Research On Dynamic Model And Internal Flow Field Characteristics Of Compressor Reed Valve

Piston refrigeration compressor is the most energy-consuming equipment in refrigeration system,which is widely used in petroleum,chemical,pharmaceutical and other fields.Increasing volume efficiency and reducing energy consumption are the inevitable trend of compressor technology development.Valve is the most critical component of piston compressor,and its performance directly affects the energy efficiency of the compressor.The valve works under the environment of high frequency excitation,alternating load,high temperature and corrosive.Bad valve design will lead to leakage,reflux,inhalation gas heating and other effects,resulting in compressor energy loss,power consumption increase,and even machine shutdown.Therefore,the improvement of compressor energy efficiency depends first on the valve.The design and optimization of the valve is an eternal and progressive research topic.The reed valve is a kind of compressor valve,which has elasticity.When the reed valve works,one end of reed is fixed,and the other end is impacted on the lift limiter and seat at high frequency under the action of high temperature and high pressure difference.It is easy to cause the motion failure and fracture failure of the reed.In order to reveal the failure mechanism of the reed valve and the influencing factors of the compressor energy efficiency,the dynamic model and internal flow field characteristics of the reed valve are studied.The main contents include:(1)According to the thermodynamic principle of variable mass system,an improved thermodynamic process model for the coupling effect of gas leakage and unstable heat transfer is established.The model is used to analyze the effects of gas leakage,unstable heat transfer and their coupling on the compression and expansion process.(2)A piston refrigeration compressor test system was established.When the speed of compressor is 1450 r/min,the motion characteristics of the reed valve under three working conditions are tested.The displacement of the discharge valve reed,the refrigeration capacity and the input power consumption of the compressor were obtained,which provided a basis for verifying the validity of the dynamic model of the reed valve.(3)A partial differential equation for the bending vibration of the reed valve is established based on the Euler-Bernoulli beam bending vibration theory.The modal superposition method and virtual displacement principle are used to solve the model,and then the dynamic model of the reed valve based on the vibration theory is obtained.The predicted resluts of the model is basically consistent with the experimental resluts,but there are some errors in the opening and closing stages of the valve reed.(4)On the basis of basic valve theory model and combined with the motion characteristics of reed bending with limiter,the improved one degree of freedom(one-DOF)model was established.The model takes into account the relationship between the effective working length,elasticity and mass of the reed and displacement.The experimental results show that the predicted value of the model is basically in agreement with the experimental value,and the prediction accuracy of the improved one-DOF model is better than that of the basic valve theory model.(5)According to the hydrodynamic lubrication theory and Laplace surface tension equation,the dynamic model of the reed valve considering the viscous effect is established.The model comprehensively reflects the relationship between the oil dynamic viscosity,the diameter ratio of the valve reed to the valve oriface,the displacement of the valve reed and the oil film viscous force.The dynamic model based on the vibration theory,the improved one-DOF model and the viscous effect model were compared.The results show that the accuracy of the dynamic model considering the viscous effect is better than that of the other two models.Then,the influence of key design parameters,such as motion viscosity,valve lift,stiffness and valve orifice diameter on the dynamic characteristics of the reed valve is analyzed by using the viscous effect model,and the reasonable range of parameters is obtained.(6)Based on the analysis of fluid-structure interaction theory,a three-dimensional simulation model of compressor discharge system is established by using ADINA software.The model was used to simulate the transient flow characteristics of the flow field in the reed valve during the discharge process.The instantaneous pressure distribution,velocity distribution and pressure distribution on the valve surface are obtained.The influence of reed stiffness on the flow field characteristics of the reed valve is also obtained.The above research shows that the dynamic model of reed valve based on the vibration theory,the improved one-DOF model and the viscous effect model can be used to analyze the dynamic characteristics of the reed valve.Compared with the other two models,the dynamic model of the reed valve considering viscous effect has higher accuracy and can describe the dynamic characteristics of the reed valve more effectively.The model can be used to analyze the influence of the main structural parameters on the dynamic characteristics of the reed valve,and provide a reference for optimizing the design of the reed valve and improving the compression efficiency.By using the three-dimensional fluid-structure interaction model of compressor discharge system established in this paper,the interaction mechanism between valve reed and fluid can be obtained,which truly reflects the working state of the reed valve,and provides a reference for the analysis of valve reed motion failure.