Research On Dynamic Characteristics And Stress Fatigue Of Small Hermetic Compressor Valves

The small hermetic refrigeration compressor is the core component of the refrigeration system.How to improve the performance of the compressor has been the market demand and research hotspot in the refrigeration field.The valve disc is a key component of the compressor’s cycle work.Its performance directly affects the compressor’s operating performance.This paper takes small hermetic compressor valve discs as the research object,and studies the movement and stress conditions of the compressor valve discs from the perspective of fluid-structure interaction numerical simulation and experimental verification,and the effects of both on the compressor performance.The main research work is as follows:(1)According to the basic working principle and working process of the small hermetic compressor,the numerical relationship between the cylinder volume of the compressor and the moving parts is established.Extract the geometric models of components such as valve groups,pistons,cylinders,and combine the theoretical foundations of fluid mechanics and structural mechanics to build a numerical model of the fluid domain and structure domain of the compressor valve group.The fluid-solid coupling method is used to solve the pressure and velocity of the fluid,the speed of the valve disc and the lift displacement.In order to verify the accuracy of the threedimensional fluid-solid coupling model of the compressor,an experimental verification platform is set up.The accuracy of the fluid-structure interaction numerical model is verified by comparing the experimental data and numerical calculation data of suction,discharge pressure and pressure in the cylinder under two operating conditions.(2)The fluid-solid coupling numerical model is used to simulate the dynamic changes of the exhaust valve disc’s movement speed and lift displacement,as well as exhaust mass flow and exhaust return under different compression ratios,different crank speeds,and different stopper heights.Analysis of the model data shows that the compressor has a compression ratio of 8.65,an exhaust stopper height of 1.68 mm,and the rotation speed is maintained at 2400 ～ 3000 r / min,the exhaust gas return flow is small and its operating performance is better.(3)The stress of the valve disc is affected by the dynamic characteristics of the valve disc.The numerical model is used to compare the stress conditions of the suction valve discs under different compression ratios,different crank speeds,and different valve disc thicknesses.It is obtained that the compressors in this paper have a compression ratio of 13.71 and a speed of 1800 ～ 2000 r / min,the valve disc runs under less stress.According to the maximum stress value and stress cloud diagram of the suction valve disc,it can be obtained that the waist region of the valve disc is heavily stressed during the movement.The numerical simulation of the stress condition of the valve disc under the standard condition of accelerated life is carried out,and it is found that the suction valve disc is greatly affected by the bending stress,and the stress fatigue of the valve disc is initially analyzed based on the valve disc design theory.(4)The compressor is used to perform four different lengths of acceleration experiments on the compressor accelerated life experiment platform.Divide the suction valve disc after the accelerated experiment,and observe and inspect the valve disc by X-ray diffractometer,three-dimensional surface measuring instrument and metallographic microscope.By comparing the microscopic phenomenon of the suction valve disc,it is obtained that in the numerical analysis the waist region where the valve disc is most stressed is slightly deformed due to cyclic working stress.The internal metallographic structure is changed,and the internal residual tensile stress is significantly increased.This thesis uses the method of fluid-solid coupling numerical model to study the compressor valve group,which make up and reduce the difficulty of experimental measurement.Based on the fluid-structure coupled compressor model,the equivalent stress values and exhaust flow values of the suction and exhaust valve discs under different operating conditions and different design parameters are compared and analyzed respectively.Relevant conclusions can provide a reference for judging compressor valve fatigue and evaluating compressor valve performance,and have certain theoretical and practical guiding significance for compressor valve design optimization and performance improvement.