What is the Carnot cycle?

The Carnot cycle represents an idealized thermodynamic cycle that establishes the maximum possible efficiency for a heat engine operating between two temperature reservoirs. It consists of four reversible processes: two isothermal processes and two adiabatic processes. During the isothermal expansion, the working fluid absorbs heat from the high-temperature reservoir, while during isothermal compression, it releases heat to the low-temperature reservoir. The adiabatic processes involve no heat transfer; instead, the working fluid does work on its surroundings or has work done on it.

The significance of the Carnot cycle lies in its theoretical framework, which serves as a benchmark against which the efficiency of real heat engines can be measured. No actual engine can achieve the efficiency of a Carnot engine due to irreversibilities and losses, but understanding this cycle helps engineers to design more efficient systems by grasping the fundamental limits imposed by thermodynamic principles.

In contrast, the other choices highlight misconceptions or specific applications that do not reflect the broader definition of the Carnot cycle. For example, while some refrigeration cycles may seek high efficiency, they do not represent the comprehensive ideal of the Carnot cycle, which is fundamentally about heat engines. Similarly, the Carnot cycle is not a practical cycle used in all heat engines,