Thermodynamics

362 | ThermodynamicsT, RT 2 = 780 RP 2P 2 = ?HeCOMPRESSOR7802IsentropiccompressionP 1 = 14 psiaFIGURE 7–40Schematic and T-s diagram forExample 7–11.P 1 = 14 psiaT 1 = 510 R5101sINTERACTIVETUTORIALSEE TUTORIAL CH. 7, SEC. 10 ON THE DVD.7–10 ■ REVERSIBLE STEADY-FLOW WORKThe work done during a process depends on the path followed as well as onthe properties at the end states. Recall that reversible (quasi-equilibrium)moving boundary work associated with closed systems is expressed in termsof the fluid properties asWe mentioned that the quasi-equilibrium work interactions lead to the maximumwork output for work-producing devices and the minimum workinput for work-consuming devices.It would also be very insightful to express the work associated withsteady-flow devices in terms of fluid properties.Taking the positive direction of work to be from the system (work output),the energy balance for a steady-flow device undergoing an internallyreversible process can be expressed in differential form asButSubstituting this into the relation above and canceling dh yieldIntegrating, we finddq rev TdsTds dh vdPdq rev dw rev dh dke dpedw rev vdP dke dpe2w rev vdP ¢ke ¢pe1kJ>kg212W b PdV1Eq. 7–1621Eq. 7–242 fdq rev dh vdP(7–51)When the changes in kinetic and potential energies are negligible, this equationreduces to2w rev vdP1kJ>kg211(7–52)Equations 7–51 and 7–52 are relations for the reversible work output associatedwith an internally reversible process in a steady-flow device. They will