Numerical Simulation And Experimental Study On Flow And Heat Transfer Characteristics Of Dual Flow Micro Channel Evaporator

Microchannel heat exchanger not only can significantly enhance heat transfer,but also can reduce the volume of the equipment,make its structure compact,higher efficiency,but also can increase the pressure resistance of the pipeline.Microchannel heat exchangers have been widely used in automotive air conditioning systems,and have also been widely used in household air conditioners.For the application of microchannel heat exchanger in evaporators,whether the distribution of internal refrigerants is uniform is the main technical problem for its promotion.Especially under the condition of two-phase flow,due to the uneven distribution of refrigerant flow in each microchannel of the flat tube,“dry evaporation” and “excessive liquid supply” often occur,which have a great impact on the performance of the heat exchanger.Therefore,this paper uses FLUENT simulation software to simulate the heat transfer and flow characteristics of dual-process microchannel evaporator.A two-dimensional model of dual-process microchannel evaporator was established,and the heat transfer and flow characteristics of refrigerant flow,dryness and undercooling in the microchannel evaporator were analyzed.The experiment of refrigerant flow on dual-process microchannel evaporator was carried out,and the experimental results were compared with the simulation results to demonstrate the reliability of the simulation.The main conclusions of this paper are as follows :（1）The influence of refrigerant flow rate on the heat transfer characteristics of microchannel evaporator was studied.The influence of flow rate on the heat transfer characteristics of microchannel evaporator is as follows : with the increase of refrigerant flow rate,the heat transfer of evaporator increases correspondingly,and the maximum heat transfer can be increased by 51.06 %,while the superheat of microchannel evaporator decreases gradually with the increase of flow rate,and the maximum decrease is 27%.The heat transfer factor increases with the increase of flow rate and undercooling.When the refrigerant flow rate increases,the heat transfer factor of microchannel evaporator increases by about 67%.（2）The influence of inlet refrigerant parameters on the heat transfer characteristics of microchannel evaporator was studied.With the increase of undercooling degree,the heat transfer also increases correspondingly,the maximum increase is 7.8%,and the undercooling degree is most affected by the inlet refrigerant parameters.The heat transfer decreases gradually with the increase of dryness,and the maximum decrease is 0.35 kw.With the increase of dryness,the superheat of microchannel evaporator increases continuously,with the maximum increase of 13.85%.With the increase of undercooling,the superheat decreases from 9.5°C to 7.4°C,and the maximum increase of heat transfer factor is 114.29%.However,the heat transfer factor decreases by 54.54% with the increase of dryness,and the heat transfer factor is most affected by undercooling.（3）The biggest factor affecting the pressure drop of microchannel evaporator is flow rate,followed by dryness,and the smallest is undercooling.When the flow rate increased from 40 kg/h to 60 kg/h,the pressure drop of evaporator inlet and outlet increased by108%,and when the dryness increased from 0 to 0.2,the pressure drop of evaporator inlet and outlet increased by 26%.When the undercooling degree increased from 1.5°C to5.5°C,the pressure drop of evaporator inlet and outlet decreased by about 35.29%.（4）Refrigerant flow,dryness and undercooling have a certain influence on the flow distribution uniformity of microchannel evaporator.The uneven distribution of refrigerant flow decreases with the increase of refrigerant flow and undercooling,and is more uneven with the increase of dryness.When the flow rate increases,the first process inhomogeneity decreases by 28%,and the second process inhomogeneity decreases by 30%.When the undercooling degree increases,the first process inhomogeneity decreases by 15%,and the second process inhomogeneity decreases by 16%.When the dryness degree increases,the first process inhomogeneity increases by 18%,and the second process inhomogeneity increases by 10.8%.The most important factor affecting the flow distribution inhomogeneity is flow.（5）The experimental platform of dual-flow microchannel evaporator was established,and the performance variation of microchannel evaporator under different refrigerant flow rates was analyzed and tested.The heat exchange,pressure drop and superheat data obtained by experimental test were compared with those obtained by simulation.The results show that the variation law obtained by numerical simulation is the same as that obtained by experimental data.Among them,the maximum difference of heat transfer is 4.67%,the superheat difference is 16.3%,the temperature difference of each flat tube is 10%,the pressure drop difference is 25%,and the calculation error is within 30%,which verifies the accuracy of the calculation model of the dual-process microchannel evaporator and provides the basis for the application of the dual-process microchannel evaporator in the future.