How many times have you heard us say, “your cleanroom filtration is critical”? Probably more than once if you’ve spent any time interacting with us. But not all filtration is the same! Depending on your filter and application, there are different cleanroom particle filtration techniques. Today, we’ll be covering 4 of them.
This technique is exactly what it sounds like: the filter strains particles out of the air. Similar to the way you strain water out of pasta, the filter has woven fibers that create a mesh to catch particles. Any particles that are larger than the holes are caught, while the air and smaller particles pass through.
This is the most basic type of filtration, so it works best for larger particles. It is impossible to create holes tiny and effective enough to catch the size of particles that cleanrooms need to be protected from. So this technique works best as a preliminary measure to strain out the largest particles and protect the more sensitive filters.
Inertial impaction uses a strategic web of fibers that increase the inertia of the particles to the point they are forced out of the air stream. They then stick to these fibers and are prevented from going any further.
This technique is also used for larger particles, but not necessarily as large as the ones caught during straining. The idea is that the web of fibers speeds up the airflow to the point that the heavier particles cannot keep up. This is how they are forced out of the airstream.
Interception does just that: it intercepts the particles. It is similar to straining, except that it is designed to capture smaller particles. Instead of creating holes that catch large particles, this technique uses methods that create an attraction between the particles and fibers. The air flow carries them near enough to the fiber to be attracted and, just like that, the fiber has a hold on them.
Diffusion is the most complicated form of filtration technique designed to snatch up the smallest of particles. This is typically particles 0.1 microns and smaller. “Diffusion” actually describes the movement of the particles.
In this technique, air is forced upon particles until they enter a state of Brownian motion. This means they are moving randomly, bouncing back and forth and all around. By creating this chaotic motion, the filter forces them to bounce about fibers they can stick to. This drastically increases the chance they will stick to a fiber.
Is there a right filtration technique for any application?
The best contamination control strategy involves multiple types of filtration techniques. Each one is designed to capture different types and sizes of particles, so, depending on your needs, you will probably need all 4.
Most likely, your cleanroom will need a basic straining filter at the start of your air filtration system. This would serve as a pre-filter: the filter your air goes through first. Its job is to take out the biggest particles and prolong the life of your more sensitive filters, namely your HEPA and, possibly, ULPA filters.
Depending on your cleanroom needs, you might only use HEPA filters. But if you are looking to eliminate the smallest of particles, you will most likely also need an ULPA filter.
Both of these filters use a combination of the techniques we discussed here.
So which filtration technique do you need to use?
Trick question: you need all of them, and your filter suppliers know that.