# Enthalpy of Wet Steam

## Wet steam, the dryness fraction and enthalpy

The actual enthalpy of evaporated wet steam is the product of the dryness fraction - *ζ -* and the specific enthalpy - *h*_{s} - from the steam tables. Wet steam has less usable heat energy than dry saturated steam.

h_{t}= h_{s}ζ + (1 - ζ) h_{w}(1)

where

h_{t}= enthalpy of wet steam (kJ/kg, Btu/lb)

h_{s}= enthalpy of steam (kJ/kg, Btu/lb)

ζ = dryness fraction

h_{w}= enthalpy of saturated water or condensate (kJ/kg, Btu/lb)

The dryness fraction can be expressed as

ζ = w_{s}/ (w_{w}+ w_{s})(2)

where

ζ= dryness fraction

w_{w}= mass of water (kg, lb)

w_{s}= mass of steam (kg, lb)