Gauge Pressure and Total Heat of the Steam
 
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Observe the relationship between gauge pressure and the total heat of the steam.Add the figures for the heat of the saturated liquid and the latent heat together, and the sum is the total heat of the steam. The total heat of the steam increases with the system pressure up to approximately 435 psig. Thereafter, the total heat decreases with increasing pressure. As the steam system approaches the critical pressure, little expansion can take place. The amount of latent heat added to vaporize the water begins to decrease rapidly relative to the increase in sensible heat needed to bring the water to boiling temperature. This results in a decrease in the amount of total heat in the system as the pressure approaches critical for water. The amount of heat available from any medium in its current state is referred to as enthalpy. From steam, the enthalpy of the vapor is the same as the total heat of the steam. This is the sum of the enthalpy of the liquid (heat of the saturated liquid) and the enthalpy of vaporization (latent heat).  |
