Dryness fraction measurement:
Sensible Heat of Water or Heat of Liquid or Enthalpy of Liquid (h)
Sol.: It is quantity of heat which is required to raise unit mass of water from 0°C to saturation temperature (or the boiling point) corresponding to given pressure of steam generation. In the figure given below, 'hf' indicates enthalpy of liquid in kJ/kg. It is different for different pressures.
Laten Heat of Vaporization of Steam (hfg): Or, Latent Heat of Evaporation
It is quantity of heat which is required to transform unit mass of water at saturation temperature to unit mass of steam at same temperature. It is different at different for pressures.
Saturated Steam
It is steam which cannot be compressed at constant temperature without condensing it. In Figure given below condition of steam in the line AB is saturated excepting the point A which indicates water at boiling point temperature. This water which is obtained is called saturated water or saturated liquid.
The steam as it is being generated from water can exist in any of the three different states of it are as follows.
(1) Wet steam
(2) Dry (or dry saturated) steam
(3) Superheated steam.
Among these, the superheated state of steam is very useful as it contains maximum enthalpy for doing useful work. Dry steam is also extensively utilized, but wet steam is of least utility. Different states of steam and stages which are in order of their evolution are shown in the figure given below. Their equivalent volumes are shown therein.