Basics of Steam Generation

The boiling of water results in the continuous absorption of heat energy until a point is reached, for any particular pressure, at which the liquid (water) changes into a gas (steam). This boiling point or (heat) saturation temperature occurs when the water vapor pressure is equal to the local pressure. 

The boiling point of water is 100 °C (212 °F) at atmospheric pressure, and at this same point the enthalpy of evaporation (latent heat of vaporization) is 970 Btu/lb. 

NOTE The boiling point of water decreases with increase in height above 

In other words, at its boiling point water requires the further addition of 970 Btu of energy to convert one pound of water to steam, which is 5.39 times as much energy as required to raise the water temperature from 0 °C (32 °F) to 100 °C. The temperature of the hot water remains constant until it has been entirely vaporized, at which point the steam is fully saturated with heat and the enthalpy of the steam (heat content as calculated from a starting point ofO °C) is 1,150 Btu/lb. 

If additional heat is applied within the confines of a pressure vessel, the pressure of the steam increases and the boiling point is raised, requiring yet more heat energy to reach the new saturation point. 

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