Numerical and experimental investigation on condensing heat transfer and flow characteristics outside horizontal dentate-fin tubes

The condensing flow and heat-transfer characteristics around dentate-fin tubes were investigated using numerical and experimental methods. Using the examined computational model, the film flow characteristics and condensing heat-transfer coefficient of the dentate-fin tubes in the circumferential and axial directions were analyzed. Comprehensive information regarding the condensation process in high-performance tubes is provided for the first time. The results showed that the circumferential and axial film thicknesses of the dentate-fin tubes increased with increasing fin density. The liquid film distribution of dentate-fin tubes with a low fin density was relatively uniform, and condensate drainage was easy. The special heat-transfer structure of dentate-fin tubes was examined, and it was found that the complex heat-transfer structure led to variations in the surface tension, which changes the liquid-film distribution. The local condensing heat-transfer coefficient of the dentate-fin tubes was very sensitive to the liquid-film distribution. The optimal fin density corresponding to the maximum overall heat-transfer coefficient was obtained, which showed that the mechanism of heat-transfer enhancement for dentate-fin tubes was a joint effect of the heat-transfer area and liquid-film thickness.