
Temperature Boundary Conditions
When a fixed temperature condition is applied at the wall, the heat flux to the wall from a fluid cell is computed as
where
=  fluidside local heat transfer coefficient  
=  wall surface temperature  
=  local fluid temperature  
=  radiative heat flux 
Note that the fluidside heat transfer coefficient is computed based on the local flowfield conditions (e.g., turbulence level, temperature, and velocity profiles), as described by Equations 7.1315 and 12.105.
Heat transfer to the wall boundary from a solid cell is computed as
where
=  thermal conductivity of the solid  
=  local solid temperature  
=  distance between wall surface and the solid cell center 
Heat Flux Boundary Conditions
When you define a heat flux boundary condition at a wall, you specify the heat flux at the wall surface. FLUENT uses Equation 7.138 and your input of heat flux to determine the wall surface temperature adjacent to a fluid cell as
where, as noted above, the fluidside heat transfer coefficient is computed based on the local flowfield conditions. When the wall borders a solid region, the wall surface temperature is computed as
Convective Heat Transfer Boundary Conditions
When you specify a convective heat transfer coefficient boundary condition at a wall, FLUENT uses your inputs of the external heat transfer coefficient and external heat sink temperature to compute the heat flux to the wall as
where
=  external heat transfer coefficient defined by you  
=  external heatsink temperature defined by you  
=  radiative heat flux 
Equation 7.1312 assumes a wall of zero thickness.
External Radiation Boundary Conditions
When the external radiation boundary condition is used in FLUENT, the heat flux to the wall is computed as
where
=  emissivity of the external wall surface defined by you  
=  StefanBoltzmann constant  
=  surface temperature of the wall  
=  temperature of the radiation source or sink on the exterior  
of the domain, defined by you  
=  radiative heat flux to the wall from within the domain 
Equation 7.1313 assumes a wall of zero thickness.
Combined External Convection and Radiation Boundary Conditions
When you choose the combined external heat transfer condition , the heat flux to the wall is computed as
where the variables are as defined above. Equation 7.1314 assumes a wall of zero thickness.
Calculation of the FluidSide Heat Transfer Coefficient
In laminar flows, the fluid side heat transfer at walls is computed using Fourier's law applied at the walls. FLUENT uses its discrete form:
where is the local coordinate normal to the wall.
For turbulent flows, FLUENT uses the lawofthewall for temperature derived using the analogy between heat and momentum transfer [ 197]. See Section 12.10.2 for details.