Water-Air VLE and Psychrometric Chart: Screencasts

Explains how to read on a psychrometric chart: dry bulb temperature, relative humidity, moisture content, dew point temperature, enthalpy, humid air volume, and wet bulb temperature.

We suggest you list the important points in this screencast as a way to increase retention.

Overview of relative and absolute humidity and how to calculate the amount of water in the vapor phase.

We suggest you list the important points in this screencast as a way to increase retention.

Optional screencast: Reading a Psychrometric Chart (Simulation)

Important Equations:

If liquid water is present and a non-condensable component such as air is present: \[y_{H_2O}P = P_{H_2O}^{sat}\] where \(y_{H_2O}\) is the mole fraction of water in the gas phase, \(P\) is the total pressure, and \(P_{H_2O}^{sat}\) is the saturation pressure of water. This equation assumes the amount of air solved water is small enough that the mole fraction of water in the liquid phase is essentially one. 

Antoine Equation: \[log_{10}P_i^{sat} = A_i \,- \frac{B_i}{C_i + T}\] where \(P_i^{sat}\) is the vapor pressure, \(T\) is the temperature (usually given in \(^oC\)), and \(A_i, B_i,\) and \(C_i\) are constants for a given component \(i\).

The relative humidity (RH) is defined as: \[RH = \frac{P_{H_2O}}{P_{H_2O}^{sat}}\] where \(P_{H_2O}\) is the partial pressure of water vapor and \(P_{H_2O}^{sat}\) is the saturation pressure of water vapor at the same temperature.

The absolute humidity is defined as: \[absolute\,\, humidity = \frac{mass \,of\, vapor}{mass\, of\, dry\, gas} = \frac{P_{H_2O}MW_{H_2O}}{(P-P_{H_2O})MW_{dry\, air}}\] where \(P_{H_2O}\) is the partial pressure of water, \(P\) is the total pressure and \(MW\) are molecular weights.