Travis E. Michalak

Design of A Microgravity Spray Cooling Experiment

Abstract : An analytical and experimental study was conducted for the application of spray cooling in a micro gravity and high-g environment. Experiments were carried out aboard the NASA KC-135 reduced gravity aircraft, which provided both the microgravity and high-g environments. In reduced gravity, surface tension flow was observed around the spray nozzle, due to unconstrained liquid in the test chamber and flow reversal at the heat source. A transient analytical model was developed to predict the temperature and the spray heat transfer coefficient within the heated region. Comparison of the experimental transient temperature variation with analytical results showed good agreement for low heat input values. The transient analysis also verified that thermal equilibrium within the heated region could be reached during the 20-25s reduced gravity portion of the flight profile.

Cooling Performance of a Partially-Confined FC-72 Spray: The Effect of Dissolved Air

Abstract : This paper discusses the heat transfer performance of a partially-confined FC-72 spray with varying dissolved air concentrations. An experimental test rig was used to obtain critical heat flux (CHF) data. A nozzle allowed the fluid to be sprayed onto a thick-film resistor heater, which was mounted onto a glass post, with a sump system to allow removal of excess fluid. Type-E thermocouples were imbedded in the post to obtain temperature data. The parametric ranges for testing were: volume-percent concentration of dissolved air, 1 < C < 20%, chamber saturation pressure, 6.90E+4 < Psat < 8.27E+4 N/rn2, subcooling, 2 < DeltaTsc < 12 deg C, volumetric flow rate, 6.31E-6 < V < 10.5E-6 rn3/s. Test data were obtained for comparison of CHF with varying C while controlling the spray chamber pressure. An empirical mathematical relationship allowing for determination of surface heat flux with varying flow rate was also developed. The model was obtained using test data at flow rates of V = 6.31E-6, 8.41E-6, and 1O.5E-6 m3/s, and was validated using experimental data obtained for flow rates of V = 7.36E-6 and 9.46E-6 m3/s.

Variable-Gravity Effects on a Single-Phase Partially-Confined Spray Cooling System

Abstract : This paper discusses the testing of a single-phase spray cooling system that was flown on the NASA KC-135 Reduced-Gravity Research Aircraft. An experimental package, consisting of a spray chamber coupled to a fluid delivery loop system, was fabricated for variable gravity flight tests. The spray chamber contains two opposing nozzles spraying on Indium Tin Oxide (ITO) heaters. These heaters are mounted on glass posts, which are part of a sump system to remove unconstrained liquid from the test chamber. Thermocouples mounted in and around the posts were used to determine both the heat loss through the underside of the ITO heater and the heat extracted by the spray. During flight tests, for Weber numbers of We = 771 plus or minus 19 and 757 plus or minus 15, the non-dimensional heat input was varied from G change; = 30 to 110 for the non-dimensional grouping [Fr(1/2)Ga](1/2) = 20 to 66. Flight test data and terrestrial data were compared to analytical and numerical solutions in order to evaluate the heat transfer in the heater and support structure. In general, the Nusselt number at the heater surface was found to decrease with increasing [Fr(1/)2Ga](1/2).