Research Of Heat Transfer Performance Of Vehicle Micro-channel Condenser

At present,owing to the large heat and less materials,micro channel heat exchanger has been widely used in car air conditioning system,household air conditioner and motorbus.However,there is no uniform standard towards the structural design and the principle of phase change heat transfer.Therefore,it still needs further exploration towards the features of micro channel heat exchanger.Based on the theoretical analysis,the current study elaborated the basic equations and methods of two-phase flow.The current study observed and analyzed the flow patterns by means of flow pattern and high-speed camera.The use of refrigerants is the most common form of two-phase flow.By comparing the indicators of the existing automotive air conditioning refrigerant R134 a and indicators of alternative products HFO-1234 yf,the author of the thesis found that both the refrigerants have their advantages and disadvantages,which needs further exploring.By using the comprehensive performance test bench of automobile air conditioner,the current study investigated the 12 mm thick core condenser and the contrast sample 16 and 18 mm thick core condenser under the same testing condition.On one hand,the testing condition can provide the boundary conditions and physical model parameters for the following simulation analysis.On the other hand,the stimulation results can be referred in other testing conditions.The calculation analysis shows that simulation of the air side heat transfer and pressure drop errors are less than 4% and the average error of the refrigerant side parameters are less than 10%.The study fully verifies the accuracy of stimulation,and provides a reliable method for the future engineering design analysis.The analysis of heat transfer characteristics of 12,16 and 18 mm thick core condenser indicates that 12 mm thick core condenser can lower 23% and 34% while the heat transfer decreases 8% and 13%.The analysis shows that 12 mm thick core condenser has a better application prospect.Then the author of the thesis further investigated the structure of 12 mm thick core condenser including the shutter opening angle and number,fin spacing and other parameters.In the end,the author finds that 12 mm thick core condenser performs best when the shutter opening angle is 30 and the opening number is 8.Besides,the author conducted regression verification towards the j,f formula and modified the exponential part of the empirical formula which can improve the prediction accuracy of the heat transfer performance of the condenser.The refrigerant flow in the entrance region has an important influence on uniformity of heat transfer performance.This thesis used the optimate+ module of 3D simulation software in the design of entrance position,regared insertion depth and flat tube insertion depth and other parameters as design variables,flow uniformity and pressure drop as target variable and used multi-objective multi parameter to optimize the design.The calculation is simple,which greatly reduces the time of structural optimization design.Besides,the pressure drop and flow non uniformity of the optimized structure are reduced by more than 10%.The study fitted parameters of refrigerant properties under different conditions and obtained the the density,viscosity,heat transfer coefficient curve with different temperature.Since it is convenient to import the curves to 3D simulation software,the simulation accuracy can be improved.The study also adopted the directional mesh to mesh the flat tube and greatly improved the precision and the speed of the grid.By setting the VOF evaporation condensation model,the author conducted the analysis of the overall transformation of condenser simulation and observed the phenomenon of uneven flow of refrigerant in the flow passage.After the optimizing the structure,the uneven flow phenomena was improved;the final temperature is reduced by 1.7 DEG C;the pressure drop is reduced by 3.9k Pa.