Juncheng Guo

General performance characteristics and parametric optimum bounds of irreversible chemical engines

Based on the weak-dissipation assumption, a general cycle model of irreversible chemical engines, including non-isothermal chemical engines, isothermal chemical engines, and other classes of heat engines is established, where finite-rate heat and mass transfers are considered. Expressions for the power output and efficiency of the cycle system are derived. The power output is optimized for a given efficiency of the cycle system by using the Lagrangian-multiplier method and the corresponding characteristic curves are represented. The region of the efficiency of the cycle system at the maximum power output is determined. The results obtained may be directly used to discuss the optimal performance of non-isothermal chemical engines, isothermal chemical engines, and heat engines. Furthermore, it is explained that when different values of two dissipation parameters in the model are chosen, these results obtained may be further used to derive the optimal performance of several novel thermodynamic cycles, such as quantum heat engines, Brownian heat engines, etc. It is thus clear that the results obtained here are not only universal but also important.

Efficiencies of two-level weak dissipation quantum Carnot engines at the maximum power output

A weak-dissipation cycle model of two-level quantum Carnot engines is proposed by adopting a generic energy spectrum and the superposition effect of quantum systems. Expressions for the power output and efficiency of the cycle are derived. The optimal relation between the power output and the efficiency is obtained and the optimally operating region of the cycle is determined. Moreover, analytical expression for the efficiency of the cycle at the maximum power output is deduced and the lower and upper bounds of the efficiency at the maximum power output are given. The results obtained are general and can be directly used to discuss the optimal performance characteristics of several types of two-level quantum Carnot engines.