Parameter Comparison of Condensation Heat Transfer of R134a Outside Horizontal Low-Finned Tubes
Experimental studies of film condensation of R134a on single horizontal smooth tube and five low-finned tubes have been conducted. The fin number per meter varies from 736 to 2156. The objective is to enrich the basic data for film condensation of R134a on enhanced tubes and to obtain optimum fin density for the condensation of R134a on low-finned tubes, and to obtain deeper understanding of the effect of surface geometries on condensation heat transfer performance. Wilson plot technique was used to obtain the vapor side heat transfer coefficients. The results indicate that the predicted condensation heat transfer coefficients of R134a on smooth tube from Nusselt theory agree with the experimental data within 10 percent. It is found that the condensation heat transfer coefficient increases with the increase of fin density, so the optimum fin density is about 2156fpm for R134a condensing outside low-finned tubes. Compared with the smooth tube, at a saturated temperature of 40? and for the identical temperature difference, the enhancement factors of the five enhanced tubes(2156fpm, 1720fpm,1475fpm, 1020fpm, 736fpm) are 6.6-9.4?6.8-8.7?6.9-7.6?5.1-5.6?4.1-4.5, respectively. Compared with five commonly prediction models, the deviations mostly agree within ±25%. The Honda model gave relatively accurate predictions compared with experimental results.