The steam in a reheat Rankine cycle leaves the boiler and enters the turbine at 60 bar and 390°C. It leaves the condenser as a saturated liquid. The steam is expanded in the high-pressure turbine to a pressure of 13 bar and reheated in the boiler at 390°C. It then enters the low-pressure turbine, where it expends to a pressure of 0.16 bar. Estimate the efficiency of the cycle if the pump and turbine efficiency is 0.8.
At point 3, P3 = 60 bar and T3 = 390°C. From superheated steam tables, h3 = 3151 kJ/kg and s3 = 6.500 kJ/kg-K.
At point 4, s4 = s3 = 6.500 kJ/kg-K. From the problem definition, P4 = 13 bar. From steam tables, h4 = 2787 kJ/kg. To find h4, we need to use Eq. (10.1) for turbine efficiency:
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