Analysis of Flow Rate and Pressure Characteristics for Multistage Thermal Transpiration Based Vacuum Pump

Thermal transpiration based vacuum pump is often designed as a multistage type in series in order to meet the needs of flow rate and pressure. In this paper, a mathematical model of working characteristics was established for multistage thermal transpiration based vacuum pump according to rarefied gas dynamics. Then the effects of temperature difference, Knudsen number and stage numbers on flow rate and pressure were discussed. Some findings are as follows in consideration of the requirement of a vacuum degree. The temperature difference in each stage of a multistage thermal transpiration based vacuum pump should reasonably be increased to obtain a relatively high flow rate and to decrease the number of stages in series. The connecting channels with large characteristic dimensions as far as possible, make the inside gas flow in a continuous flow regime. However, the characteristic dimensions of microchannels should be determined according to operating conditions to ensure the inside gas flow in the high-Knudsen-number transition flow regime. From the atmospheric end to the vacuum end, the pressure in multistage thermal transpiration based vacuum pump decreases exponentially. The closer the stage is to the atmosphere end, the more significant the change of internal pressure is. In each stage, the pressure increases slightly in the connecting channels while decreases significantly in the microchannels.