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Filtration Specification Guidelines



Have you considered calling ThermoPore with a liquid or air filtration application in mind? If you are, then you’re not alone. We receive many inquiries from a variety of different markets that involve filtration – both air filtration and liquid filtration. In an effort to make your interaction with ThermoPore as effective and efficient as possible – we thought we’d throw together a quick video to describe the information that we need to best recommend any one of our porous materials for use in your specific application.

Hi, my name is Ken Milam. I’m an application engineer here at ThermoPore. Welcome to Thermo.TV. In this installment, we’ll be discussing the makeup of a properly defined filtration specification. First we’ll introduce the three basic components of the specification. Then, we’ll briefly describe and explain each. Lastly, we’ll put them all together to demonstrate their combination into a singular filtration specification.

Let’s start with the first of three components – particle capture level. Expressed as a percentage, this component describes the number of particles that are captured or filtered from the given flow stream. For example, suppose you count the number of particles in a sample flow stream before it passes through the filter. Let’s say that the sample contains 100 particles. Next, you force that sample through the filter and you count the number of particles again. In the filtered sample, you count five particles. What does this mean? It means your filter captured 95 of the original 100 particles. Put another way – it captured 95% of the particles. So there’s our first component defined…capture efficiency.

Now, let’s turn our attention to the size of the particles. As you can probably imagines – particles come in all sizes; from larger one to small one, to everything in between. Particle size is typically expressed as an absolute number (i.e., 10 microns) or as a range (i.e., 1 – 10 micron) or as a series of ranges (.1 micron – 1 micron, 1 – 10 micron, and 10 – 50 micron). Regardless of how you might characterize particle size, we need to know the size of the particle that your application deems critical. Okay, so there’s our second component defined…particle size. That leaves us with our third and last component.

The third component that needs to be characterized is the flow conditions. Why? Well, it turns out that a filters performance is dependent upon the flow rate of the air or water through the filter. To learn more about why this occurs – I would encourage you to watch the Thermo.TV episodes that discuss Most Penetrating Particle Size – but until then, just understand that a filter’s capture efficiency varies with flow conditions.

So how do we specify the flow conditions? By describing the volumetric flow rate of the air passing through the filter per unit area of filter media. As an example – consider the scenario whereby 10 cubic feet of air is flowing through a heating/air conditioning duct each minute. The duct’s size is 1 foot by 1 foot. Installed in the duct is a filter whose dimensions also measure 1 foot by 1 foot. So, each minute, 10 cubic feet of air flow through the 1 square foot filter. Expressed as a volumetric flow rate per unit area of filter media, we’d say that the flow rate through the filter is 10 cubic feet/minute/square foot of filter media. That expression can be reduced to 10 feet per minute which is called the filters face velocity (i.e., how fast is the area moving through the face of the filter – fitting , right?). Well, either way, the flow condition of the air or liquid through the filter describes our third component of our filtration specification.

So now , let’s put these together in the form of an example. Your request for a filtration media would sound something like this – Hello, ThermoPore, I’m looking for your recommendation for a filter media with a filtration capture efficiency of 99% for particles .2 microns in size at a face velocity of 1 ft/min. That’s it – simple right? Well I hope this installment of Thermo.TV has helped provide you with some insight into the information that we need to most effectively help you with your next project.

That’s it for now – stay on the look out for later installments of Thermo.TV. If you have any additional questions or if there are some topics that you’d like to see added to the Thermo.TV channel – give us a call or drop us a line. For now, I’m Ken Milam saying thanks for watching this installment of Themro.TV – we’ll see you next time.

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