What does a Carnot cycle consist of?

The Carnot cycle consists of a sequence of isothermal and adiabatic reversible expansions and compressions. This idealized thermodynamic cycle demonstrates the maximum possible efficiency that a heat engine can achieve when operating between two thermal reservoirs.

In the Carnot cycle, two key processes occur at constant temperature: isothermal expansion and isothermal compression. During isothermal expansion, the system absorbs heat from the hot reservoir while doing work on the surroundings. Conversely, in isothermal compression, the system releases heat to the cold reservoir while work is done on it.

Between these isothermal processes are two adiabatic processes—one during expansion and one during compression. In the adiabatic expansion, the system expands without heat transfer, resulting in a decrease in temperature, while in the adiabatic compression, the system is compressed without heat exchange, leading to an increase in temperature.

This combination of isothermal and adiabatic processes illustrates how the Carnot cycle achieves a high efficiency and serves as a reference point for the performance of real heat engines.