Heat transfer coefficient in CFX code

June 12, 2008, 05:45

Does any one know how to calculate the overall (not local) heat transfer coefficient (or Nusselt number) in CFX code?

Halim

June 25, 2008, 03:24

Easiest way would be areaAve(Heat Transfer Coefficient)@<boundary>. It will give you an area weighted average of the variable

samanpnh · February 7, 2013, 18:56

I wrote a code that gives average nusselt number in steady state as a scalar number for a cylinder in cross flow with Induced Vibrations
local nusselt
nuL= (Wall Heat Flux *shoa*2[m])/(75 [K]*Thermal Conductivity )
that 75 is Temperature difference
average nusselt number
nuave=areaAve(nuL)@Pipe1

I think it works for you

but I need a way that plot average nusselt number as a function of time like the follow picture
Please somebody help me

ghorrocks · February 7, 2013, 19:54

Send your variable nuave to a monitor point, then you can see it as the transient simulation progresses on solver manager.

samanpnh · February 8, 2013, 06:33

I did exact the same thing, but it gives this error in follow picture. please help me

I have another question. Is shown in the photo. Instead of (2 * shoa) D1 or D2 should I use?

samanpnh · February 8, 2013, 06:42

this pic is better

ghorrocks · February 8, 2013, 07:00

Looks like the areaAve function can only take CFX variables, not your CEL expression. In that case just do the averaging in the nuL equation.

samanpnh · February 8, 2013, 08:36

What do you mean? Please tell me the exact code

also D1 or D2?

samanpnh · February 8, 2013, 11:50

What do you mean? Please tell me the exact code

also D1 or D2?

please help me

ghorrocks · February 9, 2013, 06:10

Replace nuL= (Wall Heat Flux *shoa*2[m])/(75 [K]*Thermal Conductivity )

with

nuL = areaAve(Wall Heat Flux)@Wall * shoa ..... * areaAve(k)@Wall

samanpnh · February 9, 2013, 07:26

Thank you very very very much. Error is cleared

samanpnh · February 9, 2013, 08:57

What do you think about D1 or D2؟؟؟

ghorrocks · February 10, 2013, 05:20

If you are trying to match a publish result then they should define how they calculated Nu. There is no general rule, you can define it anyway which makes sense to that application.

June 12, 2008, 05:45	Heat transfer coefficient in CFX code	#1
Halim Guest Posts: n/a	Does any one know how to calculate the overall (not local) heat transfer coefficient (or Nusselt number) in CFX code? Halim

June 25, 2008, 03:24	Re: Heat transfer coefficient in CFX code	#2
hsr Guest Posts: n/a	Easiest way would be areaAve(Heat Transfer Coefficient)@<boundary>. It will give you an area weighted average of the variable

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February 7, 2013, 19:54		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Send your variable nuave to a monitor point, then you can see it as the transient simulation progresses on solver manager.

February 8, 2013, 07:00		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Looks like the areaAve function can only take CFX variables, not your CEL expression. In that case just do the averaging in the nuL equation.

February 8, 2013, 08:36		#8
samanpnh New Member saman Join Date: Jan 2013 Posts: 9 Rep Power: 13	What do you mean? Please tell me the exact code also D1 or D2?

February 8, 2013, 11:50		#9
samanpnh New Member saman Join Date: Jan 2013 Posts: 9 Rep Power: 13	What do you mean? Please tell me the exact code also D1 or D2? please help me

February 9, 2013, 06:10		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Replace nuL= (Wall Heat Flux shoa2[m])/(75 [K]Thermal Conductivity ) with nuL = areaAve(Wall Heat Flux)@Wall shoa ..... * areaAve(k)@Wall

February 9, 2013, 07:26		#11
samanpnh New Member saman Join Date: Jan 2013 Posts: 9 Rep Power: 13	Thank you very very very much. Error is cleared

February 9, 2013, 08:57		#12
samanpnh New Member saman Join Date: Jan 2013 Posts: 9 Rep Power: 13	What do you think about D1 or D2؟؟؟

February 10, 2013, 05:20		#13
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	If you are trying to match a publish result then they should define how they calculated Nu. There is no general rule, you can define it anyway which makes sense to that application.