In the CFX results files that are a number of different heat transfer variables. What is the difference between "Heat Flux", "Wall Heat Flux" and "Wall Radiative Heat Flux"? Do any of these include all the modes of heat transfer (convection, conduction, radiation)? In which direction is a positive heat flux?

The variable "Wall Heat Flux" includes all the modes of heat transfer at the wall (Convective and Radiative - assuming radiation is solved). The convective heat flux is due to both advection and diffusion. Conduction in the sense of conduction into a solid domain isn't directly relevant for the heat flux at the wall; certainly conduction will effect the solid temperature at the wall, which will in turn alter the convective heat transfer at the wall, but there's is no solid conduction term to include directly when considering heat transfer at the wall. Conduction in the fluid is termed diffusion here and is included in the convective heat flux.

"Heat Flux" is a variable that is valid in the volume of the fluid domain, rather than on walls. If you take any 2D surface through which flow passes (e.g. a Plane, an Inlet or Outlet etc), the "Heat Flux" variable gives the flux of energy through that surface. A Reference Temperature is used for each fluid, which is often 25 C. So fluid flowing through an inlet at 30 C carrier positive energy, which fluid at 20 C would have negative energy. The Reference Temperature is part of the material properties, in the Specific Heat Capacity section.

"Wall Radiative Heat Flux", "Wall Convective Heat Flux" and "Wall Irradiation Flux" are described further in the documentation. Searching for any of these three terms, including the quotes, will return the appropriate page.

A positive heat flux is always into a domain.

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