SIMULATION OF HEAT AND MOMENTUM-TRANSFER IN COMPLEX MICROGEOMETRIES

In this article we present a time-accurate computational model based o n the slip-flow theory to simulate momentum and heat transport phenome na in complex microgeometries, encountered in typical components of mi crodevices such as microcapillaries, microvalves, microrotors, and mic robearings. In the first part, we present extensions to the classical Maxwell/Smoluchowski slip conditions to include high-order Knudsen num ber effects as well as to take into account the coupling of momentum a nd heat transfer through thermal creep and viscous heating effects. Th e numerical method is based on the spectral element technique; validat ion of the method is obtained by comparison of the numerical simulatio n results in simple prototype flows (e.g., channel slip-flows) with an alytical results. Reduction of pressure drop in microchannels, reporte d in similar experimental studies, is investigated using slip-flow the ory and simulations. In the second part, we consider model inlet flows and a slip-flow past a microcylinder. The effect of slip-flow on skin friction reduction and associated increase in mass flow rate as well as the variation of normal stresses is investigated as a function of K nudsen number. Finally, the effect of compressibility is examined and possible extensions of the current model to take into account such eff ect are discussed.