Well this chapter cover about the entropy. Entropy owes its existence from the extension of second law of thermodynamics . In Entropy the formula is Sgeneration = S system + S sorrounding and if the S generation is > 0 it is a irreversible process , if the S generation is = 0 it a reversible process . In this chapter , theres also a process called Isentropic Process , which the S system is = 0 which simplified to S 2 = S 1 . Many engineering system or devices such as pump , turbines , nozzles are essentially adiabatic in their operation and it perform the best in irreverseable . Then in isentropic process enable us to compare the actual performance of theses devices to the performance under idealized conditions. To determined wether the process is Isentropic or not , it depend on the state. To achieve isentropic , the system must be adiabatic and it is reversible. .
Lastly entropy change of an ideal gases, which the formula is obtained by combining entropy and ideal gases formula. S2-S1 = Cp ln (T2/T1)- R ln (P2/P1)
To find effeciencies of a turbine , N= W isentropic/ W actual . The ratio of the actual work output of the turbine to the work output that would be achieved if the process between the inlet state and the exit pressure were isntropic.