Little help needed for solid conductivity

aslaan.farjam@gmail.com · May 1, 2014, 23:09

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?

ayad · May 2, 2014, 07:23

I've the same problem, any help will help me too.

ayad · May 2, 2014, 12:56

Just now i solve my problem, post a picture to see if I could help you.

aslaan.farjam@gmail.com · May 2, 2014, 16:52

[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...

aslaan.farjam@gmail.com · May 2, 2014, 17:03

Quote:

Originally Posted by ayad

Just now i solve my problem, post a picture to see if I could help you.

hey check it out.

ayad · May 3, 2014, 11:53

Try to increase the level in contours.

aslaan.farjam@gmail.com · May 3, 2014, 17:15

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.

CFD-fellow · May 4, 2014, 15:42

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.

aslaan.farjam@gmail.com · May 4, 2014, 15:50

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?

CFD-fellow · May 4, 2014, 15:53

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

aslaan.farjam@gmail.com · May 4, 2014, 15:54

thx behrooz

aslaan.farjam@gmail.com · May 4, 2014, 15:59

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?

CFD-fellow · May 4, 2014, 16:15

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.

May 1, 2014, 23:09	Little help needed for solid conductivity	#1
aslaan.farjam@gmail.com New Member Aslan Farjam Join Date: May 2014 Posts: 10 Rep Power: 12	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?

May 3, 2014, 17:15	level increase	#7
aslaan.farjam@gmail.com New Member Aslan Farjam Join Date: May 2014 Posts: 10 Rep Power: 12	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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May 2, 2014, 07:23		#2
ayad New Member ayad Join Date: Apr 2014 Location: Iraq Posts: 25 Rep Power: 12	I've the same problem, any help will help me too.

May 2, 2014, 12:56		#3
ayad New Member ayad Join Date: Apr 2014 Location: Iraq Posts: 25 Rep Power: 12	Just now i solve my problem, post a picture to see if I could help you.

May 3, 2014, 11:53		#6
ayad New Member ayad Join Date: Apr 2014 Location: Iraq Posts: 25 Rep Power: 12	Try to increase the level in contours.

May 4, 2014, 15:42		#8
CFD-fellow Senior Member Behrooz Jamshidi Join Date: Apr 2013 Posts: 110 Rep Power: 13	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.

May 4, 2014, 15:50		#9
aslaan.farjam@gmail.com New Member Aslan Farjam Join Date: May 2014 Posts: 10 Rep Power: 12	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?

May 4, 2014, 15:53		#10
CFD-fellow Senior Member Behrooz Jamshidi Join Date: Apr 2013 Posts: 110 Rep Power: 13	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

May 4, 2014, 15:54		#11
aslaan.farjam@gmail.com New Member Aslan Farjam Join Date: May 2014 Posts: 10 Rep Power: 12	thx behrooz

May 4, 2014, 15:59		#12
aslaan.farjam@gmail.com New Member Aslan Farjam Join Date: May 2014 Posts: 10 Rep Power: 12	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?

May 4, 2014, 16:15		#13
CFD-fellow Senior Member Behrooz Jamshidi Join Date: Apr 2013 Posts: 110 Rep Power: 13	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.