(1) Psychrometric Calculations. Standard psychrometric charts are
commonly used in calculating the effects of heating and cooling moist air at
atmospheric pressure. Such charts relate enthalpy changes to wet- and dry-
bulb temperatures, relative humidity, dew point, and specific humidity, and
permit graphical solutions of usual problems. These standard charts are set
up for a single gas mixture (air) and for a single pressure (14.7 psia), and
are not suitable for use with a range of gas compositions and pressures.
Figures 6-21 through 6-23 show three psychrometric charts developed for use
at elevated pressures from 14.7 psia to 200 psia. Figure 6-22 covers the
pressure range from 100 psia to 600 psia. Figure 6-23 provides temperature
corrections for moisture enthalpy, to be applied to enthalpy data from
Figures 6-21 and 6-22. Figures 6-21 and 6-22 are similar except for the
vertical scale.
The mole has been used as the unit of gas quantity. A mole, as used in this
discussion, is a quantity having a weight, in pounds, equal to the molecular
weight of the dry gas. The volume of a mole of gas is the same for any gas
of any molecular weight, at any specified temperature-pressure. Accordingly,
the molar volume and the partial pressure of water vapor provide a means of
determining the quantity of water per mole of gas, on which all other
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