Cooling Performance of a 16-Nozzle Array in Variable Gravity

The objective of this paper was to investigate the cooling performance of a 16-nozzle spray array using FC-72 as the working fluid in variable-gravity conditions. A flight-test experiment was modified to accommodate a 16-nozzle spray array, which was then tested in the parabolic flight trajectory environment of NASA's C-9 reduced-gravity aircraft. The 16-nozzle array was designed to cool a 25.4 x 25.4 mm(2) area on a thick-film resistive heater used to simulate an electronic component. Flight tests were conducted over the course of two flight weeks (each week consisting of four flights and each flight consisting of 40 to 60 parabolas). The mass How rate through the 16-nozzle spray array ranged from 13.1 <= (m) over dot <= 21.3 g/s. The heat flux at the thick-film resistor ranged from 2.9 <= q <= 25 W/cm(2), the subcooling of the working fluid ranged from 1.6 <= Delta T-sc <= 18.4 degrees C, the saturation temperature ranged from 37.4 <= T-sat <= 47.2 degrees C, and the absorbed air content in the working fluid was C = 10.1, 14.3 and 16.8% by volume. The spray chamber pressure ranged from 42 <= P <= 78 kPa and the acceleration ranged from -0.02 <= a <= -2.02 g. Two-phase cooling was emphasized, but some single-phase data were also collected. A one-dimensional model was used to predict the heater surface temperature from the heat input and mean heater base temperature. It was found that the cooling performance was enhanced in microgravity over terrestrial and elevated gravity. In addition, a sudden degradation in performance was found at high mass flow rates in microgravity, possibly due to liquid buildup on the surface between the nozzle impact zones. A high degree of subcooling was found to be beneficial, but the dissolved air content had little effect on the heat transfer performance in either microgravity or elevated gravity.