Research On Condensation Heat Transfer Characteristics Of Low-GWP Refrigerants And The Mixtures Flowing In MPE Tube

In order to solve environment problems such as ozone depletion and global warming,developing new generation of refrigerant which is environmentally friendly,energy-saving and efficient is an important subject in refrigeration field.In the other hand,mini-channel heat exchangers can decrease the charge of refrigerant and has higher Heat transfer coefficient.Comparing with traditional copper tube fin heat exchangers of refrigeration and air conditioning industry,with strong bearing capacity and compact structure,mini-channel heat exchangers have took the place of traditional finned tube heat exchanger and become popular in the air conditioning field,especially in automobile air conditioning field.we should synthesize the two factors and develop a new generation refrigerant which can enhance heat transfer performance and decrease the refrigerant charge for mini-channel heat exchanger,.Therefore,achieving the goal of energy saving and environmental protecting and studying on condensation heat transfer characteristics of low GWP refrigerants and their mixtures in mini-channel tubes is very significant.Firstly,the thermal physical and environmental protection properties of some low GWP pure refrigerants were contrasted.And then the thermodynamic properties of the mixed refrigerants were researched,especially the new ternary refrigerant mixture R446 A and R447 A.On the basis of the experimental data,the interaction coefficients of Helmholtz free energy state equation of mixture models were calculated and optimized by fitting calculation.After that,we made the contrastive analysis of the experimental data,the new model calculation results and the calculation results of software REFPROP.The results showed that the optimized state equation had higher calculation precision and stability.Furthermore,the system cycle performance of the new mixed refrigerants R446 A and R447 A was analyzed.Owing to the similar thermodynamic properties,cycle efficiencies of R446 A and R447 A,were similar.However,their cycle efficiencies were higher than that of pure refrigerants such as R1234 ze and R410 A.Although,their unit mass refrigerating capacities were slightly lower than R32,exhaust temperatures were lower than R32,which can ensure the reliability of the compressor.Nevertheless,comparing with R410 A,temperature glide of R446 A and R447 A were higher.Over all,new mixed refrigerants R446 A and R447 A were able to be used as the environmentally friendly and high-efficiency substitution of R410 A.Secondly,condensation heat transfer characteristic of R32 in three kinds of mini-channels were studied and analyzed contrastively.The results showed that the condensation heat transfer coefficient is displayed in descending order as follow: square-hole multi-port extrud(MPE)tubes with H.D.0.715 mm,round-hole multi-port extrud tubes with H.D.0.86 mm and smooth tubes with H.D.2 mm.It demonstrated that the heat transfer property could be strengthened under the small pipe diameter.liquid membrane gather at the four edges of square tube,and become thiner in the middle.And the heat transfer coefficient of square-hole MPE tube was higher than round-hole MPE tube.Thirdly,we operated the experimental test and research on condensation heat transfer properties of pure refrigerants R134 a,R32,R1234 ze and their mixture refrigerants and R410 A,R447A in the round hole-flat tube.Compared all pure and mixed refrigerants,under the same operating condition,the results showed that the condensation heat transfer coefficient form high to low were displayed.At last,the predicted results from six correlations were compared with experimental results of some refrigerants.The results showed that the predicted results were similar to experimental results of R32 except Koyama,while for R134 a only three correlations from Cavallini,Park and Kim are ideal.However,the ideally result for R1234 ze only happened in park correlation.It demonstrated that correlations of Cavallini,Park and Kim had high-precision predicted results for these refrigerants.The best predicted results for R410 A came from the Park correlation.While the best predicted results for mixture refrigerants consisted of R32 and R134 a appeared in Cavallini correlation,the best predicted results for mixture refrigerants consisted of R32 and R1234 ze appeared in Thome correlation.Meanwhile,The best predicted results for R447 A came from the Shah correlation.