Water-Steam Mollier Diagram

Enthalpy-entropy diagram for water and steam. Used to determine enthalpy versus entropy of water and steam, and useful for analyzing the performance of adiabatic steady-flow processes such as flow in nozzles, diffusers, turbines and compressors.

StatePressure (bar)Dryness Fraction (x)Enthalpy (kJ/kg)Entropy (kJ/kg·K)Description
Saturated Liquid10417.31.303Liquid water at saturation
Wet Vapor10.513123.598Two-phase mixture at 50% quality
Saturated Vapor1126767.361Pure steam at saturation
Saturated Vapor5127946.818Saturated steam at 5 bar
Saturated Vapor10127706.586Saturated steam at 10 bar
Superheated Steam5—29607.229Superheated steam at 5 bar, 400°C
Superheated Steam10—30407.167Superheated steam at 10 bar, 500°C
Wet Vapor100.924936.58690% quality steam at 10 bar

About the Mollier Diagram

The Mollier diagram is an enthalpy-entropy diagram for water and steam. It is particularly useful for analyzing:

  • Nozzles and Diffusers: Examining flow processes with minimal pressure change
  • Turbines: Evaluating adiabatic expansion processes
  • Compressors: Analyzing adiabatic compression processes

Dryness Fraction (Quality)

The dryness fraction, denoted by x, represents the quantity of saturated vapor in unit mass of wet vapor:

  • x = 0: Saturated liquid (100% liquid)
  • 0 < x < 1: Wet vapor (two-phase mixture)
  • x = 1: Saturated vapor (100% vapor)

Key Example

For saturated steam at 10 bar pressure:

  • Enthalpy: approximately 2770 kJ/kg
  • Entropy: approximately 6.586 kJ/kg·K
  • Dryness Fraction: x = 1 (saturated vapor)

Unit Conversions

Pressure:

  • 1 bar = 10⁵ Pa = 0.1 N/mm² = 14.50 psi = 0.9869 atm

Energy:

  • 1 kJ/kg = 0.4299 Btu/lbm = 0.23884 kcal/kg