Heat Flux Wall Boundary Confusion.
 

Hi, my model is to use a heating pipe to heat the moving air driven by rotating fan in a sealed space. My prolbem is I want to set the heating pipe as a hot wall with a certain power ouput and set the heat pipe as a thermal boundary wall: Heat Flux 2000w/m2. but the simulation result by FLuent->Report->Fluxes->Total Heat Transfer Rate shows the heating pipe is -80w. Why a negative value?

Is it that the hot wall relates to positive value in Heat Flux boundary and cold wall reate to negative value?

How does Fluent use Heat Flux thermal boundary to calculate to ensure the defined power in Heat Flux is released into fluid?

My understanding is Fluent first use the T_w=(q-q_rad)/h_f+T_f to calculate the wall temperature, then use the wall temperature to q=h_f*(T_w-T_f)+q_rad. Is it right? But I can't figure out how Fluent calculate the fluid side local heat transfer coefficient h_f.

Please advise! Thanks.

Joee

for heat transfer problems, hf is calculated from empirical relations involving Re, Pr for Nu and Nu= hf*L/k .. not sure whether fluent uses this method