ABSTRACT
In recent years, micro/nanoelectromechanical systems (M/NEMS) have been rapidly developed for important applications in navigation, spaceight, and industry [1-4]. Microuidics and nanouidics are always treated as the key parts of M/NEMS. The characteristics of the microscale gas ows also differ from those of macroscale ows. For example, at normal temperatures and pressures, velocity slip and temperature jumps, which are called rare‰ed gas effects, occur on the wall surfaces in microchannels. Rare‰ed and microscale gas ows exhibit many other similar phenomena. Previous works have shown that most traditional simulation and analysis methods used for rare‰ed gas ows are effective for analyzing microscale gas ows [5]. Various studies have analyzed the similarities between microscale and macroscale rare‰ed gas ows. Because the Knudsen number of microscale gas ow is as high as that of rare‰ed gas ow, it is very important to build a bridge between them so that large number of achievements of rare‰ed gas ow could be brought into the analysis of microscale gas uidics. On the other hand, although the Knudsen number of a microscale gas ow may be of the same magnitude as that of a rare‰ed gas ow, they actually come from different reasons. In microows, the large Knudsen number is caused by the small characteristic length, whereas in rare‰ed gas ows, the large Knudsen number is due to the large molecular mean free path. Therefore, the mechanisms may be different despite the phenomena being similar. How to analyze and predict the gas ow and heat transfer in microuidics and nanouidics is a very important but challenging problem in theory and for applications.
