How to use this calculator

Pick the device and the fluid, then give the inlet pressure and temperature (or quality for wet steam), the exit pressure and the isentropic efficiency. Add the mass flow or the power to get rates. A throttle needs no efficiency: its enthalpy stays constant.

Formulas

Energyh₁ + V₁²/2 = h₂ + V₂²/2 + w (adiabatic)

Turbine, nozzleη = (h₁ − h₂)/(h₁ − h_2s)

Compressor, pumpη = (h_2s − h₁)/(h₂ − h₁)

Worked example

Steam turbine: 6 MPa and 500 °C expanded to 10 kPa with 85% efficiency (the default)

h₁ = 3423.1 kJ/kg, s₁ = 6.8826 kJ/kg·K.
At 10 kPa with s = s₁: h_2s = 2180.0 kJ/kg.
h₂ = 3423.1 − 0.85(1243.1) = 2366.5 kJ/kg (x = 0.909), so w = 1056.7 kJ/kg.

Frequently asked questions

Why does the exit get hotter in a real compressor?

Friction turns some of the work into internal energy, so the real exit enthalpy and temperature are above the isentropic values.

How do I handle air?

Air is treated as an ideal gas with variable specific heats (Çengel Table A-17): s°₂ = s°₁ + R ln(P₂/P₁) for the isentropic exit.