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Unformatted text preview: 2.3. RANKINE 33 Relative to the pump, the boiler has added much more exergy to the fluid. After the turbine, just before the condenser, we have ψ 4 = ( h 4 − T o s 4 ) − ( h o − T o s o ) , (2.153) = parenleftbiggparenleftbigg 1794 . 8 kJ kg parenrightbigg − (298 . 15 K ) parenleftbigg 5 . 7432 kJ kg K parenrightbiggparenrightbigg − parenleftbiggparenleftbigg 104 . 89 kJ kg parenrightbigg − (298 . 15 K ) parenleftbigg . 3674 kJ kg K parenrightbiggparenrightbigg , (2.154) = 87 . 1152 kJ kg . (2.155) Note that ψ 4 − ψ 3 = h 4 − h 3 because the process is isentropic. The actual exergy (or available work) at the exit of the turbine is relative low, even though the enthapy state at the turbine exit remains at an elevated value. 2.3.2 Reheat In a Rankine cycle with reheat, the steam is extracted from an intermediate stage of the turbine and reheated in the boiler. It is then expanded through the turbine again to the condenser pressure. One also avoids liquid in the turbine with this strategy. This generallycondenser pressure....
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- Fall '11
- Dynamics, Carnot cycle, Feedwater heater