Rankine Cycle Steam Power Calculator
Estimate net power output and thermal efficiency of a steam power plant by entering boiler pressure, superheat temperature, condenser pressure, mass flow rate, and component efficiencies. Used by mechanical engineers to benchmark turbine-generator sets.
Last updated: September 2026
Formula below · 2 sources (NIST, Wikipedia) · Updated Sep 2026
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About this calculator
The Rankine cycle converts heat into shaft work through four processes: compression of liquid in a pump, constant-pressure heat addition in a boiler, expansion in a turbine and constant-pressure condensation. 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). Net power is P_net = ṁ × (w_t − w_p) / 1000 in MW, where ṁ is the steam mass flow in kg/s. Superheating raises turbine inlet enthalpy and improves both output and exhaust steam quality.
How to use
Example: boiler pressure 50 bar, superheat temperature 500 °C, condenser pressure 0.1 bar, steam flow 100 kg/s, turbine efficiency 85%, pump efficiency 80%. Step 1 — turbine inlet (IAPWS-IF97): h₁ = 3434.5 kJ/kg, s₁ = 6.978 kJ/(kg·K). Step 2 — condenser at 0.1 bar (45.8 °C): h_f = 191.8, h_g = 2583.9 kJ/kg, s_f = 0.649, s_g = 8.149 kJ/(kg·K). Ideal exhaust quality x₂s = (6.978 − 0.649)/(8.149 − 0.649) = 0.844, so h₂s = 191.8 + 0.844 × 2392.1 = 2210.4 kJ/kg. Step 3 — turbine work w_t = 0.85 × (3434.5 − 2210.4) = 1040.5 kJ/kg. Step 4 — pump work w_p = 0.00101 × (5000 − 10) / 0.80 = 6.3 kJ/kg. Step 5 — net power P = 100 × (1040.5 − 6.3) / 1000 = 103.4 MW. The heat input is q_in = 3434.5 − 191.8 − 6.3 = 3236.4 kJ/kg, so the cycle efficiency is 1034.2 / 3236.4 = 32.0%.
Frequently asked questions
How does superheating steam improve Rankine cycle efficiency?
Superheating raises the average temperature at which heat is added to the cycle, which increases thermal efficiency according to the Carnot principle. More importantly, it shifts the turbine expansion path to the right on a T-s diagram, increasing steam quality at the turbine exit and reducing blade erosion from liquid droplets. A typical superheat temperature jump from 400 °C to 500 °C can raise cycle efficiency by 2–4 percentage points. Modern ultra-supercritical plants operate above 600 °C and 250 bar to maximize efficiency.
What is the difference between turbine isentropic efficiency and overall plant thermal efficiency?
Turbine isentropic efficiency (η_t) compares the actual turbine work to the ideal isentropic work for the same pressure drop — it captures internal losses like friction and irreversibility within the turbine itself, typically 80–90 %. Overall thermal efficiency (η_th) measures how much of the total heat input from fuel is converted to net electrical output, and it is always lower because it also accounts for boiler losses, pump work, condenser heat rejection, and auxiliary loads. A plant with 88 % turbine efficiency might still achieve only 38 % thermal efficiency.
Why is condenser pressure kept as low as possible in steam power plants?
The turbine exhausts into the condenser, so a lower condenser pressure means a larger pressure drop across the turbine and more work extracted per kilogram of steam. Condenser pressure is limited by the temperature of the available cooling medium (river, seawater, or cooling tower). A condenser at 0.05 bar corresponds to a saturation temperature of about 33 °C — already near ambient — so further reduction requires extremely cold cooling water. Each kilopascal reduction in condenser pressure can improve net output by roughly 0.5–1 % in large plants.