mechprocess
Mechanical
- Jun 23, 2004
- 39
Re: Pump Intake Design ANSI/HI 9.8
Subject: Minimum Submergence requirement to prevent surface vortex
I have a vertical suction pipe with a bell on the end of it located in a dished tank containing suspended solids slurry. I want to eliminate the need for a vortex breaker at the suction location so that I don't have any obstructions in my tank which may adversely impact the off bottom suspension of the particulate solids during mixing.
The formula from the above referenced code defines the minimum submergence (S) to prevent surface vortexing is given by S/D = 1 + 2.3F where F is the Froude Number also given F = v/(gD)^0.5 where g = 32.2, D is the diameter of the suction bell and v is the free stream velocity around the suction bell and F is dimensionless.
I was hoping that if I made my suction bell diameter large enough, then I could reduce my minimum submergence. Then I notice that when solving for S, there was a point of diminishing returns going on. The minimum submergence actually started increasing in proportion to D. Maybe I have a spread sheet error but I can't find it.
Although the Froude number decreases with the free stream velocity which corresponds to the larger suction bell diameter, when multiplied by D, the submergence requirement increases in that S = D(1+2.3F). What gives?
Then I read in the code that this correlation is only applicable for free stream velocities greater than 2 fps.
Well la-ti-da.
Has anyone else used this formula for free stream velocities less than 2 fps? All I'm trying to do is prove that a vortex won't occur if we slow the pump down enough to get most of the heel out without adding some contraption down around the bottom of the tank.
Thanks
Subject: Minimum Submergence requirement to prevent surface vortex
I have a vertical suction pipe with a bell on the end of it located in a dished tank containing suspended solids slurry. I want to eliminate the need for a vortex breaker at the suction location so that I don't have any obstructions in my tank which may adversely impact the off bottom suspension of the particulate solids during mixing.
The formula from the above referenced code defines the minimum submergence (S) to prevent surface vortexing is given by S/D = 1 + 2.3F where F is the Froude Number also given F = v/(gD)^0.5 where g = 32.2, D is the diameter of the suction bell and v is the free stream velocity around the suction bell and F is dimensionless.
I was hoping that if I made my suction bell diameter large enough, then I could reduce my minimum submergence. Then I notice that when solving for S, there was a point of diminishing returns going on. The minimum submergence actually started increasing in proportion to D. Maybe I have a spread sheet error but I can't find it.
Although the Froude number decreases with the free stream velocity which corresponds to the larger suction bell diameter, when multiplied by D, the submergence requirement increases in that S = D(1+2.3F). What gives?
Then I read in the code that this correlation is only applicable for free stream velocities greater than 2 fps.
Well la-ti-da.
Has anyone else used this formula for free stream velocities less than 2 fps? All I'm trying to do is prove that a vortex won't occur if we slow the pump down enough to get most of the heel out without adding some contraption down around the bottom of the tank.
Thanks
