The Carnot Cycle is a theoretical thermodynamic cycle that serves as a standard for the efficiency of heat engines. It consists of four reversible processes: two isothermal (constant temperature) processes and two adiabatic (no heat exchange) processes. In the first isothermal expansion phase, the working substance absorbs heat from a high-temperature reservoir, doing work on the surroundings. During the subsequent adiabatic expansion, the substance expands without heat transfer, leading to a drop in temperature.
Next, in the second isothermal process, the working substance releases heat to a low-temperature reservoir while undergoing isothermal compression. Finally, the cycle completes with an adiabatic compression, where the temperature rises without heat exchange, returning to the initial state. The efficiency of a Carnot engine is given by the formula:
where is the absolute temperature of the cold reservoir and is the absolute temperature of the hot reservoir. This cycle highlights the fundamental limits of efficiency for all real heat engines.
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