How fluent calculate heat-transfer-coefficient?

Shinobi · September 9, 2013, 14:57

Hi,
I have a simple test, a cube 1*1*0,2 (l*l*x).
Boundary condition T1=350°K in upper face, T2=300°k in opposite face, k=200.

So Q=k/x*A*(T1-T2)=50000

Fluent report flux no problem, Q=50000 as formula, but I want to export heat-transfer-coefficient for every cells. he must be 1000, but fluent calculate 1.2194E+003. Why?

For this case I insert only 1 cell mesh.

Far · September 9, 2013, 17:29

what is the bulk velocity?

Shinobi · September 9, 2013, 17:55

Quote:

Originally Posted by Far

what is the bulk velocity?

Why bulk velocity?
it's a simple Heat transfer in a solid plate.

Far · September 9, 2013, 18:04

you want to check the thermal conductivity?

Heat transfer coefficient is for the convection.

Shinobi · September 9, 2013, 18:20

Quote:

Originally Posted by Far

you want to check the thermal conductivity?

Heat transfer coefficient is for the convection.

Goal is

, that is conductance

Far · September 9, 2013, 18:44

isnt it obvious? As k is fixed and so is the dx

Shinobi · September 10, 2013, 03:12

Quote:

Originally Posted by Far

isnt it obvious? As k is fixed and so is the dx

Yes, in simple case. But when I have a complex structure whit fins?
Goal is to understand how fluent calculate this rate or I can calculate this from ''fluent-export''. So I can tell: this is average

of structure from report flux. That is report flux=Q, U=Q/A/(T1-T2).
From mesh I can calculate every single Q(i) by cells, so I can compare average with single station to see the difference and if this difference is high.
Imagine a structure like this:

Far · September 10, 2013, 03:40

Delta X is changing ? K is changing? If yes then you UDF.

Shinobi · September 10, 2013, 03:47

Quote:

Originally Posted by Far

Delta X is changing ? K is changing? If yes then you UDF.

Only Delta x, k is constant.
how can I proceed?

Shinobi · September 18, 2013, 10:55

Quote:

Originally Posted by Far

Delta X is changing ? K is changing? If yes then you UDF.

In report fluent I have Heat Flow [ Watt ] (Heat Rate), that is Q for every face mesh that I call Qi, and area of mesh Ai. Whit delta Temperature I have U.
U=Qi/(Ai*delta(T))

How can I calculate this division?

September 9, 2013, 14:57	How fluent calculate heat-transfer-coefficient?	#1
Shinobi Member Join Date: Oct 2012 Posts: 44 Rep Power: 13	Hi, I have a simple test, a cube 110,2 (llx). Boundary condition T1=350°K in upper face, T2=300°k in opposite face, k=200. So Q=k/xA(T1-T2)=50000 Fluent report flux no problem, Q=50000 as formula, but I want to export heat-transfer-coefficient for every cells. he must be 1000, but fluent calculate 1.2194E+003. Why? For this case I insert only 1 cell mesh.

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September 9, 2013, 17:29		#2
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	what is the bulk velocity?

September 9, 2013, 18:04		#4
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	you want to check the thermal conductivity? Heat transfer coefficient is for the convection.

September 9, 2013, 18:44		#6
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	isnt it obvious? As k is fixed and so is the dx

September 10, 2013, 03:40		#8
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	Delta X is changing ? K is changing? If yes then you UDF.