Baghouse filters are used in a variety of gas cleaning applications in order to lower dust emissions and protect the environment. State of the art filter media generally enable low particle emission levels, where a particle emission peak occurs for a short duration after filter regeneration due to penetration of particles through the filter medium. After sufficient cake formation, the emission drops to a zero level in the case of ideal, leak free operation. Leaks of the filter bag, damaged media surfaces or other defects can significantly increase the overall particle emission of the baghouse. The emission contribution of these “hotspots” may easily exceed the emission contribution of all other filter elements. Triboelectrical sensors can be installed on the clean gas side for the measurement of the total emission and alarm plant operators about an increase in particle emission, however these sensors do not offer spatial resolution and information about the location of the emission hotspot. In many applications fluorescent dust is used to determine the location of leaks and defects, however the localization of the leak itself requires a shutdown of the filter house. A potential technology for spatially resolved online measurement of particle emissions are low-cost PM-sensors due to their compact size and low investment cost. In this study, each of a total of nine filter bags of a small scale baghouse filter has been equipped with a low-cost PM-sensor of the model OPC-N3 from the manufacturer Alphasense...

The presence of water droplets in gas cleaning filtration systems due to fog, spray rain or condensation has an impact on the filters’ operating performance. The differential pressure between the raw and the clean gas side of the filter is a key parameter considering the energy efficiency of the filter.

The exposure of an established filter cake with soluble components on the filter surface to water mist leads to structural changes of the deposited particle collective. Dendrite structures collapse and particles rearrange on the filter surface. Soluble particles dissolve. The solution may penetrate through the filter medium to the clean gas side depending on the composition of the cake (e.g. ratio of soluble salt particles and insoluble dust) and the operation parameters (mainly duration of liquid exposure).

The presented work focuses on the penetration of soluble material through surface filters due to contact with water mist and the resulting change in the differential pressure, depending on the wettability of the filter (hydrophilic or hydrophobic filter medium)...

Assessment methods such as permeability, mass, and thickness are often utilized to characterize used nonwoven filtration media. Nonwoven filtration media commonly displays some degree of variation from the fabrication process, which can be exacerbated in the used filtration media. Current standard testing methods assess filtration media in three localised regions: this study shows that there is a considerable permeability variation across the vertical and axial length of the media which warrants consideration during analysis.

This novel, high resolution permeability, study illustrates the variation between pre and post pulse jet cleaning using an industrial derived sample. The test method illustrates the limitations of current industrial test methods...

Due to the Corona pandemic, the wearing of masks is mandatory in many fields of life. Inhaling and exhaling while wearing a mask can be stressful over a long period of time, especially during strenuous exertions - even for healthy persons. Providing masks with a low pressure drop at a high filtration efficiency is crucial for persons with preexisting trouble breathing who are especially vulnerable. Therefore, the aim of this work is to investigate both the near-field and the far-field protection effect of existing medical and FFP2 masks and of a proposed optimized mask with.

The set-up of the CFD model is carried out in 4 stages corresponding to 4 spatial scales. In the first stage, based on µCT scans, individual fibers of mask materials are resolved and pressure loss, filtration efficiency and macro-scale material parameters are determined by micro-scale simulation. In stage two, these macro-scale parameters are used in macro-simulations on flat sheet samples of face masks to determine the pressure loss of the entire mask material and compare them to the results obtained in stage 1. Stage 3 focusses on the near field of a mask and takes the different mask shapes into account. The simulations serve for determining pressure loss of the complete mask including the effect of the shape of the mask. Last but not least, in stage four, the exhalation of aerosols through a mask is investigated in order to determine the far-field reduction of aerosol concentration by the mask. For this purpose, the flow field corresponding to different aerosol generation processes such as breathing, talking and coughing is simulated using a Eulerian approach and a specific particle distribution for every case is injected after the steady-state flow solution has occurred (Lagrangian approach).

Simulation results of pressure drop and filtration efficiency of medical, FFP2, and optimized masks are shown and validated by comparison to experimental data. We investigate the influence of the shape of the mask, the leakage due to a bad fit of the mask as well as the effect of different aerosol injection scenarios (breathing, coughing, talking) on the reduction of the far-field aerosol particle concentration allowing to assess the protection effect of the different types of masks.

The last two years has shown an increasing awareness of the use of face masks and respirators in order to protect the wearer or the surrounding people against infections.

Two protection concepts can be distinguished: self-protection and external protection. In the first concept, the wearer wants to protect himself or herself against infectious pathogens or viruses in the surrounding. Depending on the availability, corresponding filter masks should be preferably used by people working in health and nursing care. In the second concept, the wearer protects people in the surrounding from being infected.

A reliable protection does not only depend on the filtration properties of the mask material. In the literature, it is discussed whether moisture penetration decreases the filtering efficiency. If this is the case, the safety is reduced. The most critical state is reached when the mask is imbrued entirely (moisture breakthrough) since the moisture can serve as an "infection bridge" spanning across the depth of the filter material. This holds for highly efficient filter masks (e.g. FFP-2), but even more so for masks to protect others: Coughing and sneezing can lead to the detachment of potentially infectious droplets from the outer surface, which will then spread into the vicinity. In standard test procedures such as DIN EN 14683, DIN EN 149, or 42 CFR Part 84, the temperature and the moisture content are considered as constant and static. The test material is adjusted to given conditions. However, when breathing out, the face mask is exposed to moisture and the temperature (body heat) is different from the surrounding.

Most wearing time recommendations are reference values, based on an average usage scenario. The speed and intensity of the moisture penetration of a mask depend heavily on the physical stress level of the wearing person. The time it takes until the moisture breaks through cannot be derived in a simple way ("rule of thumb") from the physical activity, which is usually fluctuating. In general, a visual check of the mask is neither feasible without aid nor reliable enough to detect a moisture breakthrough.

Specialized computer simulation tools have proven to be very useful for the innovation and optimization of filtration devices. Previous studies were mostly focused on filtration efficiency and have not considered the moisture transport. Additionally, the breathing behavior was modeled using an idealized sinusoidal profile.

The present work is devoted to the adaptation of well-known transport models to the transport of moisture in porous media...

During the COVID-19 pandemic, face coverings have been widely worn in public spaces to capture respiratory particles produced by the wearer and reduce spread of infection. These commonly consist of layers of woven fabric. Surgical masks are intended for health care staff to protect patients during surgical procedures and in other medical settings. Respiratory filtering half masks are intended to protect the wearer and are regulated as personal protective equipment (PPE) for inhaled air only.

Numerous recent studies have emphasised the possibility of airborne coronavirus transmission. While the World Health Organisation (WHO) defines droplets as ≥5-10 μm diameter and aerosols as <5 μm, both can be generated as a continuum of particle sizes during various respiratory activities including coughing, talking and singing.

In this study the filtration properties of various face mask materials were investigated across a broad range of particle sizes. The interception mechanism is important for large particle capture, for which aerodynamic diameter is the most useful measure of size. A suitable instrument for achieving this is the Aerodynamic Aerosol Classifier (AAC), which can select particle sizes between 25 nm and >5 μm by using a rotating cylinder to balance opposing centrifugal and drag forces for the desired aerodynamic diameter, so that particles move across a sheath flow to the outlet. This principle of aerosol selection is independent of the charge state and produces a truly monodisperse aerosol with a high transmission efficiency limited only by diffusion and impaction losses.

This study uses an AAC to select monodisperse test particles by aerodynamic diameter in order to assess the filtration performance of various face covering materials, in both flow directions and at filter face velocities representative of inhalation and exhalation flow rates...

During the COVID-19 pandemic, certified respiratory masks emerged as a key protective measure against direct and indirect infections from virus-laden aerosols. However, their standardised test procedures lack relevant aspects to evaluate the filtration performance with respect to respiratory aerosol particles. The presented work deals with two of these under-represented factors, namely the filtration efficiency depending on the nature and size of exhaled aerosol particles and the filtration performance associated with facial leakage considering a differentiated distinction between self-protection and third-party protection. Therefore, the fractional efficiency and the net pressure loss are experimentally determined within a screening of different medical masks (EN 14683) and filtering face pieces (FFP2, FFP3) (EN 149).

While the certification of medical masks and filtering face pieces either uses bacteria-laden aerosol particle distributions with a mean diameter of 3 µm (EN 14683) or liquid paraffin oil droplets and solid-phase sodium chloride particles (EN 149), that neither represent the species nor the size of exhaled droplet nuclei, we use aerosol particles from artificial saliva. A comparison of both artificial and actually exhaled aerosol particles shows that...

Community mask are the most common national strategies to in Europe to lift legal relationships caused by covid pandemic. Uniform security standards across Europe can be part of this, to contain the COVID-19 pandemic across borders. The CWA assist producer who switched their production to non-medical mask, the so-called community masks.Therefore, an upcoming new EU directive CWA 17553 will be released by CWA with the title “Community face coverings – Guide to minimum requirements, methods of testing and use”.

Even before that Palas already started a development of a fast, economical and easy to handle measurement device the Mas-Q-Check. The Mas-Q-Check was developed by Palas to subject protective masks to a quick, simple and yet meaningful test before use. A particle counting measurement device is used, which is able to detect efficiencies in the size range of viruses and bacteria. The system can also be used for training purposes as it immediately shows the efficiency of protective masks.

The mask is placed on the test head before use. Using a high-resolution aerosol spectrometer, the particle contamination (size and quantity) in the ambient air is measured. Afterwards the device switches automatically and determines the value of the particle contamination behind the protective mask. This can be repeated automatically several times.

The Centers for Disease Control and Prevention (CDC) continues to recommend that persons in the U.S. wear masks in public settings “around people who don’t live in your household and when you can’t stay 6 feet away from others.” Masks help stop the spread of COVID-19. In many states there is a legal requirement to wear masks in public buildings and spaces. This presentation will cover the nature of COVID-19 virus particles, the current test methods of facemask filtration, and the test results comparing N-95 mask, surgical mask, and cloth mask.

Particulate filters are a standard component in exhaust aftertreatment systems of trucks and cars to remove reactive (soot) and inert (ash) particles from the exhaust gas. The particulate filters consist of parallel channels with alternately blocked ends. Particles are deposited in the inlet channel, while the gas flows through the porous filter wall into the outlet channel. After reaching a defined pressure drop to clean the filter from the reactive components, the filter is regenerated. During the regeneration, the soot particles are oxidized and the particle layer breaks up. Agglomerates can be detached, transported along the filter channel and deposited at the end plug of the inlet channel.

Nevertheless, the influence of the particle properties on the resulting deposition pat-terns and the rearrangement of agglomerates in the particulate filters remain unclear.

In this study, the rearrangement (detachment, transport and deposition) of agglomerates without regeneration of the reactive particles in the filter is investigated in order to observe the fundamental processes of detachment and transport of agglomerates in cross-flow filters...

Depth filters are commonly used for particulate matter removal in several fields of application like air-conditioning, cleanroom technology and cabin air filters. Two main parameters are of interest for the characterization of the operating behavior: separation efficiency and pressure drop. In general, the pressure drop across a filter system is increasing with the deposited particulate mass in the filter medium (Payatakes and Gradon 1989, Kanaoka and Hiragi 1990; Brown 1993). In conventional used depth filter systems operating flow velocities are roughly below 1 m/s. At this range of velocity, the particles deposit on the fiber. At flow velocities above 1 m/s particles are likely to bounce off or being blown off from the fiber. To detach particles of 10 µm from filter fibers, high flow velocities above 1 m/s are required (Löffler 1972). All findings by Löffler are valid for stiff fibers. By stretching the fiber, mechanical shear and tensile stress are induced to the compact structure and detachment is observed at operational flow velocities of about 0.4 m/s (Poggemann et al. 2021). The particle structures are weakened and detach more likely at lower flow velocities due to the stretching process of the fiber. In the investigations of Poggemann et al., only compact structures (based on inertial deposition) were obtained on the top side of the fiber. As shown by Kanaoka et al. (1986) there is a systematic relationship between the deposited structure on the fiber and the filtration velocity during the deposition process (Kanaoka et al. 1986). It is assumed that the overall morphology of the deposited particulate structure on a single fiber has an influence on the detachment behavior during fiber stretching.

To investigate this influence on the detachment behavior, a compact or a more dendritic and open structure is deposited on a stretchable single fiber. By applying a flow velocity of...

Aerosol loading behavior of PVDF nanofiber electret filters using neutrally charged nano- and submicron aerosols was investigated experimentally for the first time. The loading behavior include variations of filtration efficiency and pressure drop and distribution of deposited aerosols in the filters all having the same fiber basis weight (3.060 gsm). Through the filtration efficiency variations of uncharged/charged, single-/multi-layer filters with aerosol loading, it was observed that mechanical PVDF filters had continuously increasing filtration efficiency, while PVDF electret filters had initially decreasing and subsequently increasing filtration efficiency until reaching 100% due to diminishing electrostatic effect and enhancing mechanical effect. By combining the pressure drop evolution of different filters during aerosol loading and detailed SEM images of the loaded filters, we have demonstrated that multilayer PVDF filters, especially the electret ones, could significantly slow down the pace of filter clogging (skin effect) and increase significantly the aerosol holding capacity during depth filtration. Generally, the multilayer nanofiber filters received the most aerosol deposit during depth filtration, whereas the single-layer nanofiber filters with the same basis weight of fibers received the most deposit during cake filtration. The multilayer nanofiber filters had approximately...

The removal of nanoparticles, especially from hot gas streams, is a challenging task and often associated with high energy demands. However, processes such as catalyst production, additive manufacturing and pyrolysis require an efficient way of particle separation. Ceramic filters are state of the art above 400 °C but they cause high pressure drops. The common assumption that electrostatic precipitation is not feasible above 400 °C at atmospheric pressure due to the convergence of corona onset voltage and sparking voltage appears to be short-sighted.

This case study evaluates the performance of a high-temperature electrostatic precipitator (HT-ESP) between 400 – 800 °C for both discharge polarities. The tube-type ESP with...

More than 2 million m² of HJS Sintered Metal Filter (SMF^®) material have been produced within the last 15 years, with a peak production of 300.000 m² p.a.. The SMF^® material is a thin (< 0.5 mm) porous sintered metal in which a precisely defined stainless steel powder is sintered with an expanded metal carrier. This results in a thin, mechanically and thermally very stable filter medium, which can be treated in further processing similar to sheet metal. The SMF^® basis material is industrially manufactured as quasi endless sheet with a width of 125 to 130 mm. Approved for hot gas and exhaust filtration, the material is further processed into filter modules that are designed for the named applications.

These SMF^® modules are proven for a very large number of exhaust gas filtration applications used by vehicle manufacturers for applications that are subject to the current European emission legislation and thus strict requirements for particle number reduction. Furthermore, there are first applications in the industrial filtration of gases. In addition to the thermal robustness of the filter material, the high retention capacity and good cleanability of inert filtrate is also a key factor.

The aim is to use the known advantages of the thin foldable SMF^® material, such as sharp separation efficiency or good cleanability, for new industrial filtration applications...

This work is a first attempt to simulate liquid spray atomization using a spiral nozzle in a spray. Spiral nozzle has a special non-axisymmetric geometry able to create a spray pattern in the form of three concentric hollow cone liquid sheets. This geometry leads to a mass transfer intensification among pollutant gas and the absorption liquid as well as a better capturing efficiency of PM. Thus, only one nozzle can be used instead of a system of several nozzles in the spray column. First, we simulated the gas phase distribution inside the scrubber chamber using a Reynolds stress model with the coupled solving scheme. This model is suitable for description of extremely turbulent flow. Second, we used a two-phase VOF model to investigate basic parameters of liquid flow escaping the spiral nozzle (refer to figure below). Both simulations can then be used to study liquid shower in the scrubber in a counter-flow with the entering polluted gas using a DPM model of the sprayed liquid. The DPM model provides us with information about distribution of liquid fragments and individual droplets to estimate the interface area necessary for adequate mass transfer rate. Result of this study can help to better optimize gas scrubbers in terms of capturing efficiency, size, usage/regeneration of absorption liquids and energy demands, which is tightly related to acquisition and operating costs...

Air filtration plays a vital role in the performance and operations of heavy-duty vehicles. The supply of clean air into all engines is critical to their performance. A good air filter supports the engine operation by ensuring that the air entering the system is clean and free of grit and dust. Fibre diameter and pore size are the two critical parameters that significantly affect the media's filtration performance and dust deposition. Nanofibers are typically fibres with less than 1 μm, and the nanofiber-coated filter media offers higher filtration performance than the conventional filters. Adding nanofibers also extends the life of the filter by making it easier to clean because the fibres keep the particulate at the surface rather than depth loading. In this study, Nylon 66 nanofibers were coated over a cellulose based conventional filter media using electrospinning and the performance of the coated media were evaluated in terms of filtration efficiency, dust holding capacity, quality factor (Q-factor), etc. The filtration performance...

Polyurethane (PU) foam has a wide variety of applications in various industries such as automobiles, textile, chemical, foundry etc. This paper focusses on the filtration application, of PU foam, used to supply clean-air in (2W) motorcycle engine. Oil impregnated PU foam is widely used in the two-wheelers motorcycle industry in India and other African countries. The oil-impregnated filter foam, in the times of ultra-high performance filter media (cellulose and non-woven filter media), is used because they are in-expensive, cleaned, re-oiled and re-used again and again. Also, as PU foam are compressible in nature, they don’t require extra special sealing material around periphery. Such an open-cell PU foam is often characterized by the unit PPI (Pores-Per-Inch). PPI of the filter foam directly affects the pressure drop of the air intake system and more importantly its filtration efficiency. Engine Air filter assembly pressure restriction has direct impact on the performance of an engine motorcycle (fuel economy, exhaust emissions, power deliver etc.) Therefore, it is crucial to predict & control the airflow resistance of such an open-cell PU foam.

This study focuses on the pressure drop prediction of dry (without oil impregnation) foam through CFD (Computational Fluid Dynamics). The aim is to predict the initial pressure drop of (open-cell) PU foam filters used in Indian motorcycle engine air filters...

When separating dusts with surface filters, the structure of the dust cake that forms in the process is of great importance, as it has a decisive influence on the operating behavior of the filter. With regard to the cyclic regeneration of the filter, the mechanical strength of the dust cake is particularly relevant, which in turn can be influenced by so-called raw gas conditioning. The adhesive forces of the particle contacts have a considerable influence on the mechanical strength of the dust cake. An increased mechanical strength in turn improves the cyclic regeneration of the filter, resulting in sufficient removal of the dust cake from the filter medium with less energy input.

In any dust cake of non-hygroscopic particles, the metered addition of a fraction of hygroscopic salt particles offers a possibility to influence the operating behavior of surface filters. For this purpose, a temporary change in gas humidity induces the deliquescence and efflorescence of the added salt particles. In this case, the deliquescence and efflorescence properties of hygroscopic salt particles are used to subsequently change the adhesive forces of the particle contacts as well as the structure of the dust cake formed on the filter medium and thus influence the operating behavior of the filter.

In the present paper experimental investigations on the influence of the concept on the operating behavior of test filters, especially with regard to the regeneration of the filter, are presented...

Precoating consists of covering filter media with particulate material forming an initial powder layer which is responsible for reaching the clogging point. The particulate matter accumulates in the fibers and in the particles already captured, forming the dendrites, and then the cake. Consequently, it increases the efficiency of dust collection at the beginning of filtration, guarantees the passage of air flow freely through the bag, promoting better detachment of the cake while extending its life span. In order to analyze the influence of moisture and precoating layer thickness on the collection efficiency for micrometric particles, were performed filtrations following the VDI 3926 Standard. Initially, the characterization of the particulate material was carried out to obtain the aerodynamic diameter, the average volumetric diameter, the chemistry composition and images in a Scanning Electron Microscope (SEM). Then, the filter medium was characterized to obtain the fiber diameter, porosity and permeability. Then, an experimental design was made, varying the conditions of humidity (5, 10 and 15%) and thickness according to the limit pressure drop (50, 100, 150, 200, 300 e 400 Pa). Precoating was carried out to the desired thickness by feeding the particulate material with the specified humidity. Then, primary sintering powder was fed to evaluate the collection efficiency...

Mostly virgin filter media have low collection efficiency, which requires superficial treatments to obtain a better performance. One of these treatments is coating filters with PTFE membrane. However, surface treatment increases the pressure drop and its cost, and consequently also increases the cost of equipment maintenance and operation. Another alternative commonly used in the industry is precoating, which is less expensive and has good performance in terms of filtration efficiency, but there are few studies on this subject. Other advantages of precoating are the lower initial filter media pressure drop, the possibility of increasing the useful life of the filter bag, and can also contributes to the chemisorption of pollutants present in the gas, such as HCl and SO₂. For the efficient use of this technique, it is necessary to know the ideal mass of precoat material that guarantees high filtration efficiency. In the present work we evaluated the necessary mass of precoating material to be used and its correlation with the clogging point.

The grade collection efficiencies for micro and nanoparticles were analyzed for different masses of limestone precoat deposited on the polyester filter medium (PE), in which, one of them was the mass obtained by the clogging point. Also a polyester filter medium with PTFE membrane (PE/PTFE) was used to compare the results. The clogging point, obtained by...

The concept of optimisation is considered one of the keyways of permanently resolving issues impacting OPEX and helping a business be sustainable. This study shows how measure the gap between the present and optimised operation levels of a dust collector system and decide on how convenient it is to proceed given existing conditions by focussing on particular areas of expertise – performances, reliability of technology, quality and savings.

In this case study, the existing dust collectors on kiln / raw mill of the cement plant are not performing according to the design conditions, the initial guaranteed value of pressure drop is always exceeded inevitably leading to the main following conditions:

• premature bags failure, mainly due to overcleaning to manage the very high pressure drop across the filter
• extremely high compressed air consumptions
• high power consumptions of the fan

Some examples of the criticalities highlighted by a preliminary analyse were related to the internal filter design, the exit available area reduced, the bottom, vertical and lateral gas velocity. Rendering the existing filter with a 3D model suitable for running a CFD simulation combined with a tailored process data collection campaign, allow both to perform a detailed gas behave analysis and rectify the mechanical criticalities affecting the equipment performances. This novel “OTP OPTIMISE PERFOMANCES^R” approach passes through the deep process analysis and equipment validation and the study of a comprehensive solution to optimize the existing bagfilter with low impact modifications and saving capex.

The main results have been...

Exposure to nanoparticles offers a great risk to human health, since, once inhaled, they can reach the bronchioles and alveoli and pass into the bloodstream, being then transported throughout the body. Several serious illnesses have been related to the inhalation of air polluted with nanoparticles, such as vascular disfunctions and permanent damages to the central nervous system. One of the promising alternatives for controlling particulate emission by industries is the hybrid filter, which combines electrostatic precipitation and fabric filtration in a single device. Even though good results have been obtained and reported for the collection of microparticles, there are few studies in the literature that assessed the performance of hybrid filters for nanoparticles. The purpose of this study was to address the question of whether the synergistic effect previously observed for larger particles in hybrid filters is also evidenced for nanoparticles, with diameters in the size range of 10-300 nm. A bench scale hybrid filter...

This work is a first attempt to simulate liquid spray atomization using a spiral nozzle in a spray. Spiral nozzle has a special non-axisymmetric geometry able to create a spray pattern in the form of three concentric hollow cone liquid sheets. This geometry leads to a mass transfer intensification among pollutant gas and the absorption liquid as well as a better capturing efficiency of PM. Thus, only one nozzle can be used instead of a system of several nozzles in the spray column. First, we simulated the gas phase distribution inside the scrubber chamber using a Reynolds stress model with the coupled solving scheme. This model is suitable for description of extremely turbulent flow. Second, we used a two-phase VOF model to investigate basic parameters of liquid flow escaping the spiral nozzle (refer to figure below). Both simulations can then be used to study liquid shower in the scrubber in a counter-flow with the entering polluted gas using a DPM model of the sprayed liquid. The DPM model provides us with information about distribution of liquid fragments and individual droplets to estimate the interface area necessary for adequate mass transfer rate. Result of this study can help to better optimize gas scrubbers in terms of capturing efficiency, size, usage/regeneration of absorption liquids and energy demands, which is tightly related to acquisition and operating costs...

In the course of progress in metal cutting processes (grinding, brushing, polishing), increasingly fine metal particles are produced. The separation of these particles is becoming more complex. Particularly in the case of submicron particles (mainly PM₁ and PM_2.5 fraction), downstream filter elements are required, which are associated with an additional pressure loss of the overall system. For this reason, new technologies with high particle separation efficiency and minimal energy input are required. One possibility can be wet-separation processes with innovative 3D-printed nozzle geometries for dispersion of the washing liquid. Since the dispersed washing fluid captures the particles, a fundamental understanding of the prevailing flow conditions is necessary. Here, numerical flow simulations can support the development in many steps of the product development cycle. Enabling pre-manufacturing studies for various designs, represents one major benefit of such an approach. Due to the degrees of freedom in terms of the geometry shapes by using rapid prototyping technology, the simulation is able to assist with the selection of design choices by predicting relevant physical properties. On the one hand, it therefore expands the overall range of possible design studies and on the other hand, reduces the amount of physical testing and premature manufacturing steps e.g. printing. This results in a reduction of time and cost in the whole development cycle.

In this contribution, an applied numerical geometry optimization with several design studies of an innovative 3D-printed wet-scrubber nozzle is presented...

Pulse-jet plug-in type compact dust collectors remove dust from the gases generated in factories. A pleated filter is widely used in this device because the filter media is folded in a pleated shape to increase the filtration area. In order to operate this device continuously, the dust particles deposited on the filter should be removed from the filter. However, since some dust particles accumulate inside the filter and form a thin layer (the primary adhesion layer) which cannot be removed, the performance of the dust collector changes with operation time.

Therefore, in this study, the effect of the pulse jet cleaning interval on the deposition state of the dust particles on the filter was analyzed and it was also aimed to develop the evaluation method for the dust collection performance...

Mechanically ventilated buildings use filtration to remove particles from supply air. In cases without recirculation, the concentration of particles in the supply air is simply the outdoor concentration multiplied by the filter penetration. However, some building ventilation systems partially recirculate exhaust air to reduce energy consumption and, to some extent, lessen particle loading on the filters. Under these circumstances the indoor air concentration is more difficult to estimate. Here, we present a case study from measurements in an office building, where the average recirculation ratio was measured as 0.6. The efficiency of the filter is compared to the true particle penetration when air is recirculated, showing...

Nanofibrous filter has a very wide range of applications in the removal of particulate matter in the air and the prevention of disease aerosol transmission because of its fine diameters and high specific surface areas. Using a denser nanofibrous structure or finer nanofiber diameters is a common approach to improve its filtration efficiency, but usually results in a striking increase of air resistance, which means high energy consumption and more likely to be blocked. Here, we have shown a novel nanofibrous composite filter that combined two layers of staggered patterned nanofibrous membranes which could improve the filtration performance due to its non-uniform packing density distribution. Electrospinning was employed to fabricate patterned nanofibrous membranes with different parameters on non-woven fabric. The air resistance and the particle penetration rate of the dual-layer staggered filter were reduced to...

Electrospinning techniques have been explored in the last years due to the high efficiency of particle collection. The population increase of the last decades contributed to global pollution, such as the emission of harmful materials into the environment. The rapid consumption and discard of PET derivatives, such as soda and water bottles, is a topic of growing concern due to the high volume of waste in the oceans and the lower decomposition of this thermoplastic. A way to reduce the global waste of PET is to recycle and give another destiny for plastic. The objective of the present work is to develop a highly efficient recycled PET filter for airborne filtration by electrospinning...

There is considerable research focusing on environmental concerns, especially on air quality improvement due to health risks. Nano-fibrous filters offer an effective, economical and straightforward method for filtration applications. It has been widely accepted that the fibrous structure of air filter media is complex and hence difficult to model. The heterogeneities in the filter structure lead to drastic changes in the filter media performance as it affects the gas flow path and the particle behaviour. A nano-fibrous filter media was considered for modelling, with composite geometry consisting of a nanolayer coated over a micro-fibrous layer. The two layers can be identified as having individual properties like air permeability, porosity, fibre size distribution, thickness, etc. In two dimensional (2D) modelling, the filter media heterogeneities are captured by the detailed representation of fibre size distribution which involves a thorough statistical analysis. Fibre distribution in nanolayer was found to follow a normal distribution, which has not been reported previously, and that of the base media follow a lognormal distribution (1, 2). SEM image of the nanolayer is shown in....

Nanofiber coated filtration medias have been used for a long time in surface loading filter systems for a long time due to easy dust cake release and easy pulsing.

In depth filtration applications nanofiber products have not gained notable success. This problems has been related to the premature blinding of the nanofiber layer collecting all the dust filtered causing a fast pressure drop increase.

On this presentation recent developments to overcome this problem is presented in a form of couple examples on HVAC and cabin air filter applications.

Fibrous filters are commonly used to separate suspended particles from air. Cellulose was previously a commonly used raw material in air filters. Presently fibrous filters are made either from plastic or glass fibres, but it would be environmentally important if one could replace them at least partly with more environmentally friendly and healthy fibres.

In this study we made generic test filters with a mixture of viscose fibres (0.5 dtex, length 5 mm, diameter 6 um) and either softwood pulp (30% of weight, KP1) or nanocellulosic fibres (10% of weight, KP2). The sample properties were: thickness 3 mm, the basis weight 200 g/m² and porosity 95%.

The samples were made using foam laying [1]. Foam enables the use of higher fiber consistencies with wood fibers and mixes of staple and wood fibers than the traditional nonwoven techniques.

Pressure drop and capture efficiency are the most important parameters for assessing the performance of these filter. The filtration efficiency was measured using the ISO16890 procedure. Both samples had similar pressure loss and capture efficiency. Their capturing performance was similar to typical EU5 filters with a two times higher pressure loss...

Seams are commonly used during the manufacturing of filter bags to ensure the cylindrical design. However, the seam may influence the filtration performance due to the presence of stitching holes. In the initial moments of filtration, more specifically in the first filtration cycle, the filter pores are filled with particles, however at that moment the stitching holes can cause preferential paths to the airflow and thus, changing the clogging point behavior. The issue of seam has been discussed in the literature from the perspective of emissions but there are few works concerning the influence of seam in clogging point of the filter media. The aims of this work were to investigate the influence of stitching holes in the clogging point behavior and to evaluate the filtration performance of microparticles using a filter material of an aromatic polyimide (PI) and polytetrafluorethylene (PTFE) scrim...

Diesel particulate filter (DPF) are used for exhaust aftertreatment in passenger cars and commercial vehicles. The particles to be separated are primarily carbon-based components formed in the engine compartment due to incomplete combustion. The aftertreatment converts those components into ash particles.

The particle-formation inside the DPF has an impact on the filtration device´s operating performance, e.g. the separation and the backpressure behaviour. Three different kinds of particle formation can be differentiated as shown in figure: The layer formation, the filling at the end of the channel, and a blocking at the front side of the channel.

At the Institute of Particle Technology of the University of Wuppertal, a wind tunnel with a DPF unit brick has been built to study the storage and rearrangement processes inside the channels...

Gasoline particle filters (GPFs) are gaining an increasing importance since regulations for engine particle emissions become more and more strict not only for diesel engines (Joshi & Johnson 2018). Thus, high effort was spent in the recent years on the development of GPFs (Lambert et al. 2017). But the current state of the art regarding production control related to particle removal efficiency is claimed to be not satisfying (e.g.: test time, GPF loading).

To fill this gap, a comprehensive testing program was performed by means of an approved production control test system (AFC 132 QC HEPA, Topas GmbH, Germany) that permits a complete particle separation efficiency testing in 30 s. On the basis of several GPF specimens with quite different separation efficiencies, a comprehensive testing program was performed using quasi-monodisperse and polydis­perse, metastable reference aerosols composed either of liquid or solid (see Fig. 1) particles. Separation efficiencies were characterised by contemporaneous analyses of up­stream and down­stream aerosol. For this purpose, different aerosol-analytical instruments/methods like con­den­­sa­tion particle counters, optical particle counters or optical particle size spectrometers were operated. Moreover, separation efficiencies of quasi-monodisperse aerosols were cross-checked with frac­tional separation efficiencies based on polydisperse test aerosols and differential electrical mobility analysis.

Received data are promising and allow....

Ashes from sewage sludge incineration contain phosphorus which is a vital and irreplaceable nutrient and is used as a fertiliser in agriculture. Due to the chemical composition of the phosphorus compounds and the excessive content of heavy metals, sewage sludge ashes do not fulfil the requirements for direct use as fertiliser in agriculture. To be able to use the ashes, they must be reduced of heavy metals. In recent years various chemical and thermal processes have been developed. Thermochemical processes are used for phosphorus recovery from sewage sludge ashes in which the desired substance conversions can be achieved by reacting the ashes with special additives. This technique is exclusively carried out in downstream process steps that are completely decoupled from the actual sewage sludge incineration but uses reaction temperatures of 800 – 1000 °C, which are in the range of the of the temperatures of the incineration process. Energetically advantageous would be processes which directly utilise the thermal energy in the incineration process to modify the ashes and, by fractionating the reaction products via hot gas filtration, enable the production of ash fractions suitable for use as fertiliser. However, the combination of hot gas filtration and thermochemical conversion is not yet a sufficiently researched process and can lead to considerable stress on the filter material.

In this work, the novel procedure with its technological challenges will be introduced and the advantages and disadvantages will be presented. Special focus will be placed on the hot gas filter, which are exposed to particularly high loads due to the new process...

Dust emissions result from the handling of bulk solids in production processes. These emissions can lead to environmental pollution, long-term diseases or cause explosive atmospheres. In order to reduce all this kind of possible hazards for the environment and humans prediction methods of dust emissions determining the dust mass reliable during a process step have to be developed.

In order to improve the dust release functions gained in a previous project collaboration between the Institute of Particle Technology (University of Wuppertal) and the Department of Mechanical Process Engineering and Solids Processing (Technische Universität Berlin) further investigations on an experimental and numerical level are carried out. Here, the first parts of the experimental studies are presented which are achieved by the Institute of Particle Technology. In contrast to previous investigations now experiments with single particles, which derive from a so-called Rerefence Test Bulk Material (RTBM), are performed. The RTBM is a blend of spheres and a well-defined powder in which the powder represents the fine material and the spheres act as the coarse material. The aim of the focus on single particles is to gain more detailed information about the impact factors of the release of fine particles (powder) from a surface (spheres) in dependency of physical parameters...

The use of various raw materials in the form of bulk material takes place in the building materials industry, agriculture and the food industry, among others. Here, the processes of handling, transport and storage result in the emission of particles due to external stresses. This discharge of material is also referred to as dusting.

The aim of the project is to demonstrate the effectiveness of the dust reduction measure "use of spray nozzles" in combination with the effect of electrostatic charging. The special feature here is that the investigations are oriented to the type of stress and the material and thus take into account the character of the dust discharge. Different test set-ups are used to realistically illustrate the handling operations during which dust is released. The effectiveness of the reduction measure is investigated under different operating parameters. The subsequent electrostatic charging of the spray mist allows the use of water and compressed air to be reduced and a standard for reduction adapted to the dust generation to be determined. An evaluation method for spray nozzle systems is being developed, which provides an assessment from the point of view of the economy of the resources used and the material-related efficiency of the abatement. This is to be made available to SMEs and thus simplify the choice of suitable dust reduction measures...

The overall objective of the research is to contribute to the development of new particulate products based on heteroaggregates formed in the gas phase. To achieve this goal, gas-phase-based processes must be established that allow the controlled formation of the aforementioned aggregates in sufficient quantity and quality.

Since the processes for this are clearly still lacking, a beam-based process is being developed, realised and simulated. The beam-based process comprises three steps. In the first, the various primary particles are dispersed and dosed as part of a carrier gas stream. In a second step, the jets interact with the different primary particles, contact occurs, allowing the formation of heteroaggregates. In a third step, the formed products have to be removed from the aggregation zone in a controlled manner.

Currently, the process parameters of the described process as well as the three sub-processes are unknown with regard to optimising the throughput and the quality of the formed heteroaggregates. The overall process including the three sub-processes must therefore be investigated in greater depth, which requires a process analysis that can be carried out offline on the basis of the aggregates formed. Spatially resolved insights into the process are obtained by laser light diffraction and characterisation of the flow field. In addition, the structure of the formed heteroaggregates should be assessed by offline imaging techniques (SEM, EDX) to link the structure to the properties of individual aggregates.

Since the time and length scales are small and therefore challenging, the gas phase-based process will also be mapped within a DEM/CFD framework. After a suitable model calibration and model validation, which is achieved by detailed benchmarking with the experimental investigations, process details that are not experimentally accessible will be addressed...

Especially in the field of paper and print post-processing on an industrial scale, continuous knife edge cutting and shearing operations generate paper dust. Despite preventive measures like dedusting units, the high paper web velocity induces the particulate dust release. As a result, the dust particles settle and accumulate on machine components and in the surrounding area. Resuspended particles around a potential ignition source represent a fire hazard. Another exemplary problem relates to particulate paper constituents adhering to greased ball bearings of conveyor systems. In the worst case, the heat transfer restriction increases the surface temperature and triggers an ignition of the paper web. Frequent servicing and maintenance prevent such fire incidents. However, the shutdown time during manual paper dust removal on industrial scale applications remains cost-intensive.

The main objective of this research project is to identify significant parameters affecting the release of paper dust particles on a micro scale. In this context, a cutting plotter executes the reproducible movement of cutting tool operations...

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 aim of this work is to investigate the flow pattern and performance of a sampling cyclone at different flow rates and reveal the dependence of main cyclone performance characteristics on flow rate (Reynolds number) using Large Eddy Simulations (LES)...

Due to their exceptionally high specific surface area and porosity, coupled with a great tunability of their chemical properties, Metal-Organic frameworks (MOFs) are promising candidates for irreversible trapping of toxic gases. Combining the conventional state-of-the-art sorbents, like active carbons, with MOFs, can lead to compounds that achieve a higher adsorption potential especially for polar gases allowing the manufacture of a new generation of clothing and respiratory cartridges that provide protection against a wider range of toxic substances at the same time.

The first step to successfully implement MOFs in protective clothing and respiratory cartridges includes the identification and selection of suitable candidates. Micro-breakthrough experiments of various gases (e.g. NH₃, H₂S etc.) conducted on several MOFs structures revealed that...

Nanomaterials (NMs) are increasing used in industries such as healthcare, cosmetics and agriculture. As a result, the likelihood that NMs will end up in the natural environment and adversely affect both the environment and indeed humans have increased in recent times. In the absence of regulations on the end-of-life management of NMs, they are treated via recycling, composting, incineration and/or landfilling. To date, only a handful of studies have been conducted on the fate of NMs in waste incineration plants particularly on the removal efficiency of nanoparticles emitted by the flue gas cleaning technologies (FGCT) present in these plants. As part of the FGCT used in waste incineration plants, scrubbers aid to remove acid gases, but they are also capable of collecting particles. The collection of particles by scrubbers is governed by several particle collection mechanisms with the primary ones been impaction, diffusion and interception. Conventionally, scrubbers are believed to be ineffective for the collection of particles less than 5 µm. However, research by Kim et al. (2001) established that under favorable operating conditions, scrubbers could be effective in collecting smaller particles. A review of the literature revealed that no study has been carried out on the capture of nanoparticles (NPs) by spray scrubber under waste incineration plant conditions.

To bridge this knowledge gap, the present study employs a design of experiment methodology (Box-Behnken Design) to evaluate the effects of the operating parameters of a spray scrubber on its NPs collection efficiency. The collection of NPs is evaluated from...

Air quality has profound health implications in all indoor environments where the world’s population normally spends most of their time. The quality of indoor air is therefore a prominent public health concern that requires a clear understanding of the transmission processes for the development and implementation of targeted infection prevention and control measures. World-wide outbreaks of severe acute respiratory syndrome (SARS) and other viral agents have caused a substantial health impact to the population and have increased public concerns for the spread of viral disease. The global pandemic caused by the novel coronavirus SARS-CoV-2, which causes the disease known as COVID-19, has changed the world in ways no one could have imagined. There is much more to learn about this ever-changing global threat, however, there are some aspects of the virus that are known such as its main route of transmission being that of an airborne nature and therefore, there is a strong desire to mitigate risk to the general population through the use of engineering controls such as filtration. Utilizing a test method developed and adopted at AAF International in collaboration with the University of Minnesota in 2018, a test for virus removal efficiency of air filters based on ASHRAE 52.2 methodology and transport particle capture was implemented as a first in the air filtration industry. At the beginning of the pandemic, AAF’s Biological Research Department launched a study utilizing a safe surrogate for the SARS-CoV-2 virus in order to evaluate the virus removal efficiency of several filters ranging in efficiency ratings of MERV 14-16. Air samples containing surrogate virus were collected upstream and downstream from the filters using aerosol test equipment such as Anderson Cascade Impactors and optical particle counters to be able to separate particles by size (approximately 0.3 to 10 microns). Then the samples were tested by quantitative reverse transcription polymerase chain reaction (RT-PCR) and a fluorometer to estimate mass. For each particle size, the particle size removal efficiency was calculated. The results showed that under the conditions of the study, filter efficiency for SARS-CoV-2 surrogate virus was comparable to filter efficiency using KCl particles (ASHRAE 52.2 standards). In addition, the efficiency of particle removal...

The COVID-19 has spread all over the world due to its high transmission rate. Because of this, demand for PPE’s has increased to protect frontline health professionals and the population. Therefore, studies are being carried out to improve PPE's, promoting better protection for people. The objective of our study was to propose methodologies of characterizations more appropriate for filter materials, such as surgical masks. We perform filtration efficiency and differential pressure (breathability) tests according to The Brazilian Standard ABNT NBR 15052 (2004). The standard proposes that the particle filtration efficiency test be performed with latex, particles of 100 nm and flow rate of 4.67x10^-4 m³/s. After performing these tests, we changed the particle to NaCl and performed the test for flow rate of 4.67x10^-4, 1.17x10^-4 and 6.67x10^-5 m³/s. These last flows were chosen after the study of the American Standard F2299 (2017) which proposes to use face speeds between 0.005 to 0.25 m/s. We tested 6 different masks, including one for non-professional use. The results exposed that...

To reduce ambient concentrations of viral particles, filtration media must allow for high fluxes of gases at low static pressure loss with high rates of particle removal and viral trapping or deactivation. Nanofiber-based filtration can achieve high aerosol filtration efficiency while exhibiting low-pressure drops. Here we report the first mass-producible air filter to possess HEPA-like pressure drop and efficiency, which is simultaneously self-sanitizing. The active filtration system is based on an electrically conductive, hybrid CNT-polyester mat that can rapidly be sanitized via resistive heating. Our material meets all relevant metrics required for HVAC filtration (i.e. filtration efficiency, pressure drop, heating rate, disinfection capabilities and price). The multifunctional aspect of the hybrid filter allows its implementation in an innovative HVAC filtration system that can act as an advanced alternative to current solutions, especially being able to tackle the well-known surface persistence of the SARS-Cov-2. The mat is produced via the direct CNT spinning method by the floating catalyst CVD (FCCVD) process. Tests showed...

The concentration of PM in urban railway tunnels (178.1 ug/m³) appears to be higher than that in the metropolitan area (49 ug/m³) addition, even in the case of NOX, which directly affect lung diseases, the concentration in the tunnel was found to be higher than the atmospheric standard of the Ministry of Korean Environment. The tunnel has a very high concentration of PM, and find particles generated by the train wind is scattered at high speed, making it difficult to process, and it is also required to develop a convenient filter in terms of maintenance. In this study, we examined the adsorption efficiency on a lab scale by using Activated Carbon Fiber (ACF), which has a high adsorption speed and a high adsorption capacity...

For the application of rotary machinery the air filter systems are an essential component of the complete turbine/compressor system. The machines have become more complex over the last few years and therefore the protection of the machines is becoming more and more important. Particulate contamination with salt or other corrosive particles can significantly impair a turbine power system through erosion, fouling or hot corrosion. Another challenge is the different climatic conditions from desert, offshore, rain forest to arctic conditions.

Due to the different requirements for the filters, the ISO 29461 standard is divided into 7 parts. It should be noted, that part 1 is the only part which is already approved by the ISO committee, the parts 2 to 7 are still under development.

Topas has developed a test system that covers the parts 1, 5 and 7 of the ISO 29461 series of standards respectively of the drafts of the ISO 29461 standard. The presentation will show the latest state of the test procedure as well as the test system and focuses on the description of the fully automated filter test system with flame photometer and optical particle counters. Furthermore, important key components for filter performance testing like humidifier, water spray system and aerosol generators (DEHS, NaCl and ISO A2 fine dust) will be presented. As well as the evaluation of the obtained measurement data such as differential pressure, particle separation efficiency, water separation efficiency, dust loading, salt and water deluge challenge. The creation of a summary report, which includes all determined and recorded parameters for a direct interpretation of the test results, is also a part of the presentation...

Face masks are currently and in future one of our major weapons to protect people from infections by airborne particles as viruses or bacteria.

As the perfect function of the mask is the basis for the safety of the user, these masks need to be tested concerning their performance in particle removal.

Standards as EN 149 in Europe, GB 2626 in China and 42 CFR 84 in United States must ensure a clear comparability of test results for the protection degree of the mask. Below is an extract of the main test parameters for the evaluation of face mask efficiency:

Filtration products need to be regularly tested in order to assess the correct protection level against harmful airborne matter. It is also important, that equipment that is used for testing the filtration products gives consistent results. Usually test equipment can be verified by tracing the results to a standard. For respiratory filter testing commonly used standards are EN 143/149, 42CFR part 84, and GB2626. These standards define key parameters for testing such as flow rate, aerosol concentration, count median diameter, geometric standard deviation, and ambient conditions. Some standards also specify the test equipment. Still, measurements that are compliant to the standards requirements don’t necessarily result in consistent penetration test results. While count median diameter and the geometric standard deviation are accurate means to define a sub-micrometer particle size distribution, the aerosol undergoes changes in the aerosol path of the filter tester that can change the size distribution.

When TSI developed a new model filter tester, the model 8130A, which replaced the model 8130, TSI executed a detailed test matrix in order to obtain continuity of measurement results between models. It consisted of:

• Two types of test aerosol, NaCl and Emery Oil
• Different types of flat-sheet media
• Different flow rates

In conclusion, these tests showed an excellent agreement between the models 8130A and 8130 for every media/aerosol combination and at different flow rates with measured penetrations typically within ±10% of the global mean.

To apply these results to in-line production filter testing requires...

It is well known that the level of uniformity of nonwoven filter materials is related to their filtration efficiency and therefore, this feature is an important subject to quality control (QC). The COVID19 pandemic has once again revealed the importance of efficient manufacturing processes for high-quality nonwovens, such as they are required for face masks that provide sufficient protection. While specialized 3D computer simulations have shown to be very helpful for the design and optimization of nonwovens, their computational cost is (in general) too high to allow for a quick assessment of the properties of a filter material. In addition, the acquisition of images of the microstructure created during production is not practicable.

This work is devoted to a fast and effective simulation-based analysis of the influence of the non-uniformity of the material distribution in nonwovens on their filtration efficiency. Both mechanical efficiency and the enhanced capturing due to fiber charging are included in the simulation model. ..

When the air in motion contacts with a solid surface, usually the air is thought to be approaching to a complete stop at the surface, and the velocity is zero relative to the solid surface. However, when the solid is so small that when the air passes the solid, only a fraction of the air molecules contact the surface. As the result, only those molecules have their velocities changed. The remaining air molecules remain their bulk flow motion. When we still consider the air as a continuum, the air velocity near the solid surface is not zero. That is the phenomenon called as slip flow.

The slip flow effect explains the low pressure drop for nanofiber filters because fewer air molecules exchange momentum with the fiber, there is less air drag on the fiber leading to less energy loss. Also because of the slip flow, the flow streamline is closer to the fiber surface and the single fiber efficiency of small particles is increased on nanofiber [1]. Therefore, the slip flow is a very important factor for nanofiber filtration. It must be considered when simulating the nanofiber filtration.

The slip flow was studied historically either with empirical equations or for very simple 1D or 2D structures, which cannot provide detailed information for a complicated 3D fibrous material structure. Cheng et al. [2] presented the approach to implement slip flow for 3D voxelized structures. In this approach, the expression of the slip velocity, which assumes the slip velocity proportional to the shear stress at the surface, is reformulated for a locally quadratic velocity profile instead of the standard linear profile, and reimplemented in our flow solver. The direct simulation of the slip flow is then possible, and it can be validated with analytic solutions.

The simulation results are compared to the newly obtained measurement data for nanofiber filters. The influence of slip flow in nanofiber structures then is studied and the results of flow and filtration simulations are presented...

This work presents simulated results of filter quality factors (FQ), also referred to as Figure of Merit (FOM), of nanofiber/microfiber mixed filters in order to produce the filter with the highest FQ. The computational scheme is based on the theory of single-fiber efficiency and the semi-empirical equation of pressure drop proposed by Davies (1953) and Bian et al. (2018). The equation cited here has considered the air molecule “slip-effect” on particle collection efficiencies and the pressure drop across the filter. We assumed here that filter with micro-size (1 μm) and that with nano-size (50 nm) contribute independently to the particle collections and air resistances. The results of pressure drop predictions, both with and without considering the effects of gas-slip on nanofiber were...

Electret filter media are commonly used in aerosol filtration to remove particles from gases. They provide a high initial particle removal efficiency combined with a low pressure drop as the fibers of the electret filter media are electrostatically charged. In addition to the mechanical deposition mechanisms (diffusion, impaction and interception), charged particles are deposited by the Coulomb effect and any (charged or uncharged) particles by dielectrophoresis.

The high initial particle deposition is reduced with increasing filter life, as already deposited particles attenuate the electrostatic effects mentioned above. In the worst case, the electrostatic effects have vanished and the aged electret filter media become conventional mechanical filter media. With regard to the application, it is necessary that even the aged filter media achieve a minimum filtration efficiency. For this reason, testing standards for electret filter media take into account ageing by discharging the electret filter media or the entire filter with isopropanol.

In this work experimental investigations on the influence of discharging methods on ten different corona charged and triboelectrically charged electret filter media are performed by means of deposition experiments. The focus is on the discharging methods with isopropanol prescribed in DIN EN 779 (liquid isopropanol) and its replacement ISO 16890-4 (isopropanol vapor)...

Nonwovens and felts from synthetic fibers (polyester, polypropylene) or from glass fibers are the mostly used filter media in air filtration. These materials offer high efficiency, long service life and a good price-performance ratio. However, the modern growing trend to replace petroleum-based fibers with bio-based and bio-degradable polymers dictates a new challenge for researchers, filter developers and manufatures.

Presented research focuses exploring PLA fibers as an alternative material for applications in air filtration. Particular emphasis was made on the characterisation of the mechanical properties of PLA monofilaments under aging conditions, which are relevant for the applications as filter media, with an aim to quantify the biodegradability of the PLA based materials. Furthermore, the air filtration characteristics of the PLA nonwovens depending on the textile media parameters were tested.

Multiple methodologies were used to characterise structural changes and mechanical properties PLA monofilaments before and after respective aging treatments. The results of the DSC analysis, tensile stress tests, 3D optical microscopy and scanning electron microscopy were...

The new filter classes based on ISO 16890 are already looking back upon more than four years since their approval, not only by national European bodies of standardization but industrial associations around the globe. Still, large portions of the facility management business segment have not yet fully embraced their existence. Even under the old standards, maintenance crews were more often than not confused about when to change filters in an air treatment system. To even add to their misperception, historically, various recommendations have in the past led to considerable confusion with installers of air filters about the legally required or economical optimum time to change the filter.

This essay should look back at the insecurity caused in the past related to filter change intervals. We will engage in the difference between the final pressure drop measured on the former EN779:2012 and the recommended air filter change intervals stated in the former EN13779. Both of these standards have long been replaced for some time: ISO 16890 for air filters and the ISO 16798 for air treatment systems. Unfortunately, none of the two regulations have given our global strive adapt the layout of air treatment systems and service thereof - to configure to real ambient conditions - any simplicity, or given more safekeeping for the consumer. Neither have the requirements for energy efficiency made the configuration and timely service of air filters any easier.

The European Energy Efficiency Directive was first passed by the European legislation 2009. It introduced an unprecedented SFP value to calculate the specific fan performance and the fans overall energy consumption in 2009 to asses each component of an air treatment system. Since then the filter community has relentlessly been heavily scrutinizing the SFP’s lack of evaluating the dynamic change of energy consumption caused by air filters.

Guided by the Eurovent energy ratings system for air filters, the EU is expected to pass a motion in 2021 to update the European Energy Efficiency Directive that shall plan to reflect new change interval for filters that will fulfill both initial claims. Not only will the service life of a filter reflect the ambient conditions, but it will moreover guide users to change intervals that will minimize energy costs induced by the air filters design and filter medium...

Wall-flow particulate filters are used for particulate matter (PM) removal from exhaust gas in a variety of aftertreatment systems of combustion engines. Here, they significantly reduce PM emissions. Inside these filters, the gas flow is forced through a porous wall between oppositely arranged inlet and outlet channels.

During this process, porous PM layers, which consist of both reactive and inert components, are formed inside the filter channels, resulting in an increase of the filter back pressure. This leads to the necessity of regenerating the filter by oxidizing the reactive components continuously or in reoccurring intervals and breaking up the continuous PM layer into individual layer fractions. When reactive-inert particulate matter structures re-arrange during the regeneration process, remaining inert material can be observed in different deposition patterns, impacting operational filter performance. The objective of this work is a deeper understanding of wall flow filter operational behaviour beyond sole engine applications.

Due to its massive parallelization capability, the Lattice Boltzmann Method has been shown...

Since many years, the software GeoDict is used to simulate filtration processes and modeling of filtration media. This includes simulation of the air flow inside the filter as well as tracking particles and simulation of their interaction on the filter surface.

In our newest version - GeoDict 2021 - we have adapted these functionalities for the simulation of Diesel Particulate Filters and Catalyst Monoliths. For example, new ways of modeling monolithic structures, detailed diffusive movement statistics, and 1^st order reaction simulation are now available. These improvements aim to model and optimize air flow, soot filtering, and noxious gas reduction in exhaust gas systems.

Exhaust gas treatment bears many challenging problems at different scales. From the larger scale, where macroscopic flow through the monolith channels is of interest, down to the diffusive movement between and even inside the highly porous ceramic grains. Surely, completely different effects take place at each scale. Nevertheless, GeoDict simulates all those effects through different modeling and simulation modules.

At different scales and using various modules, we present some examples on how:

• The flow passes through a plugged or un-plugged monolith
• The molecules interact with the washcoat layer and the catalytic centers within
• The catalytic reaction is simulated in the micro scale

In essence, we show how GeoDict helps optimizing the catalytic and filtration efficiency....

Bag filter systems for exhaust gas purification are characterized by a large number of bag filters (usually over 1000), which are loaded with dust particles and cleaned at regular intervals with a pressurized medium. In plant operation, malfunctions often occur due to uneven loading of the filters, which leads to reduced service life with typically high repair costs and plant downtime.

In the problem at hand, a bag filter system for flue gas cleaning in a power plant operation showed several failures within one year, in which cracks occurred in the filter fabric of individual bags. As a result, the specifications for air pollution control could no longer be met. The plant had to be shut down frequently and defective filters had to be replaced.

In general, CFD analyses have proven their potential for optimizing various processes, especially in plant construction industries considering the relatively high investment and operating costs of the plants, but also to avoid plant failures. But the size of the bag filtration plant with the high amount of filters to be considered as well as the dynamic interactions between the continuous particle deposition on filters, the local increase in flow resistance at the filter and the associated flow and deposition displacement make it difficult to optimize the plants with typical flow simulation tools. Since common CFD tools cannot take these interactions between deposition, resistance increase and displacement into account, adapted calculation tools are required especially for these problems.

The CFD modelling was done using the filter modelling tool from DHCAE Tools based on the CFD toolbox OpenFOAM [1] [2]. The modelling extension uses an Euler-Lagrangian approach whereby the interactions between filter loading, displacement of the continuous flow due to the increase in resistance and subsequent particle deposition are considered in an iterative process. This enabled the filters in the plant to be identified which receive a permanently increased particle load. As a result, these filters showed...

In the light of the growing awareness for air pollution, indoor air cleaners are meanwhile widely used to improve the indoor air quality. The market is expected to continue growing strongly during the COVID-19 pandemic as air cleaners may contribute to minimizing infection risks by filtration of virus-carrying droplets. Up to now, there are various national standards to test indoor air cleaners that determine the clean air delivery rate (CADR) as a measure for the cleaning performance. In the light of developing the first international testing standard ISO/IEC 63086 for air cleaners, there is the chance to harmonize and complement the current test methods. In this context, this work deals with the choice of suitable test aerosols and methods for considering ultrafine particles.

Most of the national standards use cigarette smoke as test aerosol. However, the aerosol properties such as concentration, agglomerate size, particle morphology and charge state are expected to strongly depend on the combustion conditions. Furthermore, tobacco smoke is carcinogenic and cigarettes are comparably expensive. However, for introducing an alternative test material to an international standard, different aspects have to be considered. Primarily, the new method has to yield highly repeatable results that allow a comparison between the performances of different appliances. Secondly, it is important for the testing institutions that all materials are globally available at reasonable costs, are easy to handle without risks for the operator and the properties are independent of the supplier. Thirdly, for the manufacturers and consumers it is desirable that the results using the new test material do not strongly differ from the results from the previous national standards using other test materials. Although the latter is not a strict requirement, it may facilitate the introduction of the new test method and increase the acceptance by the consumers.

With this motivation, we investigated the performance of three air cleaners using different filtration technologies with respect to NaCl, KCl and DEHS and compared it to results derived with cigarette smoke. We show that the CADR can be very reproducibly measured with all investigated test aerosols and does not strongly depend on the choice of the material. This means that the filtration efficiency curves in the relevant particle size range are sufficiently flat and discharging effects by the test aerosol are negligible at the low exposures involved.

Concerning the particle size, recent national testing standards typically consider only particles larger than about 0.3 µm since considerably smaller particles are not accessible by optical particle counters. However, a test method considering smaller particles, especially in the ultrafine particle (UFP) size range <0.1 µm, is highly desirable for different reasons: Firstly, it is know that the relevance for health effects increases with decreasing particle size, since smaller can enter deeper the human respiratory system and have a higher surface to volume ratio. Furthermore, the largest fraction of the number size distribution of typical indoor aerosols lies in this size range and is thus most representative for real conditions. Finally, a previous study has shown that the efficiency of air cleaners can considerably degrade with decreasing particle size, especially when using of electret filters (Schumacher, 2018).

For these reasons, we investigated two different methods for determination of a CADR for UFP. As test aerosol, potassium chloride (KCl) particles were generated from an aqueous solution and dispersed in a 30 m³ test chamber, where the air cleaner was located. The first approach used a condensation particle counter (CPC) to measure the total concentration of particles larger than several nanometers, depending on the exact type of CPC used. By fitting the exponential decay curves with and without air cleaner, the CADR was derived. The method is easy to perform, but has the disadvantage that there is generally a dependence on the exact size distribution of the test aerosol. We investigated how large this effect is and how reproducibly size distributions can be generated by using different atomizers.

To circumvent the dependence on the particle size distribution, the CADR was alternatively determined by measuring the decay rates for monodisperse fractions in the UFP range using a differential mobility analyzer (DMA) adjusted to classify one certain particle size. As disadvantage, this restricts information on the cleaning performance to a specific particle size and has worse statistics because of the substantially lower particle concentrations. The results from both methods were evaluated and compared. The findings from the study shall drive the development of new methods in the recently published IEC 63086 testing standard for air cleaners...

In recent years, air quality in German cities has improved continuously, but hotspots in several cities still do not comply with the 2008/50/EC immission limit values. Currently, most exceedance events in Germany are related to NO₂ values being too high. In contrast, excessive particulate matter (PM) concentrations pose the greatest challenge from a worldwide perspective. A novel approach to locally improve the contaminant level is to employ outdoor air filtration devices, as e.g. the MANN+HUMMEL Filter Cube.

Stuttgart’s ‘Am Neckartor’ area is the most prominent air quality hotspot in Germany and therefor offers an ideal location for the exemplary investigation into the effectiveness of filtration devices at an urban traffic hotspot. As part of a public-private field testing project, 23 outdoor air filtration devices (MANN+HUMMEL Filter Cube) with a nominal flow rate of 14.500 m³/h per unit were installed in the ‘Am Neckartor’ area beside federal highway B14. The employed filters were equipped with high capacity activated carbon filter media capable of reducing the local NO₂ and PM concentrations. The focus of this publication is set on the proof of concept investigations conducted at the Neckartor site...

The concentration of airborne particulate pollution and the size distribution of the mass of the particles captured during air filters service life affect strongly how their airflow resistance changes throughout their operation. Therefore, the ageing process of air filters depends strongly on the place and on the system where they are employed. Urban and industrial areas are very challenging because of the high concentration of atmospheric sub-micrometer particles which clog fibrous filter media quickly. In fact, smaller particles get into the fibrous matrix (deep filtration) and occupy the space available among the fibers. Larger particles tend to deposit on the top of the filtering material (surface filtration) and increase much less its airflow resistance.

Depending of the type of filter material, natural ageing can show very different behaviors. For sure it is very useful to compare service life of filter elements in severe conditions. However, such testing programs should last six to twelve months to be meaningful and reliable. Moreover, the trend observed in data sets obtained during various years may differ because of the season or atmospheric conditions.

These considerations are relevant and of practical interest for most air filters and especially for those used in gas turbine air intake systems. In fact, their service life, maintenance costs and energy implications are strongly influenced by the type of airborne particulate pollution in a specific place and system. The availability of a repeatable and reproducible laboratory procedure to predict the natural ageing process, as closely as possible, is highly desirable. This procedure would allow to design and to optimize the filter media and the filter cartridge geometry, together with the combination of the most appropriate prefiltration choice.

For this reason, Ahlstrom-Munksjö and Politecnico di Torino carried out a research project to develop a new synthetic ultrafine aerosol able to clog a full scale filter element in laboratory in a few hours...

Fibrous coalescence filters are widely applied in gas cleaning processes to separate liquid droplets from a gas flow (e.g. oil mist). When separated on the fibres of the filter medium, the oil droplets can take many shapes dependent on the wettability, roughness and diameter of the fibres, droplet volume and fibre arrangement (e.g. axisymmetric barrel-shaped droplets and axially asymmetric clamshell-shaped droplets). The overall morphology of the deposited droplets on the filter fibres is well known from optical microscopy, however, no studies exist regarding the impact of these separated droplets within the filter matrix on the separation efficiency. To investigate a change in the filtration efficiency the exact morphology of oil structures on and between adjacent filter fibres has to be characterised. Thus, the spatial deposition of the droplets on the fibres (upstream, downstream or partially upstream and downstream side) as well as...

Today, liquid aerosols are generated in many industrial processes like machining, manufacturing of catalysts or in pneumatic compressors. Liquid aerosols may be harmful since small droplet may enter the respiratory system and cause lung cancer, allergies, or other diseases. Also, due to the recent COVID-19 outbreak, aerosols containing viruses are classified as dangerous. We present results of micro-scale simulations of mist deposition on fibrous structures and validate them by comparison to single fiber efficiency (SFE) theory and to experimental data...

Oil mist coalescence filtration is widely used in process industry. Efficient removal of micro droplets and enhancement of filtration performance of filter media are the focus of attention at present. In this work, different methods were used to modify the traditional filter materials for oleophilic (dry and wet) and oleophobic (dry and wet) treatment. The effects of the modification methods on the coalescence filtration performance and surface liquid distribution of the filter media were studied, and the optimal performance enhancement method for liquid aerosol separation with high efficiency and low resistance was proposed. The results show that...

Conventional filters consist of one or more filter layers, which are either woven or composed of tangled fibers. The quality of the separation results almost only from density of the fiber arrangement. Due to the manufacturing process, compromises between separation and pressure loss that are in the opposite relationship to each other are inevitable.

The development of additive manufacturing has made great progresses in recent years. Using this technology, filter manufacturing is no longer restricted to conventional methods. At this point, the adjoint topology optimization of filters is a promising alternative opportunity of filter development. The idea behind this is to use the adjoint solver to generate geometries that have been optimized with regard to pressure loss and the filtration efficiency. The complex non-linear relationships between the separation mechanisms and the pressure drop offer the opportunity for improvement. The fluid region with the CAD model of the initial geometry is divided into volume cells. The cells at the fibers are then varied by mesh deformation until an optimum is found. Using the often bionic-looking optimized structures physical prototypes are generated using additive manufacturing. In a further process step the structure is coated and thus, functionalized. The new approach offers the chance to develop filters in a new way, avoiding the previous parametric development and even crossing the Pareto front in the multi-objective optimization of filtration efficiency and pressure loss.

The key to topology-optimized "bionic" filters are...

Nonwovens are commonly used in aerosol filtration to remove particles from gases. The nonwovens can differ, for example, in fiber diameter (distribution), porosity, thickness and grammage, which affect air permeability and filtration performance. In conventional nonwovens, the particles are deposited by the mechanical deposition mechanisms (diffusion, impaction and interception). The fibrous structure can also be electrostatically charged (electret nonwovens). In addition to the mechanical deposition mechanisms, charged particles are deposited by the Coulomb effect and any (charged or uncharged) particles by dielectrophoresis. This increases filtration performance while maintaining air permeability.

This allows a wide range of variation in the development and selection of suitable nonwovens for the desired application. Accordingly, experimental investigations can be performed using existing or specially manufactured nonwovens. However, experiments are time-consuming, so that more or less complex model calculations appear useful. Empirical models or formulas are not sufficient for complex three dimensional structures as nonwovens, since they are based on single fiber theories. Numerical simulations are more suitable, although the computational power is high for fiber diameters in the submicron and nanometer size range.

In this work, a new and time-optimized approach for predicting filtration performance based on machine learning (LeCun et al. 2015, Nature) is established. For a first...

Infectious diseases occur by spreading into the air through particulate matter (PM) and droplets containing viruses. To prevent the virus transmission in the air, research on inactivation of floating viruses is needed. In this study, we examined inactivation characteristics of MS2 bacteriophages according to the thickness of Activated Carbon Fiber (ACF). ACF is a material processed in the form of fibers to improve the adsorption performance of activated carbon, which has a high performance on the removal of gaseous and particulate matter. In, the effects of inactivation MS2 bacteriophages was examined by comparing before and after passing the ACF. The experimental results showed that...

Today aerosols are produced in many industrial processes like machining or in pneumatic compressors. The harmfulness of these industrially produced droplets often lies in the liquid itself as it can be toxic or cancerous while exhaled natural aerosols can carry viruses or other pathogens. For health protection, the filtration of these aerosols is an important task. The wetting properties of the fibers have a large influence on the filtration efficiency and coalescence of droplets on the fibers. Oleophilic fibers are better in capturing the oil aerosols while the drainage increases with oleophobic fibers. For improved efficiency and drainage properties, a mixed-wet fiber system could therefore be advantageous.

Deposition of droplets and the resulting coalescence is highly complex and extremely dependent on the wetting properties. Describing these processes in filter-scale simulations is computationally extremely demanding, if not infeasible. We present a new approach for simulating oil mist deposition and droplet coalescence correctly accounting for the wettability of the fibers, especially for mixed-wet filter media. The aim is to gain a more realistic pressure loss of a fibrous filter structure which takes the presence of the filtered phase into account as well as the coalescence of the liquid phase on the fibers depending on the wettability and the fluid parameters...

Liquid aerosols endanger human health if their concentration in the air is too high or if people are exposed to them for too long. In the industrial sector, oil mist can cause severe lung diseases in workers. Therefore, coalescing filters are used for air purification. The use of filters results in a pressure loss of 2 – 5 % at the filter medium and residual emissions of more than 20,000 particles/m³. There is a conflict of objectives between a low pressure drop and a high degree of separation. In addition, clogging due to oil occurs quickly inside the filter media.

Therefore, a novel fiber for coalescing filters is presented in this paper...

Fibrous materials are subjected to compression in many industrial processes, such as natural gas filtration at high pressures. A number of investigations have been conducted to study the relationship among compression load, pore size and permeability. However, the effect of structural parameters on the filtration performance of compressed media has not been reported.

In our study, the variation of packing density, pore size distribution and contact angle for both oleophilic and oleophobic glass fibrous materials with different degrees of compression were experimentally measured. Furthermore, the filtration performance of compressed filters such as wet pressure drop, penetration, saturation, and liquid distribution are investigated.

The results showed that...

The novel coronavirus (COVID-19), average size 100 nm, can be aerosolized by cough, sneeze, speech, and breath of infected persons. The airborne carrier for the COVID-19 can be tiny droplets and particulates from infected person, fine suspended mists (humidity) in air, or ambient aerosols in air. To-date, unfortunately there are no test standards for nano-aerosols (≤100 nm). A goal in our study is to develop air filters (e.g., respirator, facemask, ventilator, medical breathing filter/system) with 90% capture on 100-nm airborne COVID-19 with pressure drop of less than 30 Pa (3.1 mm water). There are two challenges. First, this airborne bio-nanoaerosol (combined virus and carrier) is amorphous unlike cubic NaCl crystals. Second, unlike standard laboratory tests on NaCl and test oil (DOP) droplets, these polydispersed aerosols all challenge the filter simultaneously and they are of different sizes and can interact among themselves complicating the filtration process. For the first time, we have studied these two effects using ambient aerosols (simulating the bio-nanoaerosols of coronavirus plus carrier of different shapes and sizes) to challenge electrostatically charged multilayer/multimodule nanofiber filters...

As the management of airborne pathogens in the indoor air has emerged due to the COVID-19 pandemic, active quarantine technologies using air conditioning systems are being developed. Since 2019, the Korea Institute of Materials Science has been actively developing material parts that can effectively trap and sterilize or inactivate pathogens such as bacteria and viruses floating in indoor air. We developed a low-temperature plasma filter that physically traps pathogen particles and sterilizes or inactivates pathogens with ozone, which has strong oxidation potential. A low-temperature plasma filter uses a ceramic foam with pores of several tens of micrometers, which simultaneously acts as a dielectric for plasma generation and as a filter for collecting pathogens. The currently developed low-temperature plasma filter has a size of 100 cm² and generates ozone at a level of 0.5 ppmv at a wind speed of 1 m/s to oxidize captured pathogens. The catalyst located at the rear end of the low-temperature plasma filter reduces the emitted ozone to a level of...

A matter that threaten health are increasing due to deterioration of air quality. Among, bio-aerosols and fine particulates are the main causes of air quality deterioration. There are two methods for reducing such particulate matter: a fiber filter method or an electrostatic precipitation method. However, due to the characteristics of microbes, they can survive for long period of time and changing these filters improperly could lead to the transmission of pathogenic bacteria or virus, and even to outbreaks. In addition, the existing electrostatic precipitation method has a problem in that ozone is generated. In this study, a copper fiber type ionizer that operate at low voltage to reduce ozone generation and inactivate viruses using antibacterial properties was studied...