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

Halim

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

[samanpnh]

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]

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

[samanpnh]

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]

this pic is better

[ghorrocks]

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]

What do you mean? Please tell me the exact code

also D1 or D2?

[samanpnh]

What do you mean? Please tell me the exact code

also D1 or D2?

please help me

[ghorrocks]

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

with

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

[samanpnh]

Thank you very very very much. Error is cleared

[samanpnh]

What do you think about D1 or D2؟؟؟

[ghorrocks]

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.