Research Of The Flow And Heat Transfer Characteristics Of Vehicle Mini-channel Evaporator

The parallel flow mini-channel evaporator technology has been promoted and widelyused in the air-conditioning system to meet the require of the lightweight, low cost and highefficiency.The flow and heat transfer process of evaporator consists: convection heat transferbetween the louver fin and the air; thermal conductivity between the fins and the tube; flowboiling heat transfer in mini-channel. There is a widespread concerned problem whenmini-channel heat exchanger used as an evaporator that is the distribution of the refrigerant.Numerical simulation methods and exceprimental benchs were applied in this paper tostudy the flow and heat transfer characteristics. The flow and heat transfer correlations whichwere applicable to mini-channel evaporator was summarized and the flow distributioncharacteristics was researched to optimize the structure of the evaporator.The performance of evaporator under steady-state condition was researched byprogramming based on the finite volume method,and distributed parameter model.Kew-Cornwell correlations taken into account the effects of dryness were much moreapplicable to the micro-channel evaperator reseached in this paper according to thesimulation results and experimental results. If the sigle-phase region of refrigerant side usingDitus-Boeleter correlation and the air side using the Dong Junqi correlation, the calculationerror of the heat transfer and pressure drop can be less than5%. The effects of the blindsangle, fin spacing, fin height, the number of channels in each tube, channel width and theprocess arrangement on heat transfer performance were researched to optimize theevaporator structure.The literature references indicated that the rearches about the refrigerant flowdistribution mostly studied only one process, even Simplified to simulate several tubesjointing to a header. However, the whole evaporator including four processes were taken asthe rearch modle to study the effects of structure factors (the relative position of the importand export pipe with the header; the combined altitudes between flat tube and header),different inlet dryness and different inlet mass flow to mass flow distribution.Threedimensionless parameters (P_in, P_out, H) were introduced to represent three relativepositional relationships, and the calculation results indicated that when P_in=0.591， P_out=0.402，H=0.239, the uniformity of the refrigerant flow distribution should bepreferably.To make clear the phase change process of the refrigerant and correct the calculationerrors resulted from the assumption of uniformed refrigerant flow distribution in theone-dimensional simulation, a three-dimensional simulation analysis was conducted in thispaper.The numerical results indicated that refrigeration capability of the structure after flowdistribution optimization was7%higher than the original structure.Two different structures and two different refrigerant inlet mass flow cases werestudied on experimental bench. The error between three sets of one-dimensional simulationresults and the experimental values is less than5%. The heat transfer coefficient got from theone-dimensional simulation was set as heat transfer boundary conditions for solvingthree-dimensional simulation. Due to nonuniform refrigerant flow distribution, therefrigerant enthalpy change in the three-dimensional simulation is less than the experimentalvalue. The error between the calculation result and the experimental value is less than8%,and which verified simulation method was practicable and accurate.The result of this paper provided a theoretical basis for the application and optimizationdesign of parallel flow mini-channel evaporator in the field of automotive air conditioningsystem.