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Wet Steam - Enthalpy

Wet steam, dryness fraction and enthalpy.

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

ht = hs ζ + (1 - ζ) hw                    (1)


ht= enthalpy of wet steam (kJ/kg, Btu/lb)

hs = enthalpy of steam (kJ/kg, Btu/lb)

ζ = dryness fraction

hw= enthalpy of saturated water or condensate (kJ/kg, Btu/lb)

The dryness fraction can be expressed as

ζ = ws / (ww + ws)                      (2)


ζ = dryness fraction

ww = mass of water (kg, lb)

ws = mass of steam (kg, lb)

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