STUDY OF HEAT TRANSFER MECHANISM IN POOL BOILING

Abstract

Boiling is complex processes in which mass, momentum, and energy transfer (single and two-phase) involving a solid wall, liquid, and vapour are tightly coupled. Pool boiling has different modes of regions of heat transfer but nucleate pool boiling is one of the most efficient modes of pool boiling heat transfer and finds application in areas such as cooling towers, refrigeration, power generation, chemical processing, quenching process and nuclear reactors where quickly removal of heat energy from hot surface is desired. Heat transfer in nucleate boiling is a highly complex phenomenon as it depends on several parameters like thermophysical properties of liquid, input heat flux and heat surface conditions. Further the mechanism of boiling heat transfer has been observed to differ considerably in different regimes. Under high heat flux condition (when heat flux is more than about 60% of critical heat flux to near critical heat flux), the individual bubble coalesce due to very high bubble site density and form vapor mass entrapping a relatively thicker film of liquid known as 'macrolayer between the growing vapor mass and the heating surface. Under this condition, major portion of heat transfer has been thought to be through this liquid layer. An experimental setup was designed and fabricated for the measurement of superheat of boiling surface, heat flux and vapour mass emission frequency at boiling surface for water at atmospheric pressure on a brass surface under high heat flux condition. In view of the above, the present investigation aims to investigating experimentally the phenomenon of nucleate pool boiling under high heat flux condition......