Electrically and frictionally derived mound temperatures in carbon graphite brushes

Numerical and analytical simulations of mound temperatures are presented as the mound evolves from cold to hot. The temperature field about a thermal mound in an electrical brush is estimated using a heat conduction equation with frictional and electrical internal heat sources. Computed temperatures seem to agree with measured temperatures, but thermal nonlinearities can result in temperatures that are higher and hot zones that are larger than the mathematical sum of the frictional and joule thermal fields. It is found that combined heating coupled with nonlinear effects can significantly shorten the formation time of very hot temperature zones. Computed thermal fields mature within about 4 ms, the approximate lifetime of a stationary mound on the brush face. This suggests validity for the assumption that the mound is stationary on the brush during thermal evolution.<>