On the possibility to improve heat transfer of a sphere by natural convection and water mist

Abstract

This paper aims to evaluate the effects of water mist on steady natural convection heat transfer from a sphere. Experimental investigations were performed for the Nusselt number (Nu) under a range of water mist concentration in both cases, sphere located in an open volume space with constant surrounding temperature and inside a cylindrical channel with sphere-to-channel diameter ratio (d/D=0.73). The results obtained from the related experimental work indicated that the heat transfer rate was enhanced over that for the single-phase air flow as a result of water mist evaporation on the heated surfaces. Compared to air cooling over a range of heat flux investigated, the percentage enhancement in the overall thermal factor was about 40%, 95.4%, 129.4%, and 156.8% respectively for all water mist concentration. In addition, an empirical correlation was also formulated to estimate the real benefits of using the water mist of the enhanced sphere. © 2019 Published under licence by IOP Publishing Ltd.