FLOW OF RAREFIED-GASES IN NONISOTHERMAL SYSTEMS

The flow of gases at low pressures in vacuum systems is determined by pressure and temperature gradients. Simplified treatments consider pressure gradients only, the throughput is considered to be constant along the system and the conductance depends on the square root of the temperature. A more general approach, which includes temperature gradients, shows that the molecular current and the mass flow are constant while the throughput is not conserved. The resistance to gas flow offered by any component part of the vacuum system can be shown to be independent of the temperature. The implications of these results for the design of vacuum systems is discussed.