Gauge Pressure and Specific Volume of Saturated Steam



Observe the relationship between gauge pressure and the specific volume of the saturated steam.


The specific volume of steam decreases as the system pressure increases. At atmospheric pressure a pound of steam occupies about 1,600 times the volume of a pound of condensate. As pressure increases in the system, the specific volume of the steam decreases. Because of this principle, a greater quantity of steam is available in a smaller space (pipe, heat exchanger) at higher pressures. This is why steam is often distributed at higher pressure but is reduced to a lower pressure to perform specific heat-transfer functions.

Rising pressure constrains the molecules from moving apart when water vaporizes. At the critical pressure of 3206.2 psia, the specific volumes of liquid and gas are equal.