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

An experimental investigation was performed with R22 and R410A for single-phase flow and condensation inside seven micro-fin tubes with the same outer diameter 5 mm and helix angle 18° to obtain pressure drop and heat transfer coefficient characteristics of tubes with different apex angle α. Data are for mass fluxes at 200~650 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 a positive correlation between surface heat-transfer area ratio and heat exchange enhancement ratio. When R22 is used, Tube 1 has the relatively high heat transfer coefficient and relatively low pressure drop, the same as tube 7 when R410A is used. In addition, Pressure drop correlations for plain tubes were applied to micro-fin tubes by using a friction factor calculated by the Churchill model^[27] and a suitable relative roughness. The Kedzierski and Goncalves correlation ^[11]has been modified to be based on the nominal heat transfer area adopting the fin root diameter instead of the actual inner surface heat transfer area, which can predict all data points within a ± 20% error band.