Experimental investigation of natural dehumidification over an annular finned-tube

• Natural dehumidification over a compact finned-tube is investigated experimentally.
• Variation of heat and mass transfer with humidity and temperature is presented.
• No condensation is observed between the fins due to small fin spacing.
• A sinusoidal pattern is observed for condensation dripping.
• Experimental correlations are presented for dimensionless heat and mass transfer.

In this study, heat and mass transfer during natural condensation of humid air over a horizontal annular finned-tube is investigated experimentally. The finned-tube is made by extruded process and fins are circular with rectangular cross-section. Outer diameter of central tube, fin diameter, fin thickness and fin density are 25.4 mm, 0.4 mm, 56.0 mm and 433 FPM (fins per meter), respectively. The test case is placed in a specially constructed insulated test room to control test conditions and simulate pure natural dehumidification. Ambient air temperature and relative humidity are controlled by heating, cooling and humidifying equipment. Ethylene glycol–water solution is used as refrigerant to control and keep fin base temperature constant. Experiments are performed for ambient air temperature of 25 °C, 30 °C and 35 °C, relative humidity of 40%, 50%, 60% and 70% and fin base temperature of 4 °C, 6 °C and 8 °C. Observations indicate that the water drops form mainly on tip of the fins and for the conducted tests, no condensation is observed between the fins which is mainly due to small fin spacing (2.0 mm) and lack of convective heat and mass transfer between the fins. The test results also show that condensation and heat transfer rate depend mainly on the temperature and relative humidity of the surrounding air and fin base temperature. The increase in ambient air temperature and relative humidity and the decrease in fin base temperature lead to increase in heat and mass transfer rate. Furthermore, based on the results, new correlations are developed for heat and mass transfer during natural dehumidification over compact annular finned-tubes.