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Old   May 1, 2014, 22:09
Default Little help needed for solid conductivity
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Aslan Farjam
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Hello Everyone,

I modelling a row of 3D fins. Also there is an applied heat from the bottom of these fins and air is passing from the top side of these fins in a channel. All of the surrounding boundaries are insulated except the bottom which receives applied heat,inlet and outlet of the channel.

Problem :When I change the value of conductivity in these fins, nothing in my model changes, even the cross section of fins have the same temperature profile as other cases with different K conduction.

Does anyone know why?
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Old   May 2, 2014, 06:23
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I've the same problem, any help will help me too.
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Old   May 2, 2014, 11:56
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Just now i solve my problem, post a picture to see if I could help you.
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Old   May 2, 2014, 15:52
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[ATTACH]Attachment 30566[/ATTACH]Attachment 30565Attached is the configuration of my problem.
Again when i change the K conduction for fins nothing will change in my model. I even change the K to 1 and next time I changed it to 1000. Still no change...
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File Type: jpg Drawing1 Model (1).jpg (91.5 KB, 11 views)
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Old   May 2, 2014, 16:03
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Quote:
Originally Posted by ayad View Post
Just now i solve my problem, post a picture to see if I could help you.
hey check it out.
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Old   May 3, 2014, 10:53
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Try to increase the level in contours.
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Old   May 3, 2014, 16:15
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Hey,

I increased the levels but still the temperature is the same when I change the K conduction. It seems Fluent is not applying the K conduction change effect in the solution. I dont know why.
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Old   May 4, 2014, 14:42
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Hi
Im really not expert in heat transfer, but i think Fluent is right. From fin to air, heat transfer(Nu) is a function of Re and Pr which none of them are relevant to fin conductivity.Lets write energy equation for fin(energy in=energy out), so the heat from bottom=h(Ts-Tinfinity) so Ts would be constant even with considering different conductivities.

**Use Temperature for fin bottom as boundary condition, then i think the surface temperature of the fin with higher conductivity has higher value.
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Old   May 4, 2014, 14:50
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Hi Behrooz,

Thats right, but (Nu) is in fact is the fraction of convection over conduction (hL/K) so K conduction is effective in Nusselt number. what do you think about this?
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Old   May 4, 2014, 14:53
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Yes, Nusselt is the fraction of convection over conduction of working fluid. That K is the conductivity of fluid not solid( Im sure about this).
Good luck
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Old   May 4, 2014, 14:54
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thx behrooz
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Old   May 4, 2014, 14:59
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Sry Behrooz,

another thing is that it is not really applicable for me to change the fin base boundary condition from heat flux to temperature, because I dont have the value. Any idea of what i can do in order to solve this issue?
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Old   May 4, 2014, 15:15
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Temperature was just an example, i meant that when you set temperature then the fin with higher conductivity takes more heat and eventually has higher surface temperature.There is no issue. Conductivity value doesnt have effect on fin surface temperature in steady mode and with heat boundary condition, but in transient run the fin with higher conductivity reaches sooner to Ts.
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