Internal Flow Analysis Of CO₂ Single Screw Compressor

Using natural refrigerants represented by CO2 as refrigerants in refrigeration systems can effectively reduce CO2 emissions.CO2 single screw compressors,as key equipment in refrigeration systems,have advantages such as good force balance,and have good development prospects in the commercial refrigeration industry.This article takes a CO2 single screw compressor with a screw diameter of 114mm as the research object,and applies numerical simulation methods to study the flow characteristics of CO2 fluid in the screw groove and leakage channel of the compressor.The main content is as follows:This article designs and calculates the relevant parameters of the meshing pair based on the operating conditions of the CO2 single screw compressor.Based on the meshing principle of screw and star gear,combined with conjugate surfaces and spatial meshing theory,a mathematical model of the front and rear surfaces of the single line enveloping meshing pair screw groove teeth is established,and a threedimensional solid model of the screw and star gear is established based on this.According to the working principle of CO2 single screw compressor,the fluid region inside the compressor is extracted,and the unsteady flow characteristics of CO2 fluid in the screw groove are numerically simulated using overlapping grids.Through the pressure change curve,it was found that the CO2 fluid pressure in the spiral groove increases uniformly during the compression process,and rapidly increases during the exhaust process due to exhaust backflow;Through the law of velocity variation,it was found that the flow velocity of CO2 fluid in the spiral groove is mainly affected by the screw speed and radius,and there is a vortex phenomenon in the spiral groove;When the speed is 2960rpm,the inlet pressure is 1MPa,and the inlet temperature is 238K,the CO2 single screw compressor has an exhaust pressure of 3.5MPa,an exhaust temperature of 375.2K,a mass flow rate of 0.332kg/s,and a fluid flow velocity of 20m/s to 30m/s.The pressure inside the screw groove and the mass flow rate at the inlet and outlet show periodic changes.Based on the unsteady flow simulation calculation model in the screw groove,the prism layer grid method is used to encrypt the fluid grid in each leakage channel of the compressor,accurately simulating the unsteady flow characteristics of CO2 fluid in each leakage channel of the compressor.The results indicate that the pressure in each leakage channel gradually decreases along the leakage direction.The greater the pressure difference before and after the leakage channel,the more obvious the leakage phenomenon.The flow velocity of CO2 fluid in the leakage channel is greater,and the maximum flow velocity occurs in the meshing channel between the screw and the star wheel,reaching over 400m/s.Simulate and calculate the unsteady flow inside the compressor under different operating conditions.The results show that when the speed remains constant,the exhaust pressure and temperature change with the changes in intake pressure and temperature,but the compression ratio remains basically unchanged;When the inlet pressure and temperature remain constant,as the speed decreases,the compressor leakage increases,and the compression ratio,exhaust pressure,and exhaust temperature all decrease.