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billow August 30, 2005 06:20

Gas generation with resistance in porous media
Hello: I got a curious result in my case recently. wish someone could help me. My case is simulate the gas generating and flowing in porous media. In my Q1 file I set these lines: ------------------------------------------------ PATCH (SOR1 ,VOLUME,1,NX,1,NY,1,NZ,1,1) COVAL (SOR1 ,P1 , FIXFLU , 2.400000E-07)

PATCH (SOR2 ,VOLUME,1,NX,1,NY,1,NZ,1,1) COVAL (SOR2 ,W1 , 1.345000E+07, 0.000000E+00) ---------------------------------------------------- I set the domain matiral as 'Air useing ideal gas law', and, it was 'one_phase,one dimension'. which i want to do is set gas generate in whole domin(size:1m*1m*50m) with rate 2.40E-07(m**3/m**3.S).

And there were resistance presented by PATCH 'SOR2'(in porous media which μ/K = 1.345000E+07).

In my mind , in result file the Nett source of R1 at patch named: SOR1 should be 2.40E-07*Volume = 2.40E-07*1*1*50 =1.20E-05, but the reality is: --------------------------------------------------- Nett source of R1 at patch named: SOR1 = 3.967191E-02 ---------------------------------------------------

that makes me so puzzled, and have no idea with it:(

ps:the result is right when i set the domain matiral as water(imcompressable) OR delete the Patch named SOR2(resistance)

billow August 30, 2005 06:30

Re: Gas generation with resistance in porous media
sorry, the unit of generation rate is (Kg/m**3.S), I write it incorrectly above.

Mike September 8, 2005 05:49

Re: Gas generation with resistance in porous media
My suspicion is that the contribution -Pp*V*Cm, which is usually negligible, is responsible for the incorrect gas generation inflow rate. The source term is:

Sm = Cm*(Vm-Pp)*V

and since Cm=FIXFLU=2.E-10, the contribution -2.E-10*Pp*V is usually negligible compared to 2.E-10*Vm*V/2.E-10 where Vm is the mass generation rate per unit volume. However, in a porous media the in-cell pressure may be quite large.

A hand check of your RESULT should be able to ascertain whether this surmise is correct. If proved correct, you need to use a much smaller value of FIXFLU, say 1.E-20, to render the contribution -Pp*V*Cm negligible.

billow September 9, 2005 11:36

Re: Gas generation with resistance in porous media
Thanks for your help, and I think that is the right point. Through my experiment I found that the Coefficient FIXFLU can convert the Value to source/Coefficient automatically. So it is necessary to set Value= source/1.0E-20 manually when I set the Coefficient = 1.0E-20. Is that right? But I really got a right RESULT:)

mick September 20, 2005 09:51

Re: Gas generation with resistance in porous media
No in ground or elsewhere should not need to set VAL=VAL/FIXFLU, this should be done automatically inside the code. But you can tell at a glance from your results as the source would be incredably wrong.

zhhjll June 21, 2011 19:11

I want to model a micro filter, This filter (membrane) is rectangular (105 cm) with the thickness 12e-5. so,I calculate this parameters from Ergun equation which D=1e-6, because of the Micro filter type. is this assumption true??
i think this is very thin filter so there in not flow through in the membrane, in this situation is inertial coefficieant higher in Y direction? or not?when i set y-direction inertial coefficient higher than x-direction got better answer! is this resonable?

I am looking forward to hearing from you.
Sincerely yours

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