Losses in the Inlet and Outlet Ducts of Oil-Free Scroll Vacuum Pumps

Scroll vacuum pumps are widely used for producing low and medium vacuum. The production of scroll pumps in Russia has just begun, and a reliable method for calculating pump characteristics is necessary to further develop and upgrade the pumps. A mathematical model of a pump should take into consideration the flow between the working chambers, heat exchange, thermal deformations of the scroll elements, mobility of the channel walls, resistance of the inlet and outlet ducts. In this work, flow coefficients of the inlet and outlet ducts of a typical scroll pump are obtained by modeling using the finite volume method. Geometry of the outlet duct varies according to the rotation angle of the driveshaft because partial overlap of the outlet vent occurs when the orbiting scroll element moves. That is why for the outlet shaft, the calculation is performed for different positions of the scroll element. The calculations cover laminar and turbulent flow regimes. The dependence of the pumping speed on the inlet pressure is calculated using the obtained flow coefficients. It is shown that the influence of duct resistance becomes apparent only in the low pressure range.

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