The objective of this thesis was to investigate the cooling performance of a 16-nozzle spray array, using FC-72 as the working fluid, in variable gravity conditions with additional emphasis on fluid management and flow stability. 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] area on a thick film resistive heater used to simulate electronic components. Data was taken and reduced as a result of flight tests conducted over the course of two flight weeks (each week consisting of four flights, each flight consisting of 40 to 60 parabolas). The flight tests were conducted in order to examine gravity effects on spray cooling performance and to evaluate a novel liquid-vapor separator design. The mass flow rate through the 16-nozzle spray array ranged from 13.1 < m < 21.3 [g/s] for the spray cooling analysis and 14 < m < 35 [g/s] for the separator evaluation. The heat flux at the thick film resistor ranged from 2.9 < q" < 25 [W/cm2], the subcooling of the working fluid ranged from 1.6 < Tsc < 18.4 [C], the saturation temperature ranged from 37.4 < Tsat < 47.2 [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] while the acceleration ranged from -0.02 < a < -2.02 [g]. Two-phase cooling was emphasized, but some single-phase data was 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 micro-gravity over terrestrial and elevated gravity. In addition, a sudden degradation in performance was found at high mass flow rates in micro-gravity, 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 either in micro-gravity or elevated gravity. Also, an improved liquid-vapor separator concept was implemented to enable flow stability during the micro-gravity portions of the flight. Multiple liquid-vapor separator concepts were tested during micro-gravity flights until a final design was settled on. The final separator design went through more rigorous evaluation to compare performance at multiple fill levels, each with a higher percentage of vapor space within the reservoir. It was found that, using the final reservoir design, stable flow operation was achieved in micro-gravity for mass flow rates m = 14, 17.5, and 21 [g/s].