Study of Gas Microconvection for Synthesis of Rarefaction and Nonrarefaction Effects

Gas microconvection is a strategic research area in transport phenomena since it is the basis for a wide range of miniaturized high-performance applications like microelectromechanical systems. The literature reveals that in the single-phase continuum regime, microconvection characteristics significantly differ from those in the conventionally sized channels. Deviations from the expected behavior have been attributed to scaling effects that surface at the microscale. For most gas microflow applications that are in the slip or early transition regimes, the analysis is further complicated by rarefaction and compressibility effects. Therefore, microslip flows are comprehensively reviewed to identify the implications of reported findings with respect to the validity of continuum-based models. Based on the synthesis of studies, the need to better demark the continuum and free-molecular flow regimes is revealed, which necessitates the identification of important nonrarefaction scaling effects. This would enable the computationally inexpensive continuum models to be extended to higher Knudsen numbers. The analyses suggest that early transition regime behavior is characterized more by conjugate nonrarefaction scaling effects and higher order slip boundary conditions than purely by rarefaction.