Systematic experimental investigation of the effects of geometric parameters on film-wise condensation of externally finned tubes

This study systematically investigates the effects of five key geometric parameters: fin density, height, thickness, root structure, and secondary fin depth, on the condensation heat transfer performance of externally two-dimensional (2D) and three-dimensional (3D) finned tubes. Using R134a as the working fluid at a saturation temperature of 36 °C, experiments were conducted on 17 enhanced tubes under heat fluxes ranging from 10 to 80 kW/m². Results show that 3D fins significantly outperform 2D fins, particularly under higher heat flux conditions, due to improved condensate drainage and liquid film disruption. An optimal fin density of 48 fpi for the 3D finned tubes was identified, balancing increased surface area and drainage efficiency. Square fin root structures are better suited for tubes with low fin density, while deep-secondary-fin tubes exhibit better condensation performance under high heat flux. Increased thickness of 3D fins leads to a decrease in the optimal fin density. This work clarifies the effects of 3D fin parameters, identifies optimal configurations, and provides data to guide the design of high-efficiency condensers.