This simulation was prepared using Mathematica. Download the free Wolfram player, and then download the simulation CDF file (link given below or click on figure to download). Try to predict the behavior when a parameter changes before using a slider to change that parameter. For this simulation, a screencast is provided to explain how to use it.

This Demonstration shows how to read a psychrometric chart (also known as a humidity chart). Select the dry bulb temperature (x-axis) and the relative humidity (green curves). You can decide which lines are displayed: enthalpy (blue lines), specific volume (red lines), or temperatures (gray arrows). When the “temperatures” box is selected, mouse over each of the three arrows to see the dry-bulb, wet-bulb, and dew-point temperatures.

Try to answer these questions before determining the answer with the simulation. We suggest that you write down the reasons for your answers.

  1. If the dry bulb temperature increases (without changing the moisture content), how does the relative humidity change?
  2. If the dry bulb temperature increases at constant relative humidity, how does the enthalpy of the air (+water vapor) change?