| With the official launch of the National Carbon Neutralization and peak carbon dioxide emissions Plan,it has become a research hotspot to replace the traditional working medium with carbon dioxide as the main environmental friendly natural working medium in refrigeration,heat pump and other industries.CO2 compressor is the core of heat pump system,but the research on its key components,such as suction and exhaust valves,is still unclear.Under the technical requirements of modern compressor working medium replacement,high efficiency and high reliability,the research on valve is facing great technical challenges.Because the valve in transcritical CO2 compressor is in a highly complex thermal-fluid-solid coupling environment,the traditional quasi-static simplified model can not accurately characterize the dynamic characteristics of the valve plate.Based on the CFD fluid-solid coupling simulation method,this paper establishes a three-dimensional fluid-solid coupling model of the suction and discharge valve of CO2 piston compressor,and studies the dynamic characteristics of the valve during opening,the characteristics of the surrounding flow field and the impact characteristics under supercritical conditions.The main research contents are as follows:Based on the fluid-solid coupling simulation method and the classical valve theory,the fluid field inside the compressor is extracted and the suction and exhaust drainage basin is simplified.Structured grid and unstructured grid are used for intake and exhaust,and surface grid encryption is carried out around the valve dynamic grid to meet the calculation conditions of grid solution.UDF is used to define the motion of dynamic grid in cylinder basin to realize the analysis of adiabatic compression in CO2 piston compressor.Constraints and contact conditions with the valve plate and limiter are imposed in the structural unit to realize the motion state of the valve plate in real freedom.The simulation results show that the displacement of the valve plate is strictly affected by the pressure difference between the two sides during the intake and exhaust process.During the exhaust process,the flow rate of CO2 shows a trend of "big-small-big",and the maximum flow rate is 381.959 m/s.Based on the structural resonance theory,the modal analysis method is used to study the vibration mode and natural frequency of the exhaust valve plate in the free state.The results show that the first natural frequency of the valve plate is 355.42Hz,which is far lower than the maximum frequency of the compressor under variable frequency condition.Based on the fluid-solid coupling simulation method,a supercritical dynamic model with the maximum exhaust pressure of 8MPa was established to explore the motion state of the exhaust valve when it hit the limiter.The results show that the top of the reed valve is deformed and displaced greatly,and it contacts the limiter first during the opening process,and only 2/3 of the valve plate is attached to the surface of the limiter after it is completely opened.Combined with the stiffness theory of valve plate,the influence of different structural parameters on the impact characteristics of valve plate is further explored.The results show that the impact resistance of the valve plate is closely related to the stiffness of the valve plate,the valve plate with large stiffness has better impact resistance,and the valve plate with small stiffness has higher impact speed during impact.In different dynamic simulation schemes,the valve plate thickness has the greatest influence on the valve plate stiffness,and the valve plate with 0.7mm has the best impact resistance,and the maximum impact stress is reduced by 36.3%,but its maximum opening speed is reduced by 54%,and the maximum speed peak value is delayed. |
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