Convection coefficient h

[QuentinG]

Hello,
I'm doing a very simple simulation of a flow around an object and I would like to compare the convection coefficient from the theory and my simulation.

Case : I have a flow with a velocity of 4m/s, with a pressure of 5 bars, and a temperature of 180°C.
The object has a constant temperature of 80°C. (cf picture)
I did a 2D mesh (my block is 0.4m * 0.15m * 0.001m and the two faces with the normal z have symmetry condition)

I am wondering how to determine h ?
My first guess was to use the input thermal flux (Phi) such as h=Phi/(180-80).
But I dont know if Phi is in W/m² or in W. But then I saw that the boundary temperature was not exactly equal to 80°C, it's in fact varying from 82°C to 112°C.

1) Is the input thermal flux in W or in W/m² ?
2) Shall I use the boundary temperature instead of 80°C ?
3) Shall I use the fluid temperature at the boundary instead of 180°C ?


Thank you,
Regards,

Quentin

[QuentinG]

Does anyone knows what are the parameters I should use ?
Regards,

Quentin

[Yvan Fournier]

Hello,

The input thermal flux is in W/m^2.

Interpreting the exchange coefficient is not trivial, since h(Twall -Tfluid) depends on which distance from the wall you consider the fluid. The safest approach is to consider the bulk fluid temperature.

Regards,

Yvan