Quantum Brayton cycle with coupled systems as working substance

TL;DR

This paper investigates the quantum Brayton cycle using coupled systems as the working substance, revealing novel cycle behaviors, efficiency characteristics, and the potential for subsystem refrigeration within the cycle.

Contribution

It introduces two types of quantum Brayton cycles for coupled systems and analyzes their efficiencies, work output, and thermodynamic roles, including subsystem refrigeration.

Findings

Subsystem can undergo a quantum Brayton or Otto cycle.

Total system work exceeds sum of subsystem works.

Subsystem can act as a refrigerator while the total system functions as a heat engine.

Abstract

We explore the quantum version of Brayton cycle with a composite system as the working substance. The actual Brayton cycle consists of two adiabatic and two isobaric processes. Two pressures can be defined in our isobaric process, one corresponds to the external magnetic field (characterized by $F_x$) exerted on the system, while the other corresponds to the coupling constant between the subsystems (characterized by $F_y$). As a consequence, we can define two types of quantum Brayton cycle for the composite system. We find that the subsystem experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized by $F_x$), whereas the subsystem's cycle is of quantum Otto in another Brayton cycle (characterized by $F_y$). The efficiency for the composite system equals to that for the subsystem in both cases, but the work done by the total system are usually larger than the sum of work done by the two subsystems. The other interesting finding is that for the cycle characterized by $F_y$, the subsystem can be a refrigerator while the total system is a heat engine. The result in the paper can be generalized to a quantum Brayton cycle with a general coupled system as the working substance.