Numerical simulations on performance of MEMS-based nozzles at moderate or low temperatures

Abstract

Performance of microelectromechanical sys- tems (MEMS)-based nozzles at moderate and low tem- peratures is numerically analyzed using the direct simulation Monte Carlo method. Considering the in- termolecular attractive potential caused by low temper- ature, the generalized soft sphere collision model is introduced. The Larsen-Borgnakke model for the gen- eralized sphere model is used to model the energy ex- change between the translational and internal modes. The results for nozzle flows at an initial temperature of 300 K show that the temperature behind the throat is quite low and the intermolecular attractive potential cannot be ignored. Different working conditions in two- dimensional (2D) nozzles are simulated using the present method, including exit pressure, inlet pressure, initial temperature, nozzle geometry, and gas species. The ef- fects on the nozzle performance are analyzed. Simula- tions on flows in a three-dimensional (3D) low aspect ratio flat nozzle show that the increased surface-to-vol- ume ratio, which leads to high viscosity dissipation, causes a much lower flow characteristic and perfor- mance comparing with the 2D case.