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Thermodynamics: Isentropic Process

A process that does not have a change in entropy is an isentropic process. Though very similar to a reversible adiabatic process, an isentropic process is not necessarily reversibly adiabatic, but a reversibly adiabatic process is always isentropic.

In real life there are no processes that are truly isentropic or adiabatic, since those two processes are ideal processes. However, there are some engineering devices that can be considered essentially adiabatic. They are pumps, turbines, nozzles, and diffusers to name a few. So when studying these devices an isentropic model can be used. Below is an image of an isentropic process on a T-s diagram, and an adiabatic process on an h-s diagram for a steady flow device.

Isentropic process T-s diagram and h-s diagram

The h-s diagram is used to relate the first and second law for a steady flow device since enthalpy is a primary property of the first law of thermo dynamics, while entropy accounts for irreversibilities during an adiabatic process.

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