The Performance Characteristics And Optimal Analyses Of Quantum Brayton Refrigeration Cycles

The Brayton cycle is one of the typical and familiar cycles. The Brayton engine cycle is used in the steam power plants and air propellant systems widely, while the Brayton refrigeration cycle is used in the refrigeration and cryogenic fields more and more widely. However, the lower the temperature is, the stronger the quantum degeneracy of the working substance of the cycle. Consequently, the influence of quantum characteristic of the working substance on the performance of the cycle has to be taken into account. Like other thermodynamic cycles, it is very important not only in the theoretical research but in the practical application to investigate the quantum Brayton refrigeration cycle. It will be helpful to promote the development of cryogenic refrigeration technology.In this thesis, the performance characteristics of the quantum Brayton refrigeration cycle using an ideal Bose or Fermi gas as the working substance are researched. In chapter 2, the thermodynamic properties of an ideal Bose gas and Fermi gas are introduced. It is pointed out that due to the existence of Bose-Einstein condensation for the Bose gas, some typical thermodynamic cycles such as the Carnot, Brayton, Otto, Ericsson, Diesel and Atkinson cycles cannot be operated across the critical temperature of Bose-Einstein condensation of an ideal Bose gas. In chapter 3, an irreversible regenerative cycle model of the quantum Brayton refrigeration cycle using an ideal Bose gas as the working substance is established. Based on the theory of statistical mechanics and thermodynamic properties of an ideal Bose gas, the expressions for some important performance parameters, such as the refrigeration load, regenerative heat load, work input and coefficient of performance are derived. By using numerical calculation, several important performance characteristic curves are generated. The influence of the quantum degeneracy, irreversibility and regeneration on the performance of a Bose Brayton refrigeration cycle is analyzed. In chapter 4, an irreversible cycle model of the quantum Brayton refrigeration cycle using an ideal Bose or Fermi gas as the working substance is established. The synthesis influence of the degeneracy of the quantum gas, the internal irreversibility of the working substance and the finite-rate heat transfer between the working substance and the heat reservoirs on the optimal performance of the cycle is investigated. Some optimum criteria of the cycle are given. The results obtained indicate that the optimal performance characteristics of the irreversible quantum Brayton refrigeration cycles using ideal Fermi or Bose gases as the working substance are different. The results obtained here will not only provide some theoretical bases and references for the optimal design and manufacture of air refrigerators but also play an important promotion role for the further investigation of ultra-low temperature air refrigerators.