Studies of water mist cooling on heated emetal surfaces

摘要

A water mist cooling process was studied. Computational and experimental studies were conducted to reveal the heat transfer of water mist on high temperature metal surfaces. Computational modeling helped to select the desirable dropet size and veloity in this study. The 20 micron droplet size and 20 m/sec velocity were considered. It reveraled interactions between the droplets and surfaces. Local heat transfer coefficients were measured in film boiling regime for water mist cooling at various air velocities and volumetric liquid flexes. The test conditions included variations of air velocity of 0 m/sec to 50.288 m/sec, volumetric liquid flux of 0 m~3/m~2 sec to 0.00767 m~3/m~2sec, and surface temperature of stainless steel between 525 deg C and 500 deg C. Radial heat transfer distributions were also presented at different liquid mass fluxes. It reveraled that the radial variation of heat transfer coefficients of water mist have a similar trend to the air jet cooling. The heat transfer coefficient increases with air velocity and can be predicted with the correlaton in the literature. The water mist heat transfer coefficient increases linearly with the volumetric liquid flux. The total heat transfer coefficient can be viewed as two separable effects, which is the summation of the heat transfer coefficient of air and of liquid flux, respectively. The Leidenfrost temperature aganist the air velocity and the volumetric liquid flux was mesured. The Leidenfrost temperatue increased with air velocity and volumetric liquid flux. This study shows that with a small amount of water in the air aimpacting jet, the heat transfer is dramatically increased.