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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, Mechanical Components, Briefs

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Gifford-McMahon/Joule-Thomson Refrigerator Cools to 2.5 K

This system is relatively simple. A compact refrigerator designed specifically for cooling a microwave maser low noise amplifier is capable of removing heat at a continuous rate of 180 mW at a temperature of 2.5 K. This refrigerator is a combination of (1) a commercial Gifford-McMahon (GM) refrigerator nominally rated for cooling to 4 K and (2) a Joule-Thomson (J-T) circuit. The GM refrigerator pre-cools the J-T circuit, which provides the final stage of cooling. The refrigerator is compact and capable of operating in any orientation. Moreover, in comparison with a typical refrigerator heretofore used to cool a maser to 4.5 K, this refrigerator is simpler and can be built at less than half the cost.

Posted in: Mechanics, Mechanical Components, Briefs

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Integrated Structural Analysis and Test Program

An integrated structural-analysis and structure-testing computer program is being developed in order to: • Automate repetitive processes in testing and analysis; • Accelerate pre-test analysis; • Accelerate reporting of tests; • Facilitate planning of tests; • Improve execution of tests; • Create a vibration, acoustics, and shock test database; and • Integrate analysis and test data.

Posted in: Test & Measurement, Briefs

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Synchrotron High-Speed Magnet Monitoring Using Ethernet-Based System

Synchrotron monitoring instruments that interface to Ethernet data communication systems can reduce cost and improve accuracy. Since the 1930s, synchrotrons have become essential in the widely diverse fields of scientific research and engineering development, including chemistry, biology, material science, and microelectronic engineering. Some synchrotron radiation applications include:

Posted in: Test & Measurement, Briefs

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Program Calculates Forces in Bolted Structural Joints

A FORTRAN 77 computer program calculates forces in bolts in the joints of structures. This program is used in conjunction with the NASTRAN finite-element structural-analysis program. A mathematical model of a structure is first created by approximating its load-bearing members with representative finite elements, then NASTRAN calculates the forces and moments that each finite element contributes to grid points located throughout the structure. The user selects the finite elements that correspond to structural members that contribute loads to the joints of interest, and identifies the grid point nearest to each such joint. This program reads the pertinent NASTRAN output, combines the forces and moments from the contributing elements to determine the resultant force and moment acting at each proximate grid point, then transforms the forces and moments from these grid points to the centroids of the affected joints. Then the program uses these joint loads to obtain the axial and shear forces in the individual bolts. The program identifies which bolts bear the greatest axial and/or shear loads. The program also performs a “fail-safe” analysis in which the foregoing calculations are repeated for a sequence of cases in which each fastener, in turn, is assumed not to transmit an axial force.

Posted in: Test & Measurement, Briefs

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Tools for Basic Statistical Analysis

Statistical Analysis Toolset is a collection of eight Microsoft Excel spreadsheet programs, each of which performs calculations pertaining to an aspect of statistical analysis.

Posted in: Software, Briefs

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Solving Common Mathematical Problems

Mathematical Solutions Toolset is a collection of five software programs that rapidly solve some common mathematical problems.

Posted in: Software, Briefs

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