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  • 1
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    Magnetic bearings for cryogenic turbomachines (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Magnetic bearings offer a number of advantages over gas bearings for the support of rotors in cryogenic turboexpanders and compressors. Their performance is relatively independent of the temperature or pressure of the process gas for a large range of conditions. Active magnetic bearing systems that use capacitive sensors have been developed for high speed compressors for use in cryogenic refrigerators. Here, the development of a magnetic bearing system for a miniature ultra high speed compressor is discussed. The magnetic bearing has demonstrated stability at rotational speeds exceeding 250,000 rpm. This paper describes the important features of the magnetic bearing and presents test results demonstrating its performance characteristics.
    Keywords: MECHANICAL ENGINEERING
    Type: In: Advances in cryogenic engineering. Vol. 37B - Proceedings of the 1991 Cryogenic Engineering Conference, Univ. of Alabama, Huntsville, June 11-14, 1991 (A93-48578 20-37); p. 809-816.
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    High efficiency pump for space helium transfer (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A centrifugal pump was developed for the efficient and reliable transfer of liquid helium in space. The pump can be used to refill cryostats on orbiting satellites which use liquid helium for refrigeration at extremely low temperatures. The pump meets the head and flow requirements of on-orbit helium transfer: a flow rate of 800 L/hr at a head of 128 J/kg. The overall pump efficiency at the design point is 0.45. The design head and flow requirements are met with zero net positive suction head, which is the condition in an orbiting helium supply Dewar. The mass transfer efficiency calculated for a space transfer operation is 0.99. Steel ball bearings are used with gas fiber-reinforced teflon retainers to provide solid lubrication. These bearings have demonstrated the longest life in liquid helium endurance tests under simulated pumping conditions. Technology developed in the project also has application for liquid helium circulation in terrestrial facilities and for transfer of cryogenic rocket propellants in space.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-CR-177595 , A-92050 , NAS 1.26:177595
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    All-metal, compact heat exchanger for space cryocoolers (1990)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This report describes the development of a high performance, all metal compact heat exchanger. The device is designed for use in a reverse Brayton cryogenic cooler which provides five watts of refrigeration at 70 K. The heat exchanger consists of a stainless steel tube concentrically assembled within a second stainless steel tube. Approximately 300 pairs of slotted copper disks and matching annular slotted copper plates are positioned along the centerline axis of the concentric tubes. Each of the disks and plates has approximately 1200 precise slots machined by means of a special electric discharge process. Positioning of the disk and plate pairs is accomplished by means of dimples in the surface of the tubes. Mechanical and thermal connections between the tubes and plate/disk pairs are made by solder joints. The heat exchanger assembly is 9 cm in diameter by 50 cm in length and has a mass of 10 kg. The predicted thermal effectiveness is greater than 0.985 at design conditions. Pressure loss at design conditions is less than 5 kPa in both fluid passages. Tests were performed on a subassembly of plates integrally soldered to two end headers. The measured thermal effectiveness of the test article exceeded predicted levels. Pressure losses were negligibly higher than predictions.
    Keywords: ENGINEERING (GENERAL)
    Type: NASA-CR-190861 , NAS 1.26:190861 , TM-1450
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Noncavitating Pump For Liquid Helium (1996)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Immersion pump features high efficiency in cryogenic service. Simple and reliable centrifugal pump transfers liquid helium with mass-transfer efficiency of 99 percent. Liquid helium drawn into pump by helical inducer, which pressurizes helium slightly to prevent cavitation when liquid enters impeller. Impeller then pressurizes liquid. Purpose of pump to transfer liquid helium from supply to receiver vessel, or to provide liquid helium flow for testing and experimentation.
    Keywords: MACHINERY
    Type: ARC-13229 , NASA Tech Briefs (ISSN 0145-319X); 20; 3; P. 84
    Format: text
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  • 5
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    Miniature Gas-Circulating Machine (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Proposed gas-circulating machine consists essentially of centrifugal pump driven by induction motor. Noncontact bearings suppress wear and contamination. Used to circulate helium (or possibly hydrogen or another gas) in regeneration sorption-compressor refrigeration system aboard spacecraft. Also proves useful in terrestrial applications in which long life, reliability, and low contamination essential.
    Keywords: MACHINERY
    Type: NPO-18486 , NASA Tech Briefs (ISSN 0145-319X); 17; 5; P. 88
    Format: text
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  • 6
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    Miniature Centrifugal Compressor (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Miniature turbocompressor designed for reliability and long life. Cryogenic system includes compressor, turboexpander, and heat exchanger provides 5 W of refrigeration at 70 K from 150 W input power. Design speed of machine 510,000 rpm. Compressor has gas-lubricated journal bearings and magnetic thrust bearing. When compressor runs no bearing contact and no wear.
    Keywords: MACHINERY
    Type: GSC-13093 , NASA Tech Briefs (ISSN 0145-319X); 13; 3; P. 78
    Format: text
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  • 7
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    Radial displacement sensor for non-contact bearings (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A radial position sensor includes four capacitive electrodes oriented about a shaft, arranged in two diametrically opposite pairs. Sensor circuitry generates an output signal in proportion to the capacitance between the electrodes and the shaft; the capacitance between an electrode and the shaft increases as the shaft approaches the electrode and decreases as the shaft recedes from the electrode. The sensor circuitry applies an alternating voltage to one electrode of a pair and a 180 degree out of phase alternating voltage to the other electrode of the pair. The electrical responses of the two electrodes to their respective input signals are summed to form a radial deviation signal which is relatively free from the alternating voltage and accurately represents the position of the shaft relative to the electrodes of the pair.
    Keywords: Electronics and Electrical Engineering
    Format: application/pdf
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