Isentropic process
[7] This process is idealized because reversible processes do not occur in reality; thinking of a process as both adiabatic and reversible would show that the initial and final entropies are the same, thus, the reason it is called isentropic (entropy does not change).
Thermodynamic processes are named based on the effect they would have on the system (ex.
Even though in reality it is not necessarily possible to carry out an isentropic process, some may be approximated as such.
The word "isentropic" derives from the process being one in which the entropy of the system remains unchanged.
is the amount of energy the system gains by heating,
The equal sign refers to a reversible process, which is an imagined idealized theoretical limit, never actually occurring in physical reality, with essentially equal temperatures of system and surroundings.
For reversible processes, an isentropic transformation is carried out by thermally "insulating" the system from its surroundings.
Temperature is the thermodynamic conjugate variable to entropy, thus the conjugate process would be an isothermal process, in which the system is thermally "connected" to a constant-temperature heat bath.
The entropy of a given mass does not change during a process that is internally reversible and adiabatic.
[12] Some examples of theoretically isentropic thermodynamic devices are pumps, gas compressors, turbines, nozzles, and diffusers.
Most steady-flow devices operate under adiabatic conditions, and the ideal process for these devices is the isentropic process.
The parameter that describes how efficiently a device approximates a corresponding isentropic device is called isentropic or adiabatic efficiency.
Real cycles have inherent losses due to compressor and turbine inefficiencies and the second law of thermodynamics.
That is, no heat is added to the flow, and no energy transformations occur due to friction or dissipative effects.
For an isentropic flow of a perfect gas, several relations can be derived to define the pressure, density and temperature along a streamline.
Note that energy can be exchanged with the flow in an isentropic transformation, as long as it doesn't happen as heat exchange.
An example of such an exchange would be an isentropic expansion or compression that entails work done on or by the flow.
For an isentropic flow, entropy density can vary between different streamlines.
) is given by Then for a process that is both reversible and adiabatic (i.e. no heat transfer occurs),
This leads to two important observations: Next, a great deal can be computed for isentropic processes of an ideal gas.
For any transformation of an ideal gas, it is always true that Using the general results derived above for
(per mole), Thus for isentropic processes with an ideal gas, Derived from where:
