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Old   December 3, 2013, 10:02
Default CFX conjugate heat transfer problems
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Nicholas Lee
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hi every one, recently i am doing a CHT simulation related to heat transfer by using CFX. with defined AIR INLET&OUTLET conditions and WATER INLET&OUTLET conditions (mass flow and Temp. for both), two interfaces ( interface air-solid and interface water -solid) , heat transfer option and thin material and GGI method, the case normally converged, and it can be found out that the outlet temp. for air is down and that for water is up.

but
1, for the CFX CHTproblems, there is not the method like than in FLUENT just seting wall and wall-shadow to be coupled and acting the energy model, but i have to define the interface and activate heat transfer and thin material option, are there any other methods for CHT simulation in CFX? i really prefer to the easy-operating CFX.

2, it's strange that when i just changed my inlet mass flow(from 0.15kg/s to 0.3kg/s) for cooling water with others unchanged. The outlet Temp for gas and cooling Temp hardly changed, just like the same simulion.

All your replys will be appreciated. and best wishes!
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Old   December 3, 2013, 10:05
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the simulation structure including two fluid standing for air and cooling water, and solid that is real heat exchanger or called cooler
Attached Images
File Type: jpg 1.jpg (42.7 KB, 27 views)

Last edited by dingsheng1206; December 3, 2013 at 18:43.
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Old   December 3, 2013, 10:10
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the results for two cases which just differed in the mass flow for cooling water(0.15kg/s or 0.3kg/s) are almost just the same.
attached are the air temperature distribution and that for cooling water. Looking forward your earliest reply.
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File Type: jpg 2 Temp distribution for air.jpg (60.6 KB, 21 views)
File Type: jpg 3 temp distribution for cooling water.jpg (42.5 KB, 17 views)
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Old   December 3, 2013, 15:12
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1 - The concept wall-wall shadow-coupled in Fluent is equivalent to creating the domain interface, and using option Conservative Interface Fluxin CFX. You do not need to activate the interface heat transfer model option unless you want to sub-model the interface even further.

NOTE: using the interface heat transfer model option = None, it is the same of using a zero constant resistance model, or infinitely conducting thin material.
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Old   December 3, 2013, 20:13
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Quote:
Originally Posted by Opaque View Post
1 - The concept wall-wall shadow-coupled in Fluent is equivalent to creating the domain interface, and using option Conservative Interface Fluxin CFX. You do not need to activate the interface heat transfer model option unless you want to sub-model the interface even further.

NOTE: using the interface heat transfer model option = None, it is the same of using a zero constant resistance model, or infinitely conducting thin material.
Dear Opaque, thank you for your reply.

do you mean that for simulating heat transfer between solid and fluid without any heat resistance, i just have to apply Solid Fluid Interface and the option of Conservative Interface Flux in CFX, but without acting Interface Model?

and the Interface Model is just suitable for application of real thermal resistance, or real coating materials on domain,etc?

do i perfectly follow you? many thanks!
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Old   December 3, 2013, 22:41
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you got it..
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Old   December 3, 2013, 22:51
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Quote:
Originally Posted by Opaque View Post
you got it..

dear Opaque, i am not sure if you should be in the daytime now or at night , sorry to trouble you, for i am really excited that i have almost handled the problem.

following you instructions, i have just applied Conservative Interface Flux in CFX but without interface model, and eventually it worked that the outlet air temperature is coming down and that for water is up.

but when i changed the mass flow rate for water inlet (from 0.15kg/s to 0.3kg/s) toghet with other settings kept unchanged, the simulation result was hardly affected that the the both temperatures for outlet air and outlet water remained the same.
I am confused how to explain it, would you give me some advice?

thank you! Opaque!
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Old   February 13, 2014, 14:29
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hardik thakkar
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can you please send me a tutorial based on your problem..
because i am trying to solve that kind of problem for my dissertation..

thank you
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