Mechanical & Fluid Systems

Improving Control in a Joule-Thomson Refrigerator

A report discusses a modified design of a Joule-Thomson (JT) refrigerator under development to be incorporated into scientific instrumentation aboard a spacecraft.In most other JT refrigerators (including common household refrigerators), the temperature of the evaporator (the cold stage) is kept within a desired narrow range by turning a compressor on and off as needed. This mode of control is inadequate for the present refrigerator because a JT-refrigerator compressor performs poorly when the flow from its evaporator varies substantially, and this refrigerator is required to maintain adequate cooling power. The proposed design modifications include changes in the arrangement of heat exchangers, addition of a clamp that would afford a controlled heat leak from a warmer to a cooler stage to smooth out temperature fluctuations in the cooler stage, and incorporation of a proportional + integral + derivative (PID) control system that would regulate the heat leak to maintain the temperature of the evaporator within a desired narrow range while keeping the amount of liquid in the evaporator within a very narrow range in order to optimize the performance of the compressor. Novelty lies in combining the temperature- and cooling-power-regulating controls into a single control system.

Posted in: Mechanics, Briefs, TSP

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High-Temperature, High-Load-Capacity Radial Magnetic Bearing

Speed and temperature limits of rolling element bearings can be exceeded. A radial heteropolar magnetic bearing capable of operating at a temperature as high as 1,000 °F (≈540 °C) has been developed. This is a prototype of bearings for use in gas turbine engines operating at temperatures and speeds much higher than can be withstood by lubricated rolling-element bearings.

Posted in: Briefs, TSP

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Blended Buffet-Load-Alleviation System for Fighter Airplane

Reductions in buffet loads translate to longer fatigue lives. The capability of modern fighter airplanes to sustain flight at high angles of attack and/or moderate angles of sideslip often results in immersion of part of such an airplane in unsteady, separated, vortical flow emanating from its forebody or wings. The flows from these surfaces become turbulent and separated during flight under these conditions. These flows contain significant levels of energy over a frequency band coincident with that of low-order structural vibration modes of wings, fins, and control surfaces. The unsteady pressures applied to these lifting surfaces as a result of the turbulent flows are commonly denoted buffet loads, and the resulting vibrations of the affected structures are known as buffeting. Prolonged exposure to buffet loads has resulted in fatigue of structures on several airplanes. Damage to airplanes caused by buffeting has led to redesigns of airplane structures and increased support costs for the United States Air Force and Navy as well as the armed forces of other countries. Time spent inspecting, repairing, and replacing structures adversely affects availability of aircraft for missions.

Posted in: Briefs

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Split-Resonator, Integrated-Post Vibratory Microgyroscope

This design is better suited to mass production. An improved design for a capacitive sensing, rocking-mode vibratory microgyroscope is more amenable to mass production, relative to a prior design. Both the improved design and the prior design call for a central post that is part of a resonator that partly resembles a cloverleaf or a flower. The prior design is such that the post has to be fabricated as a separate piece, then bonded to the rest of the resonator in the correct position and orientation. The improved design provides for fabrication of the post as an integral part of the resonator and, in so doing, makes it possible to produce a waferful of microgyroscopes, without need to fabricate, position, and attach posts.

Posted in: Briefs, TSP

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Fast Laser Shutters With Low Vibratory Disturbances

Opposing cantilevered piezoelectric bending actuators balance each other to minimize vibration. The figure shows a prototype vacuum-compatible, fast-acting, long-life shutter unit that generates very little vibratory disturbance during switching. This is one of a number of shutters designed to satisfy requirements specific to an experiment, to be performed aboard a spacecraft in flight, in which laser beams must be blocked rapidly and completely, without generating a vibratory disturbance large enough to adversely affect the power and frequency stability of the lasers. Commercial off-the-shelf laboratory shutter units — typically containing electromagnetcoil-driven mechanisms — were found not to satisfy the requirements because they are not vacuum-compatible, their actuators engage in uncompensated motions that generate significant vibrations, and their operational lifetimes are too short. Going beyond the initial outerspace application, the present vacuum compatible, fast-acting, long-life shutter units could also be used in terrestrial settings in which there are requirements for their special characteristics.

Posted in: Briefs, TSP

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Powder-Collection System for Ultrasonic/Sonic Drill/Corer

Powder is blown from the drill/rock interface to sampling locations. A system for collecting samples of powdered rock has been devised for use in conjunction with an ultrasonic/sonic drill/corer (USDC) — a lightweight, lowpower apparatus designed to cut into, and acquire samples of, rock or other hard material for scientific analysis. The USDC was described in "Ultrasonic/Sonic Drill/Corers With Integrated Sensors" (), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 38. To recapitulate: The USDC includes a drill bit, corer, or other tool bit, in which ultrasonic and sonic vibrations are excited by an electronically driven piezoelectric actuator. The USDC advances into the rock or other material of interest by means of a hammering action and a resulting chiseling action at the tip of the tool bit. The hammering and chiseling actions are so effective that unlike in conventional twist drilling, a negligible amount of axial force is needed to make the USDC advance into the material. Also unlike a conventional twist drill, the USDC operates without need for torsional restraint, lubricant, or a sharp bit.

Posted in: Briefs, TSP

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Semiautomated, Reproducible Batch Processing of Soy

Processing conditions are selectable and are consistent from batch to batch. A computer-controlled apparatus processes batches of soybeans into one or more of a variety of food products, under conditions that can be chosen by the user and reproduced from batch to batch. Examples of products include soy milk, tofu, okara (an insoluble protein and fiber byproduct of soy milk), and whey. Most processing steps take place without intervention by the user. This apparatus was developed for use in research on processing of soy. It is also a prototype of other soy-processing apparatuses for research, industrial, and home use.

Posted in: Briefs

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