Using Stoke's Law for determination of terminal velocity. 2

[enguest]

Dear sirs,

Now I am working on the project where we are installing a line to transport a water which can contain significant quantity of sand. Main purpose is to size this line diameter small enough to have the actual fluid velocity less that terminal velocity to avoid the sedimentation of sand. Particle size is < 250 micron. Reynolds number in the piping is 90805 ....
I want to use a Stoke's Law for the determination of the terminal velocity, am I right?

Thanks in advance.

 

[SNORGY]

I think you mean "actual fluid velocity GREATER than terminal velocity" to avoid sedimentation.

Otherwise I think your approach is as correct as it needs to be. You might want to see GPSA Volume 1 Chapter 7 for some basic salient equations.

Regards,

SNORGY.

 

[ione]

Isn't Stokes law valid for laminar flow, isn't it?

 

[DubMac]

Keep it above 7-8 feet per second to avoid settling out.

 

[katmar]

No, Stokes Law is not what you want to use here. Try to get your hands on a copy of "Introduction to Practical Fluid Flow" by RP King. The lowest velocity that re-entrains particles that have settled to the bottom of the pipe is called the saltation velocity. Googling that might help you.

Katmar Software - Engineering & Risk Analysis Software

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[SNORGY]

Be careful not to confuse the Reynolds Number in the pipe with the Reynolds Number around the particle. Turbulent flow of the fluid with respect to the pipe does not necessarily equate to turbulent flow with respect to the entrained particle.

Katmar is correct; there are better theories and correlations with respect to re-entrainment and saltation. I have not looked at the reference katmar has listed, but another book is suggested by me here:

The Flow Of Complex Mixtures In Pipe - Govier, Aziz et al



Regards,

SNORGY.