Experimental Study Of Boiling Heat Transfer Of R417A And R22Outside Air-conditioning Heat Transfer Tubes

R22has the medium pressure and temperature，which has been widely used in theAir-conditioning and refrigeration department. But the constant depletion of the ozone layer andglobal warming have resulted in numerous international environmental problems, which is crucialfor humans to take effective measures to limit utilization of R22. It is essential that humans shouldsearch the replacing refrigeration fluids, which kept the value of ozone depletion potential equals tozero, and low global warming potential and high energy efficiency.R417A (R125,R134a,R600;46.6%,50%,3.4%by weight respectively) that has no chlorine content (ODP=0) and anappropriate global warming potential (GWP=1950), is the more recommended for air conditioningequipment, which replacing directly the R22in the experimental apparatus without majormodifications. This refrigerant adds a small percentage of hydrocarbon, which satisfy the return ofthe lubricant oil to the compressor and the compatibility with traditional mineral oils or lubricantssuch as AB, MO and POE.The works analyzed the boiling heat transfer experimental data R417A and R22outside of thesmooth and four enhanced tubes, and the conclusion was carefully analyzed as follows:（1）A modified Wilson plot technique was used to determine the boiling heat transfercoefficients, and the results indicated that the in-tube convective heat transfer coefficient of theenhanced tubes （E30, E31, E32and E33）were2.737,2.782,2.325and2.634times of that of thesmooth one, respectively.（2）The boiling heat transfer coefficient increases significantly with the increase of heat fluxand temperature difference, and the boiling heat transfer coefficient of R417A outside fourenhanced tubes was obviously less than that of R22. To the same type of tube, the relationshipbetween performance of boiling heat transfer coefficient of enhanced tube and the density of fin should be paid more attention to. And the type directly decided the performance of heat transfer tothe different of tube. Above all, the heat transfer performance of GDHT-B11was better than that ofGDHT-B12.（3）TheboilingheattransfercoefficientofR22outsidesmoothtubewas1.468timesofthatof R417A in the same heat flux. The boiling heat transfer coefficient of R22outside E32was1.9times of that of R417A in the same heat flux. When in the same refrigeration fluids, the boiling heattransfer coefficient of enhanced tubes were better than the smooth tube in the same case. Theboiling heat transfer coefficient of R22, R125and R134a was2to3times of that of R417A in theheat flux of35kW.m-2, and the boiling heat transfer coefficient of R134a was larger than R417A atthe different saturation temperature, which attached to the theory of minimum nucleation radius.（4）Thepercentageofwaterandrefrigerantsideoftheenhancedtubesarealmostthesame,atthe water Reynolds number is3.7×104for the R22, and the heat transfer performance was in thegood condition. The percentage of refrigerant side is much larger than that of water-side in theoverall thermal resistance for the R417A, and the percentage of tube wall thermal resistance is nomore than3percent for all the test tubes, so the surface of tube needed to be further enhanced toimprove the whole heat transfer performance.