R417A和R22在光管和强化管外的凝结换热特性比较

Characteristic Comparison of Condensation Heat Transfers Outside the Smooth and Enhanced Tubes when Using R417A and R22

对氟利昂R417A与R22在水平单管外的凝结换热性能进行了试验研究,试验工况温度40℃,试验管为光管和两根双侧强化管（其中C32为肋密度50fpi二维强化管,C36为相同肋密度三维强化管）。目的是获得R417A在光管、二维、三维强化管外的凝结换热特性,进而研究R417A替代R22的可行性。通过Wilson热阻分离试验获得管内对流换热系数,进而从总传热热阻中分离出管外凝结换热热阻。结果显示,光管管外R22凝结Nusselt理论值与实验值偏差在±5%以内。R417A在光管外凝结换热系数约为R22的65%,而在C32、C36管外凝结换热系数分别占R22的50.8%~60.0%,31.7%~42.7%。R22在三维强化管C36外凝结换热系数是相同肋密度下二维强化管C32的1.27~1.44倍,而R417A在C32管外凝结换热系数略高于C36管,表明三维强化表面未必能进一步强化非共沸工质R417A的凝结换热。

An experimental study on R417A and R22 film condensation on single horizontal tubes （one smooth tube and two doubly enhanced ones） was conducted at the refrigerant saturation temperature of 40℃. The object of study was to reveal the condensation heat transfer on the outsides of smooth tube, two dimensional enhanced tube and three dimensional enhanced tube, respectively, and the possibility of using R417A as substitution for R22. A modified Wilson plot was used to obtain the water-side and vapor-side heat transfer coefficients. The results show that the predicted condensation heat transfer coefficients of R22 on smooth tube calculated by Nusselt theory agree well with the experimental data within ± 5%. Condensation heat transfer coefficients of R417A are about 65% of those of R22 for smooth tube. Meanwhile, the condensation heat transfer coefficients of R417A are 50.8%-60.0% and 31.7%-42.7% of those of R22 on the outsides of the tubes C32 and C36, respectively. For R22, the condensation heat transfer coefficients on C36 are 1.27-1.44 times higher than those on C32 with the same fin density. For R417A, the condensation heat transfer coefficients on C32 are slightly higher than those on C36. This indicate that, using three dimensional enhanced tube can not further enhance the condensation heat transfer of using two dimension ones for non-azeotropic mixtures of R417A.