Rankine Cycle Power Plant Calculator
Estimate the thermal efficiency of a steam power plant modeled on the Rankine cycle, accounting for turbine and pump efficiencies and plant configuration. Useful for mechanical engineering students and power-plant designers.
Last updated: September 2026
Formula below · 2 sources (NIST, Wikipedia) · Updated Sep 2026
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About this calculator
The simple Rankine cycle converts heat into work through four processes: pump compression, constant-pressure heat addition in the boiler, turbine expansion and constant-pressure heat rejection in the condenser. This calculator models the simple cycle with dry saturated steam entering the turbine at the boiler pressure. Thermal efficiency is η = (w_t − w_p) / q_in × 100%. Values come from the IAPWS-IF97 industrial formulation (region 1 for liquid water, region 2 for steam, region 4 for the saturation line), the same equations used in published steam tables. The turbine inlet state is set by the boiler pressure and steam temperature; the ideal turbine exhaust is found at the condenser pressure with the same entropy (a wet mixture of quality x₂s = (s₁ − s_f)/(s_g − s_f) in most cases). Turbine work is w_t = η_t × (h₁ − h₂s). The pump raises saturated liquid from condenser to boiler pressure: w_p = v_f × (P_boiler − P_condenser) / η_p. Heat added in the boiler is q_in = h₁ − (h_f + w_p). Reheat and regenerative plants need extra data (the reheat pressure and temperature, or the feedwater-heater bleed pressures), so those options return a message instead of a guessed multiplier.
How to use
Example: boiler pressure 50 bar, condenser pressure 0.08 bar, turbine efficiency 88%, pump efficiency 85%, plant type simple. Step 1 — saturated steam at 50 bar (263.9 °C): h₁ = 2794.2 kJ/kg, s₁ = 5.974 kJ/(kg·K). Step 2 — at 0.08 bar (41.5 °C): h_f = 173.9, h_g = 2576.2 kJ/kg, s_f = 0.593, s_g = 8.227 kJ/(kg·K), so x₂s = (5.974 − 0.593)/(8.227 − 0.593) = 0.705 and h₂s = 1867.1 kJ/kg. Step 3 — w_t = 0.88 × (2794.2 − 1867.1) = 815.9 kJ/kg. Step 4 — w_p = 0.00101 × (5000 − 8) / 0.85 = 5.9 kJ/kg. Step 5 — q_in = 2794.2 − 173.9 − 5.9 = 2614.5 kJ/kg. Efficiency η = (815.9 − 5.9) / 2614.5 = 31.0%. Note the low exhaust quality (about 0.75 after losses): this is why real plants superheat or reheat.
Frequently asked questions
What is the difference between a reheat and a regenerative Rankine cycle power plant?
In a reheat cycle, steam is partly expanded in a high-pressure turbine, returned to the boiler to be reheated, then expanded again in a low-pressure turbine; this adds work and keeps the exhaust drier. In a regenerative cycle, steam is bled from intermediate turbine stages to preheat the boiler feedwater, which raises the average temperature of heat addition and cuts fuel use. Each typically adds a few percentage points of efficiency, depending on the reheat temperature and the number of feedwater heaters. Modern large plants combine both. This calculator models only the simple cycle, because the gains depend on reheat and bleed conditions that a single plant-type choice cannot capture.
Why does condenser pressure affect Rankine cycle efficiency so strongly?
Lower condenser pressure means the turbine exhausts to a deeper vacuum, allowing steam to expand further and extract more work per kilogram of steam. The efficiency gain comes from the increased enthalpy drop across the turbine. However, achieving very low condenser pressures requires large, expensive condensers and efficient cooling-water supplies. Below about 0.05 bar the efficiency gains become marginal and the engineering costs escalate, so most plants operate condensers in the 0.05–0.15 bar range.
How accurate is this Rankine cycle efficiency calculation?
The steam enthalpies and entropies come from the IAPWS-IF97 equations used in published steam tables, so the cycle efficiency is a proper thermodynamic result for the simple cycle with saturated steam entering the turbine. It ignores pressure drops in pipes and the boiler, heat losses, and auxiliary loads, so a real plant with these conditions will be a little less efficient. For superheated inlet steam, use the Rankine cycle efficiency calculator, which takes the steam temperature as an input.