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Minimum Level for Vortex

Minimum Level for Vortex

Minimum Level for Vortex

(OP)
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

RE: Minimum Level for Vortex

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.

RE: Minimum Level for Vortex

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

RE: Minimum Level for Vortex

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
 

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