Mixing in porous media

vishyaroon · April 17, 2009, 13:34

How good (are trustable) are predictions of mixing of two fluids in porous regions (any software - Fluent, STAR)? I know from the basic formulation of porous media, that the constants are defined for computing the pressure drop across the region, but can we believe the results of mixing of two fluid streams in the region?

otd · April 17, 2009, 22:19

Are mixing liquids, gases, both?

harishg · April 18, 2009, 02:29

Trial and error and literature survey is what you need to do.

vishyaroon · April 18, 2009, 17:13

I am looking at two gases that mix as they pass through a porous zone.

otd · April 19, 2009, 15:11

Sorry I didn't read your question closely. It appears you are asking about the ability of Fluent to do your problem.

Have you asked the question on the Fluent forum or, perhaps, asked the Fluent support staff directly?

andy2o · April 19, 2009, 18:49

Consider these two examples of domains which could be modelled as porous medium flows, but have very different mixing characteristics:

1) Flow through many parallel micro-channels - which will permit zero cross-flow mixing because the flow is confined to the individual channels.
2) Flow through a random bed of spheres, where fluid will be spread as it hits each sphere, causing cross-flow motion which will help mixing.

I guess your application lies somewhere between these extremes. The point is that a drag correlation only computes the drag. It does not distinguish between these two different mixing scenarios. Therefore you need to supply a model for the effective momentum and mass diffusion caused by the porous medium as well as the drag force to complete your model of a porous medium. This diffusion model will need to take the form of correlation / approximation based on experimental data (or perhaps very detailed CFD) just like the drag coefficients do.

As always: The results will be only as good as the correlation! So you can only trust the results if you trust your correlation and validate your model!!

Best regards,
andy2o

vishyaroon · April 20, 2009, 09:41

Thank you all for replying to the question. I guess as Andy mentions I'll have to do a detailed CFD or get some correlataions based on experiments.

April 17, 2009, 13:34	Mixing in porous media	#1
vishyaroon Senior Member Aroon Join Date: Apr 2009 Location: Racine WI Posts: 148 Rep Power: 17	How good (are trustable) are predictions of mixing of two fluids in porous regions (any software - Fluent, STAR)? I know from the basic formulation of porous media, that the constants are defined for computing the pressure drop across the region, but can we believe the results of mixing of two fluid streams in the region?

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April 17, 2009, 22:19		#2
otd Member private Join Date: Mar 2009 Posts: 74 Rep Power: 17	Are mixing liquids, gases, both?

April 18, 2009, 02:29		#3
harishg Senior Member N/A Join Date: Mar 2009 Posts: 189 Rep Power: 17	Trial and error and literature survey is what you need to do.

April 18, 2009, 17:13		#4
vishyaroon Senior Member Aroon Join Date: Apr 2009 Location: Racine WI Posts: 148 Rep Power: 17	I am looking at two gases that mix as they pass through a porous zone.

April 19, 2009, 15:11		#5
otd Member private Join Date: Mar 2009 Posts: 74 Rep Power: 17	Sorry I didn't read your question closely. It appears you are asking about the ability of Fluent to do your problem. Have you asked the question on the Fluent forum or, perhaps, asked the Fluent support staff directly?

April 19, 2009, 18:49		#6
andy2o New Member Join Date: Mar 2009 Posts: 5 Rep Power: 17	Consider these two examples of domains which could be modelled as porous medium flows, but have very different mixing characteristics: 1) Flow through many parallel micro-channels - which will permit zero cross-flow mixing because the flow is confined to the individual channels. 2) Flow through a random bed of spheres, where fluid will be spread as it hits each sphere, causing cross-flow motion which will help mixing. I guess your application lies somewhere between these extremes. The point is that a drag correlation only computes the drag. It does not distinguish between these two different mixing scenarios. Therefore you need to supply a model for the effective momentum and mass diffusion caused by the porous medium as well as the drag force to complete your model of a porous medium. This diffusion model will need to take the form of correlation / approximation based on experimental data (or perhaps very detailed CFD) just like the drag coefficients do. As always: The results will be only as good as the correlation! So you can only trust the results if you trust your correlation and validate your model!! Best regards, andy2o

April 20, 2009, 09:41		#7
vishyaroon Senior Member Aroon Join Date: Apr 2009 Location: Racine WI Posts: 148 Rep Power: 17	Thank you all for replying to the question. I guess as Andy mentions I'll have to do a detailed CFD or get some correlataions based on experiments.