CFX  wall heat flux
I 've a question about sign convention in CFX. I made a simulation of steady state heat transfer of an insulated box, with internal T_in= 293 K, and outer of T= 213 K. I've to estimate the optimal thickness of insulating layer, so I created a boundary condition on the internal walls of heat transfer with heat source (energy). I've plotted the wall heat flux on a line across the layer, and noticed that heat flux varies with a peak in a range going from negative to positive values, whereas I expected that it decreases linearly, and in the best case it goes from 0 to negative flux equal to energy input source. Can you explain why this and what does it mean a negative heat flux? Thank you. Eng. Igor Di Varano

Re: CFX  wall heat flux
Fluxes into the computational domain are positive, out are negative. A negative wall heat flux means heat is going into the wall, out of the fluid domain.
Robin 
Re: CFX  wall heat flux
Thank you very much, I've found some information on help soon after my previous email. Now there 's another point. I've plotted the wall heat flux through the thickness, but I have only a few points and I've been requested to enhance the number of points in the layer. I've tried to fit the mesh, but without success, as I have always the same points(7). I 've read on the handbook that wall heat flux is sensitive in proximity of wall surfaces, and in a lesser way within the wall. Is it true or with more elements I can expect the desired result? Thanks a lot. Igor

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