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Two Phase Flow Patterns and Cooling Power of Mixed Refrigerant in Micro Cryogenic Coolers

[+] Author Affiliations
Ryan Lewis, Hayley Schneider, Yunda Wang, Y. C. Lee

University of Colorado at Boulder, Boulder, CO

Ray Radebaugh

National Institute of Standards and Technology, Boulder, CO

Paper No. ICNMM2012-73110, pp. 501-506; 6 pages
doi:10.1115/ICNMM2012-73110
From:
  • ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 Fluids Engineering Division Summer Meeting
  • ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels
  • Rio Grande, Puerto Rico, USA, July 8–12, 2012
  • Conference Sponsors: Heat Transfer Division, Fluids Engineering Division
  • ISBN: 978-0-7918-4479-3
  • Copyright © 2012 by ASME

abstract

Micro cryogenic coolers (MCCs) operating in the Joule-Thomson cycle with mixed refrigerants offer an attractive way to decrease the size, cost, and power draw required for cryogenic cooling. Recent studies of MCCs with mixed refrigerants have, when employing pre-cooling, shown pulsating flow-rates and oscillating temperatures, which have been linked to the refrigerant flow regime in the MCC. In this study we investigate those flow regimes. Using a high-speed camera and optical microscopy, it is found that the pulsations in flow correspond to an abrupt switch from single-phase vapor flow to single-phase liquid flow, followed by 2-phase flow in the form of bubbles, liquid slugs, and liquid slug-annular rings. After this period of 2-phase flow, the refrigerant transitions back to single-phase vapor flow for the cycle to repeat. Under different pre-cooling temperatures, the mole fraction of the vapor-phase refrigerant, as measured by molar flow-rate, agrees reasonably well with the quality of the refrigerant at that temperature as calculated by an equation of state. The frequency of pulsation increases with liquid fraction in the refrigerant, and the volume of liquid in each pulse only weakly increases with increasing liquid fraction. The cooling power of the liquid-flow is up to a factor of 7 greater than that of the 2-phase flows and single-phase vapor flow.

Copyright © 2012 by ASME

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