Isentropic process

An isentropic process is a thermodynamic change in which entropy remains constant. For a closed system, it is both adiabatic and reversible.

Entropy: A thermodynamic state function that measures energy dispersal and the number of microscopic arrangements compatible with a macroscopic state. An isentropic process is defined by entropy remaining unchanged.
Isentropic efficiency: A measure comparing a real turbomachine's performance with the ideal performance of an isentropic process. It quantifies how closely actual equipment approaches the isentropic ideal.
Thermodynamic state: The condition of a thermodynamic system specified by properties such as pressure, temperature, and volume. An isentropic process connects equilibrium states while holding entropy fixed.
Isothermal process: A thermodynamic process in which temperature remains constant. Unlike an isentropic process, an isothermal change generally involves heat transfer and changing entropy.
Adiabatic process: A thermodynamic process in which no heat crosses the system boundary. For a closed system, an isentropic process must be adiabatic.
Turbine: A rotary machine that extracts work from a moving fluid as the fluid's pressure or enthalpy decreases. An isentropic expansion provides the ideal work benchmark for turbine performance.
Ideal gas: A model gas whose particles have negligible volume and interact only through elastic collisions. Ideal-gas assumptions yield simple equations for isentropic changes.
Polytropic process: A thermodynamic process modeled by a pressure–volume power law with a specified polytropic exponent. Polytropic paths can represent behavior that departs from the ideal isentropic relation.
Reversible process: An idealized process that can be reversed by infinitesimal changes without leaving net changes in the system and surroundings. Adiabatic reversibility prevents entropy generation in a closed system.
Compressor: A machine that raises a gas's pressure by supplying mechanical work. Isentropic compression estimates the minimum work input for a specified pressure rise.

Linked from 3 pages

Otto cycleRelated: The cycle idealizes compression and expansion as isentropic processes.