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AMC filters are the first line of defense in commercial operation cleanliness and a key factor to ensuring high productivity. Activated carbon filters are widely used to remove a variety of low concentration chemical contaminants from commercial operations. It is difficult and unviable to test developmental filters at real-world concentration levels, which is why filter developers or independent labs test them under accelerated conditions. In the absence of standards for filter test concentrations, performance claims can vary widely from vendor to vendor, making it difficult for the end user to compare and understand the capabilities of various filters for fab applications.

In this study we show the impact of testing filters at various concentrations and the understanding of the filter performance consequently and why an evaluation is conducted at specific lower concentrations is more effective.

The HVAC industry often tests filters at concentrations as high as 100 parts per million (ppm, 10^‑6). Many AMC filter vendors test filters (or potentially only adsorbent samples) at con­cen­tra­tions between 3 and 100 ppm, the ISO standard 10121-1:2014 suggests a range of 9-90 ppm, all far above real-world applications, which might be as low as a few parts per billion (ppb, 10^-9). In other words, those applications are a factor of 1000-100000 below test concentrations. Filters being evaluated at 100 ppm vs. 1 ppm can significantly skew the understanding of the filter performance in terms of lifetime or capacity.

Controlled filter testing for single chemicals at varying concentrations shows the impracticality of performing tests at high concentrations much higher than the actual environmental concentrations. However, there are certain models that can, to a certain extent, predict performances at lower concentrations based on results at higher concentrations. These models, too, are limited, and the accuracy of measurements at single digit ppb levels is questionable.

Filtration solutions are often deployed without accurately knowing the contamination challenges of the environment to be protected. This is usually done to either implement a solution as quickly as possible, or to minimize cost by using pre-defined and readily available off-the-shelf solutions. However, this approach neither assures an efficient contaminant removal nor does it optimize cost of ownership. An inexpensive filter, which is replaced often, may have a higher cost of ownership over time than a customized, more expensive solution that has a greater capacity and longer life. Considering the high cost of the ...

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

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

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

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

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

INTRODUCTION

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

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

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

MATERIALS AND METHODS:

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

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

RESULTS & VALIDATION

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

CONCLUSIONS

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