# Should I be using True or Superficial Velocity for Porous Domain?

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 November 16, 2010, 07:29 Should I be using True or Superficial Velocity for Porous Domain? #1 Senior Member   Stuart Join Date: Jul 2009 Location: Portsmouth, England Posts: 484 Rep Power: 15 Hi, I've measured the pressure loss (del_p) across an air filter as a function of volumetric flow flow (Q) in the laboratory using a real air filter. I've plotted the data and got a 2nd-order polynimal equation, with coefficients A and B: del_p = (A * Q) + (B * Q^2) I've then calculated an average velocity (V_ave) across the air filter as a function of the volumetric flow rate. So now I have an equation: del_p = (C * V_ave) + (D * V_ave^2) where the coefficients C and D have different values to A and B. So what I'd like to know is if I should be using the True or Superficial velocity model? I think true velocity because I started with experiemental data from a real air filter but I'm also thinking Superficial velocity because my final coefficients have used an averaged velocity. No doubt I'll try both, but I'd like some understanding from the CFX community. Thanks. Last edited by siw; November 16, 2010 at 07:31. Reason: Typo

 November 17, 2010, 06:36 #2 Senior Member   Matthias Voß Join Date: Mar 2009 Location: Berlin, Germany Posts: 446 Rep Power: 12 hi superficial velocities are derived from the velocities and the volume fractions. Do you follow a multiphase approach? neewbie

 November 17, 2010, 08:52 #3 Senior Member   Stuart Join Date: Jul 2009 Location: Portsmouth, England Posts: 484 Rep Power: 15 Hi, This is for single phase (air) only. I'm going to neglect the particles that the air filter removes for this particular simulation.

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