×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Froude Number Equations

## Froude Number Equations

(OP)
Dear Colleagues,
I found in a literature the different form of the Froude No. equation: Fr= V^2/g*D, instead of the well-known form: Fr= V/SQRT(g*D).
At the same velocity the equations gave the different Froude numbers.
Which of the equations is more correct?

Thank you,
Mike

### RE: Froude Number Equations

The derivation of the Froude Number equation is dependent on geometry and the application. It can take several forms. Be careful you pick the right one.

Good Luck,
Latexman

### RE: Froude Number Equations

Where have you found the first equation - all other definitions I can find have the second equation.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Froude Number Equations

All that I know of are forms of the second one.
That isn't to say that one of them doesn't reduce to the first one, but I don't know of it.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

### RE: Froude Number Equations

(OP)
Thank you All.
I found the 1st equation in the "Beggs-Brill Two--phase flow in pipes" book. Please see the attached. In the equation Vm is 2-ph mixture velocity.
For which applications the 1st and 2nd forms are applicable?

Thanks, Mike

### RE: Froude Number Equations

You missed actually attaching the file - this forum software uses a separate upload and then attach function. No, I have no idea why.

(OP)

### RE: Froude Number Equations

All I can figure is that it may not matter; The Foude number = 1 is a transition point and squaring the term doesn't cause a value to move from one side to the other. Numbers less than one, squared, are still less than one. Similarly those greater than one, squared, remain greater than one.

Squaring is normally done to eliminate negative values; if somehow a negative velocity crept in, that would be taken care of.

I see the same construction in https://www.sciencedirect.com/topics/engineering/f... as used in a number of articles.

### RE: Froude Number Equations

That correlation is 50 years old (1972). That was way back, before hand-held scientific calculators, when it was a lot easier to square a number with pencil and paper, than to find the square root of a number using a slide rule. I am speculating that Brill and Beggs took the easy way out and used the square of the dimensionless Froude number for their works in that book, so they would not have to find (gd)1/2 time and time again. Again, that's me speculating.

If you are using the correlations, charts, graphs, etc. in their book, use their definition.

If you are not using the resources in their book, use v/(gd)1/2.

Or, it's an error in their book. Try to search for errata for the book, or contact the authors, if they are still alive.

My \$0.02.

Good Luck,
Latexman

### RE: Froude Number Equations

Having used a slide rule, squaring and square roots were just as easy. There was typically a cube root scale as well. 5th roots was where trouble would begin.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!