[enayath]

Hello everyone,

I would like to calculate the Nusselt and heat transfer coefficient in my domain. I use "Reports" and then "area-weighted average", wall fluxes and surface Nusselt number on the walls that I would like to investigate.

The question is about the reference value for Temperature. As I change this value, I get different NU or h values. what is the right way to choose the reference value? I used Boussinesq and the applied BCs are a constant temperature value of 310 and 320 K.

I read the FLUENT tutorial and was expecting that NU is calculate based on the wall temperature and the temp near the wall. If that's the case, the reference temperature should not change the results.

What am I missing?!

Thank you in advance!

[LuckyTran]

Before Nusselt number you need the heat transfer coefficient. The reference temperature is needed to calculate the heat transfer coefficient in Newton's law of cooling.

Usually there is some common sense value to set the reference temperature to (the temperature that drives the heat transfer). Otherwise, you need to find some convention for your problem. If a convention does not exist, then you get to make it up.

From a theoretical point of view, the pair of heat transfer coefficient and reference temperature are defined together. I.e. it makes no sense to speak of a heat transfer coefficient unless you have also defined the reference temperature. There is no meaning to one without the other.

[enayath]

Thank you for your reply.

How the heat transfer coefficient is being calculated?

[LuckyTran]

Heat transfer coefficient is again calculated using Newton's law of cooling and the wall heat flux. This heat flux is what is calculated using the wall temperature and temperature near the wall, and it is this heat flux that does not depend on the reference temperature.