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Thermodynamic Optimization of a Gifford-McMahon Cycle using Exergy Analysis

Ghaderi, Hanieh | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57196 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Afshin, Hossein
  7. Abstract:
  8. Helium, a valuable substance with unique properties, is widely used in various fields such as medicine, life sciences, electronic and military industries, and the industries which require low- temperature cooling. Driven by the increasing global demand for helium, research laboratories and industries are turning to small-scale refrigeration and liquefaction cycles. GM cryocoolers have found widespread applications in cryogenics due to its simplicity, high reliability and cost-effectiveness. The complexities of GM cryocooler performance pose significant challenges to achieving optimal efficiency and operation so developing a simplified model of the cycle is crucial. In this research, the models for single-stage, two-stage GM cycles and GM liquefaction cycle has been developed in Aspen HYSYS software. The modeling employed the 32-parameter MBWR equation of state and the model predictions were verified against data from published experiment studies. Following the development of exergy analysis relationships, exergy losses in compression, expansion, and heat exchange processes have been calculated and the impact of low pressure, pressure ratio and regenerator effectiveness on exergy efficiency has been investigated. This study identified optimal operating conditions for a single-stage GM cycle, achieving a 32% improvement in exergy efficiency compared to the baseline case. These optimal conditions include a low pressure of 600 kPa, a pressure ratio of 6, and a regenerator with effectiveness of 99.4%. For the two-stage GM cryocooler, the exergy efficiency improvement was 11% , using a lower pressure of 550 kPa, a pressure ratio of 4.5, and regenerators with effectiveness of 97.7% and 94.4%. The liquefaction rate for cryocooler-based liquefiers depends on the pressure at which the helium is liquefied. This study investigated that increasing the pressure to near the critical pressure of helium resulted in a significant 38% increase in liquefaction rate of GM liquefaction cycle. and also achieving a 40% improvement in exergy efficiency at a pressure ratio of 5.3 for the GM liquefaction cycle
  9. Keywords:
  10. Helium Gas ; Modeling ; Exergy Analysis ; Cryocooler ; Gifford-McMahon Cryocooler ; Liquefaction Rate

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