How to use the Rankine Cycle Calculator
- 1. Look up the statesFrom your steam table: h1 and s1 at the turbine inlet, and hf, hfg, sf, sfg and vf at the condenser.
- 2. Enter the pressuresBoiler and condenser pressure, and the turbine and pump efficiencies.
- 3. Get the cycleDryness, works, heat supplied, efficiency and specific steam consumption.
Rankine cycle steps
This tool has no steam tables inside it. Type the property values from the steam table your college uses. States are numbered 1 turbine inlet, 2 turbine exit, 3 condenser exit (saturated liquid) and 4 pump exit.
- Isentropic expansion: x2 = (s1 − sf)/sfg and h2 = hf + x2·hfg
- Turbine work wt = ηt (h1 − h2s)
- Pump work wp = vf (p1 − p2) / ηp, with p in kPa to get kJ/kg
- Heat supplied qin = h1 − h4, where h4 = h3 + wp
- Efficiency η = (wt − wp) / qin and steam rate = 3600 / wnet kg/kWh
Worked example and exam tips
Steam enters the turbine at 3 MPa and 350 °C (h1 = 3116.1, s1 = 6.7450) and the condenser is at 75 kPa (hf = 384.44, hfg = 2278.0, sf = 1.2132, sfg = 6.2426, vf = 0.001037). x2 = 0.886, so h2 = 2403.0 kJ/kg. wp = 0.001037 × 2925 = 3.03 kJ/kg and qin = 2728.6 kJ/kg. Net work = 710.1 kJ/kg, so η = 26.0%.
- Pump work is tiny (under 1% of turbine work), but examiners still expect you to find it.
- If s1 is larger than sg at the condenser pressure, the exhaust is superheated. Use the superheated table for h2.
- A higher boiler pressure or a lower condenser pressure raises efficiency, but it leaves wetter steam at the turbine exit.
Frequently asked questions
Why do I have to enter the steam properties?
Steam tables are large and every textbook prints slightly different values. Typing the values from your own table keeps your answer the same as your book's.
What is the back work ratio?
Pump work divided by turbine work. In a steam cycle it is very small because pumping a liquid takes little work.
What dryness at the turbine exit is acceptable?
Many designs keep it above about 0.88. Wetter steam erodes the last turbine blades, which is one reason plants use reheat.
Is this calculator free?
Yes. You fill in a short form once to see your result, and the other Uncodemy tools then open without it. Every calculation runs in your browser and nothing you type is sent anywhere.