# A question about one conjugate heat transfer example

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May 6, 2020, 10:58
A question about one conjugate heat transfer example
#1
New Member

Alex
Join Date: May 2020
Posts: 21
Rep Power: 6
I try to simulate a heat exchanger like fig1 below，

and set the gas material's density as ideal gas like fig2.

set the mass flow inlet and pressure outlet.

I've tried two simulations, the only difference between two simulations is that the gas outlet pressure:from 5bar to 200bar.

But the results of two simulations are almost the same! Why?

I thought the higher pressure would give rise to higher heat exchange efficiency! Because in fluent theory guide, there are density in energy equation Like fig3,

The coupled walls's thermal boundary conditions are coupled like fig4.
The outside walls's thermal boundary conditions are thermal insulation.

Is there something I did wrong? who can tell me? thanks very much!

PS:
The Energy Equation in fluent theory guide:

https://ansyshelp.ansys.com/account/...er_theory.html
Attached Images
 heat exchage.jpg (31.4 KB, 11 views) fig2.jpg (69.7 KB, 8 views) fig3.jpg (61.9 KB, 9 views) fig4.jpg (63.3 KB, 7 views)

 May 6, 2020, 11:04 Boundary Conditions #2 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36 What are the boundary conditions for the gas? __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 6, 2020, 21:33
#3
New Member

Alex
Join Date: May 2020
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[QUOTE=vinerm;769061]What are the boundary conditions for the gas?[/QUOTE

mass flow inlet
pressure outlet
the gas's wall--thermal-coupled(fig1、fig2)

Regards!
Attached Images
 gas1.jpg (45.6 KB, 1 views) gas2.jpg (46.1 KB, 1 views) gas3.jpg (39.6 KB, 0 views)

 May 7, 2020, 05:59 Flow Rate #4 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36 If your flow rate is same, then you should not expect much difference. Since it is ideal gas, there will be difference in velocity due to different density, which is a function of pressure but you have to plot velocity contour to observe what kind of difference do you get in velocity field. Heat transfer is ultimately a function of flow field and material properties and I don't expect flow-fields to be a lot different in both of your cases. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 9, 2020, 11:19
#5
New Member

Alex
Join Date: May 2020
Posts: 21
Rep Power: 6
Today,I do the same compared simulations one by one, and I found that the higher pressure of the gas ,the lower temperature of outlet gas. Maybe I did some wrong settings or the fluent's parameter simulation have some bug before.
Thank you very much all the same.
Best Regards!

Quote:
 Originally Posted by vinerm If your flow rate is same, then you should not expect much difference. Since it is ideal gas, there will be difference in velocity due to different density, which is a function of pressure but you have to plot velocity contour to observe what kind of difference do you get in velocity field. Heat transfer is ultimately a function of flow field and material properties and I don't expect flow-fields to be a lot different in both of your cases.

 Tags conjugate heat transfer, fluent