Experimental investigations on condensation heat transfer outside enhanced tubes—Effect of tube types

Experimental investigations on condensation of R22 on single horizontal smooth tube and three kinds of enhanced tubes have been conducted. The objective is to obtain deeper understanding of the effect of surface geometries on condensation heat transfer performance and gain the average enhancement factors of three enhanced tubes. The results indicate that the predicted condensation heat transfer coefficients of smooth tube from Nusselt theory agree within ±5 percent with the experimental data. Experimental results show that the integral-fin of the tube can effectively enhance condensation heat transfer. In the investigations three kinds of enhanced tube C32, C33 and C36 are selected. At the saturation temperature of 35°C, the average enhancement factor of tube C32, C33 and C36 are 8.72, 9.37 and 11.07, respectively, and when the saturation temperature is 40°C the average enhancement factor of tube C32, tube C33 and tube C36 are 8.85, 9.55 and 11.14, respectively. In this paper the reasons of different enhancement factor are analyzed, these imply in the relationships between overall heat transfer coefficient and velocity, condensation heat transfer coefficient and temperature difference, enhancement factor and temperature difference.