How to use this calculator
Enter the boiler and condenser pressures, the turbine inlet temperature (or choose saturated vapor), and the isentropic efficiencies (1 for the ideal cycle). Add a reheat stage or the net power output if your problem has them.
Formulas
Pumpwp = v1(P2 − P1)/ηp
Turbineh4 = h3 − ηt(h3 − h4s), s4s = s3
Efficiencyηth = (wt − wp)/qin, qin = h3 − h2
Worked example
Ideal Rankine cycle: 3 MPa and 350 °C at the turbine, 75 kPa in the condenser (the default; Çengel Example 10-1)
- h1 = hf at 75 kPa = 384.44 kJ/kg; wp = 0.001037(3000 − 75) = 3.03 kJ/kg.
- h3 = 3116.1 kJ/kg, s3 = 6.7450 kJ/kg·K; at 75 kPa this gives x4 = 0.886 and h4 = 2403.0 kJ/kg.
- qin = 3116.1 − 387.5 = 2728.6 kJ/kg, wnet = 713.1 − 3.0 = 710.0 kJ/kg, so η = 26.0%.
Frequently asked questions
Why reheat?
Reheating the steam partway through the expansion raises the average temperature of heat addition and, mainly, keeps the turbine exhaust drier, which protects the blades.
Why is pump work so small?
Liquid water is nearly incompressible with a tiny specific volume, so pumping it takes about 1% of the turbine work. Compressing a gas, as in a Brayton cycle, takes far more.