Hi,

Let´s supose this: I have two air-filters. They were manufactured with the same material but one has bigger volume than the other.

If I have a and b coefficients from one filter, can I use the same values to simulate the other?

Thanks

When I did research on porous media my coefficients were based on the measured pressure drop at different velocities. So, I believe, that unless you pressure drop is the same the coefficients will be different.

It is true that the coefficients depend on the flow rate. But very weakly. You should be fine with using them for different pressure drops.

But, for different porous media, that's a big no. The coefficients have nothing to do with the material that porous media was manufactured from. They are all about the pore geometry. For example, if one is more porous than the other (I think this is what you meant), you need new coefficients.

I used Forcheimer's equation for flow thru porous media, which is quite dependent on fluid velocity. I measured the pressure drop, knew everything except for my intertia coefficient and permeability. From the data I curve fit a second order equation and solved for the two coefficients. But, since it is dP/(length) it might not matter that the length changes. I am not sure how pressure changes as the length changes; ie..does the ratio change?

As I said, the permeability and Forcheimer (or Ergun) coeffs. are claimed to not change. They actually do change but not always important. See:

Sozer, E. and Shyy, W., "Multi-scale thermo-fluid transport in porous media", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 18, Issue 7/8, (2008), pp. 883-899.

I think he was asking if they change..

In addition to the paper listed above, these authors have written numerous papers dealing with that type of flow. My research was based on the thermal non-equilibrium, which Jiang and Whitaker did a lot of research on.

PX Jiang, Vafai, Stephan Whitaker, Bejan