Topic outline

  • Calculation of Gas Density and Viscosity

    Credits: 2 PDH

    PDH Course Description:

    The density and/or viscosity of a gas is often needed for some other calculation, such as pipe flow or heat exchanger calculations. This course contains discussion of, and example calculation of, the density and viscosity of a specified gas at a given temperature and pressure.

    If the gas temperature is high relative to its critical temperature and the gas pressure is low relative to its critical pressure, then it can be treated as an ideal gas and its density can be calculated at a specified temperature and pressure using the ideal gas law.

    If the density of a gas is needed at a temperature and pressure at which it cannot be treated as an ideal gas law, however, then the compressibility factor of the gas must be calculated and used in calculating its density. In this course, the Redlich Kwong equation will be used for calculation of the compressibility factor of a gas.

    The Sutherland formula can be used to calculate the viscosity of a gas at a specified temperature and pressure if the Sutherland constants are available for the gas. It will be discussed and used in example calculations.

    Another method for calculating the viscosity of air at a specified temperature and pressure will also be presented and discussed. Some of the equations that will be discussed and illustrated through examples are shown below.

    Topics:

    At the conclusion of this course, the student will:
    • Be able to calculate the density of a gas of known molecular weight at a specified temperature and pressure at which the gas can be treated as an ideal gas.
    • Be able to calculate the compressibility factor for a gas at a specified temperature and pressure, using the Redlich-Kwong equation, if the molecular weight, critical temperature and critical pressure of the gas are known.
    • Be able to calculate the density of a gas at a specified temperature and pressure for which the gas cannot be treated as an ideal gas, if the molecular weight, critical temperature and critical pressure of the gas are known.
    • Be able to calculate the viscosity of a gas at a specified temperature if the Sutherland constant for the gas is known and the viscosity of the gas at a suitable reference temperature is known.
    • Be able to calculate the viscosity of air at specified air temperature and pressure.
    • Be able to make all of the calculations described in these learning objectives using either U.S. or S.I. units.

    To take this course:

    1.) Enroll in Course: Click below to enroll:
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    2.) Study: Once enrolled, click below to begin the course:

    Download the Study Guide

    3.) Test: Once you've thoroughly read the course materials, please click below to take the final examination.

    Take the final exam

    4.) Certificate: A passing grade of 70% or higher on the exam, is required to receive the certificate of completion for this PDH course.
         NOTE: After the exam is completed, you will need to return to this page, in order to print (download) the certificate of completion.

    Print the Certificate of Completion

    Intended Audience: This course is intended for chemical, mechanical and environmental engineers. After completing this course, you will have knowledge about methods for calculating the density and viscosity of a gas at specified temperature and pressure.
    Publication Source: Harlan H. Bengtson, PhD, PE

    Harlan Bengtson PhD, PE