Direct simulation of compression characteristics for a simple drag pump model

Abstract

The pumping characteristics for a simplified drag pump model (Gaede's type) are simulated by the direct simulation Monte-Carlo (DSMC) method using the hard sphere molecular model and No Time Counter (NTC) collision scheme. Model geometry is a two-dimensional channel of constant height, with the length of the channel varied within the range 1 to 3000 times the channel height. Maximum compression ratio and throughput are calculated in the flow regime ranging from free molecular to continuum. The results of calculation show that the existing theories for maximum compression ratio give inaccurate results when the pressure variation in the channel is large, and the transmission probability of a pumped gas molecule in. flow direction have a nearly constant value irrespective of channel length and exhaust pressure in normal operational conditions. Copyright (C) 1996 Elsevier Science Ltd.