Formula & Engineering Notes
Quality (dryness fraction):
hf, hg and hfg are read at the given pressure from the saturated table by linear interpolation. x = 0 is saturated liquid, x = 1 saturated vapour; outside [0,1] the state is single-phase.
All steam properties are interpolated from the shared IAPWS-IF97 steam-table datasets — see the full steam tables and the Steam Property Calculator.
Quality is the single most useful number in wet-steam work, and yet it's just a ratio. Picture the saturation enthalpy as a ruler running from hf (all liquid) to hg (all vapour); your measured enthalpy lands somewhere on that ruler, and how far along it sits is the quality. That's all x is.
Why you care: low quality means wet steam, and wet steam carries water droplets that erode turbine blades and slug control valves. If your number comes back below about 0.95 going into a turbine, that's a red flag worth chasing before it chews up hardware.