ii) Isothermal compression(c>d) at T to state d. During this compression, heat q, per unit mass IS Reversible adiabatic (i. e, isentropiccompression(d a) in which the vapor condenses to liquid and the state returns to In the T-s diagram the heat received, qH, is abef and the heat rejected, qL, is dcef. The net work sented by abcd. The thermal effi b In the h-s diagram, the isentropic processes are vertical lines as in the T-s diagram. The isotherms in the former, however, are not horizontal as they are in the latter. To see their shape we note that for these two-phase processes the isotherms are also lines of constant pressure(isobars), since P P(n. The combined first and second law is ra=dh-中 For a constant pressure reversible process, darey =Tds= dh. The slope of a constant pressure line in h-s coordinates is thus T=constant; slope of constant pressure line for two-phase medium The heat received and rejected per unit mass is given in terms of the enthalpy at the different states qL =hd-he.(In accord with our convention this is less than zero. The thermal efficiency is n="m=+=(-h)+(ba or, in terms of the work done during the isentropic compression and expansion processes, which correspond to the shaft work done on the fluid and received by the fluid (h-h)-(h2-h h Example: Carnot steam cycle: Heat source temperature = 300C Heat sink temperature= 20C What is the(i)thermal efficiency and (ii) ratio of turbine work to compression(pump) work if reversible? b) the turbine and the pump have adiabatic efficiencies of 02B-9 iii) Isothermal compression (c
d) at T1 to state d. During this compression, heat qL per unit mass is rejected to the source at T1. iv) Reversible adiabatic (i.e., isentropic) compression (d
a) in which the vapor condenses to liquid and the state returns to a. In the T-s diagram the heat received, qH , is abef and the heat rejected, qL , is dcef. The net work is represented by abcd. The thermal efficiency is given by η = = =− w q abcd abef T T net H Area Area 1 1 2 . In the h-s diagram, the isentropic processes are vertical lines as in the T-s diagram. The isotherms in the former, however, are not horizontal as they are in the latter. To see their shape we note that for these two-phase processes the isotherms are also lines of constant pressure (isobars), since P = P(T). The combined first and second law is Tds dh dp = − ρ . For a constant pressure reversible process, dq Tds dh rev = = . The slope of a constant pressure line in h-s coordinates is thus, ∂ ∂ h s T P       = = constant; slope of constant pressure line for two-phase medium. The heat received and rejected per unit mass is given in terms of the enthalpy at the different states as, q hh H ba = − q hh L = −d c . (In accord with our convention this is less than zero.) The thermal efficiency is η = = + = ( ) − + − ( ) ( ) − w q q q q hh h h h h net H H L H ba dc b a , or, in terms of the work done during the isentropic compression and expansion processes, which correspond to the shaft work done on the fluid and received by the fluid, η = ( ) − − − ( ) ( ) − hh hh h h bc a d b a . Example: Carnot steam cycle: Heat source temperature = 300o C Heat sink temperature = 20o C What is the (i) thermal efficiency and (ii) ratio of turbine work to compression (pump) work if a) all processes are reversible? b) the turbine and the pump have adiabatic efficiencies of 0.8?