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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Device set to allow heat to flow across gap (switch "on") or decrease rate of transfer of heat to relatively low value (switch "off"). Operates at temperatures in approximate range of 100 to 1,500 degree C. Central cylindrical object thermally connected to (or disconnected from) environment by filling gap between inner and outer sleeves of switch (or evacuating gap) to increase (or decrease) thermal conduction across gap.
NASA's Genesis sample return mission will be the first to return material from beyond the Earth-Moon system. NASA Langley Research Center supported this mission with aerothermodynamic analyses of the sample return capsule. This paper provides an overview of that effort. The capsule is attached through its forebody to the spacecraft bus. When the attachment is severed prior to Earth entry, forebody cavities remain. The presence of these cavities could dramatically increase the heating environment in their vicinity and downstream. A combination of computational fluid dynamics calculations and wind tunnel phosphor thermography tests were employed to address this issue. These results quantify the heating environment in and around the cavities, and were a factor in the decision to switch forebody heat shield materials. A transition map is developed which predicts that the flow aft of the penetrations will still be laminar at the peak heating point of the trajectory. As the vehicle continues along the trajectory to the peak dynamic pressure point, fully turbulent flow aft of the penetrations could occur. The integrated heat load calculations show that a heat shield sized to the stagnation point levels will be adequate for the predicted environment aft of the penetrations.
The use of a novel plasma switch based on the inverse-pinch mechanism can reduce local current density over spacecraft power system electrodes, thereby minimizing damage to the insulator. The current density involved is 2 orders of magnitude smaller than that of the z-pinched current in a spark-gap switch; local heating is therefore about 4 orders of magnitude less than that to the electrodes of the spark-gap switch. Over 2000 tests of the plasma switch have been conducted for a forward current of more than 1 MA and up to 20 kV holdoff voltage.
Hand control proven superior to foot control. Hand-operated switch added to hand-held brazing-alloy-paste dispenser yields improved, more consistent brazing-alloy beads. Dispenser used to apply paste between adjacent tubes in heat exchanger. Switch reliable and safe, and removed and reattached easily.
Tests results obtained with an ATS axial groove aluminum extrusion adapted for use as a cryogenic thermal diode and/or a variable conductance heat pipe are presented. Ethane at a nominal operating temperature of 185 C was used as working fluid. In addition to both active and passive gas control, diode designs utilizing gas blockage or liquid trap were investigated. Specific requirements and performance parameters such as transient behavior, reservoir sizes, shutdown energy, etc., were evaluated. Results are also presented for tests where the liquid trap was used as a secondary heat pipe to demonstrate thermal switching with simultaneous heat pipe operation and diode shutdown.
An automatic thermal switch to control heat flow includes two thermally conductive plates and a thermally conductive switch saddle pivotally mounted to the first plate. A flexible heat carrier is connected between the switch saddle and the second plate. A phase-change power unit, including a piston coupled to the switch saddle, is in thermal contact with the first thermally conductive plate. A biasing element biases the switch saddle in a predetermined position with respect to the first plate. When the phase-change power unit is actuated by an increase in heat transmitted through the first place, the piston extends and causes the switch saddle to pivot, thereby varying the thermal conduction between the two plates through the switch saddle and flexible heat carrier. The biasing element, switch saddle, and piston can be arranged to provide either a normally closed or normally opened thermally conductive path between the two plates.
This paper summarizes experiments on the behavior of hydrogen in the gas gap switch and formation of methane in the CE sorbent beds.
A temperature controllable heat pipe switching device is reported. It includes separate evaporating and condensing chambers interconnected by separate vapor flow and liquid return conduits. The vapor flow conduit can be opened or closed to the flow of vapor, whereas the liquid return conduit blocks vapor flow at all times. When the vapor flow path is open, the device has high thermal conductivity, and when the vapor flow path is blocked the device has low thermal conductivity.
Hydrogen sorption crycoolers are being developed for the European Space Agency Planck mission to provide nominal 19 K cooling to instruments for measuring the temperature anisotropy of the cosmic microwave background with extreme sensitivity and resolution.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Hydrogen isotherms have been measured for activated LaNi(sub 4.6)M(sub 0.4) alloys from 300 K to 473 K or 493 K, where M= Si, Ge, Sn. Thermodynamic parameters have been obtained from the isotherms using van't Hoff plots for hydride decomposition.
Systematic studies of the hydriding behavior of LaNi(sub 5-x)Sn(sub x)H(sub z) alloys with tin contents in the range between 0.20 and 0.25 have revealed changes in the pressure-composition-temperature (PCT) isotherms measured after heating the hydrides above 450 K. These changes are indications of degradation processes and increased disorder within the alloy structure.
The development of hydrogen sorption cryocoolers over the past thirty years is briefly reviewed.
In the 1998 timeframe increasing numbers of proposed space-instrument programs within NASA and the Balistic Missile Defense Organization (BMDO) were in need of high-reliablility, long-life, low-vibration space cryocoolers.
Continuous-duty hydrogen sorption cryocoolers are being developed for the European Space Agency (ESA) Planck mission. To achieve an acceptable level of performance and robust operation with these hydride refrigerators during flight, detailed investigations have been performed on the sorbent materials and on critical hardware components.