Study Of Radial Clearance Bubble Characteristics For Rolling Piston Compressor

The study of microchannel oil film bubble in compressor radial clearance is of great practical significance to improve the performance of oil film in radial clearance.However,the current researches on microchannel bubbles are mostly about the morphological characteristics of the bubbles in the static chamber.Moreover,few studies have been focused on the bubbles in the motion pair and the influence of the bubbles on the oil film.In this paper,the radial clearance microchannel oil film of rolling piston compressor is studied.The pressure and velocity distribution of oil film are analyzed by means of theoretical calculation and the property of bubbles in oil film is preliminarily determined.On this basis,the CFD simulation model of radial clearance microchannel is established.The influence of rotor speed and lubricating oil viscosity on bubbles are investigated,the pressure and velocity trace lines in the microchannel are analyzed,and the influence mechanism of various factors on bubbles is described.The radial clearance microchannel in the equivalent observation device is observed in real time by the high speed photography.The effects of rotating speed,viscosity,clearance value and oil content on bubbles are investigated and the simulation model is validated.The main research contents of this paper are as follows:(1)Based on the geometric relation of radial clearance,the pressure and velocity distribution calculation formula of the oil film in radial clearance is derived.The pressure fitting curve,which is calculated by fitting method,is combined with the velocity curve to obtain the change rule of them.According to the cavitation conditions,the oil film pressure is compared with the saturated vapor pressure.The bubble properties at different speeds and the critical speed of cavitation are obtained.And the properties of bubbles in oil film from radial clearance of compressor are determined.Taking the Mitsubishi rolling piston compressor used in this paper as an example,when the speed is lower than the critical speed(56873RPM),the bubble group is the precipitated industrial gas;when the speed is higher than the critical speed,the bubble group is a mixture of cavitation bubbles and precipitated gases.(2)Based on the radial clearance model of the compressor,Fluent software is used to simulate and analyze the radial clearance microchannels with different speeds and viscosity.The gas content phase diagram is analyzed quantitatively by the image processing procedures which is independently programmed in Matlab.The gas content distribution is converted to equivalent calculated area for subsequent test verification.In addition,the pressure distribution and velocity trace obtained by the simulation are used to further explain and analyze the change trend of bubble influenced by the rotating speed and viscosity.The results show that the gas at the radial clearance increases with the increase of rotating speed,and the increase is obvious at low speed but it tends to be gentle at high speed;the gas at the radial clearance increases with the increase of viscosity,and the growth is slow at low viscosity but the increase is obvious at high viscosity.(3)A set of radial clearance bubble observation device is designed and processed independently to set up a 360° real-time observation test bench with high-speed photography,by which the morphological characteristics of bubbles are observed dynamically.By the real-time adjustment of rotor speed,radial clearance value,lubricating oil viscosity and lubricating oil content,the law of bubble change effected by the above factors is obtained and the results match the simulation results after comparison.The experiment also finds that,as the gap value increases,the precipitated gas will be less and less at the radial clearance;at high speed and medium viscosity,the change trend affected by various factors under low oil supply is basically the same as when the oil is full.In addition,the collapse of bubbles in the open area of the cylinder helps to explain the influence of the adjustable factors on the bubbles.