Thermal Transpiration Effect and Flow Characteristics of Gas in Trapezoidal Microchannel in Slip Flow Region

The Knudsen compressor is an effective non-mechanical gas-boosting micropump, which has great potential for applications in transporting and compressing gases. In this paper, a two-dimensional numerical model of the gas flow inside a trapezoidal microchannel adapted to the slip flow region is established based on the Navier-Stokes equations with slip and jump boundary conditions. The effects of the inclination angle and the temperature difference between the hot and cold chambers on the Knudsen number distribution, pressure rise and flow characteristics of the gas inside the microchannel are analyzed. The results show that when the inclination angle of the microchannel increases from 0° to 5.72°, the pressure rise decreases from 129.181 Pa to 48.291 Pa, which is 62.618% lower. In addition, the larger the inclination angle is, the smaller the gas Knudsen number is, but the gas flow rate gradually increases, and the maximum flow velocities of the Poiseuille flow and the thermal transpiration flow are 0.106 m/s and 0.200 m/s, respectively. The temperature difference between the hot and cold chambers increases from 20 K to 100 K, and the pressure rise of the Knudsen compressor increases from 16.081 Pa to 92.974 Pa, which is an increase of 478.161%. For every 20 K increase in temperature difference, the Knudsen number increases by 0.001, and the maximum flow velocity of the Poiseuille flow and the thermal transpiration flow increase by about 0.020 m/s and 0.039 m/s, respectively. The results of this study provide guidance for the construction of complex microchannels in the Knudsen compressor and the optimal design of its performance.