Modeling And Simulation Of Heat Exchangers And Automotive Air Conditioning System

Condensers and evaporators are key heat exchange equipments for automotive air conditioning system.Their structural dimensions and heat transfer performance have an important impact on the layout,operating characteristics and economic performance of automotive air conditioning systems.Usually experimenting with physical objects requires a lot of capital and time support,and the results are often affected by various factors such as manual operation specifications and experimental conditions,while computer simulations have low cost and short cycle.Computer simulation has become an important means of automotive air conditioning research.In this paper,MATLAB/Simulink is used to establish the steady-state simulation model of automotive air-conditioning,and the overall performance of automotive air-conditioner evaporator and condenser is analyzed.The reference for heat exchanger selection and structural optimization is proposed.The specific work is as follows:(1)The R134 a physical property calculation model was established by using MATLAB/Simulink,which solved the accuracy and speed of the physical parameters of the computer call.The final calculation results verified the accuracy of the established refrigerant thermal property model by comparing with the literature data.The degree is high,which can meet the needs of refrigeration cycle simulation.(2)The parallel flow condenser and parallel flow evaporator models were established by the lumped parameter method.The control equation,the air side heat transfer coefficient and pressure drop formula,the refrigerant side heat transfer coefficient and pressure drop formula,and the corresponding algorithm flow were given.The model of scroll compressor was established by the lumped parameter method,and the displacement,volumetric efficiency and isentropic efficiency were given.(3)Using the Function in MATLAB to write the relevant program,the heat transfer design calculation of the condenser and evaporator(liquid phase,gas phase and two-phase zone)is carried out,and the performance of the heat exchanger in each phase zone is simulated and analyzed.The heat transfer flow of fin-structure heat exchangers with equal-section flat tubes was studied,and the performance of heat exchangers in single-phase and two-phase regions was simulated and discussed.(1)The single-phase zone simulation shows that the air flow rate can be increased to a certain extent and the heat exchange area of the low temperature zone can be increased to a certain extent,and the volume of the condensation superheat zone can be effectively reduced.(2)In the simulation of the two-phase region,the heat transfer coefficient on the refrigerant side decreases along the length of the tube,and the pressure on the refrigerant side gradually decreases.The pressure drop is much stronger than that in the gas phase,and the pressure drop is even greater when the heat transfer coefficient is larger.Obvious,The simulation of the partition is the epitome of the whole heat exchanger research.The change of the partition structure parameters can directly affect the heat transfer of the heat exchanger.The results of this study can provide a reference for the optimal design of the heat exchanger.(4)The effects of changes in structural parameters on the air side and the refrigerant side on the performance of the heat exchanger were studied by simulation models,such as the influence of fin spacing,louver window opening angle,number of flat tubes,and shape of the holes on the performance of the heat exchanger.The research structure shows that the fin height can take a larger value within the allowable range;the fin spacing and the louver window spacing should be smaller;the louver window angle should be 27.5°;the number of flat tubes can be increased appropriately.(5)Simulink is used to establish a steady-state simulation model of the automotive air conditioning system,which in turn connects the compressor subsystem,the heat exchanger subsystem,the expansion valve and the refrigeration pipeline.Study the effects of changes in operating conditions on system performance under normal operating conditions,such as: air inlet air temperature of heat exchanger,wind speed of oncoming surface of heat exchanger,speed of compressor,system performance,and corresponding Optimization suggestions.Research indicates:(1)The increase of inlet air temperature on the condenser side increases the condensation and evaporation of the system,the compressor consumes more power,the cooling capacity decreases,and the COP decreases.The increase of the inlet air temperature on the evaporator side increases the condensation temperature of the system,and at the same time,the cooling capacity and compression.There is a certain increase in machine power consumption,and the COP has increased slightly.(2)The increase of the oncoming wind speed on the condenser side reduces the condensation and evaporation temperature of the system,the cooling capacity increases,the compressor consumes less power,and the COP increases.The increase of the oncoming wind speed on the evaporator side increases the condensation and evaporation temperature of the system,and the cooling capacity decreases.Increased power consumption and increased COP.(3)When the compressor speed increases,the system condensation temperature increases,the evaporation temperature decreases,the cooling capacity and compressor power consumption increase,and the system COP gradually increases.The analysis of the simulation results can provide reference for the design and optimization of automotive air conditioning,and propose corresponding optimization suggestions.