Physical Sciences

Regulating Pressure-Volume Control of a Gas Blanketing Liquid R-124

A system for storing and circulating a refrigerant liquid [R- 124 (chloro- tetrafluoroethane)] includes a reservoir and a subsystem that regulates the pressure of nitrogen gas in the head space of the reservoir. The purpose of the pressurization is to prevent cavitation in a pump that circulates the liquid. It is necessary to keep enough nitrogen in the system to keep the pressure high enough to prevent cavitation even when the liquid is at its coldest and thus at its smallest volume. It is also necessary to satisfy a competing requirement to, when the refrigerant is at its warmest and thus at its greatest volume, prevent the pressure from exceeding the level at which a relief valve opens and vents the head-space gaseous mixture of refrigerant vapor and nitrogen to the atmosphere. The pressure-control subsystem includes a supply of nitrogen at a pressure of 80 psig (gauge pressure of 552 kPa), a commercial electronic pressure regulator, a programmable-logic controller, and pressure and temperature sensors in the reservoir. The pressure-control subsystem adjusts the nitrogen pressure to the optimum value for the sensed temperature, thereby preventing both cavitation and venting.

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Aircraft Anti-Icing Heaters Made From Expanded Graphite

These heaters could be lightweight and inexpensive enough to be practical for small aircraft. Improved electrical resistance heaters for preventing the accum- ulation of ice on aircraft surfaces are undergoing development. The primary intended market for these heaters is that of small single- and twin-engine airplanes and helicopters, most of which have not been equipped with anti-icing heaters because the weights and costs of such heaters have made them impractical. The improved heaters are expected to add very little to the weights of aircraft and, when massproduced, to cost about half as much as do anti-icing systems of prior design. The aircraft could be equipped with high-output alternators to supply the additional electric power needed for the heaters.

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Electrostatic Systems Keep Dust Off Surfaces

These lightweight systems operate unattended and contain no moving parts. Electrostatic dust- collection systems that comprise wire grids connected to lightweight, low-power high-voltage sources have been invented for preventing the accumulation of dust on surfaces. Intended originally for use in keeping spacecraft solar panels free of dust, these systems could also be used on Earth to keep dust off such critical surfaces as those of semiconductor surfaces that await processing, highly sensitive optical instruments, and optoelectronic devices.

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Wind and Mountain Wave Observations From a Flight Test of a Solar-Powered Airplane

This airplane was shown to be useful for observing atmospheric waves. In support of NASA’s Environmental Research Aircraft and Sensor Technology (ERAST) program, flight tests of the Pathfinder solar-electric-powered, remotely piloted aircraft (RPA) were conducted at the Navy’s Pacific Missile Range Facility (PMRF), Barking Sands, Kaua’i, Hawaii, from May to November 1997 and from June to August 1998. This airplane was designed to operate at low speeds and low Reynolds numbers for long duration at altitudes above 60,000 ft (18 km). Three successive altitude world records for propellerdriven aircraft were established during these tests: 67,400 ft (20.54 km) on June 9, 1997; 71,350 ft (21.75 km) on July 7, 1997; and 80,201 ft (24.445 km) on August 6, 1998.

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Pyrolytic-Graphite Gauges for Measuring Large Heat Fluxes

These gauges exploit the high-temperature endurance and thermal-conduction anisotropy of pyrolytic graphite. Gauges made of slugs of pyrolytic graphite with thermocouples em- bedded in them have been invented for use in measuring large, short-duration heat fluxes in hot, highly corrosive environments. These gauges were originally intended for use in combustion chambers of rocket engines; they might also be useful in terrestrial combustion chambers (e.g., in furnaces) and metal-processing equipment.

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Preparing High-Quality Micrographic Samples of Oil Paintings

Cross-sectional specimens are prepared with wet grinding followed by dry polishing. A technique similar to that of metallography has been devised for preparing cross-sectional micrographic specimens from small samples cut from oil paintings. Art experts at the Cleveland Museum of Art use the technique in their efforts to determine painters’ methods and to verify the authenticity of paintings. By implementing the technique with automated polishing equipment, they can prepare a cross-sectional specimen in 20 min, and a publication-quality photomicrograph (see figure) can be made from the specimen. In contrast, the prior manual preparation technique took about 4 h and yielded specimens that contained scratches and were not flat enough for viewing at higher magnifications.

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Optical Fourier-Plane Analysis of Suspended Particles

This technique would be used to diagnose samples of blood cells and other biological materials. Optical Fourier-plane analysis may prove useful for obtaining statistical data on the densities, sizes, shapes, indices of refraction, and perhaps other properties of particles (particularly, biological cells) suspended in liquids. This concept could potentially be the basis of a new class of simple, portable, relatively inexpensive instruments for diagnosis of samples of blood and other biological materials.

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