Fig 4.12 The Rankine cycle process diagram superimposed on the EOS of water
Pump The efficiency of the pump in Fig. 4.11 is calculated using Eq (4.13a). For compressed liquid water, v ~ 0.001 m3/kg. The pump's inlet pressure is 15 kPa and the outlet pressure is 2 MPa. Using these values in Eq (4.13a) yields:
The actual work required for pump operation is 4 kJ/kg, so the pump efficiency is 50%.
The turbine and pump efficiency calculations indicate the presence of irreversibilities in the Rankine power cycle. The entropy increase of the cycle (the system) and the reservoirs (the surroundings) are expressed by:
AStot = ASfluid+ ASpump+ ASturbine+ ASthermal reservoirs (4.14)
Because the working fluid (water) cycles through four states but returns to the starting state,
The component irreversibilities are obtained from Table 4.2:
ASturbine= 7.29 - 6.77 = 0.52 External irreversibilities due to heat exchange with the hot and cold reservoirs contribute:
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