Analytical and numerical prediction of the flow and performance in a claw vacuum pump

This paper presents the use of a 0-D thermodynamic chamber model and 3D Computational Fluid Dynamics (CFD) to predict the performance of a claw vacuum pump. The 0-D model can be used for pump sizing during the initial design or concept phase. Parameters such as the compression ratio (π), the built-in volume ratio (θ), the volumetric efficiency (ην), the isentropic efficiency (ηis), the volume compression ratio (υi) and the intermediate pressures (pz, pi) are essential to the performance of such machines. To determine these parameters, the volume-curve of the pump is determined as a function of the rotational angle. Using this model, it is possible to enhance the pump performance. For example, by decreasing the carry-over volume and by limiting or preventing over and under compression which can lead to an increase in the power consumption. This paper presents the results of the 0-D thermodynamic chamber model followed by the results of the 3D CFD simulations and validation with measurement data. After the benchmarking, CFD was used to improve the aerodynamic design of the pump discharge tube which led to a decrease in the power consumption of the pump compared to the baseline case. The diffuser angle was decrease to limit the boundary layer size and flow separation and recirculation at the discharge. When left unchecked, it can lead to large pressure drop and to an increase in the power consumption. Using CFD, other phenomenon such as such as pressure jump, which is commonplace in such machines, can be prevented. Otherwise, it can lead to shock wave generation and to noise in the pump.