A Numerical Simulation Study on Condensation Heat Transfer Performance of Serrated Spiral-Finned Tube

Serrated spiral-finned tubes have been extensively applied in heat exchangers, but the main research on them is about sensible heat transfer processes and only a few studies focus on condensation behavior. In this research, a model of mass and heat transfer about condensation of water vapor on the outside tube surfaces is developed by Fluent combined with a user-defined function. The effects of different finned tube geometrical parameters are investigated. The model's reliability is verified by experiments on smooth tubes. The model is applied to finned tubes with different structures. A simple evaluation index $\left(q_{\ln }·j\right)/f$ about the dimensionless condensation rate $q_{\ln }$, the dimensionless heat transfer factor j, and the resistance factor f is used to assess the comprehensive heat transfer performance of these finned tubes. The simulation results reflect that the increase of the base tube's outer diameter could enhance the comprehensive heat transfer performance, whereas the increase of the height and width of the open tooth will weaken the comprehensive condensation heat transfer performance to a different degree. Finally, the correlation equations of Nu, Eu, and dimensionless condensation rate $q_{\ln }$ with wet air flow rate, water vapor content, base tube's outer diameter, and height and width of the open tooth are fitted, the deviations of Nu are not more than 5%, and the relative deviations of $q_{\ln }$ and Eu could satisfy that 93% of the data is within 30%. Then, the finned tube geometry with optimal integrated condensation heat transfer performance ( $d_o$ = 23 mm, $h_2$ = 6 mm, w = 2.97 mm) is obtained.