[CFXer]

Dear everyone.

I want to calculate local heat transfer coefficient in a semicircular tube.

h_localwall=qw/(Tw-Tb)

I want to use this correlation, but I cannot know how can I export the Tw, Tb, and qw in CFD-post.

Anyone can teach me how can I get these data?

By exporting a temperature contour, I can notice it has severe temperature distribution, so I think there should be a large difference in bulk and local wall heat transfer coefficient.

Thank you in advance.

[piu58]

If you want to use the formula given you need the local heat transfer which is not hard to get. It is easier to get this form the thickness of the Prandl boundary layer δ_P. This can be calculated by extrpolation the velocity near the wall until the free stream velocity is reached.

From this you need to calculate the Nernst diffusion layer δ_N:

δ_N = δ_P / Pr^0.33

Pr is the Prandl number.

You get the local h by

 h = λ / δ_N

λ is the thermal conductivity.

You may calculate the thickness of the Nernst layer directly by extrapolating the temperature, but this requires a finer mesh.

[evcelica]

please see the FAQ's for Heat Transfer Coefficient:
https://www.cfd-online.com/Wiki/Ansy...ficient_in_CFX

I see you have a closed geometry, so working out your bulk temperature will be a bit different than what the FAQ's say.

[Opaque]

Originally Posted by evcelica

please see the FAQ's for Heat Transfer Coefficient:
https://www.cfd-online.com/Wiki/Ansy...ficient_in_CFX

I see you have a closed geometry, so working out your bulk temperature will be a bit different than what the FAQ's say.

If that is the case, the local heat transfer coefficient definition will be different as well. The concept of bulk temperature as the mass flow average of the enthalpy is no longer meaningful.

Very likely the heat transfer coefficient is defined on two fixed temperatures, for example:

1 - flow over a flat plate uses wall temperature and free stream temperature
2 - natural convection in a differentially heated cavity uses the fixed temperature potential

Food for thought..