Theoretical And Practical Research To Clearance Design Of Screw Expander

The efficiency of screw expander mainly depends on the volumetric efficiency.The smaller clearance and the less leakage lead to the higher volumetric efficiency.However,screw expander under rated condition will be affected by many factors such as temperature and pressure,then its casing will deform.If the cold clearance cannot meet the thermal deformation,rotor will scratch and bite each other.As a result,reasonable clearance design is one of the key factors ensuring screw expander excellent performance.This article focuses on the clearance design of screw expander.The deformation of rotor is analyzed from aspects of temperature and pressure while the deformation of casing is analyzed from aspect of temperature.Study have shown:(1)Transverseof rotor magnifies and minifies with equal proportion based on the centerthrough thermal deformation.The deformation tendency on normal vector of helical surface shows a W-shaped curve in the process of addendum-cogging-another addendum.(2)Mechanical deformation account for little proportion of the total deformation.It mainly affects the clearance between rotors and casing.It has nearly no influence on the clearance of rotors.(3)In the aspect of thermal deformation of casing,two circular cylinders turn into irregular oval.Both intake and exhaust havelittle moving distance on axial direction.Experimental research to clearance design of screw expander is carried outon the basis of theoretical analysis.Establish the screw expander test bench for generating electricity from residual steam pressure.According to the critical temperature from test and measured clearance,deduce thatthe ratio between highest temperature of rotor and temperature of inlet steam is 0.78.Through the theoretical analysis and practical research,calculating method of clearance designof screw expander is concluded which can supply theoretical guide to manufacture of screw expander.