Spray Cooling in Terrestrial and Simulated Reduced Gravity

Initial baseline 1-g heat transfer results are reported for an instrumented spray cooling experiment, developed to study effects of electric body forces on spray cooling heat transfer in variable gravity conditions. Heat transfer performance in 1-g for both vertical downward and horizontal spray impingement has been documented for spray volume flow rates of 4.8X10-6 m3/s Q 9.8X10-6 m3/s, and heater power levels from 10 W to 70 W using a Thick Film Resistor (TFR) heater. As flow rate is increased at fixed heater power the heat transfer effectiveness increases, as indicated by reduced heater surface temperatures. Heat transfer effectiveness for the vertical downward spray and horizontal spray configurations are nearly identical, but the horizontal spray has slightly better heat transfer performance when a confining cap is removed at the highest flow rate of 9.8X10-6 m3/s. A transparent Indium-Tin-Oxide (ITO) heater consistently has somewhat better performance than the TFR heater. The heat transfer coefficient increases with increased spray flow rate, but is only weakly dependent on the heater power level. Preliminary flow visualization of the spray and liquid film motion for the ITO heater using a high-speed digital video camera and a laser light sheet indicates a highly contorted free surface for the liquid film that forms on the heater surface. Outward radial motion of the wave-like craters and ridges that form on the interface is observed. The liquid droplets that splash off of the heater surface are also observed to move radially, but more slowly than the impinging spray droplets, and are also significantly larger.