Experimental visualization and analysis of transient heat and mass transfer during natural dehumidification of air around square finned tubes under various operating conditions

Abstract

This study aims to experimentally investigate the natural dehumidification of humid air on the surface of square fins. Different stages of dehumidification process including nucleation, droplet growth, coalition, and collapsing of droplets are visualized and analysed for various operating conditions. A detailed parametric study is conducted to study the effect of relative humidity, ambient temperature and fin spacing on the heat transfer coefficient, heat transfer rate and mass transfer rate. Transient behavior of heat and mass transfer characteristics is quantitatively and qualitatively assessed through various images at different times. The results show that an increase in the relative humidity and fin spacing has significantly increased the rate of dehumidification process and droplet growth, while increasing the ambient temperature exhibits a minimal influence on these two criteria. The heat transfer coefficient and rate reach the steady state condition after 15 min under various operating conditions, while the steady state condition for mass transfer is achieved at different times depending on the experimental conditions. As a case in point, an enhancement in fin spacing from 5 mm to 9 mm and 14 mm increases the heat transfer rate, heat transfer coefficient, and mass transfer by about 62% and 22%, 171% and 188%, and 63% and 130% at the relative humidity of 60% and ambient temperature of 30°C, respectively.