Two Phase Heat Transfer And Pressure Drop Characteristics Of Refrigerant-oil Mixture Flow Inside Microchannel Heat Exchanger And Modeling Validation

Microchannel heat exchanger has been widely used in HVAC system,the investigation on the microchannel is diving deeper and further,such as flow boiling and condensating mechanisim inside microchannel tubes and optimization design,including pure refrigerant and refrigerant and lubricant mixtures heat transfer characteristics,the impact of distributor in evaporator,etc.The modeling and simulation for micro channel heat exchanger including overall performance of heat transfer,pressure drop and charge inventory.It is critical to HVAC system design optimization and modeling analysis.This study is focusing on improving accuracy of two phase flow boiling heat transfer and pressure drop models in microchannel tubes,the author set up a test facility and produce testing on R134 a,R410A and R134 a & RL32 H and R410 A & RL32 H at boiling heat transfer and pressure drop characters,approperaite models are developed to chapture the test results.Via applying modeling and simulation technology on to heat exchanger design,set up segment by segment microchannel condenser model and air conditioning system model,analize the impaction of heat transfer and pressure drop characteristics on heat exchanger and system level performance,and set up system charge simulation model.With the help of charge testing results on heat exchangers,propertiate void fraction models are selected to be used in heat exchanger models to simulate system charge migeration between components at different system running conditions.The main outcomes of this investigation are as following:1.The heat transfer and pressure drop test facility was set up for refrigerant and lubricant flow boiling and condensing inside multi-channel microchannel tube.The refrigerant system is driven by refrigerant gear pump,with effective measurements of oil retention rate in the mixture flow,supply a useful way to investigate impact of refrigerant and lubricant flow boiling and condensing inside tubes within air conditioning normal conditions.2.Experimental study on R134 a and R410 A pure refrigerant flow boiling heat transfer characters inside multi-channel microchannel tube.With the increasing of entering quality,mass flux and heat flux,the heat transfer coefficiencts are increasing,with the increasing of entering quality around 0.6,the dryout phenominal is obtained,therefore local heat transfer coefficient decreases.Compare to published correlations,one of them can be used to match pressure drop test data,however new pre-dry heat transfer model and dryout quality model need to be developed based on test data,and the accuracy of prediction is imporved for R134 a flow boiling.3.Experimental study on R134 a and R410 A with lubricant mixture flow boiling heat transfer and pressure drop characters inside multi-channel microchannel tube.With the increasing of entering quality,mass flux and heat flux,heat transfer coefficients and pressure drop are decreasing and firctional pressure drop are increasing.New frictional pressure drop correlation and heat transfer correlation are developed based on mixture property saturated temperature and local lubricant concentration,and thus imporved the accuracy of prediction for R134 a and lubricatn flow boiling.4.Set up segment by segment microchannel heat exchanger model for investigating heat exchanger performance and imporving the heat exchanger design.Therefore,the model is validated by heat exchanger testing data,and the model is used to evaluate impaction of non-uniform air flow at front area on one row and multi-row microchannel heat exchanger,and optimize the design of those heat exchangers.5.Several refrigerant charge tests are conducted at heat exchanger level to help with analize refrigerant mass distribution in different parts of the refrigerant system.Via selecting properate void fraction models,set up refrigerant system models to simulate refrigerant charge.The bridge between models from heat transfer testing results and component and system simulation are set up.