Psychrometric Charts Reference Page
Dry Bulbs, Wet Bulbs, and My Will to Live: Mastering the Psych Chart

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Intro to Dry Bulbs, Wet Bulbs, and My Will to Live: Mastering the Psych Chart

Psychrometric charts are graphical tools used to analyze mixtures of air and water vapor. They allow engineers to determine properties such as humidity, enthalpy, and specific volume without repeatedly solving equations.

These charts are widely used in HVAC design, drying operations, and many other processes involving humid air. By knowing two independent properties—such as dry-bulb temperature and relative humidity—you can determine many other properties of the air–water vapor mixture directly from the chart.

Dry Bulbs, Wet Bulbs, and My Will to Live: Mastering the Psych Chart

This video explains how psychrometric charts are organized and demonstrates how to use them to determine properties of humid air, including humidity ratio, enthalpy, and dew point.

Visuals

Examples and Definitions

Definitions

Dry Bulb Temperature
The temperature of an air–water vapor mixture measured with an ordinary thermometer.
Wet Bulb Temperature
The temperature measured by a thermometer covered with a moist porous material and exposed to airflow.
Dew Point
The temperature at which moisture begins to condense from an air–water vapor mixture.
Relative Humidity
The partial pressure of water vapor in an air–water vapor mixture divided by the saturation pressure at the same temperature.
Absolute Humidity or Humidity Ratio
The mass of water vapor per mass of dry air in an air–water vapor mixture.
Specific Enthalpy
The enthalpy per unit mass. In psychrometry it is commonly reported as the enthalpy of moist air per kilogram of dry air.
Specific Volume
The volume per unit mass. In psychrometry it is commonly reported as the volume of moist air per kilogram of dry air.
Sling Psychrometer
A device containing both a dry-bulb thermometer and a wet-bulb thermometer that is spun through the air to measure the dry-bulb and wet-bulb temperatures.