Physical Sciences

Improved Cryostat for Cooling a Wide Panel

Less technician time and lower consumption of helium translate to lower cost.An improved cryostat has been developed for cooling a wide panel evenly over its surface to a temperature of -423 °F (-253 °C) by use of liquid helium. Originally, the cryostat was to be used in measuring apparent strains in wide aluminum/ lithium panels as functions of temperature in order to develop data for temperature compensation of the readings of strain gauges on a tank containing liquid hydrogen. Relative to the cryostat used previously for this purpose, the improved cryostat can be prepared for a test in less time, and it loses less helium during each test.

Posted in: Physical Sciences, Briefs

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Current Pulses Momentarily Enhance Thermoelectric Cooling

Transient cooling could be attractive for some semiconductor devices. The rates of cooling afforded by thermoelectric (Peltier) devices can be increased for short times by applying pulses of electric current greater than the currents that yield maximum steady-state cooling. It has been proposed to utilize such momentary enhancements of cooling in applications in which diode lasers and other semiconductor devices are required to operate for times of the order of milliseconds at temperatures too low to be easily obtainable in the steady state. In a typical contemplated application, a semiconductor device would be in contact with the final (coldest) somewhat taller stage of a multistage thermoelectric cooler. Steady current would be applied to the stages to produce steady cooling. Pulsed current would then be applied, enhancing the cooling of the top stage momentarily.

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Calculating Mass Diffusion in High-Pressure Binary Fluids

This model could contribute to understanding of high-pressure combustion. A comprehensive mathematical model of mass diffusion has been developed for binary fluids at high pressures, including critical and supercritical pressures. Heretofore, diverse expressions, valid for limited parameter ranges, have been used to correlate high-pressure binary mass- diffusion- coefficient data. This model will likely be especially useful in the computational simulation and analysis of combustion phenomena in diesel engines, gas turbines, and liquid rocket engines, wherein mass diffusion at high pressure plays a major role.

Posted in: Physical Sciences, Briefs, TSP

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Time-Transfer System for Two Orbiting Spacecraft

A report describes the time-transfer system of the Gravity Recovery and Climate Experiment (GRACE), in which information on the distribution of Earth mass is extracted from position and time measurements for two spacecraft about 200 km apart in a circular, nearly polar orbit. Each spacecraft carriers a Global Positioning System (GPS) receiver, a K/Ka-band ranging (KBR) instrument, and an ultra-stable oscillator (USO) that serves as a clock for the GPS and KBR units.

Posted in: Physical Sciences, Briefs, TSP

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Nonlinear FEA Analysis of Filament-Wound Composite Container Tanks

Filament-wound composites are replacing metals as the material of choice for tanks to hold liquids and gases. The composites have a high strength-to- weight ratio, making them ideal for use in aerospace and commercial ground transport. Also, the automated winding process is less expensive than other manufacturing methods for composites.

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Pseudoslit Spectrometer

Functioning similarly to a slit spectrometer, this instrument would be optomechanically simpler. The pseudoslit spectrometer is a conceptual optoelectronic instrument that would offer some of the advantages, without the disadvantages, of prior linear- variable etalon (LVE) spectrometers and prior slit spectrometers. The pseudoslit spectrometer is so named because it would not include a slit, but the combined effects of its optical components would include a spatial filtering effect approximately equivalent to that of a slit.

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Waste-Heat-Driven Cooling Using Complex Compound Sorbents

Development of improved sorbents revives a long-neglected heat-pump concept. Improved complex-compound sorption pumps are undergoing development for use as prime movers in heat-pump systems for cooling and dehumidification of habitats for humans on the Moon and for residential and commercial cooling on Earth. Among the advantages of sorption heat-pump systems are that they contain no moving parts except for check valves and they can be driven by heat from diverse sources: examples include waste heat from generation of electric power, solar heat, or heat from combustion of natural gas.

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