THE EFFECT OF SURFACE FLOW ON THERMAL TRANSPIRATION IN POROUS MEDIA

In finely porous media at low temperatures it is known that gas transport occurs both through the gas phase and in the surface film. When such a nnedium is subject to a temperature gradient and both ends are blocked to prevent any net gas flow, then either the surface and gas phase flow rates both vanish, or, alternatively, the two are nonvanishing and oppositely directed. A theoretical study of the low pressure case, when the surface coverage is also low, leads to the conclusion that countercurrent flow rates of considerable magnitude must arise. Arguments are advanced for believing that such flows arise for condensed films as well. (auth)