Introduction to Food Engineering

Home Syllabus

Properties of Air and Water Vapor Mixture

Learning Outcomes

At the end of this module, you will be able to:

  1. describe what are psychrometric properties
  2. know the different units used for Universal Gas Constant
  3. use ideal gas law to determine properties of air and water vapor mixtures

In this module, we will consider the properties of air and water vapor mixtures. Knowledge of these properties is necessary when designing food dehydration systems as well as optimal storage conditions to prevent the exchange of moisture between food and its surrounding atmosphere. In the first introductory video, you will develop an understanding of the need for psychrometric properties and recall the components of ideal gas law that form a basis of mathematical relationships to determine these properties.

In the next video, you will learn various units to represent the Universal Gas Constant expressed in the ideal gas law. You will also learn Dalton’s law regarding total pressure and partial pressure of the constituents of air and water vapor mixture. Understanding these concepts helps describe psychrometric properties.

In the next video, we will examine ten psychrometric properties as they relate to designing food dehydration and storage systems. The values of these properties are obtained either by using equations that are based on ideal gas laws or graphically using a Psychrometric Chart (to be discussed in the next module).


In this video, you learned how to use the ideal gas law to determine the psychrometric properties of air and water vapor mixtures. Next, you learned the units of the Universal Gas Constant and the use of Dalton’s law regarding pressure. You gained an understanding of ten psychrometric properties and how you may obtain them using mathematical expressions.