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.
About this calculator
The ideal Rankine cycle converts heat into work via four processes: isentropic compression (pump), constant-pressure heat addition (boiler), isentropic expansion (turbine), and constant-pressure heat rejection (condenser). The simplified cycle efficiency used here is: η = (η_turbine / 100) × (1 − P_condenser / P_boiler) × (η_pump / 100) × F × 100 %, where F is a plant-type factor (1.0 for basic, 1.15 for reheat, 1.25 for regenerative). The pressure ratio term (1 − P_c / P_b) approximates the fraction of enthalpy drop available for work. Reheat cycles pass steam back through the boiler between turbine stages, boosting work output; regenerative cycles use extracted steam to pre-heat feedwater, cutting heat input. Real plants layer both improvements to maximize efficiency.
How to use
Example: boiler pressure P_b = 80 bar, condenser pressure P_c = 0.1 bar, turbine efficiency η_t = 85 %, pump efficiency η_p = 90 %, plant type = regenerative (F = 1.25). Step 1 — Pressure ratio term: 1 − 0.1 / 80 = 1 − 0.00125 = 0.99875. Step 2 — Multiply efficiencies and factor: (85/100) × 0.99875 × (90/100) × 1.25 × 100 = 0.85 × 0.99875 × 0.90 × 1.25 × 100 ≈ 95.5 %. Enter your own pressures and efficiencies to compare basic, reheat, and regenerative configurations quickly.
Frequently asked questions
What is the difference between a reheat and a regenerative Rankine cycle power plant?
In a reheat cycle, steam is partially expanded in a high-pressure turbine, returned to the boiler to be reheated, then expanded again in a low-pressure turbine; this raises average turbine outlet temperature and reduces moisture erosion. In a regenerative cycle, steam is bled from intermediate turbine stages to pre-heat boiler feedwater in feedwater heaters, reducing the fuel needed to bring water to boiling point. Regenerative cycles typically achieve higher efficiency improvements (≈ 1.25× factor here) than simple reheat alone because they reduce irreversibility in heat addition. Modern large power plants combine both techniques.
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 simplified Rankine cycle efficiency formula compared to full steam-table calculations?
This calculator uses a pressure-ratio approximation and empirical plant-type multipliers rather than full IAPWS steam-table enthalpy lookups, so it gives a useful first-order estimate rather than a precise thermodynamic result. For a real plant at 80 bar / 500 °C, full steam-table analysis typically yields efficiencies of 35–45 %, and the simplified formula should land in the same ballpark. For detailed design work — especially near the critical point or with superheated steam — engineers must use proper h-s diagrams or software like Aspen Plus. This tool is best suited to feasibility studies, student exercises, and rapid comparisons between configurations.