Opportunities for variable rotor lead in screw compressors depending on dimensionless numbers

Abstract

The paper deals with the optimisation of the geometry of screw machines, focussing on the wrap angle of the rotors. The Pi-theorem is used to identify independent thermodynamic and geometric factors for the optimisation of dry running twin screw compressors with uniform and dual lead rotors. Dual lead rotors possess two segments with different rotor leads, which can be selected to optimise the progression of chamber volume, clearance size and outlet area. Energy efficiency of the compressors is determined using a multi-chamber model simulation in which fluids are treated as ideal gases. The wrap angles of the rotors are optimised for a given set of characteristic numbers using the Nelder–Mead algorithm. Optimisation results reveal that the optimal geometry mainly depends on the circumferential Mach number and isentropic exponent of the fluid since these influence discharge throttling and the pressure progression due to volumetric compression. The results point out that dual lead compressors are most beneficial for fluids with low speed of sound and low isentropic exponent.

Keywords

Chamber model simulation dimensionless numbers efficiency optimisation geometry optimisation screw compressor variable rotor lead

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