STUDY OF POOL BOILING OF AMMONIA/WATER MIXTURE OVER A HORIZONTAL TUBE

Abstract

When a liquid is in contact with a surface maintained at a temperature above the saturation temperature of the liquid, boiling will eventually occur at that liquid-solid interface. 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 thermo-physical properties of liquid, input heat flux and heat surface conditions.. The rate of evaporation and the rate of heat transfer in nucleate boiling- increases with increasing ATe and reach a maximum at some point. In film boiling regime we get a lower limit for the heat flux. At higher temperatures heat transfer across the vapor film by radiation becomes significant and needs to be considered. The present investigation aims to investigating experimentally the phenomena of nucleate pool boiling under high heat flux condition. In view of the above, an experimental setup was fabricated for the measurement of the wall heat flux, wall super heat, and transfer coefficient of ammonia/water mixture and pure water. In this dissertation report, the nucleate pool boiling heat transfer coefficient of ammonia/water mixture was investigated on a cylindrical heated surface at low mass fraction of 0< XNH3 < .25 at different heat flux. The effect of mass fraction, heat flux on boiling heat transfer coefficient was studied. The results indicate that the heat transfer coefficient in mixture decreases with increase in ammonia mass fraction, increases with increase in heat flux.