Calculate reference or actual Rankine-cycle thermal efficiency, specific work, heat rate, steam rate, and flow for a target net shaft power. Actual mode requires isentropic-reference heat transfers and pump work, with fixed pump-inlet and turbine-inlet states and unchanged endpoint pressures. Already-actual heat transfers must not be corrected a second time. Steam-property feasibility, fuel/boiler losses, generator losses, and auxiliary loads are outside this energy-balance model.

Energy-balance model using supplied isentropic-reference enthalpies. Actual mode holds turbine inlet, condenser outlet and endpoint pressures fixed. Steam-property feasibility and electrical losses are not evaluated.

Rankine Cycle Efficiency Formula

The following formula is used to calculate the Rankine Cycle Efficiency.

Erank = [(h3 - h2) - (h4 - h1)] / (h3 - h2) × 100
  • Where Erank is the Rankine Cycle (thermal) efficiency (%)
  • h3 − h2 is the heat added in the boiler per unit mass (e.g., kJ/kg)
  • h4 − h1 is the heat rejected in the condenser per unit mass (e.g., kJ/kg)
  • h2 − h1 is the pump work input per unit mass (e.g., kJ/kg); it does not change the efficiency if h3 − h2 and h4 − h1 are already known, but it is used for other results like turbine work and back‑work ratio

How to Calculate Rankine Cycle Efficiency?

The following illustrative energy-balance example uses the ideal reference mode; its enthalpy differences are not a verified set of water/steam states.

Example Problem #1

  1. First, determine the heat added h3 − h2. In this example, h3 − h2 is given as 30 kJ/kg.
  2. Next, determine the heat rejected h4 − h1. For this problem, h4 − h1 is given as 20 kJ/kg.
  3. Next, determine the pump work h2 − h1. In this case, h2 − h1 is found to be 15 kJ/kg.
  4. Finally, calculate the Rankine Cycle Efficiency using the formula above: 

Erank = [(h3-h2) - (h4-h1)] / (h3-h2) * 100

Inserting the values from above and solving yields: 

Erank = [30 - 20] / (30) * 100 = 33.33 (%)

FAQ

What is the Rankine Cycle?

The Rankine cycle is a thermodynamic cycle used to generate electricity in the majority of thermal power plants. It is the fundamental operating cycle of all thermal power plants where an operating fluid is continuously evaporated and condensed. The cycle includes the generation of steam in a boiler, expansion of steam in a turbine, condensation of steam into water in a condenser, and then the pumping of the condensed water back into the boiler.

Why is Rankine Cycle Efficiency important?

Rankine-cycle thermal efficiency measures the fraction of heat transferred to the working fluid that becomes net shaft work. Overall fuel-to-electric efficiency additionally depends on boiler, generator, and auxiliary losses, which this calculator excludes.

How can Rankine Cycle Efficiency be improved?

Superheating, suitable pressure changes, reheat, and regenerative feedwater heating can improve efficiency under appropriate operating conditions. Their benefit depends on consistent steam properties, condenser conditions, moisture limits, and equipment constraints. Reheat and regeneration require a more detailed model than this simple-cycle calculator.