Browsing by Author "Velson, Nathan Van"
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Item Multiple Loop Heat Pipe Radiator for Variable Heat Rejection in Future Spacecraft(45th International Conference on Environmental Systems, 2015-07-12) Velson, Nathan Van; Tarau, Calin; DeChristopher, Mike; Anderson, William G.As NASA refocuses its human mission ambitions to colder areas of exploration beyond Low Earth Orbit, the need for improved variable heat rejection thermal control systems increases. To account for large variations in heat loads and environment temperatures, a thermal control system with a large turndown ratio is required. This paper presents a variable heat rejection system that uses multiple Loop Heat Pipes (LHPs) to reject large heat loads from a single-phase pumped loop, with high turndown ratios. A novel method of LHP control through local flow rate modulation of the single-phase fluid is developed and demonstrated. Systematic Thermal Desktop modeling of multiple LHP systems was performed to demonstrate the potential of this method. A modeled 2.5 kW three LHP system was shown to have a turndown ratio of 10:1 at a sink temperature of -41°C K and a turndown of 1.5:1 at a sink temperature of -269°C. Finally, an experimental study of a two-LHP system was performed to support the conclusions of the modeling effort.Item Two-Phase Thermal Switch for Spacecraft Passive Thermal Management(45th International Conference on Environmental Systems, 2015-07-12) Velson, Nathan Van; Tarau, Calin; Anderson, William G.Future manned and unmanned spacecraft will venture far beyond the relatively benign environment of low Earth orbit. The combination of extreme environments and high turndown requirements present a significant challenge for spacecraft thermal control systems. Thermal switches are among the thermal control devices that will be required to dissipate a wide range of heat loads in widely varying environments. A novel two-phase passive thermal switch technology has been developed and demonstrated. This technology uses the condensing vapor of a saturated two-phase working fluid to both transfer the heat and provide the contact pressure for the heat transfer surfaces of the switch. The switching mechanism is passively triggered by the temperature of the heat source. In addition to the On/Off capability of a thermal switch, the technology serves as a variable thermal link while in the On condition to maintain a heat source set point temperature. This set point temperature is determined by the design of the switch. In this paper, the principles of operation of the two-phase thermal switch are presented. A prototype switch was built and tested over a range of conditions. The set point temperature was determined for a range of enclosure gas counter pressures, and the maintenance of a heat source set point temperature is demonstrated. The performance of the unoptimized prototype switch is characterized and shown to have a nominal On thermal conductance of 0.7 W/K and an On/Off conductance ratio of 20.