Momentum source / porous loss

ijk · May 14, 2011, 06:53

Hi all,

I am modelling a radiator and want to account for the pressure loss across it.

I have data of pressure loss vs velocity.

From that data and the depth of the radiator, I worked out my linear and quadratic resistance coefficients.

I then set up a test case to see if the CFX model gave me sensible results.
I set up a tunnel with the radiator in the middle and a velocity inlet of 10m/s. I used free slip walls.

The pressure drop from CFX was 266 Pa and it should be 230. Can anyone please suggest why the two are different?

Thanks,

ijk

siw · May 14, 2011, 08:54

Have you tried the CFX Catalytic Converter tutorial? That deals with flow through a porous medium and could assist in setting up your model.

ghorrocks · May 15, 2011, 18:51

http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

ijk · May 16, 2011, 08:15

Got it solved.

It was a bug in Excel - I plotted a polynomial trendline in excel and the coefficients it gave me were wrong.

gwheeler · May 20, 2011, 08:38

I'm trying to do the same thing - I have pressure drop vs. flow rate across a filter, and I need to include this loss in my CFX model. Can you share the spreadsheet or at least point me to the equations?

Thanks!
Greg

ijk · May 20, 2011, 10:30

I modelled the flow through a radiator so in my case the flow can only go in one direction. Therefore I used the directional loss model.

I simply plotted (pressure drop/depth of radiator) vs. velocity and fitted a second order polynomial to the data points. (this was the problem in excel)

The coefficients are the linear and quadratic resistance coefficients.

May 14, 2011, 06:53	Momentum source / porous loss	#1
ijk Member Join Date: Apr 2010 Posts: 33 Rep Power: 16	Hi all, I am modelling a radiator and want to account for the pressure loss across it. I have data of pressure loss vs velocity. From that data and the depth of the radiator, I worked out my linear and quadratic resistance coefficients. I then set up a test case to see if the CFX model gave me sensible results. I set up a tunnel with the radiator in the middle and a velocity inlet of 10m/s. I used free slip walls. The pressure drop from CFX was 266 Pa and it should be 230. Can anyone please suggest why the two are different? Thanks, ijk

May 20, 2011, 08:38	calculation?	#5
gwheeler New Member Greg Join Date: May 2011 Location: Boise, ID Posts: 3 Rep Power: 14	I'm trying to do the same thing - I have pressure drop vs. flow rate across a filter, and I need to include this loss in my CFX model. Can you share the spreadsheet or at least point me to the equations? Thanks! Greg

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May 14, 2011, 08:54		#2
siw Senior Member Stuart Join Date: Jul 2009 Location: Portsmouth, England Posts: 733 Rep Power: 25	Have you tried the CFX Catalytic Converter tutorial? That deals with flow through a porous medium and could assist in setting up your model.

May 15, 2011, 18:51		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

May 16, 2011, 08:15		#4
ijk Member Join Date: Apr 2010 Posts: 33 Rep Power: 16	Got it solved. It was a bug in Excel - I plotted a polynomial trendline in excel and the coefficients it gave me were wrong.

May 20, 2011, 10:30		#6
ijk Member Join Date: Apr 2010 Posts: 33 Rep Power: 16	I modelled the flow through a radiator so in my case the flow can only go in one direction. Therefore I used the directional loss model. I simply plotted (pressure drop/depth of radiator) vs. velocity and fitted a second order polynomial to the data points. (this was the problem in excel) The coefficients are the linear and quadratic resistance coefficients.