and standard tests carried out, evidence was provided of a significant improvement in cake detachment due to favourable process conditions. In addition to determining ...

Surface filters are used in various technical processes to separate particles from a particle laden gas stream. The particles are mainly separated on the surface of the filter medium and on the surface of the already formed dust cake. A main focus in the operation of surface filters lies on the particle emission and the stable operation of the filtration plant.

Besides widely-used flat filter media (e.g. bag filters), folded (pleated) filter media can be applied to increase the theoretical filtration area. When applying pleated filter media or pleated filter elements (e.g. cartridge filters), certain problems can occur during operation, such as insufficient regeneration or an unstable operation of the filter. These problems can mainly be attributed to the pleats of the filter media or the pleating process itself.

The pleating process can lead to differences in media permeability and thus a homogeneous flow through the entire media is not possible. The inhomogeneous flow can result in velocity gradients between the pleats and lead to a loss in effective filtration area. Besides the arising problems due to manufacturing, the filter operation can be influenced by certain geometrical aspects. An increase in the pleat density (pleats per area) results in an increase in theoretical filtration area, but the effective filtration area does not follow the same trend. This is due to a few factors, such as insufficient regeneration of the pleat bottom. The insufficient regeneration leads to blockage of a certain filtration area and as a result to a reduction of effective filtration area. The loss of effective filtration area increases the mean filtration velocity and leads, assuming a Darcy pressure drop model, to an increase of pressure drop. The increase of pressure drop and the blockage of pleats can hinder stable filter operation.

The main focus of this contribution is the experimental determination on the influence of pleating and of different pleat densities on the operating behaviour of filter media in a filter media test rig ....

Stairmand's cyclone separators are highly valued in multiple industries for their exceptional effectiveness in separating solid particles from gas streams. Their effectiveness arises from the vortex created within the cyclone, enabling the separation of particles through centrifugal force. Nevertheless, the formation of this strong vortex motion produces a significant drop in pressure throughout the device. Cyclones with lower pressure drops are essential in applications where energy consumption is a major concern. This work explores the use of computational fluid dynamics (CFD) and design of experiments (DoE) to optimise a Stairmand's cyclone separator with the goal of minimising energy consumption.

This study utilises Ansys Fluent as the simulation platform for the CFD simulations. The Reynolds stress turbulence model is employed in conjunction with second-order numerical schemes to improve the accuracy of the simulations. The CFD simulation results for the base case are compared to experimental data obtained by Hoekstra using laser Doppler velocimetry (LDA) and pressure drop measurements. The outcomes of the CFD simulation fall within the expected range of experimental error.

The DoE involve varying several key dimensions of the Stairmand's cyclone separator. The dimensions encompass the overall height of the cyclone, the height of the cylindrical section of the cyclone body, the diameter of the vortex finder, the height of the vortex finder, and the cone tip diameter. A total of 28 simulations are conducted. The dimensions in these simulations are varied using the face-centred central composite design methodology.

The investigation indicates that the diameter of the vortex finder is the most significant factor influencing the pressure drop in a Stairmand's cyclone separator. In contrast, the remaining parameters have a significant smaller impact on the pressure drop. In order to assess the overall impact of the dimensions, a response surface methodology, in conjunction with the screening method, was utilised to determine the most optimal design. As a result, the optimal design succeeds in achieving a 40% decrease in pressure drop compared to the original Stairmand's cyclone separator.

In order to assess the effectiveness of the optimised design, a physical test specimen is manufactured using additive manufacturing and then evaluated on a specialised test rig. The experimental results show a strong correlation between ...

Cross-flow filters are used in exhaust gas after-treatment sytems of modern combustion engines to separate ash and soot particles from the exhaust gas stream. The filter consists of parallel porous channels positioned lengthwise in the exhaust system with alternately blocked ends. The particles are deposited in the inlet channel and form a layer while the gas passes through the porous filter wall to the outlet channel.

The ash and soot particulate layer deposits can lead to unfavorable operating behavior. For example, the pressure loss of the filter increases with increasing layer thickness. The filter must therefore be regenerated regularly (continuous passive C-NO₂ or discontinuous active O₂ regeneration), whereby the hot exhaust gas oxidises the deposited soot particles.

The break-up of the particulate layer is a crucial process that depends on the temperature and the velocity of the exhaust gas, as well as the composition of the layer and the reactivity of the soot. The influence of temperature and velocity has already been sufficiently investigated.

However, the impact of the particulate properties and their reactivity on the resulting ash deposition patterns following the regeneration of the particulate filter remains uncertain. Studies on soot particle sizes have shown a correlation with high reactivity. E-fuels and biomass fuels can also produce different types of soot with different reactivities and dispersities.

In this study, the layer-break up of Carbon Black as reactive particulate material during the regeneration of the filter is investigated to observe the fundamental processes and transport of agglomerates in cross-flow filters. To achieve this purpose..

In recent years, the focus on air quality and its impact on human health has become increasingly prominent. Efficient filtration for vehicle cabins (Cabin Air Filters) is considered as more and more important.

A Smart Cabin Air Filter System has been developed to provide drivers with the best possible protection from pollutants in the car cabin. This system includes up to three different filtration stages: a pre-filter, a HEPA filter and optionally a state-of-the-art cabin air filter in the air conditioning system. Additionally, the system is equipped with particle sensors to measure PM2.5 concentration inside the vehicle and in the ambient air, as well as CO₂ sensors to monitor the CO₂ levels inside the car. These sensors control the proportion of fresh air and the operation of the HEPA filter to achieve the best air quality in the cabin while optimizing energy consumption.

The development of suitable filtration materials for this purpose should not only be based on laboratory tests according to DIN 71 460. Additional field tests are essential to achieve optimum results for the development of efficient particle filtration. Thus, an electric demo car was equipped with such a system to prove its functionality and effectiveness in the field.

Proof-of-concept studies in vehicle air conditioning, especially for comparative tests of suitable filter materials, are strongly dependent on a stable size distribution of the ambient air aerosol in order to ensure comparable conditions for the tests. However, the ambient conditions in road traffic are highly variable, even on the same route and stable weather conditions, which significantly limits comparability.

To build a bridge between standardized laboratory tests with monodisperse aerosol according to DIN 71 460 on filter elements and tests in the air conditioning system or filtration unit of a vehicle in the field, tests with the Smart Cabin Air Filter System were carried out in the vehicle in a climatic chamber. These stationary tests were conducted with simultaneous measurements of PM2.5 and ultrafine particle concentrations.

For this purpose, an artificial aerosol with a similar size distribution compared to the ambient aerosol was generated. Many years of experience from field tests in various driving situations formed the basis for this artificially generated aerosol with a mixture of sodium chloride (NaCl, many very small particles, but hardly any particle mass) and ISO fine dust A2 (high number of larger particles, high particle mass PM2.5 / PM10). The aerosol was supplied into the test chamber ....

According to the world health organization, air pollution is currently the greatest environmental risk to human health and is associated with around 7 million premature deaths each year. According to the German Federal Environment Agency, traffic is a primary contributor to poor air quality, especially in urban areas. Although legally binding limit values have to be met at official measurement stations, particularly in places where the exhaust air from ventilation systems of parking garages or metro stations is discharged without being filtered, higher levels of pollution can locally occur. There are no clear rules on how to deal with air pollutants in these areas, but there is a great need for efficient mitigation measures.

Biological air purification with plants has various advantages over technical systems. One of these are lower prices compared to the acquisition and operational costs of technical systems. In addition, certain pollutant groups can be partially degraded and metabolized by plants instead of just being stored. In an urban context, there are other positive effects of planted systems. These include for example the retention of rainwater, a climate-regulating effect and an increase in biodiversity. Finally, the biodegradability of the plants leads to a more sustainable circular economy...

Plant-based filters such as moss walls have been partially implemented in the past in urban areas. However, their efficacy was rather low especially due to the fact that the polluted air did not pass the filter structure, but was just in diffusive contact with the surface. Furthermore, the filtering materials could not be installed near the source of the pollutants, but typically on sidewalks, where concentrations were already strongly diluted. Thus, the aim of the publicly funded project BioLu is to develop a plant-based filter which can be used to clean the exhaust air from parking garages, which has been shown to contain a large variety of particulate and gaseous pollutants, mainly originating from the vehicle exhaust as well as tire and break wear. The filter shall be capable of being retrofitted to existing ventilation exhausts and directly penetrated by the exhaust air in order to maximize its efficacy.

An efficient plant-based filter medium needs to be constructed from at least four different layers: ...

In a first step, suitable individual layers for all stages of the filter were tested with respect to their filtration efficiency and air flow resistance. The results were fed to a self-developed calculation tool to predict the most promising candidates for a layered structure. Those combinations were then tested under realistic flow conditions to find the best compromise between filtration efficiency and pressure drop. The media were tested under dry conditions as well as fully saturated with water since both states can occur in the later application. First results show that the optimized layered structures can filter at least ...

In the next step, the project partner NIRA will establish large trial plots with the optimized combination of the materials and plants. The best procedures for laying the vegetation carrier on the field for pre-cultivation as well as for care, irrigation and harvesting will be investigated. Cuttings from the plant-based filter medium will then be exposed in a custom-built test rig to typical outdoor conditions (i. e., sunlight, rain, different temperatures, etc.) while a continuous air flow is passing through it like in the later application on the ventilation exhaust of a commercial parking garage. Changes in the filtration efficiency and pressure drop as well as the resistivity of the plants to these conditions will be regularly monitored.

The project BioLu is supported by the Federal Ministry for Economic Affairs and Climate Action (BMWK) on the basis of a decision by the German Bundestag.

There is currently growing appreciation for the positive impact of urban green infrastructure in society and politics. However, reliable figures are needed to justify the design of green living spaces.

The metrological proof of a significant reduction in the concentration of fine dust in the ambient air through plants was achieved through our own preliminary work on a laboratory scale. In practice, the use of the classic upwind-downwind measurement is difficult due to frequently occurring unstable wind conditions.

A possible solution is the use of a large number of cost-effective, freely programmable, interconnected multi-sensors. The sensors are distributed around an area to be assessed. They independently determine their role in the upwind-downwind system depending on the wind direction. Using this setup, the ecosystem-performance of the plants in the area is calculated.

In order to test the project idea on a laboratory scale, a height-adjustable test facility was designed and built in-house with different planting from Helix Pflanzensysteme GmbH.

The focus was on the question of the accuracy and repeatability of the measurement results obtained with smart multi-sensors. The evaluation of the operational performance of the low-cost multi-sensors developed by HANZA Tech Solutions GmbH compared to the professional reference devices was carried out in the laboratory facility in the presence of test plants.

Fuel cells are basically considered as a green technology addressing the high demand for a sustainable and climate friendly mobility. Without the use of fossil energy, fuel cells provide electrical energy by the electrochemical reaction of oxygen (O₂) of the environmental air with hydrogen (H₂) of the storage tank in the vehicle yielding pure water as the final product. However, since environmental air comprises a wide variety of different gases, some of them negatively affecting the functional performance and the life time of fuel cell stacks, the incoming air must be selectively filtered before entering the fuel cell stack. Basically, air filtration makes use of adsorbents that capture target gases by physisorption and chemisorption, both depending on environmental influences, like relative humidity (i.e. water molecules), air temperature and gas concentrations. In terms of cathode air filtration, the interplay between temperature, water molecules and gases and their interaction with the adsorbent is poorly understood under long term conditions, but mandatory for developing tailored filtration materials. Especially, gaseous air pollutants, such as ammonia (NH₃) and sulfur dioxide (SO₂), were shown in the past to have a negative impact on the functional integrity and on the life time of fuel cell stacks.
In this study, the gas concentrations of ammonia and of sulfur dioxide as well as the environmental air temperature and relative humidity should be continuously monitored for a long period of time, thereby receiving a sophisticated image of environmental conditions. Therefore, dedicated sensors will be installed into a container that is located in a highly frequented street in Ludwigsburg, Germany. Furthermore, besides detection of environmental conditions, a gas adsorption filter, intended for protection of fuel cell stacks, will be additionally mounted into the same container and the ammonia and sulfur dioxide concentrations after the gas filtration step, i.e. on the downstream side of the filter will be detected in situ as well. The results of this approach will enable...

Solid state batteries (SSB) are considered a promising future technology in the field of energy storage. In contrast to conventional lithium-ion batteries, they use solid materials instead of liquid electrolytes, which can lead to a higher energy density, improved safety and a longer lifetime. To this end, a jet-based direct mixing process in the gas phase for mixing, coating and agglomeration of cathode materials for SSB was proposed and realised to improve the homogeneity and electrochemical properties of the battery materials. In the method used, the various particle systems lithium iron phosphate (LFP), carbon black (CB) and lithium halide (LIC) are dispersed in the gas phase. The materials are then brought together as particle-laden aerosol jets in a turbulent mixing zone in which the different primary particles can interact with each other and form hetero-agglomerates. The microstructures produced in the process are analysed using scanning electron microscopy in combination with focused ion beam (SEM-FIB) and the resulting material functions are characterised by measuring the electrochemical properties (e.g. electronic/ionic conductivity, specific capacity). Furthermore, a laser light diffractor and a cascade impactor are used to determine the particle size distribution (PSD) of the materials. In addition, the gas phase process is analysed using a CFD/DEM approach in order to investigate process details that are not accessible experimentally using numerical simulations.

In experimental work, the influence of various process parameters on the mixing and structuring of the cathode material is investigated to optimise the existing process and finally to link ...

Dust emissions from bulk material handling are difficult to calculate. In this study, a Bulk Immission Ratio (BIR) is introduced, which results from experimental wind tunnel studies. These findings are interpreted using a model, published by Schulz et al. [1].

For the experiments dry lime stone with a bi-modal size distribution (1^st mode 4.7 µm, 2^nd mode 955 µm) is used as bulk material. 4 kg are dropped from different heights, resulting in different impact velocities. The BIR describes the ratio of the dust mass measured in the air flow to the material mass in the 1^st mode.

The model calculates the dust dispersion ratio (DR) - the ratio of dust released upon impact to dust (20 µm lime stone, 5 %wt) primarily adhering to a single dropping particle (1500 µm steel ball) - for different impact velocities and plate materials.

Similar to the modeled DR, the measured BIR first rises, followed by a plateau around 7 m•s^-1 and a further sharp increase. This paper discusses the experimental results in the context of the model predictions...

In order to improve a numerical model for bulk solid investigations calculating dust emissions when handling bulk materials [1] adhesion force measurements were carried out for the used reference material. This reference material represents a bulk solid in its main parts, the fine fraction and the coarse fraction.

Here, the coarse fraction is represented by metal spheres (diameter of 1500 µm) and as fine fraction a calcium carbonate powder (x_50,3 = 19.5 µm) is used. Since, the determination of the adhesive force between these two fractions is not trivial, measurements were performed. The aim was to identify the adhesive force between a metal sphere and the calcium carbonate powder in order to improve dust detachment functions at a single particle level [2]. However, it turned out that ...

Background: Electrical mobility techniques such as the Differential Mobility Analyser (DMA) have been used for many years by aerosol scientists to classify particle size, and their operation for filtration measurements is covered in ISO 29463 (high efficiency air filters) for determining the most penetrating particle size (MPPS) of a filter sample. Since 2016, classification by a particle’s aerodynamic diameter is possible using the Aerodynamic Aerosol Classifier (AAC), which uses rotating concentric cylinders with a controlled sheath flow to induce known centrifugal and drag forces on each particle sampled. Crucially, the AAC holds the advantage of operating independently of particle charge. This means there is no need to condition the aerosol charge state for classification as with the DMA, which is designed to transmit only singly charged particles (generally a fraction of the particle population) yet larger, multiply charged particles with the same electrical mobility may also pass. The AAC consequently offers significantly higher transmission efficiency, and its output is truly monodisperse. These advantages may be important for precise size-resolved measurements for filtration efficiency required in ISO 29463 and future standards.

Aim: Evidence of limited discrepancies in particle penetration measurements between the DMA and AAC was previously presented at FILTECH (Payne et al., “A New Methodology for Measuring Filtration Efficiency as a Function of Aerodynamic Diameter Using a Monodisperse Aerosol Source”, FILTECH 2018). The present research explores scenarios in which these discrepancies significantly worsen due to multiple charging artifacts, depending on the position of the DMA setpoint relative to both the peak of the input aerosol size distribution and the MPPS of the filter. This can result in incorrect reporting of the MPPS and local and integral filtration efficiencies.

A neutraliser device (usually containing a radioactive source or X-ray emitter) is mandatory in many filter testing standards to ensure the media are challenged with particles possessing an equilibrium charge distribution; examples were considered in this study where the input aerosol contains few charges, and the neutraliser was omitted from the filter testing set-up. This may be of significant benefit considering resources available at testing locations, and health and safety regulations.

Method: An AAC and a DMA were used back-to-back to measure particle penetration through flat sheet media samples of high efficiency air filters certified according to EN 1822 and ISO 29463. In tests with the AAC, results were compared with and without a Kr-85 neutraliser device between the classifier and filter sample, while with the DMA, results were compared with and without an impactor at the classifier inlet. The particle charge state of the nebulised Di-Ethyl-Hexyl-Sebacate (DEHS) test aerosol was also characterised.

Results: It was found that multiple charging artifacts in the DMA output can have a substantial effect on ...

Particle-filtering face masks are designed to protect against various (droplet) infections, such as COVID-19 and others. The viruses that settle in the respiratory tract of an infected person become airborne through fine infectious droplets when sneezing, coughing, or speaking, but also when breathing itself, and can thus be inhaled by other people.

Face seal leakage plays a significant role in estimating the protection efficiency provided by face masks. Thus, there is a risk to be infected with a certified face mask. This work aims to quantify the air and particle leakages through face seal for three different types of FFP2 face masks. This was realised using Computational Fluid Dynamics (CFD) simulations.

To reveal the spots where main leakage occurs, a Sheffield test head fitted with three face masks of different shape (Fig. 1) was scanned using a microcomputed tomography (µCT). The tomographic images showed that the greatest leakage zones are located in the vicinity of the nose. Based on the obtained form (µCT) geometries, computational meshes were generated for CFD simulations.

Particle-filtering face masks are designed to protect against various (droplet) infections, such as COVID-19 and others. The viruses that settle in the respiratory tract of an infected person become airborne through fine infectious droplets when sneezing, coughing, or speaking, but also when breathing itself, and can thus be inhaled by other people.

Face seal leakage plays a significant role in estimating the protection efficiency provided by face masks. Thus, there is a risk to be infected with a certified face mask. This work aims to quantify the air and particle leakages through face seal for three different types of FFP2 face masks. This was realised using Computational Fluid Dynamics (CFD) simulations.

To reveal the spots where main leakage occurs, a Sheffield test head fitted with three face masks of different shape (Fig. 1) was scanned using a microcomputed tomography (µCT). The tomographic images showed that the greatest leakage zones are located in the vicinity of the nose. Based on the obtained form (µCT) geometries, computational meshes were generated for CFD simulations.

Particles were then simulated in addition to the air flow, using sodium chloride in a size range from 10 to 500 nm. Simulations showed that ...

Air quality is one of the highest risks to human health worldwide, with vehicles and road transportation being major contributors, especially in urban areas. While EURO standards have successfully targeted exhaust emissions from diesel and gasoline engines over the past decades, non-exhaust emissions remain as a significant and unregulated problem, especially for road transportation.

These non-exhaust emissions, including particles from tires, brakes, and road abrasion, as well as resuspension due to passing traffic, are now more relevant than exhaust emissions for PM10 and PM2.5 and are to be regulated in the upcoming EURO standard. This study presents a fine dust filtration system developed to compensate vehicles emissions and proposes a method for characterizing the collected particles.

The filtration system was tested in the field over one year focusing on particle size distribution, composition, and the quantification of potential sources such as tire, brake, and road wear particles. The effectiveness of the filtration system for exhaust and non-exhaust emission particle collection was assessed using various analysis methods, based primarily on SEM-EDX combined with a machine learning algorithm, to identify and quantify the source apportionment of PM10 and PM2.5 size fractions .

The findings were compared with existing literature to validate the proposed method. Finally, the system's compensation potential was evaluated under different operating scenarios and ambient air pollution levels, demonstrating its suitability for widespread use in supporting vehicle manufacturers to meet future emission regulations such as EURO standards.

Coalescers are well-established for filtering tiny droplets out of mist. The commonly used filter materials are based on fibrous material and are employed in various applications and industrial environments such as oil-mist separation in oil and gas production, in aviation as part of the cabin air supply system, and in industrial air conditioners. As a result, coalescence filters are often placed near rotary machinery and in vibrating environments, where vibrations can affect their performance. The impact of vibrations on the filter performance and the underlying mechanisms of droplet-fiber interaction has not been previously investigated. In our current work, we aim to study the interaction of an already separated droplet on a single fiber acting as a collector. We use high-speed imaging technology to observe the microscopic events with state-of-the-art temporal and spatial resolution. Depending on the excitation of the fiber, the droplet can exhibit different basic forms of movement (elongation, deformation, lateral - and rotational movement). A sequence and/or a superposition of these basic forms of movement can be interpreted as mechanisms. The identified mechanisms include static, pulsating, rotating, and collapsing droplets on the fiber.

As a result of strong pulsating or rotation, a droplet can ...

Background

Mechanical fibrous filters including Hepa H13 can achieve very high filtration efficiency. However, hepa filters have no drainage and the high concentration of oil mist in industrial machining processes, makes the efficiency of drainage filter cassettes upstream of the hepa filter critical to achieve long changing intervals. Fibre diameter is a critical parameter that greatly influences both efficiency and pressure drop. The effect of reducing the fibre diameter from 10 µm to 8 or 6 µm was therefore investigated in this study.

Objective

Is it preferable to use a smaller fibre diameter to increase the efficiency, even if this reduces the oil drainage capacity? Will the pressure drop increase more than the efficiency by using thinner fibres?

Method

Experiments were carried out on four fibre cassettes loaded with oil mist (63 mg/m³). Three different glass filter materials were tested with fibre diameters of 10 µm, 8 µm and 6 µm. The three needle mat materials had different thicknesses (10, 7.5 and 5 mm) but quite similar pressure drops (118, 109 and 105 Pa). The 6 µm material was also tested in a thicker version (10 mm). Efficiency, pressure drop and oil accumulation in the cassettes were monitored until steady state was reached.

Main results

The oil trapped in the cassettes caused a continuous increase in ... After 19 to 25 days, the cassettes reached a steady state where the drainage of oil was similar to ... The pressure drop then stabilised ...

Coalescing filters play a pivotal role in filtering invisible oil mist from dirty air streams. Fibrous filters are the most commonly used method in industries such as air compressor systems, automation devices, and clean rooms. When oil mist passes through filter media, Contal et al. (2004) identified four stages during mist filtration: deposition, clogging, filming, and drainage. Kampa et al. (2014) provided a comprehensive view of liquid transportation within filters and propose a phenomenological model called “Jump and Channel Theory” to describe the filter loading process. Chang et al. (2017) demonstrated that arranging a drainage layer influences the saturation rate of each filter layer. However, previous research has focused on the filter media during the loading of oil mist, but it does not account for the changes in filters that have been pleated or assembled into cartridges. Available manufacturing method is much more crucial for the commercial market and mass production. In the market, there are two major types of manufacturing methods: pleat-type and round-type. Therefore, we not only focus on the filter cartridge during loading but also propose a schematic method to improve the performance of coalescing filters. This approach is essential for the industrial market and end users.

In this work, we introduce a new evaluation method and an improved design for coalescing filters, particularly aimed at enhancing their longevity. To compare the two manufacturing structures, we applied a novel loading system (Figure 1a) specifically for assembled filters. The concentration distribution of the challenge DEHS aerosol (Figure 1b) is applied with a loading rate of 3g/hr. Both structures utilize identical single filter media, same size of filter (Figure 2a), and adhere to a uniform 6-layer design. The only different is the inner structure. One is pleat-type filter (Figure 2b). The other is round-type filter (Figure 2c). To further compare the loading performance, the initial performance of pressure drop curve (Figure 3a) and efficiency curve (Figure 3b) are very similar under the same filtration test.

As a result of our study, the loading curves of both structures (Figure 4) demonstrates that ...

Waste incineration (WI) generates highly polluting gases requiring treatment technologies that ensure compliance with EU emission standards. With growing health and climate change concerns, limit values for particulate emissions from WI are expected to evolve to consider particle size. It is therefore crucial to ensure that fumes treatment facilities are equipped with air pollution control (APC) devices capable of capturing all particle size ranges. Simple wet scrubbers (SWS), a widely employed APC device, are not considered performant for collecting particles with a diameter of less than 1 µm. However, studies [1] have shown that by adjusting the scrubber operating conditions (e.g. droplet size, liquid to gas ratio), collection of submicron particles can be improved. Given the widespread use of these units and their potential for submicronic particle collection, it is crucial to study their behavior and optimize their performance. In this work, a downscaled wet scrubber was designed, built, and set-up in a municipal WI plant to be fed with real fumes and to study its efficiency regarding the removal of particulate matter contained in WI fumes.

The downscaled system was implemented at the municipal WI plant in Nantes (France), where domestic, medical, and industrial waste are incinerated, and which consists of a furnace, a heat recovery boiler, a cooling tower, a baghouse filter with sodium bicarbonate and lignite coke injections, and a selective catalytic NOx reduction system. The wet scrubber was installed after the cooling tower, where the fumes reach ...

...

The particle size distribution (PSD) at the inlet (Cin) and outlet (Cout) of the scrubber was measured to quantify its performance under operating conditions presented in Table 1. Samples were taken with isokinetic nozzles located inside the scrubber, aligned with the gas flow, and properly isolated from the spray. The inlet sample was taken at a height of 2 m, in the center of the tower and the outlet sample was taken next to the scrubber gas outlet. Particle counting was performed by using an Electrical Low Pressure Impactor (ELPI, Dekati). Short (30 – 45 s) and sequential ...

The PSD at the inlet of the downscaled wet scrubber measured by the ELPI is presented in Figure 2. This distribution can be considered as the PSD in the main industrial duct, subject to losses in the scrubber inlet line. The modal diameter is 0.31 µm for a concentration between 7 and 9 x 10⁵ #.cm^-3. Figure 3 illustrates the collection efficiency of the downscaled wet scrubber as a function of the aerodynamic particle diameter, for the above-mentioned operating conditions. As the particle size decreases, the scrubbing efficiency also diminishes, reaching a minimum of 7% at 0.31 µm. Negative collection efficiencies (-12%) were obtained for ...

Bag filter systems play a crucial role in various industries by providing an efficient and reliable method of separating contaminants from production processes. These systems are essential for maintaining clean air in environments where dust and other particulate matter are generated. In bag filter systems, exhaust air from various processes is fed through flexible bag filter elements, which effectively separate and capture dust emissions, ensuring a cleaner and safer workspace.

The patented Kappa Waveline bag filter can be used to optimize existing or newly planned bag filter systems.

The Kappa Waveline® bag filter has 25% more filter surface area, supported on the patented Waveline® support basket with the installation size of a standard bag filter.

The increased filter surface area leads to a lower filter surface load at the same volume flow and thus to a reduced pressure loss. The result is significantly reduced energy consumption, in some cases by 30-60%, and thus lower operating costs for the filtration of emissions.

The 25% increase in filter surface area also supports the cleaning effect and reduces the number of cleaning sequences required. This improved cleaning leads to significant savings in compressed air.

These two effects can reduce the operating costs of both new bag filter systems and existing bag filter systems while maintaining at least the same cleaning efficiency.

Alternatively, the extended filter area can be used to increase capacity without structural measures or extensions, thus helping to better comply with current and future limit values.

The effectiveness of this new type of bag filter design can be demonstrated both by empirical measurements in practical use and by scientific analyses carried out by the Institute of Air Handling and Refrigeration in Dresden (ILK Dresden).

More than 2 million m² of HJS Sintered Metal Filter (SMF^®) material have been produced within the last nearly 20 years, with a peak production of 300.000 m² p.a.. The SMF^® modules are proven for a very large number of exhaust gas filtration applications for diesel engines.

Based on a comprehensive market analysis, the areas of oil / hydraulic filtration and gas dedusting were identified as the most promising market segments for SMF^®. Accordingly, the filter material was qualified in accordance with the test guidelines multipass acc. ISO 16889 and VDI 3926.

The best match with the requirements of the corresponding market segment and the properties of the SMF^® material was demonstrated in the area of hot gas filtration. The focus of further activities is therefore on the development and implementation of manufacturing processes that are as close as possible to series production and the further validation of such filter elements in real applications, including the optimisation of the respective regeneration parameters.

The great interest in the approach of high-temperature filtration with SMF^® filter elements is mainly due to the potential CO₂ savings that this offers. The effort previously required to cool the hot, dust-laden gases before filtering, which is necessary for environmental reasons, can be omitted. Furthermore, by utilising the significantly hotter, cleaner gas, energy recovery, e.g. by generating electricity, can be made much more efficient than before...

Laboratory investigation of the filtration performance according to VDI 3926 were done with different test dusts. They include two typical test dusts and one real word dust taken from a lime plant. With this results a comparison was possible to theoretical values coming from empirical formulas.

An important step for the commercialisation of this new filter technology is the capability to produce filter candles in the dimensional range today known from textile-based filter bags. For this task the final welding step on ...

Similar to the welding of the flat filter media strips to a wider raw material the final welding seam has to fulfil all the quality criteria from mechanical aspects and the possible impact of filter performance.

In customer supported projects first industrial installations of the metallic filter media were done to proof the good laboratory results in the final environment. As an example described here, a filter house was designed to fit in the existing filtration path of a lime plant...

Running the metallic filter media with different test dusts showed some significant deviation from the theoretical expected results. The real word test dust has a...

DNSlab is a software for analysis and simulation of mass transport and deposition especially in microporous filter media. The computation of gas or liquid flow fields in 3D models of the media is used for the determination of the permeability, the filter efficiency and filter cake build-up and backwashing, amongst others.

DNSlab provides Finite Differences (FD) and Lattice-Boltzmann (LB) schemes to compute flow fields. The FD schemes are advantageous for slow creeping flows, the LB schemes for faster inertial flows. DNSlab’s FD schemes feature low memory consumption and ultimate numerical stability for creeping flows, as they always converge for any 3D geometry.

The contribution shows the recent FD scheme improvements in DNSlab, which enable the users to run simulations faster with larger, more representative 3D models, and less computing resources. A typical nonwoven model is used to compare the performance of the different FD scheme versions. The simulations are run on a practicable low-cost gaming PC.

The 2024 version has the lowest computing time, the lowest memory requirement and gives the most precise result on the non-coarsened voxel grid, meaning that it performs...

A new, clean filter medium for dust separation always begins with an initial phase in which dust separation can be described according to the principle of depth filtration in the given medium. If dust separation is carried out on the given filter medium for a sufficiently long time, a dust cake can form after a completed clogging phase. This is often a gradual process. For typical depth filter applications, the longest possible clogging phase with a moderate increase in pressure loss is advantageous. In contrast, when using surface filters, the cake-forming filtration after the shortest possible clogging phase is desirable. While the filtration kinetics of a depth filter can be investigated using various model approaches (dendrite growth model or fiber growth model) to describe particle separation in the clogging phase, the transition to surface filtration by continuing the same model calculation is not yet possible, as the dust cake growth, which simultaneously means the expansion of the initial packing, is not achieved by the underlying separation theory, but by a separate add-on model. So far, there is no coherent model for a holistic view of the entire filtration process.

In this paper, a multi-layer model with offset for dust cake growth is presented, which enables the description of particle separation during the entire filtration process without a separate add-on model for switching between depth and surface filtration. The results of the model calculations are compared ...

In the present world of constant redevelopment and construction, the amount of dust freely floating in the air near major streets and roads are extremely high and inconsistent which can lead to filtration products not performing as per requirement.

The study aims to develop a CFD methodology to simulate the Dust Holding Capacity (DHC), Filtration Efficiency and understand Dust particle behaviour when it flows through a 2W Air intake Assembly. The Dust that is present in the air is of various compositions, sizes, shapes etc and these properties of the dust effect the behaviour when it floats through the air. A primary performance evaluation factor for Air Filter assembly is the Dust holding capacity, which also decides the service interval for the filter element along with filtration efficiency.

Our goal for this study is to develop a CFD methodology by which both DHC and efficiency can be evaluated for a Filter Assembly and results are going to be verified using Test Bench data. Filtration of particles based on particle size will also be used to accurately predict how much of the dust particle will be captured by the filtration media. From this study we hope to prepare a robust methodology to setup air filter assemblies using CFD to predict DHC and Filtration efficiency which will help us develop better and more efficient products resulting in lower vehicle emissions and reduced wear and tear of critical engine internal components..

It is well known that filter media are exposed to compression during the manufacturing process. The transportation via conveyor belt rolls compacts the medium over the entire surface, changing the filter performance, i.e. efficiency, pressure drop and dust holding capacity. Further processing steps such as pleating compress the filter media locally at the tops and bottoms. The nonuniform permeability leads to a reorientation of the flow field so that the filter surface is not utilized optimally. Experimental measurement series are very helpful for the design and optimization of the manufacturing process and the nonwoven fabric. Nonetheless, they are associated with large efforts in time and cost.

This work provides an overview of the influence of compression on the filter performance of flat filter media. The pressure drop across the media as well as the fractional efficiency are predicted by models. The approach is based solely on measured material characteristics of the uncompressed nonwoven and requires no additional experimental effort for the compressed material (see Figure 1).

The data basis for the analysis of pressure drop is provided by five nonwovens, which differ by their fields of application and media structure to ensure a broad validity of the presented model. SEM images as well as measurements of the thickness, the area weight and the correlation between pressure and velocity characterize the uncompressed media. The prediction of the pressure drop for multiple compression levels is based on the Darcy-Forchheimer law [1] whereby relevant model parameters (permeability, inertial loss coefficient) are scaled with suitable models [2] referring to the change of material thickness and the corresponding reduction of porosity.

Based on one of the five filter media, which is an electret filter, the experiments are extended to include the fractional efficiency. Single fiber efficiency (SFE) models [3] are a reasonable choice for modeling porous media that consist of fibers. The mechanisms of diffusion, direct interception, inertial impaction, electrophoresis and dielectrophoresis are distinguished. Numerous models are available in the literature (see e.g. [4]), although the accuracy of the models can vary depending on the filter medium or moreover the manufacturing process. A suitable combination of these models paired with weighting factors describes the initial efficiency and can be extended by considering only the changes of material thickness and porosity.

The proposed methods allow for ...

Electret filters find widespread application across various industries due to their exceptional filtration efficiency. These filters operate on the principle of electrostatic attraction between charged fibers and particles, electrophoresis and dielectrophoresis. However, research on electret filter media faces numerous challenges and complexities, such as charge stability over time, charge uniformity, and distribution of charges, particularly on the fibers.

In this context, numerical simulations play a crucial role in deepening the understanding of the fundamental mechanisms governing the behavior of electret filter media. They provide valuable insights into the complex interplay among electrostatic forces, airflow dynamics, and particle behavior, aspects not easily observable or measurable through experiments.

For the simulations of particulate filtration in filter media and elements, the FilterDict module of GeoDict stands out as a powerful software tool. Its capabilities to perform direct numerical simulations of electrophoresis are currently being enhanced in the framework of the ElekSim project, funded by the German Federal Ministry for Economic Affairs and Climate Action (BMWK). The overall objective of this project is to develop a new simulation environment focusing specifically on electret filters with the aim to streamline the optimization of electret filter media and to validate it against measurements. So far we have the comparison of simulation results of real filter media originating from different charging processes such as hydro charging, corona charging and triboelectric charging. The FilterDict developments include simulating diverse charge distributions in both particles and fibers, adding dielectrophoresis to existing electrophoresis capabilities, and tracking surface charge decay in electret filter media over time.

The initial verification of this simulation methodology is compared against results from Fluent® on a single fiber and simple multi-fiber models and includes a comparison of the computed filter efficiency across a given particle size distribution. Next, the new features will be validated against measurements on provided µCT scans. To investigate the effects of electrostatic charge on the filter efficiency, the filter media are additionally discharged using isopropanol to expose the pure mechanical filtration characteristics.

These insights will allow drawing new conclusions for the design of innovative next-generation electret filter media with different charge distribution methods, structural configurations, and improved charge stability.

Natural gas is one of the important sources of energy and, due to the huge reserves of natural gas, it is transferred using a network of pipelines and through the urban network, it is available to industrial, commercial and domestic consumers. In natural gas tanks, a significant amount of it is available, but along with that, there are also amounts of condensate, moisture, and solid particles, which can cause pressure drops and damage the transmission lines and facilities [1]. Using a suitable filtration system with optimal performance while preventing gas flow pressure drop in the gas supply network, prevents damage to the equipment of gas stations. The best economical solution to deal with problems and save operating and maintenance costs is to use a high-efficiency filtration system that separates solid particles and moisture from natural gas [2]. The results show that changes in key parameters such as particle diameter, fibre diameter and fluid velocity have a significant impact on filtration performance. Also, the filtration efficiency for particles with an average diameter of 2.5 and 5 to 8 microns is only about 83% and 89% to 92% [3]. From examining the performance of 4 different types of filter cartridges that were used to purify high pressure natural gas, it was observed that the decrease in the performance of the filters is related to the increase in the pore size of the cartridge layer [4].

The objective of this project is to simulate the flow of natural gas, considering a mixture of gas and sand, passing through a filter separator, inlet a gas reduction station, in order to calculate the efficiency and pressure drop of the filter under operating conditions. The results obtained from the software will be compared with the pressure drop data obtained from DP which is installed on the inlet of the filters of the gas reduction station, and the results were consistent. In previous research the material and dimensions of the dry filter medium were obtained based on the information provided in the gas standards. The fluid flow simulation is using ANSYS FELUENT 2021 software. This project dealt with a three-phase gas-liquid-solid flow due to the presence of solid particles (sand) and moisture in the natural gas pipelines. The Eulerian-Lagrangian method and Discrete Phase Model (DPM) and k-ε turbulent model have been used to investigate gas-solid three-phase flow. The operating pressure of the filter separator ranged from 150 to 250 pounds per square inch (psi), the permissible flow rate was between 400 to 2500 cubic meters per hour. Compressible flow is assumed. The results show that

Clean air and water are increasingly in focus, while the demand for energy-efficient solutions to address these issues is growing. Filter development must rise to this challenge. Filters should be used in a resource-efficient way. This can be achieved by precisely matching filters to the application, both in terms of particle size distribution and the conditions of the fluid flow to be treated. Conventional filters often consist of one or more layers of filter media, which are either woven or composed of tangled fibers. The efficiency of these filters depends mainly on the tightness of the fabric.

The development of additive manufacturing has made great progresses in recent years. Using this technology, filter manufacturing is no longer restricted to conventional methods. In addition, computers have become more powerful and can carry out numerical flow simulations in a short time. The limits of additive manufacturing in terms of material and resolution have not been reached yet. A great potential for the developed method is expected here in the future.

The aim of this work is to present two methods to optimize filter structures with respect to the filtration efficiency and the pressure loss: first a simple geometry-based shape optimization of initial structures with the adjoint method and second an Eulerian Multiphase approach inspired by the adjoint method.

Both approaches are based on the same workflow, but are different with respect to the cost function used. The first steps are application-dependent: Creating an initial geometry in Computer Aided Design (CAD), meshing the initial geometry in Computational Fluid Dynamics (CFD) and determining pressure loss and separation efficiency for e.g. pollen separation in car ventilation systems. The cells at the fibers are then varied by mesh deformation until an optimum is found. While the first method requires cost functions that can be derived to run the adjoint solver, the second method can use arbitrary functions. These cost functions have to account for the different separation mechanisms and the pressure loss. The combination of the sensitivities was realized by an algorithm. Lagrange and DEM simulations were performed to determine the percentage of impaction and interception in the total separation efficiency. Physical prototypes of the often bionic-looking optimized structures can be generated using additive manufacturing.

The whole workflow was successfully tested for ...

DNSlab is a software for analysis and direct numerical simulation of fluid and particle flows by means of 3D models especially of microscale porous structures.

The new DNSlab Python Interface was introduced with the first DNSlab release in 2024, Release2024a. It enables DNSlab users to automize and customize the pre- and postprocessing of DNSlab applications. The interface is provided in the form of a package of classes and functions which are imported in the user’s python code, and which enable to read and write DNSlab input and output data. The basic working principle is that by the user’s python code, DNSlab runs are prepared, executed and evaluated. In particular for the evaluation, Python’s comprehensive plotting capabilities are applicable.

Airborne Molecular Contamination (AMC) is a critical issue for numerous state of the art manufacturing processes. These contaminants degrade features and effect yield in the semiconductor manufacturing process, where feature sizes continues to shrink.

AMC chemical filters play a pivotal role in removing AMC contaminants and provide purified air to SEMI cleanrooms, which is a key requirement in generating quality products. Long filter lifetime is desired, and design optimization plays a central role in filter development. Filter removal efficiency (RE) and life cycle are critical design parameters. However, it is challenging to obtain removal efficiency experimentally, particularly at very low gas concentrations, due to long test time, high experimentation cost and logistical limitations. Although computational modeling is an efficient means to generate predictive models, long computational lead time and inability to capture a live Failure Mode Engineering Analysis (FMEA) analysis are shortcomings.

The digital twin (DT) is a machine learning model which is a virtual representation of real word entities and processes, synchronized at a specified frequency and fidelity. It can track the past, provide insights into the present and predict and influence future system behavior and can offer live, system-level simulated prediction with real-time data inputs. Therefore, DTs offer a unique opportunity to study virtual and physical systems, either separately or together.

This study was a pioneering effort to successfully develop and deploy Digital Twin technology in the AMC filter optimization process. A static and dynamic Digital Twin were developed from initial validated Computational Fluid Dynamics (CFD) model of a specific AMC chemical filter. The newly developed Twin model was able to predict the filter performances instantly along with live FMEA by its developed virtual sensors which critically can help filter optimization process by reducing cost of ownership significantly...