| Heat engines converts thermal heat into useful work.When working with microand even nano-scale systems,the engines should outperform their macroscopic counterparts.In that context,we study the thermodynamic performance of heat engines working with microscopic systems in this thesis.By considering the Mpemba effect(the anomalous relaxation phenomenon)in the working substance,we first investigate the finite-time performance of heat engines and clarify the role of the Mpemba effect on the power and power fluctuations,and then we turn to a finite-time Otto engine using a spin-1/2 system weakly coupled to blackbody radiation as its working substance,with special emphasis on the universal behavior of efficiency at maximum power.In Chapter 1,we recall the relevant theoretical background of thermodynamics associated with our work,which allows us to understand the importance of the theoretical research present in this thesis.In Chapter 2,we analyze the thermodynamic performance and fluctuations of Otto heat engines in presence of the Mpemba effect,compared to corresponding those for Otto engines without the Mpemba effect.We show that the Mpemba effect can significantly increase the power,without sacrifice of machine stability well captured by relative power fluctuations.In Chapter 3,we are in a position to investigate a finite-time quantum Otto engine working with the spin-1/2 system coupled to blackbody radiation.Based on quantum master equation,we analyze the heat and work per cycle to obtain the compact expressions of the power and efficiency.In the high temperature limit,we obtain an analytical expression of the efficiency at maximum power showing the same universality as the famous Curzon-Ahborn efficiency.The universality of the optimized efficiency can further be confirmed by appropriate identification of the thermodynamic forces and fluxes within context of linear irreversible thermodynamics.We finally conclude with a summary and discussions in Chapter 4,where the interesting issues related to the research presented here are highlighted. |
