Investigation Of The Performance Characteristics And Optimal Performance Of Quantum Dot Energy Conversion Devices

Due to the global energy shortage and fossil energy caused by serious environmental pollution problems,so the investigation on the use of solar energy,wind energy,hydrogen and other renewable energy has attracted the attention of the world's vast number of researchers.One of the effective ways to solve energy problems and environmental pollution is to improve energy efficiency and develop renewable energy.With the development of materials science and thermoelectric material preparation technology,people can make more efficient use of renewable energy and improve energy conversion efficiency.In recent years,experts and scholars have extensively studied the performance characteristics of different types of micro/nano thermoelectric devices,such as nanotubes,nanowires,quantum dot superlattices and molecular knots,and obtained some very interesting results.In addition,the principle and method of finite time thermodynamics are used to study the performance characteristics and optimization performance of the thermoelectric devices such as molecular heat engine,random heat engine,Ferman ratchet and quantum dot heat engine.In this paper,the performance characteristics of quantum dot thermoelectric devices are mainly studied,and their performance optimization is analyzed,and the optimization criterion of important performance parameters is given.The quantum dot thermoelectric model is composed of the quantum dots coupled into two heat sources with different chemical potentials and temperatures.In the model,the electron which is driven by chemical potential gradient and temperature gradient can be randomly tunneled between two electronic libraries and quantum dot systems.In the case of weak coupling(kBT(29)(29)?(38))and single electron sequential tunneling,the energy level width can be neglected.The probability of the state of the system can be expressed by the quantum master equation.In the steady state condition,the heat flow and electronic current of the system are analyzed by the quantum master equation.The electron transport characteristics of quantum dot thermoelectric devices are discussed and the performance characteristics of quantum dot heat engine and refrigerator areanalyzed.Their performances are optimized and the optimization ranges of some important performance parameters are obtained.The main contents of the master's thesis are as follows:In chapter 1,the research background of this paper is briefly described.This paper introduces the development of the micro/nano thermoelectric device model and the research status of the quantum dot thermoelectric device in recent years is introduced.Finally,the content of this paper and the arrangement of each chapter are given.In chapter 2,the theory of finite time thermodynamics and the theory of quantum master equations,and their application conditions and scope are introduced.In chapter 3,a kind of refrigeration model which is composed of single orbital interaction quantum dots and two heat sources with different chemical potential and temperature in the magnetic field is established.In the model,not only the Zeeman splitting of energy levels resulting from an external magnetic field but also the effect of a linear fade of the Coulomb energy caused by the splitting are taken into account simultaneously.By using the quantum master equation under the steady state condition,the occupation probabilities of the quantum state of electrons at the quantum dots are determined.The general expressions of the particle fluxes,heat flows,power input,cooling rate and the coefficient of performance(COP)are derived.By applying numerical simulations,three-dimensional diagrams of the cooling rate and COP varying with the magnetic field and energy level are given.The maximum COP and the optimal values of corresponding parameters as well as the maximum cooling rate are obtained.The influences of the energy level and external magnetic field on the performance characteristics and optimal performance of the refrigerator are discussed in detail.The optimal regions of the magnetic field and the energy level are determined.The optimized scopes of the COP and cooling rate are provided.Some significant verdicts in the preceding references can be immediately deduced from the current model under the different extreme conditions.In chapter 4,a three-terminal quantum dot thermoelectric device driven by magnons is established as the heat engine model,in which a spin-splitting quantum dot is embedded in between two ferromagnetic metals and one ferromagnetic insulator at different temperatures.According to the theory of quantum main equations,the expressions of the electron and magnons currents,heat flow,output power and efficiency of the three-terminal quantum dot heat engine are derived,and the thermodynamic performance characteristics of the heat engine are analyzed.The changing curves of the efficiency and output power of the heat engine with some important performance parameters are drawn.The performance characteristics of the heat engine in the two operating modes are analyzed and compared in detail.The effects of polarization factors,magnetic field,temperatures ratio and output voltage on the performance of heat engine were discussed.The optimal ranges of the magnetic field,output voltage,output power and efficiency are determined.Compared the optimization interval in the two modes of operation,and obtained some interesting conclusions.In summary,we mainly study the performance characteristics and performance optimization of the two-or three-terminal quantum dots energy conversion devices at both ends and three ends in this academic dissertation.On the basis of some existing quantum dot models,a new class of new quantum dot energy conversion device model is established.The performances of the two-terminal quantum dot refrigerator and the three-terminal quantum dot heat engine in the external magnetic field were optimally analyzed by the cooling rate,the output power,the performance coefficient and the efficiency as the objective function respectively.The optimization areas of some important performance parameters such as external magnetic field,interaction,output voltage,output power,efficiency,temperature ratio,and runoff loss factor are determined.In describing the dynamic performance characteristics of quantum dot thermoelectric devices,the overall output performance of the system is optimized from the thermodynamic point of view.The results obtained in this paper are of paramount importance for the study of the performance characteristics of the three-terminal quantum dot thermoelectric conversion device driven by the magnons.It is general and can provide a theoretical basis for the optimal design and optimal operation of practical quantum dot energy conversion device systems for various classes.It can also provide some theoretical guidance for parameter optimization and control ofquantum dot devices in practical applications in the future.