Question

Define or explain each work done isothermal adiabatic isotropic process

Answer 1

In thermodynamics, an isentropic process is an idealized thermodynamic process that is both adiabatic and reversible.[1][2][3][4][5][6] The work transfers of the system are frictionless, and there is no transfer of heat or matter. Such an idealized process is useful in engineering as a model of and basis of comparison for real processes.[7]

The word 'isentropic' is occasionally, though not customarily, interpreted in another way, reading it as if its meaning were deducible from its etymology. This is contrary to its original and customarily used definition. In this occasional reading, it means a process in which the entropy of the system remains unchanged, for example because work done on the system includes friction internal to the system, and heat is withdrawn from the system, in just the right amount to compensate for the internal friction, so as to leave the entropy unchanged.[8]

Background

Isentropic processes in thermodynamic systemsEdit



T-s (Entropy vs. Temperature) diagram of an isentropic process, which is a vertical line segment.

The entropy of a given mass does not change during a process that is internally reversible and adiabatic. A process during which the entropy remains constant is called an isentropic process, written {\displaystyle \Delta s=0} or {\displaystyle s_{1}=s_{2}}. [11] Some examples of theoretically isentropic thermodynamic devices are pumps, gas compressors, turbines, nozzles, and diffusers.

Isentropic efficiencies of steady-flow devices in thermodynamic systemsEdit

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.[12]

Isentropic efficiency of Turbines:

{\displaystyle \eta _{T}={\frac {\text{Actual Turbine Work}}{\text{Isentropic Turbine Work}}}={\frac {W_{a}}{W_{s}}}\cong {\frac {h_{1}-h_{2a}}{h_{1}-h_{2s}}}}

Isentropic efficiency of Compressors

{\displaystyle \eta _{C}={\frac {\text{Isentropic Compressor Work}}{\text{Actual Compressor Work}}}={\frac {W_{s}}{W_{a}}}\cong {\frac {h_{2s}-h_{1}}{h_{2a}-h_{1}}}}

Isentropic efficiency of Nozzles

{\displaystyle \eta _{N}={\frac {\text{Actual KE at Nozzle Exit}}{\text{Isentropic KE at Nozzle Exit}}}={\frac {V_{2a}^{2}}{V_{2s}^{2}}}\cong {\frac {h_{1}-h_{2a}}{h_{1}-h_{2s}}}}

For all the above equations:

{\displaystyle h_{1}} is the specific enthalpy at the entrance state{\displaystyle h_{2a}} is the specific enthalpy at the exit state for the actual process{\displaystyle h_{2s}} is the specific enthalpy at the exit state for the isentropic process

Isentropic devices in thermodynamic cyclesEdit

CycleIsentropic StepDescriptionIdeal Rankine Cycle1→2Isentropic compression in a pumpIdeal Rankine Cycle3→4Isentropic expansion in a turbineIdeal Carnot Cycle2→3Isentropic expansionIdeal Carnot Cycle4→1Isentropic compressionIdeal Otto Cycle1→2Isentropic compressionIdeal Otto Cycle3→4Isentropic expansionIdeal Diesel Cycle1→2Isentropic compressionIdeal Diesel Cycle3→4Isentropic expansionIdeal Brayton Cycle1→2Isentropic compression in a compressorIdeal Brayton Cycle3→4Isentropic expansion in a turbineIdeal Vapor-compression refrigeration Cycle1→2Isentropic compression in a compressor

NOTE: The isentropic assumptions are only applicable with ideal cycles. Real cycles have inherent losses due to compressor and turbine inefficiencies and the second law of thermodynamics. Real systems are not truly isentropic, but isentropic behavior is an adequate approximation for many calculation purposes.
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