Simulation of Leakages for Different Clearance Geometries in Twin Screw Compressor

Abstract

In an oil-free twin-screw compressor, design clearances between rotors and between rotors and housing are provided to avoid the wearing of rotors and housing. The leakages through these clearances can be calculated using the isentropic nozzle equation. The limitation of the isentropic nozzle equation is that it does not consider the friction in the flow and leakage clearance shape. In the present work, the simulation of leakages through these clearances is carried out. The triangular clearance shape and equivalent circular clearance shape are considered for the leakages through blowhole clearance while the rectangular clearance shape is considered for the leakages through interlobe clearance. The blowhole clearances were experimentally investigated using circular clearances in available literature and in the present study the simulation of circular clearance shape and triangular clearance shape having same cross-section area for various pressure conditions is carried out. The leakage rate through triangular clearance shape is found to be 2% to 5% lower than circular clearance shape having same cross-section area. The leakage rate through rectangular shape is calculated for various pressure conditions and the effect on leakage rate for width variation (keeping height constant) and height variation (keeping width constant) is carried out alongwith the effect of air temperature on leakage rate through rectangular shape.