Vaporization of a solid surface in an ambient gas

The net flux of vapour from a solid surface in an ambient gas is analysed w ith the aim to estimate the effect of vaporization cooling on the energy ba lance of an are cathode under conditions typical for a high-power current b reaker. If the ratio of the equilibrium vapour pressure p(nu) to the ambien t pressure p(infinity) is smaller than unity, the removal of vapour from th e surface is due to diffusion into the bulk of the gas. As a consequence, t he net flux of the vapour from the surface is much smaller than the emitted flux. An estimate of the diffusion rate under conditions typical for a hig h-power current breaker indicates that vaporization cooling plays a minor r ole in the energy balance of the cathode in this case. If ratio p(nu)/p(inf inity) is above unity, the flow of the vapour from the surface appears and the net flux is comparable to the emitted flux. A simple analytical solutio n has been obtained for this case, which is in a good agreement with result s of the Monte Carlo modelling of preceding authors. If p(nu)/p(infinity) e xceeds approximately 4.5, vaporization occurs as into vacuum and the net fl ux is about 0.82 of the emitted flux.