Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

Wet Steam Quality and Dryness Fraction

Introduction and definition of steam quality and dryness fraction including calculating wet steam enthalpy and specific volume

Sponsored Links

The steam dryness fraction is used to quantify the amount of water within steam.

  • Dry steam - all water molecules are in the gaseous state
  • Wet steam - a portion of the water molecules have lost their energy - latent heat - and condensed to tiny water droplets

To produce 100% dry steam in an boiler and keep the steam dry throughout the piping system is in general not possible. Droplets of water will escape from the boiler surface due to turbulence and splashing when bubbles of steam break through the water surface. The steam leaving the boiler space will contain a mixture of water droplets and steam.

In addition heat loss in the pipe lines condensates parts of the steam to droplets of water.

Steam - produced in a boiler where the heat is supplied to the water and where the steam is in contact with the water surface of the boiler - contains approximately 5% water by mass.

Dryness fraction of Wet Steam

If the water content in the steam is 5% by mass, then the steam is said to be 95% dry with a dryness fraction 0.95.

Dryness fraction can be expressed:

ζ = ws / (ww + ws)                                (1)

where

ζ = dryness fraction

ww = mass of water (kg, lb)

ws = mass of steam (kg, lb)

Enthalpy of Wet Steam

Actual enthalpy of wet steam can be calculated with the dryness fraction - ζ - and the specific enthalpy - hs - of "dry" steam picked from steam tables. Wet steam will always have lower usable heat energy than "dry" steam.

ht = hs ζ + (1 - ζ ) hw                              (2)

where

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

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

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

Specific Volume of Wet Steam

The droplets of water in wet steam occupies a negligible space in the steam and the specific volume of wet steam will be reduced by the dryness fraction.

vt = vs ζ                                      (3)

where

vt = specific volume of wet steam (m3/kg, ft3/lb)

vs = specific volume of the dry steam (m3/kg, ft3/lb)

Example - Enthalpy and Specific Volume of Wet Steam

Steam with pressure 5 bar gauge (6 bar abs) has a dryness fraction of 0.95. From the steam table 

hs = 2755.46 (kJ/kg)

hw = 670.43 (kJ/kg)

The total enthalpy can be calculated:

ht = (2755.46 kJ/kg) 0.95 + (1 - 0.95) (670.43 kJ/kg)

    = 2651 kJ/kg

Specific volume can be calculated:

v = (0.315 m3/kg) 0.95

    = 0.299 m3/kg

Sponsored Links

Related Topics

Related Documents

Sponsored Links

Share

Search Engineering ToolBox

  • the most efficient way to navigate the Engineering ToolBox!

SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro .Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.

Topics

Unit Converters

Temperature

oC
oF


Load Calculator!

Length

m
km
in
ft
yards
miles
naut miles


Load Calculator!

Area

m2
km2
in2
ft2
miles2
acres


Load Calculator!

Volume

m3
liters
in3
ft3
us gal


Load Calculator!

Weight

kgf
N
lbf


Load Calculator!

Velocity

m/s
km/h
ft/min
ft/s
mph
knots


Load Calculator!

Pressure

Pa (N/m2)
bar
mm H2O
kg/cm2
psi
inches H2O


Load Calculator!

Flow

m3/s
m3/h
US gpm
cfm


Load Calculator!

9 13

This website use cookies. By continuing to browse you are agreeing to our use of cookies! Learn more