# Stefan–Boltzmann law: Which applies? Stagnation temperature or static temperature?

1. May 14, 2012

### kmarinas86

http://en.wikipedia.org/wiki/Stagnation_temperature
It appears to me that if we have two fluids which are in "heat conduction" contact with each other, then the body with the highest stagnation temperature will transfer heat to the body with the lowest stagnation temperature.

However, it is possible for the fluid having the higher stagnation temperature to also have a lower static temperature, provided that it has a higher velocity (with respect to the chosen frame of reference). Now, if one were to remove the ability for heat to transfer by means of conduction and also that of convection, then any heat between them must be radiation. The radiative emissions would flow from one fluid to the other according to which medium has highest temperature from the point of view of Stefan–Boltzmann law. Is the temperature relevant to heat transfer by radiation, in this case, the static temperature and not the stagnation temperature? If that is so, doesn't it suggest that one can reverse heat flow between the two fluids (as evaluated by the arbitrary inertial observer) by simply adding or removing means of conducting heat between them so as long as the two fluids have relative motion?