Print this page The Reynolds Number - Units in a Dimensionless Number
Course Outline
The dimensionless ratio of the inertial forces to the viscous forces in a fluid flow is known as the Reynolds Number (Re). This seemingly simple ratio is seen in the literature written in a variety of forms; one version may use absolute viscosity in the equation, another kinematic viscosity. Still another version may use flow rate (GPM) and kinematic viscosity while another version uses fluid velocity and kinematic viscosity - both have constants in the equation, but the derivation of the constants is not apparent.
While knowledge of how these formulas were derived is not required to use them successfully, a thorough understanding will aid in the prevention of errors attributed to conversion of units associated with the variables.
An EXCEL spreadsheet is provided as part of the course to calculate a series of test cases using different formulas for Reynolds Number and different units of viscosity. The format of the EXCEL spreadsheet is useful because it allows the user to compare results in a tabulated form. Also, using the “What-If Analysis” feature of “Goal Seek” in EXCEL allows further manipulation of the data for comparative purposes.This course includes
a multiple choice quiz at the end,
Learning Objective
With the completion of this course, the student will learn:
- the origin of the Reynolds Number from the study of Dimensional analysis;
- about a selected assortment of the different formulas used to calculate Reynolds Number;
- details regarding the derivation of the constants associated with some of the different formulas;
- common units used for viscosity;
- not so common units for viscosity;
- the origin of the constant gc;
- how to solve for pressure losses (including minor losses) in a simple piping system using an EXCEL spreadsheet;
- details of the formulas used to calculate pressure loss;
- how to solve for the friction factor using the Colebrook equation with iteration; and
- how to find a required flow rate, or other variable for a given Reynolds Number.
Intended Audience
This course is intended for the curious engineer interested in the origin and relationship of the various forms of the formula for Reynolds number. It is also useful for the cautious engineer who strives to eliminate mistakes related to units associated with variables.
Benefit to Attendees
Working with variables and formulas that can utilize a variety of units can be challenging. This course examines some of the different forms of the Reynolds Number, variables associated with them, and uses these formulas in practical examples to solve for pressure losses in a simple piping system. The intent is to bring some clarity to this common dimensionless ratio.
Course Introduction
The course “The Reynolds Number - Units in a Dimensionless Number” provides basic information on the derivation of various forms of the Reynolds Number and focuses on units associated with the variables, especially viscosity. This is followed by coverage of equations of flow, minor losses and a discussion of “g sub c”. Finally, a simple fluid flow problem is solved in EXCEL using some of the formulas covered in the course.
Course Content
In this lesson, you are required to download and study the following course content in PDF format:
The Reynolds Number - Units in a Dimensionless Number
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Course Summary
The Reynolds number is written in the literature in a multitude of different forms, using a variety of variables. If the task is a relatively simple one, such as finding the pressure drop in a basic piping system, the vast assortment of different formulas and their associated variables utilizing different units can make this task somewhat challenging. This course will eliminate some of the confusion by highlighting some of the different forms of this dimensionless number, the variables associated with it, and finally, solve some simple fluid flow problems in an EXCEL spreadsheet.
Related Links and References
Crane Flow of Fluids, Technical Paper No. 410, 1981
Mechanical Engineering Reference Manual, 9th Edition; Lindeburg
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
