Study On Thermodynamic Performance Of Irreversible Carnot Machine

The rapid development of economy leads to increasing energy consumption,and the consumption of non-renewable energy also leads to increasingly prominent environmental problems.Saving and effective use of energy is a necessary way to achieve sustainable development.Heat engine is an important device for energy conversion.In theory and practice,the performance optimization of heat engine is still an important field of thermodynamics research.However,Carnot’s theorem puts forward a theoretical upper limit for the efficiency of heat engine,but the Carnot engine lacks the practical application value,which leads to the emergence of finite time thermodynamics.As an important branch of non-equilibrium thermodynamics,finite time thermodynamics can provide theoretical and method basis for energy saving and efficient utilization.In this thesis the performance optimization problem of three types of heat engines is systematically analyzed by using the finite time thermodynamics principle.The research results can provide the physical principle support for the design and operation of actual heat engines.In Chapter 2,we study the effect of ambient temperature on the minimally nonlinear irreversible heat devices by using the ecological criteria,and obtain the expressions of the efficiency and coefficient of performance(COP).For the minimally nonlinear irreversible heat engines,the optimization efficiency decreases first and then becomes stable with the increase of dissipation ratio.The variation of ambient temperature and coupling strength leads to different behaviors of the efficiency.The evolution characteristics of the efficiency curve under different coupling intensities are explained clearly.For the minimally nonlinear irreversible refrigerators,the COP and thermodynamic bound region under ecological optimization are given.It is found that the change of ambient temperature can increase or decrease the COP,and the change of dissipation coefficient ratio provides the possibility of obtaining a larger COP.In Chapter 3,by constructing the ecological function,we study the optimization characteristics of low dissipation heat devices under the ecological criteria.For the low dissipation heat engine,the efficiency and its thermodynamic bound region are obtained.It is found that increasing the ambient temperature is beneficial to improve the efficiency,but the efficiency decreases with increasing the temperature of cold reservoir.For a low dissipation refrigerator,the COP and its thermodynamic bound region under ecological optimization are given.It is found that the increase of ambient temperature and cold reservoir’s temperature can enhance the refrigeration coefficient,but the change of dissipation ratio can not significantly increase the optimization space.In Chapter 4,based on the in-depth analysis of the working mechanism of a coupled thermoelectric generator,we investigate thermodynamic behaviors of the coupled thermoelectric generator by means of the trade-off optimization method.Based on the objective function of trade-off optimization,the power and efficiency formulas under trade-off optimization are derived,which provides a theoretical basis for in-depth analysis of thermodynamic behavior of coupled thermoelectric generators.It is found that the increase of internal resistance leads to the increase of the large efficiency region,which makes it possible to obtain higher power and efficiency.By comparison,we find that the efficiency under trade-off optimization is obviously greater than the efficiency at maximum power.It is found that the region of the bound curve optimization efficiency is narrow,but the efficiency within the bound curve is obviously greater than the efficiency at maximum power.In Chapter 5,we summarize the thesis and give the prospect.This thesis contains 28 figures and 106 references.