Experimental investigation of condensation in micro-fin tubes of different geometries

An experimental investigation was performed for single-phase flow and condensation characteristics inside five micro-fin tubes with the same outer diameter 5 mm and helix angle 18°. Data are for mass fluxes ranging from about 200 to 650 kg/m2 s. The nominal saturation temperature is 320 K, with inlet and outlet qualities of 0.8 and 0.1, respectively. The results suggest that Tube 4 has the highest condensation heat transfer coefficient and also the highest condensation pressure drop penalty, while Tube 5 has the highest enhancement ratio due to its lowest pressure drop penalty and intermediate heat transfer coefficient. Condensation heat transfer coefficient flattens out gradually as G decreases when G < 400 kg/(m2 s) for Tube 2 and Tube 4. This nonlinear mass-flux effect may be explained by the complex interactions between micro-fins and fluid, including liquid drainage by surface tension and interfacial turbulence. In addition, the experimental data was analyzed using seven existing pressure-drop correlations and four heat-transfer models to verify their respective accuracies.