The Effect of Variable Gravity on the Cooling Performance of a Partially-Confined FC-72 Spray

by Michalak, Travis Edward

This thesis discusses the effects of a variable-gravity environment on the performance of a subcooled partially-confined spray. An experiment, consisting of a test chamber, the associated flow loops, and instrumentation, was fabricated and flown on the NASA Reduced-Gravity Testing Platform. This modified KC-135 aircraft followed a parabolic flight path to provide various acceleration levels. The spray chamber contained two opposing nozzles spraying onto Thick Film Resistor (TFR) heaters, which were mounted on insulating glass pedestals. Only the upward facing heater was used during this testing. Thermocouples under the heater in the glass pedestal were used to determine the heater surface temperature. The glass pedestals were surrounded by an annular sump system, which was used to collect and remove the cooling fluid from the test chamber. The fluid used for this testing was FC-72, which is a non-toxic, non-flammable, and non-reactive refrigerant. Due to its dielectric nature, FC-72 was sprayed directly onto the electric thick film heaters. The parametric ranges of this experiment were as follows: Heat flux to the spray, 21.1 ? q?sp ? 69.0 W/cm^2; acceleration field, 0.15 ? a ? 1.80 g; coolant volumetric flow rate, 6.18 ? V ? 8.94 ml/s; and coolant subcooling, 23.1 ? ”Tsc ? 31.7 K. The heat fluxes tested were below the critical heat flux q?CHF. The wall superheat ”Tsat = Ts - Tsat was found to increase with heat input and acceleration, and decrease with subcooling and volumetric flow rate.