Bihong Lin

Optimal analysis of the performance of an irreversible quantum heat engine with spin systems

It is considered that the cycle of a quantum heat engine using many non-interacting spin-1/2 systems as the working substance is composed of two adiabatic and two isomagnetic field processes and is referred to as a spin quantum Brayton engine cycle. Based on the quantum master equation and semi-group approach, expressions for the efficiency and power output of the cycle are derived. By using numerical solutions, the power output of the heat engine subject to finite cycle duration is optimized. The maximum power output and the corresponding parameters are calculated numerically. The optimal region of the efficiency and the optimal ranges of temperatures of the working substance and times spent on the two isomagnetic field processes are determined, so that the general optimum performance characteristics of the cycle are revealed. Moreover, the optimal performance of the cycle in the high-temperature limit is also analysed in detail. The results obtained here are further generalized, so that they may be directly used to describe the performance of a quantum Brayton heat engine using spin-J systems as the working substance.

The unified cycle model of a class of solar-driven heat engines and their optimum performance characteristics

The unified cycle model of a class of solar-driven heat engines is presented, in which the heat loss of the solar collector and the external and internal irreversibilities of the heat engine are taken into account and used to investigate the optimal performance of the cyclic system. The maximum overall efficiency of the system is calculated. The optimally operating temperature of the solar collector, the optimal temperatures of the cyclic working substance, and the optimal ratio of the heat-transfer areas of the heat engine are determined. The influence of the heat loss of the solar collector and the external and internal irreversibilities of the heat engine on the cyclic performance is discussed in detail. Some important characteristic curves are given. It is more important that the results obtained from the unified cycle model are very general and useful, from which the optimal performance of the solar-driven Brayton, Braysson, and Carnot heat engines and some solar-driven heat engines can be directly d...

The influence of quantum degeneracy and irreversibility on the performance of a Fermi quantum refrigeration cycle

An irreversible cycle model of the quantum refrigeration cycle using an ideal Fermi gas as the working substance is established. The cycle consists of two adiabatic and two isobaric processes and consequently may be simply referred to as the Fermi Brayton refrigeration cycle. The performance of the cycle is investigated, based on the equation of state of an ideal Fermi gas. Expressions for several important performance parameters, such as the coefficient of performance, work input and refrigeration load, are derived. The influence of the quantum degeneracy of the Fermi gas and the irreversibility in the cycle on the performance of the Fermi Brayton refrigeration cycle is analysed. The minimum pressure ratio of the cycle is determined. The optimally operating problems of the cycle and several special cases are discussed in detail. The results obtained here are general and may reveal the general performance characteristics of the Fermi Brayton refrigeration cycle.

Performance analysis of irreversible quantum Stirling cryogenic refrigeration cycles and their parametric optimum criteria

The influence of both the quantum degeneracy and the finite-rate heat transfer between the working substance and the heat reservoirs on the optimal performance of an irreversible Stirling cryogenic refrigeration cycle using an ideal Fermi or Bose gas as the working substance is investigated, based on the theory of statistical mechanics and thermodynamic properties of ideal quantum gases. The inherent regeneration losses of the cycle are analysed. Expressions for several important performance parameters such as the coefficient of performance, cooling rate and power input are derived. By using numerical solutions, the cooling rate of the cycle is optimized for a given power input. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal regions of the coefficient of performance and power input are determined. In particular, the optimal performance of the cycle in the strong and weak gas degeneracy cases and the high temperature limit are discussed in detail. The analytic expressions of some optimized parameters are derived. Some optimum criteria are given. The distinctions and connections between the Stirling refrigeration cycles working with the ideal quantum and classical gases are revealed.

The performance characteristics of an irreversible regenerative quantum refrigeration cycle

An irreversible regenerative model of the Brayton refrigeration cycle working with an ideal Fermi gas, which is simply called the quantum refrigeration cycle, is established. Expressions for several important performance parameters, such as the coefficient of performance, work input, refrigeration load and regeneration heat, are derived, based on the equation of state of an ideal Fermi gas. The influence of quantum degeneracy of the gas, regeneration and irreversibility on the performance of the quantum refrigeration cycle is analysed comprehensively. The general performance characteristics of the cycle are revealed. Moreover, two special cases are discussed and compared in detail. Consequently, the importance of regeneration in the cryogenic refrigeration is expounded from theory. Finally, the performance of the Brayton refrigeration cycle at high temperatures is directly deduced.

The Regenerative Criteria of an Irreversible Brayton Heat Engine and its General Optimum Performance Characteristics

An irreversible cycle model of the Brayton heat engine is established, in which the irreversibilities resulting from the internal dissipation of the working substance in the adiabatic compression and expansion processes and the finite-rate heat transfer in the regenerative and constant-pressure processes are taken into account. The power output and efficiency of the cycle are expressed as functions of temperatures of the working substance and the heat sources, heat transfer coefficients, pressure ratio, regenerator effectiveness, and total heat transfer area including the heat transfer areas of the regenerator and other heat exchangers. The regenerative criteria are given. The power output is optimized for a given efficiency. The general optimal performance characteristics of the cycle are revealed. The optimal performance of the Brayton heat engines with and without regeneration is compared quantitatively. The advantages of using the regenerator are expounded. Some important parameters of an irreversible regenerative Brayton heat engine, such as the temperatures of the working substance at different states, pressure ratio, maximum value of the pressure ratio, regenerator effectiveness and ratios of the various heat transfer areas to the total heat transfer area of the cycle, are further optimized. The optimal relations between these parameters and the efficiency of the cycle are presented by a set of characteristic curves for some assumed compression and expansion efficiencies. The results obtained may be helpful to the comprehensive understanding of the optimal performance of the Brayton heat engines with and without regeneration and play a theoretical instructive role for the optimal design of a regenerative Brayton heat engine.

Optimum performance analysis of a two-stage irreversible magnetization Brayton refrigeration system

A two-stage magnetization Brayton refrigeration cycle model using a paramagnetic material as the working substance is established, in which the regeneration and the irreversibility in the adiabatic processes are taken into account. On the basis of the thermodynamic properties of a paramagnetic material, the expressions of some important parameters such as the coefficient of performance, refrigeration load and work input are derived and used to analyse the performance characteristics of the refrigeration cycle. The influence of the inter-magnetization process, irreversibility in the adiabatic processes and regeneration on the performance of the cycle is discussed in detail. The advantage of adding the inter-magnetization process is expounded and the magnetic field ratio related to the inter-magnetization process is optimized. Moreover, the optimal values of the temperatures of the working substance at different state points and the optimally operating region of the cycle are determined. The results obtained here are compared with those derived from some relevant magnetic Brayton refrigeration cycles, and consequently, some significant conclusions are obtained.

Optimum performance analysis of an irreversible quantum cryogenic refrigeration cycle working with an ideal Bose or Fermi gas

An irreversible model of the Carnot cryogenic refrigeration cycle working with an ideal Bose or Fermi gas is established, which is composed of two irreversible adiabatic and two isothermal processes. The effects of the quantum degeneracy of the working substance, the irreversibility of the finite-rate heat transfer between the working fluid and the heat reservoirs, and the internal irreversibility in two adiabatic processes on the optimum performance characteristics of the quantum refrigeration cycle are analyzed. The performance characteristics of the cycle in strong and weak gas degeneracy cases are discussed. Expressions for several important performance parameters such as the coefficient of performance, cooling rate and power input are derived. By using numerical solutions, the cooling rate of the cycle is optimized for a given power input. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal regions of the coefficient of performance and power input are determined. Some optimum criteria are given.