Learning Forum

[zgao04]

Hello,

I am simulating a boiling flow in a channel, and I try to calculate the surface heat transfer coefficient (h) at the wall. h depends on the reference temperature (Tref). For my case, the reference temperature is the saturation temperature. Since the saturation temperature changes along the channel and Fluent only allows a constant reference temperature, I have to extract the Total Surface Heat Flux (q") and the wall temperature (Tw) and calculate the heat transfer coefficient manually by

h=q"/(Tw-Tref) (1)

To validate my calculation, I did a comparison by using Tref in equation (1) as the same value as in Fluent reference value, but I found that the value calculated by equation (1) is much larger than the Fluent report value (surface heat transfer coefficient).

Can anybody help me resolve the issue?

Thanks,

Zhaosheng

[Nikhil N]

Hello,

What Report type are you using? Can you try using 'Area-Weighted Average' report type to find out T_wall and q''. Also, compare the manually calculated 'h' with the fluent calculated 'Surface heat transfer coef.', determined using 'Area-Weighted Average' report type.
Let me know if this works.

Nikhil

[zgao04]

Nikhil Thank you for your reply. I did use 'Area-Weighted Average' report type for all the variables, and Surface heat transfer coef. from FLUENT for the heat transfer coefficient.
Thanks Zhaosheng

[zgao04]

Nikhil Attached please find some snapshot and calculation. I will appreciate if you could do some investigation about the discrepency.
Thanks Zhaosheng

[Rob]

We aren't permitted to open or download attachments.
Rather than focus on the HTC, calculate the heat flux and then decide what reference temperature(s) to use.

[zgao04]

Rob Thank you for your reply, but you did not answer my question. Let me repeat my question with real numbers.
Reference temperature (Tref) set in FLUENT is 19.3 C
reported Area-Weighted Average Static Temperature (Tw) on the wall is 23.057 C
reported Area-Weighted Average Total Surface Heat Flux (q") is 598965.75
Then the calculated heat transfer coefficient h_cal is q"/(Tw-Tref) =598965.75/(23.075-19.3)=161882.635 W/(m^2 K)
But the reported Area-Weighted Average Surface Heat Transfer Coef. h_report directly from FLUENT on the same wall surface is 46901.06 W/(m^2 K)
It turns out that the calculated heat transfer coefficient is much larger than reported value directly from FLUENT. Why is that?
By the way, boiling occurs on this wall. I also tried a different wall where no boiling occurs, and I found that h_cal and h_report match with each other very well. so how to make the calculated heat transfer coefficient matches with the FLUENT report value on the boiling wall surface using the same reference temperature? because later on I need to change the reference temperature to reflect the real world.
Thanks Zhaosheng

[DrAmine]

Can you report the AreaAve of Wall Temperature and not of Static Temperature. That is what you need to use!

[zgao04]

DrAmine I just tried. It does make the result close to the FLUENT reported value. Thank you very much for pointing that out. Best regards Zhaosheng

[atulsingh92]

Hello Zhaosheng,
Were you able to solve the reference temperature conundrum?
Was interested to know what (or rather how) should the reference temperature be set? (I am performing a simulation for pipe flow with non smooth surfaces), so it is an internal flow simulation like yours.
Hope this post is not very old?

[zgao04]

atulsingh92
I used saturated temperature for my case because it is boiling heat transfer.

[DrAmine]

Create a custom function or expression for the htc snd sfter that do the average sndcdo not average the temperature to calculate the htc.