What is the Rankine cycle?

The Rankine cycle is the ideal thermodynamic cycle used by steam power plants. It consists of four processes: isentropic compression in a pump, isobaric heat addition in a boiler, isentropic expansion in a turbine, and isobaric heat rejection in a condenser.

What units should enthalpy values be in?

Enter enthalpies in kJ/kg, which is the standard unit found in steam tables (e.g., NIST, textbook appendices). All four states (h₁ through h₄) must use the same unit for the formula to work.

Why must h₁ > h₂ and h₄ > h₃?

h₁ > h₂ ensures the turbine produces positive work (steam expands and loses enthalpy). h₄ > h₃ ensures the pump consumes work (liquid is compressed and gains enthalpy). Violating these conditions means the inputs are physically inconsistent.

What is the back work ratio?

Back work ratio (BWR) = pump work / turbine work = (h₄ − h₃) / (h₁ − h₂). For steam Rankine cycles BWR is typically 0.5–2%, much lower than gas cycles (30–50%), because pumping liquid requires far less work than compressing gas.

How do I get h₁, h₂, h₃, h₄?

Look them up in steam tables based on the cycle pressures and temperatures. h₁ is at boiler pressure (superheated or saturated vapor). h₂ is at condenser pressure after isentropic expansion (use quality x if wet). h₃ is saturated liquid at condenser pressure. h₄ = h₃ + v₃(P_high − P_low)/1000 or read from tables.

What is a typical Rankine efficiency?

Ideal Rankine cycles for steam power plants achieve 35–45% thermal efficiency. Real plants are 30–40% due to irreversibilities in turbines, pumps, and heat exchangers. Advanced supercritical plants can reach 45–48%.

Rankine Cycle Efficiency Calculator

Name: Rankine Cycle Efficiency Calculator
Availability: InStock
Author: Nham Vu

Enter turbine inlet/outlet enthalpies and pump work to calculate the thermal efficiency of an ideal Rankine steam cycle.

Cycle State Enthalpies (kJ/kg)

Ideal Rankine cycle states:

h₁ — Turbine inlet (high-P steam) h₂ — Turbine outlet (low-P steam) h₃ — Pump inlet (sat. liquid) h₄ — Pump outlet (compressed liquid)

Flow: Boiler → Turbine (h₁→h₂) → Condenser → Pump (h₃→h₄) → Boiler

h₁ — Turbine Inlet Enthalpy (kJ/kg)

h₂ — Turbine Outlet Enthalpy (kJ/kg)

h₃ — Pump Inlet Enthalpy (kJ/kg)

h₄ — Pump Outlet Enthalpy (kJ/kg)

Quick Presets

Results

Enter enthalpies and click Calculate

Summary

Enter turbine inlet/outlet enthalpies and pump work to calculate the thermal efficiency of an ideal Rankine steam cycle.

How it works

Enter the specific enthalpy at the turbine inlet (h₁) — superheated or saturated steam entering the turbine.
Enter the specific enthalpy at the turbine outlet (h₂) — wet or saturated steam leaving the turbine.
Enter the specific enthalpy at the pump inlet (h₃) — saturated liquid at condenser pressure.
Enter the specific enthalpy at the pump outlet (h₄) — compressed liquid leaving the pump.
The calculator applies η = W_net / Q_in = [(h₁ − h₂) − (h₄ − h₃)] / (h₁ − h₄) to find thermal efficiency.
Results include net work output, heat input, back work ratio, and pump work fraction.

Use cases

Solve thermodynamics coursework on Rankine steam power cycles.
Estimate efficiency of steam turbine power plants from steam table data.
Compare ideal Rankine cycle performance at different operating pressures.
Evaluate the impact of pump work on overall cycle efficiency.
Validate enthalpy-based steam cycle calculations from textbooks.
Understand back work ratio and why it is much lower than in gas cycles.
Perform sensitivity analysis — how much does raising boiler pressure improve efficiency?

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu