It can be shown that this definition of the heat flux vector also satisfies the second law of thermodynamics,
2.
The definition of heat flux vector, however, is different; but the RHC definition is merely a 4D upgrade of the original linear Fourier approximation.
3.
Most of these results remain relevant to RHC, but because the definition of heat flux vector is different, final closed-form solutions may not be the same.
4.
The four-heat flux vector field, is essentially similar to the 3d heat flux vector field "'q "', in the local frame of the fluid:
5.
The four-heat flux vector field, is essentially similar to the 3d heat flux vector field "'q "', in the local frame of the fluid: