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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Improved Capacitive Quality Meter for a Two-Phase Fluid

Features include a better electrode configuration and several hardware improvements. A previously developed quality/flow meter has been redesigned to improve its performance as a device for mea- suring the quality (but not the flow) of two-phase (liquid + vapor) oxygen or nitrogen flowing in a pipe. As used in engineering disciplines concerned with two-phase flows, “quality” denotes, loosely, volume fractions of liquid or gas. Like some other quality meters, the previously developed meter and the present meter are based on a capacitance-measurement concept: The fluid flows through a space between electrodes, the capacitance between the electrodes is measured, and the volume fractions of liquid and gas are estimated from the effective permittivity, using the known relationships (a) between the effective permittivity and the capacitance and (b) between the volume fractions and the effective permittivity. The estimate of quality can be refined by use of additional data from pressure and temperature sensors.

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Ellipsoidal Collecting Horns for Ultrasonic Leak Detectors

Ellipsoidal reflectors have been proposed as collecting horns for ultrasonic leak det- ectors. Exploiting the classical focusing characteristics of ellipsoids, these ref- lectors would facilitate and enhance the detection of leaks in situations in which it is possible to bring leak-detecting sensors to within distances of the order of centimeters from leaks, but not closer. Leak detectors based on this concept could complement commercially available ultrasonic leak detectors equipped with paraboloidal reflectors for focusing over much longer distances. In a typical application, an ultrasonic receiving transducer would be positioned at one of the two foci of an ellipsoidal reflector. At the end opposite the transducer, the reflector would be truncated to provide an opening for the entry of sound and for positioning the reflector near a leak. When the reflector-and-transducer assembly was positioned to make the leak (or, for that matter, any other small source of ultrasound) lie at the other focus of the ellipsoid, the maximum amount of radiated ultrasound would be focused onto the transducer, resulting in maximum detector response. The principle of operation has been verified in experiments.

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Electrohydrodynamic Conduction Pumps

Pumping is achieved without moving parts and without direct charge injection. Electrohydrodynamic (EHD) conduction pumps have been investigated in theo- retical and experimental studies. In general, EHD pumps contain no moving parts. They generate pressure gradients and/or flows in dielectric liquids via any of a variety of inter- actions between (1) applied electric fields and (2) free and/or bound electric charges in the liquids. Like a related prior device denoted an EHD iondrag pump, an EHD conduction pump exploits interactions with free charges in liquids, but unlike an ion-drag pump, a conduction pump functions without direct injection of electric charges into the liquid. In the absence of direct injection, EHD conduction pumps are the only EHD devices that can pump isothermal liquids. EHD conduction pumps could be suitable for use as compact, low-power-consumption pumps to enhance flows and thus heat-transfer rates in heat pipes and capillary-pumped loops.

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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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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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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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