Research Of The Flow And Heat Transfer Characteristics Of Vehicle Micro-Channel Condenser

With the rapid development of automobile industry and consciousness enhancementof energy saving in our country, hight efficiency, energy saving and light micro-channelheat exchanger has become the development direction of heat exchanger used inautomobile air-conditioning. In this paper, the overall performance, air-side structure, tubeand collector pipe structure of micro-channel condenser are analyzed and optimized byone dimension programming calculation, three dimension simulation, couplingoptimization and experimental verification. A quick optimization design method and anoptimized structure and suggestion to the automobile micro-channel condenser areprovided in this paper.Parametric modeling, coupled CFD software and optimization software, andresponse surface analysis are used in the automatic analysis of air-side fin unit. The finspace and louver angle are set as input variable, and minimum pressure drop andmaximum heat transfer are set as target variable. Sobol sampling method and NSGA-∏optimization algorithm are used to set up optimization process, and15data points wereactually calculated，and the response surface was constructed by radial basis function, andthen101virtual data points were automatically selected, finally the optimization analysisbased on the116data points above were accomplished. The optimization results indicatedthat fin spacing between1.1mm and1.2mm, louver angle between24°and28°have thebest comprehensive performance.An one-dimensional condenser model was programmed by using finite volumemethod to divide the flat tube into multiple micro-units in which the condition of flow andheat transfer was calculated by ε-NTU method. Suitable correlations were chosenrespectively for gas phase, two phase, and liquid phase. The change of refrigeranttemperature, pressure, enthalpy, dryness along the flow direction were calculated andanalyzed. The influence of channel number, channel diameter, flow path distribution on the condenser performance also researched in this paper. If the channel diameter ofsubcooling flow path varied from0.5mm to0.7mm, it will sharply lower the condenserinternal resistance with litter impact on heat-exchange. Combining with air side structureoptimization results, a suitable structure scheme was recommended which can enhance152W condenser performance and reduce nearly30%of the internal resistance to52.51kPa. Find a reasonable solution to the problem of too big internal resistance causedby micro-channel.By the commercial CFD software, some ignored parts of the one-dimension modelwere analyzed, such as flow distribution and inlet end resistance affected by condenserinlet position and flat tube insert depth. Results indicated that change the inlet position tothe middle will great improve the uniformity of flat tube flow and reduce3.6kPa inletend resistance. The flow distribution uniformity will be the best when the insert depthchanged to2.7mm.The three-dimension phase-change of the whole condenser was analyzed by thephase-change model and extruder mesh. By comparing the phase change of original andoptimized one, the influence of inlet position and insert depth on the whole condense flowand heat transfer characteristics was obvious. Results indicated the structure improvementcan increase10%performance and reduce21kPa internal resistance of whole condenser.Based on the automotive air-conditioning heat exchanger performance test bench,which uses the air enthalpy potential method to test the automotive condenser of thispaper, and the test results were compared with the one-dimension calculation results. Thedeviation of temperature, enthalpy and total heat transfer was under6%, the air-sidepressure drop deviation was under8%, the deviation of condenser internal resistance wasabout12%for the reason of ignoring the resistance of collecting pipe inlet and outlet end.With checking the reliability of the model used in chapter three, the simulation resultsoverall meet the real engineering need.