Project ForgeAn ideal reheat Rankine cycle operates between the pressure limits of 10 kPa and 8 MPa, with reheat being done at 4 MPa. The temperature of steam at the inlets of both turbines is 500°C and the enthalpy of steam is 3185 kJ/kg at the exit of the high pressure turbine and 2247 kJ/kg at the exit of low pressure turbine. The enthalpy of water at the exit from the pump is 191 kJ/kg. Using the superheated-steam data at 500°C: h=3446 kJ/kg at 4 MPa, and h=3399 kJ/kg at 8 MPa. Disregarding the pump work, the cycle efficiency (in percentage) is __________.
Explanation
Boiler heat: Qb=h(8MPa,500°C)−hpump,exit=3399−191=3208 kJ/kg. Reheat: Qr=h(4MPa,500°C)−h(HP exit)=3446−3185=261 kJ/kg. Total Qin=3208+261=3469 kJ/kg. HP turbine work=3399−3185=214 kJ/kg. LP turbine work=3446−2247=1199 kJ/kg. Total Wt=214+1199=1413 kJ/kg. Efficiency (disregarding pump work)=1413/3469≈40.7%.
Source: GATE ME 2014 (Session 1 / Set-1) (2014)
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