MULTIPHASE SPRAY COOLING OF STEEL PLATES NEAR THE LEIDENFROST TEMPERATURE - EXPERIMENTAL STUDIES AND NUMERICAL MODELING

Abstract

Experimental studies were conducted to reveal the heat transfer mechanism of impacting water mist on high-temperature surfaces. A numerical model was developed to simulate, for atmospheric applications, air and water mist spray cooling of surfaces heated to temperatures ranging from nucleate to film boiling. Local heat transfer coefficients were measured in the film-boiling regime at various air velocities and liquid mass fluxes. The test conditions of water mist cover the variations of air velocity from 0 to 50.3 m/s, liquid mass flux from 0 to 7.67 kg/m(2)s, and surface temperature of stainless steel between 525 degrees C and 500 degrees C. Radial heat transfer distributions were measured at different liquid mass fluxes. The tests revealed that the radial variation of heat transfer coefficients of the water mist has a similar trend to that of air jet cooling. At the stagnation point, the heat transfer coefficient increases with both the air velocity and the liquid mass flux. The convective air heat transfer is consistent with the published correlation in the literature. The heat transfer contribution due to the presence of water increases almost linearly with the liquid mass flux. For dilute sprays, the total heat transfer coefficient can be established as two separable effects, which is the summation of the heat transfer coefficient of air and of liquid mass flux. This study shows that with a small amount of water added in the impacting air jet, the heat transfer is dramatically increased. The Leidenfrost temperature associated with the water mist cooling was also measured. The Leidenfrost temperature increased with both the air velocity and the liquid mass flux. The model simulation was compared against available test data at atmospheric conditions, and the simulation compared favorably well with the test data.