Steam Properties Calculator
Estimate steam enthalpy for saturated, superheated, or liquid states at a given temperature. Useful for quick thermodynamic cycle calculations before consulting full IAPWS steam tables.
About this calculator
Steam properties — enthalpy, entropy, and specific volume — vary with both temperature and phase state. This calculator uses linearised approximations anchored at the 100 °C, 1 atm reference point. For saturated steam: h ≈ 2676 + (T − 100) × 2.1 kJ/kg. For superheated steam: h ≈ 2676 + (T − 100) × 3.6 kJ/kg. For subcooled liquid: h ≈ 419 + T × 4.18 kJ/kg (using cp ≈ 4.18 kJ/kg·K). The value 2676 kJ/kg is the specific enthalpy of dry saturated steam at 100 °C; 419 kJ/kg is the saturated liquid enthalpy at 100 °C. These are linear fits and will deviate from IAPWS-IF97 tables at extreme pressures or temperatures, so treat results as engineering estimates rather than precise data.
How to use
Suppose you have saturated steam at 150 °C and want to estimate its specific enthalpy. Select state = 'saturated' and enter temperature = 150 °C. The calculator applies: h = 2676 + (150 − 100) × 2.1 = 2676 + 50 × 2.1 = 2676 + 105 = 2781 kJ/kg. If the mass flow rate is 2 kg/s, the total enthalpy flow rate is 2 × 2781 = 5562 kW. Compare: IAPWS tables give h_g ≈ 2748 kJ/kg at 150 °C, so this approximation is within about 1%, suitable for preliminary design work.
Frequently asked questions
What is the difference between saturated and superheated steam enthalpy?
Saturated steam exists at the boiling point for a given pressure; its enthalpy includes the latent heat of vaporisation. Superheated steam has been heated beyond the saturation temperature at the same pressure, so it contains additional sensible heat. For this reason the superheated slope in the approximation (3.6 kJ/kg·°C) is larger than the saturated slope (2.1 kJ/kg·°C). In a power plant, superheated steam is preferred because it has higher enthalpy available for work and avoids condensation droplets that erode turbine blades.
How accurate are these steam property approximations compared to IAPWS steam tables?
The formulas are linear interpolations around the 100 °C atmospheric reference and are typically within 1–3% of IAPWS-IF97 values for temperatures between 100 °C and 250 °C at moderate pressures. At higher pressures (above ~10 bar) or temperatures above 300 °C the deviations grow because real steam properties are nonlinear. For precise engineering design, boiler sizing, or turbine blade calculations, always cross-check against published IAPWS-IF97 tables or software. These estimates are best suited to coursework, feasibility studies, and sanity checks.
Why does specific enthalpy of liquid water increase linearly with temperature?
For subcooled (compressed) liquid water at moderate pressures, the specific heat capacity cp is nearly constant at about 4.18 kJ/kg·K, making enthalpy rise almost linearly: Δh ≈ cp × ΔT. This linear behaviour holds well from 0 °C to around 150 °C. Above 150 °C, cp begins to increase more steeply as the saturation line is approached and molecular hydrogen bonding weakens, causing slight nonlinearity. The 419 kJ/kg intercept in the formula represents the reference enthalpy of saturated liquid at 100 °C.