Performance Optimum Studys Of Two Thermodynamic Cycle Systems

Finite-time thermodynamics, as a significant branch of the modern thermodynamics, is mainly aimed to investigate the regulation of energy and entropy flows of non-equilibrium systems in finite time. Since the 1970s, research into identifying the performance limits of thermodynamic processes and optimization of thermodynamic cycles has seen tremendous progress made by scientists and engineers with finite time thermodynamics. Finite-time thermodynamics has been widely applied to many fields such as industrial and agricultural production, chemical engineering and thermal economics. It is also important in theory to open up new energies, improve ecological environments, and protect natural resources, etc. Finite-time thermodynamics has gained many great achievements in many research fields, particularly in the investigation of optimizing the performance of thermodynamic cycles. A finite-time thermodynamic cycle may be classical or quantum. Recently, research into quantum thermodynamic cycles has become a new branch of research into finite-time thermodynamic cycles.In this thesis, the investigation of performance of finite-time thermodynamic cycles including classical thermodynamic cycles and quantum thermodynamic cycles will be presented by the following chapters.In chapter II, the performance characteristics of the internal, irreversible solar-driven heat engine cycle are discussed. In the cycle model used, it's assumed that the heat transfer from the hot reservoir is to be in the radiation mode while the heat released to the cold reservoir is to be convection mode. Based on a cycle model of an internal irreversible solar-driven heat engine, the optimal relations among the performance parameters under maximum power and maximun power density condition are derived, respectively. By using numerical solution, the effects on optimal performance caused by internal irreversiblities and external irreversilbilties of heat transfer are investigated. The results obtained under maximum power and power density condition are compared and discussed, the conclusions in the present chapter are meaningfully instructive to the optimal design of the practical heat engine systems.In chapter III, Based on a cycle model of an external irreversible solar-driven heat engine, the optimal relations among the performance parameters under the ecologic objective function. Comparing the result with the one under the maximum power condition. The conclusions in the present paper are meaningfully instructive to the optimal design of the practical heat engine systems.In chapter IV, An endoreversible Braysson heat-engine model which obeys the Newton's heat transfer law in the heat source and the linear phenogmenological heat transfer law in the heat sink and considers heat-resistance and heat leak is set up in this paper, the expressions of output power , output power density and efficiency of the endoreversible Braysson heat engine are derived. The influence of the efficiency of hot-side heat exchanger, the heat conductances of the clod-side exchange and heat leak on the performance parameters of this engine is discussed. The results obtained here provide some significant guidance for the optimal design and operation of practical heat-engine.In chapter IV, Based on the ecological optimum criterion the performance parameters for an irreversible space solar energy power Braysson cycle are optimally analyzed. The ecological objective function is defined as the power output minus the power loss which is equal to the product of the environmental temperature and the entropy production. A solar energy power system is composed of the solar energy collector and an irreversible Braysson cycle. The heat transfer between the Braysson cycle system and the hot reservoir obeys Newton's heat transfer law, and the heat transfer between the Braysson cycle system and the cold reservoir obeys the radiant heat transfer law. The detail expressions of the performance parameters including efficiency, power output and ecological objective function are derived. Moreover, these performance parameters of the cycle are optimized under the condition of the maximum ecological function.