The now famous line from the Star Trek series…”To boldly go where no man has gone before,” has become an iconic phrase used shamelessly by TV, radio and print media for decades. So, as a blog writer I will also paraphrase this line in relationship to the topic of this blog. This blog is about HEPA filters and going where no man has gone before.. inside the HEPA.
HEPA media is basically wet laid and rolled out like newspaper material and incorporates large amounts of tiny glass material to give it some strength. It is very thin and fragile and therefore when it is used in filtration the HEPA media is pleated and has either aluminum separators or glue beads between each pleated layer to keep the media from rubbing against itself and damaging the fragile media.
The HEPA media is extremely dense creating a significant amount of resistance or pressure drop creating a challenge to pull air through the media for filtration purposes. As compared to general duty air filters, such as fiberglass or ring panel filters, the amount of energy required, in motor HP, to pull the air through the HEPA is significant. Usually requiring at least a 1/3 HP motor for small HEPA filters and up to 1 HP and greater for the larger 24″x 24″ by 12″ deep metal framed HEPA filters.
HEPA filters are composed of a mat of randomly arranged fibres. The fibres are typically composed of fiberglass and possess diameters between 0.5 and 2.0 micrometers. Key factors affecting function are fibre diameter, filter thickness, and face velocity. The air space between HEPA filter fibres is much greater than 0.3 μm. The common assumption that a HEPA filter acts like a sieve where particles smaller than the largest opening can pass through is incorrect. Unlike membrane filters at this pore size, where particles as wide as the largest opening or distance between fibres cannot pass in between them at all, HEPA filters are designed to target much smaller pollutants and particles. These particles are trapped (they stick to a fibre) through a combination of the following three mechanisms:
- Interception, where particles following a line of flow in the air stream come within one radius of a fibre and adhere to it.
- Impaction, where larger particles are unable to avoid fibres by following the curving contours of the air stream and are forced to embed in one of them directly; this effect increases with diminishing fibre separation and higher air flow velocity.
- Diffusion, an enhancing mechanism that is a result of the collision with gas molecules by the smallest particles, especially those below 0.1 µm in diameter, which are thereby impeded and delayed in their path through the filter; this behaviour is similar toBrownian motion and raises the probability that a particle will be stopped by either of the two mechanisms above; it becomes dominant at lower air flow velocities.
Pure Air Systems, in Indianapolis, Indiana has been manufacturing HEPA based air filtration systems since 1985 and has thousands of their units installed in a wide variety of applications across most of the US and over seas. These units use the commercial grade, certified, scanned HEPA filters for all of their systems providing the best available technology for the reduction and removal of airborne contaminants, pathogens and allergens as small as .012 microns.
For more information on their complete line of HEPA based filtration systems please go to our website at: https://www.pureairsystems.com . Or call us on our toll-free number at: 800-869-8025.
About the Author: Don Musilli
My name is Don Musilli. I started Pure Air Systems in 1985 and then sold it in 2006. I continue to consult for PAS and write their blog and control their Twitter account. I also, on occasion, make changes to the website. The company is now almost 26 years old and has been a major player in offering commercial grade, high performance HEPA and Carbon based filtration systems for the commercial, institutional, industrial and residential markets.
I currently reside in Englewood, Florida where I write blogs and do social media marketing for a number of clients.
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