R410A、R404A、R407C在水平强化换热管外的凝结换热

摘要

The performance of condensation heat transfer of R410A、R407C and R404A were experimentally studied and compared to horizontal tubes. The enhanced tubes in this study have three dimensional inner screw and outer diagonal fins. The Wilson plot method was used to treat experimental data and obtain the coefficient of convective heat transfer in tubes and convective heat transfer correlation in the form of Dittus-Boelter. Then the condensation heat transfer coefficient on tubes can be figured out on the basis of separation of thermal resistance. The results showed that under the same conditions,the condensation heat transfer coefficient is the sequence of R410A>R404A > R407C. The outer enhancement factor of these three refrigerants is 9.53—14.07、6.81—11.48 and 3.23—5.28. The enhancement ratio of R410A、R404A and R407C is 1.77,1.73,1.76. The condensation heat transfer coefficient of R410A decreased with the increasing degree of super-cooling,the same as the condensation characteristics of the single refrigerant. However,as the increasing degree of super-cooling,the condensation heat transfer coefficients of 404A and R407C increase. The reason is that a layer of vapor film forms in the condensation process of the non-azeotropic,which increased the heat transfer resistance.%研究了 R410A、R404A、R407C 在水平强化管外的凝结换热，并进行了换热性能的对比。实验管为常用的管内螺纹、管外斜翅的三维低肋管。应用威尔逊图解法对实验数据进行处理，得到管内对流换热系数并给出Dittus-Boelter 形式的强化管管内对流换热关联式，再根据热阻分离的方法得到管外凝结换热系数。结果表明，在相同换热参数下，凝结换热系数大小依次为R410A、R404A、R407C。3种制冷工质应用于该强化换热管的换热增强倍率分别在9.53～14.07、6.81～11.48和3.23～5.28的范围。而R410A、R404A和R407C在强化管内的强化倍率分别为1.77、1.73和1.76，三者相差不大。R410A管外凝结换热系数随着壁面过冷度的增大而减小，与单一制冷工质这一冷凝特性相同；而R404A和R407C与R410A不同，随着壁面过冷度的增大，管外凝结换热系数增大，这主要是非共沸制冷工质管外凝结过程存在的气膜热阻所致。