Minimum Level for Vortex

[mjpetrag]

I was looking to find an equation for minimum tank level for a vortex to occur in outlet piping and found this...

http://www.pumpfundamentals.com/help11.html

My application is a bottom drained tank (3" discharge nozzle) connected to a pump flowing between 20-60 GPM. Unfortunately, the equation on the site is only valid for 2-8 ft/s and I'll be in 1-2.5 ft/s range.

Can I still use this equation? Is there any other equation to determine this minimum vortex height for lower flow applications?



-Mike

 

[ione]

The minimum submergence required to prevent vortexing is an increasing function of flow rate and velocity (check also this

http://wycopump.com/pdfs/pumpclinic33.pdf

at page 5). So if you adopt as minimum tank level the one foreseen for a higher flow and higher velocity, it would ever be a conservative approach.

 

[rmw]

What I can't find anywhere is a discussion of what effect viscosity has on vortex formation. I have beau coup references that give minimum submergence formulae for water as do the above, but the vortex is a moving living organism (see tongue in cheek) and its angular acceleration and velocity HAS to be affected by the viscosity and/or even the density of the fluid since both of those have known effects on flow of fluids (or the friction thereof).

I can't imagine that a pit containing water at a level above a pump or offtake (right at minimum submergence) that is at the brink of forming a vortex would be at that same point of vortex generation at that same level if the fluid were suddenly changed to something like 40W lube oil. Or worse, #6 fuel oil. It might be better, it might be worse, but I can't see it being the same.

If I am wrong, someone please educate me fast and give some good references. Thus far my searches haven't produced them. I need more than my gut here.

This isn't homework.

rmw

 

[PumpSmart]

mjpetrag,
THE VORTEX SUBMERGENCE IS ONE DIMMENSION OF OTHER IMPORTANT DIMMENSION CRITERIA/DIMMENSION AND CONSIDERATION.
MORE COMPLETE DATA YOU FILN IN:
ANSI/HI 9.8
American National Standard for Centrifugal and Vertical Pump Intake Design

 

[ione]

rmw,

A couple of links which could be of interest

http://www.scientiairanica.com/PDF/Articles/00001249/borghei.pdf

http://www.josephsmiller.com/Papers/evaluation_of_vortex_formation0001.pdf