| Joule-Thomson (J-T) refrigeration cycle has many applications in the field of energy, national defence, biomedical storage and cryosurgery, due to its simple structure, reliable performance and low cost. With mixed-refrigerant, the thermodynamic efficiency of J-T cooler can be greatly improved. In this thesis, an open fast-cool-down J-T cooler driven by the high pressure pure nitrogen is investigated, and we also proposed mixed-refrigerant J-T coolers driven by a single stage oil-lubricated air-conditioning compressor. These two systems were studied both in theory and experiment.The internal working process of the mixed-refrigerant J-T coolers is considerably complicated, therefore the working mechanism of the J-T coolers has not been well understood. The author solved the following thermodynamic problems in this dissertation:1. We reviewed the historical development of J-T refrigeration cycle and its current study at home and abroad. Using cubic equation of state, the vapor-liquid equilibrium of cryogenic mixtures containing nitrogen and hydrocarbons and their thermodynamic properties were calculated. Based on these calculations, the system and its components were designed.2. The analysis and design method for small miniature counter flow heat exchangers with mixed-refrigerant is presented. Under the guidance of the above method, the type of Hampson heat exchanger for mixed-refrigerant J-T coolers is designed.3. According to the working theory of the Joule-Thomson throttle coolers, the characteristics of mixed refrigerant and thermodynamic performance of a mixed-refrigerant J-T refrigeration cycle are analyzed systematically. The essence of improving thermodynamic efficiency of J-T coolers with mixed-refrigerant is revealed in-depth.4. An open fast-cool-down cycle J-T cooler and a small closed cycle J-T cooler are investigated both in theory and experiment.The obtained theoretical and experimental results are very meaningful, the experimental results verified the theoretical model and also showed some problems during design and operation. However, many thermodynamic problems are not solved and understood thoroughly, and they are needed to study further. |
