CONCEPT OF THE TRANSMISSION CONDUCTANCE

The geometric conductance defined in a normal tube is not useful for d escribing transmission characteristics of a sticky tube with wall pump ing in which the gas throughput is not uniform. To find a proper solut ion to this problem the concept of transmission conductance is introdu ced instead of the geometric one. The transmission conductance is expr essed as a function of the pressures and the throughputs at the inlet and outlet of the sticky tube. Applying the concept of the transmissio n conductance to the tubes with wall sorption and/or wall outgassing, then a few selected mathematical expressions of the transmission condu ctance and adsorption speed are derived. A combination rule of the tra nsmission conductance for constructing a composite tube, equivalent to the Oatley's principle for normal tubes, is also discussed. Compariso n of analytic calculations and Monte Carlo simulations shows good corr espondence as long as the sticking coefficient on the tube wall is not much larger than 0.1. (C) 1998 American Vacuum Society. [S0734-2101(9 8)03206-0].