3 Replies Latest reply on Jun 3, 2014 8:38 PM by Jared Conway

    Filter Porosity

    Nick Goodwin

      Hi,

       

      I have been working on a flow simulation of an air system which has a couple of HEPA filters and a blower.  I have flow rate and pressure drop from the filter supplier and a blower curve.  When I asked the filter supplier for the porosity of the filter they told me that it was N/A, however any setting I try to use for the filter within the porous media features require me to enter porosity. I havent been able to find this information anywehere else either, so I have set the porosity at 0.3 as a best guess.

       

      The filter has a spec of 510 CFM at 0.40" H20 and the blower has a rate of 475 CFM at 0.78" H20.  Since I have two filters I expect the flow through the filter should be laminar, but the simulation shows that flow is uneven and almost in a vortex. 

       

       

      Is there another way to set up a porous material that does not require entering a porosity? 

       

      From what I have read there is no direct correlation between micron size and porosity; is there any other way to link these properties?

        • Re: Filter Porosity
          Jared Conway

          there are other ways to define porous mediums, check the help

          but i think they all need porosity

          but even then, if your provider doesn't have porosity, will they have other properties to set it up differently?

           

          the effect that porosity has is on velocity

          so you may have to do some physical tests to come up with porosity to match whats happening in the simulation

          however from what i remember, it only affects velocity inside the porous medium but that is something you could check pretty easily in flow simulation

            • Re: Filter Porosity
              Nick Goodwin

              Thanks Jared.

               

              You are right that there are other ways of setting up the porous mediums, and they all require entering a porosity.  My supplier has been able to provide data for the flow rates and pressure drops, but I'm concerned that the guess at porosity is creating inaccurate results.  The goal of the project is to create laminar flow through a channel within a target velocity range (not specifically within the filter), so as long as the porosity does not affect the velocity before and after the filter then I should be good no matter what porosity I use, right?