Mathematical Model of Screw Vacuum Pump Working Process

The screw vacuum pump combines high performance, low ultimate pressure and ability to create an oil-free vacuum. The calculation of the pump characteristics can be performed using mathematical modeling. The article considers main stages of creating a mathematical model: constructing the geometry of the rotors, calculating the dependence of the working cavity volume and the area of the suction and discharge windows on the angle of rotor rotation, determining the main directions of gas flows, calculating the dependence of pressure and temperature on the angle of rotor rotation.
The thermodynamic model of the working process is based on gas state differential equations describing the laws of mass and energy conservation in control volumes, taking account of heat transfer and overflows. The classification of slotted channels in a screw pump is given, and a method for calculating gas backflows through them is proposed. The calculated dependences of the speed of action on the inlet pressure for various rotor speeds are presented. The developed model can be used for calculating the pumping characteristics of a screw vacuum pump at the design stage.

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