Study On The Performance Of Finite Time Thermodynamic Cycles

Finite-time thermodynamics, as a significant branch of the modernthermodynamics, is mainly aimed to investigate the regulation of energy and entropyflows of non-equilibrium systems in finite time. Since the 1970s, research intoidentifying the performance limits of thermodynamic processes and optimization ofthermodynamic cycles has seen tremendous progress made by scientists andengineers with finite time thermodynamics. Finite-time thermodynamics has beenwidely applied to many fields such as industrial and agricultural production, chemicalengineering and thermal economics. It is also important in theory to open up newenergies, improve ecological environments, and protect natural resources, etc.Finite-time thermodynamics has gained many great achievements in many researchfields, particularly in the investigation of optimizing the performance ofthermodynamic cycles. A finite-time thermodynamic cycle may be classical orquantum. Recently, research into quantum thermodynamic cycles has become a newbranch 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 cycleswill be presented by the following chapters.In chapterâ…¡, the performance characteristics of the internal irreversiblesolar-driven heat engine cycle are discussed. In the cycle model used, it's assumedthat the heat transfer from the hot reservoir is to be in the radiation mode while theheat released to the cold reservoir is to be convection mode. Based on a cycle modelof an internal irreversible solar-driven heat engine, the optimal relations among theperformance parameters under maximum power and maximun power densitycondition are derived, respectively. By using numerical solution, the effects onoptimal performance caused by internal irreversiblities and external irreversilbilties ofheat transfer are investigated. The results obtained under maximum power and powerdensity condition are compared and discussed, the conclusions in the present chapter are meaningfully instructive to the optimal design of the practical heat enginesystems.In chapterâ…¢, the performance of Carnot heat engine whose working substanceconsists of non-interacting extreme relativistic particles confined to an infinitepotential well is studied. In this chapter, a new cyclic model of quantum Carnot heatengine is set up. It is shown that the engine whose cycle consists of two adiabatic andisothermal quantum processes are close analogues of the corresponding classicalprocesses and the efficiency of this engine is equal to the Carnot efficiency becausequantum dynamics is reversible. Consequently, the expectation value of theHamiltonian in the expression of the efficiency is similar to the temperature in that ofthe classical one.A cycle model of an irreversible Brayton heat engine cycle working withharmonic systems is established in the chapterâ…£. Based on quantum master equationand semi-group approach, the time evolution of the cycle is analyzed. Generalexpressions of the times spent on the two constant-frequency processes, work,thermal efficiency and power output are derived. For a fixed cycle period, thecharacteristic curves between some parameters are plotted and the performanceparameters of the heat engine cycle are optimized. This analysis may offer furtherunderstanding of the optimum performance of the quantum thermodynamic cycles aswell as classical thermodynamic cycles.In chapterâ…¤, optimization on the performance of an irreversible heat enginecycle working with harmonic systems will be performed. The cycle model consists oftwo constant-frequency processes and two adiabatic processes. According to thequantum adiabatic theorem, the adiabatic process can be described by the timeevolution of the harmonic system with slowly changing frequency. Non-adiabaticphenomenon arises from rapid change in the energy level structure of the system,meaning that although there is no heat transferred the working substantce heats up inthe corresponding process. It's therefore that the internal friction similar to theinternally dissipative friction is introduced to describe the quantum heat engine cycle.With the help of master equation, semi-group approach, and harmonic theory, thegeneral expressions for several important parameters such as the work, efficiency, power output, and rate of entropy production are derived. The optimally operatingregions and the optimal values of performance parameters of the cycle are determinedunder the condition of maximum power output. Some special cases such as hightemperature limit and frictionless case, will be disused.In chapterâ…¥, the anlysis of performance of spin quantum heat engine cycle ispresented. Based on spin theory, quantum master equation, and semi-group approach,the expressions of several important parameters including the efficiency, poweroutput, rate of entropy production are obtained. By using numerical solution, themaximum power output and corresponding performance parameters are caculated.The optimally operating regions of the efficiency, temperature of the workingsubstance, and cycle period are determined. Some special cases such as thefrictionless case and high temperature limit are also briefly discussed. Finally, theresults obtained here are generalized to the performance optimization of the heatengine working with spin-J systems.