Research Of The Heat Transfer Of Binary Non-azeotropic Mixed Refrigerant Condensate Outside Tubes

The condenser is an important equipment in air conditioning system, the heat transfer efficiency of the condenser has a great influence on the performance of the air conditioning system. The research and application of the high-efficient condenser does a great important role in achieving energy conservation and emission reduction. At present, the mature calculation models of condensation heat transfer are all for the pure refrigerant. There is no relatively mature heat transfer calculation model for the mixed refrigerant due to the complexity of the mixed refrigerant condensation, and it’s undoubtedly a loss for the wide application of the mixed refrigerant. Therefore, the research and establishment of the heat transfer calculation model for the mixed refrigerant will have important meaning and value.The experiment was conducted for the pure R134 a and the mixed R125 / R134a(The mass fraction of R125 is 6%, 12%, 18% respectively)at the working temperature 40±0.05℃.The test tubes are smooth tube,five two-dimensional enhanced tubes and two three-dimensional enhanced tubes. The theoretical analysis was also done and the calculation model for the mixed refrigerant was established. The main achievements from the paper are as follows:(1) The tendency of condensation heat transfer coefficient change with heat flux are same for the pure R134 a and the mixed R125 / R134 a outside the smooth tube, that is the heat transfer coefficient of condensation decreases as the heat flux increases. With the increase of R125 concentration, the mixed refrigerant condensation heat transfer coefficient decreases. When the heat flux is 20 k W/m2, the coefficients of R134a/R125 mixed refrigerant(The mass fraction of R125 is 6%, 12%, 18% respectively)outside smooth tube are respectively 88%, 84%, 71% of the pure R134 a.(2) The tendency of the condensation heat transfer coefficient of the mixed R125/R134 a refrigerant varied with the heat flux is different with the pure R134 a. The mixed refrigerant R125/R134 a condensation heat transfer coefficient outside the enhanced tubes increases with the increasing heat flux, and the increasing of heat transfer coefficient of condensation becomes slowly along with the increasing of the heat flux, The condensation heat transfer coefficients of different components of mixed refrigerant have a trend to close.(3) The heat transfer coefficient of two-dimensional enhanced tubes(C31, C37, C39, C40, C41) are 15.1-22.0, 13.7-21.8, 12.4-16.4, 12.0-13.5, 9.5-9.6 times of the smooth tube at the identical heat flux respectively. The heat transfer coefficient of condensation increases when the fin density of the tubes increases within limits, there exist an optimum fin density for the condensation outside two-dimensional enhanced tubes, the range is from 1960 to 2439 fpm.(4) The experimental data are compared with five kinds of commonly used condensation heat transfer calculation models, which include B-K model, Owen model, Webb model, Honda model and Rose mode. The error between Honda model and the experimental data error is small, so does Rose model. The B-K model has high precision for the tubes with low fin density.(5) A heat transfer calculation model of the mixed refrigerant condensation outsides tubes has been established. The deviation of the calculation results from the experimental values is within ±20% compared with the experimental data of the smooth tube, two and three dimensional enhanced tubes. It can provide guidance for the experimental study and engineering application.