1 reply to this topic

[Steve Hall]

A vortex forms when pumping a tank down. When will the vortex reach the tank outlet nozzle and begin affecting the flow rate?

 

The predictive methods I've found use velocity through the outlet and liquid height in the tank to calculate the depth of the vortex. For example, see http://www.pumpfunda...com/help11.html

 

My colleagues insist that if the tank is pressurized the vortex will be reduced. They ran a test and claim to have confirmed this hypothesis. 

 

My question: does anyone have a theoretical explanation that supports or disputes the hypothesis that pressurizing a tank (with compressed air) will reduce the depth of the vortex during pumping?

 

The tank in question has a standard F&D head, the bottom outlet is centered, and there are no baffles in the tank. The specific tank has a diameter of 82 inches (2080 mm) with a 3" outlet (75 DN). The desired pumping rate is 80 gpm (18 m3/h), and the goal is to keep the tank as empty as possible during pumping - this is a tank cleaning operation where water (forgot to mention, it's 80C hot!) is spraying into the tank and it must be removed at the same rate as it is supplied. The pump is a centrifugal type, located at least 10 ft (3 m) downstream of the tank outlet nozzle, with 3 or 4 elbows in the pipe on the suction side of the pump.

Edited by Steve Hall, 07 March 2014 - 07:17 AM.

[PingPong]

Normally there is a vortex breaker installed on all liquid outlet nozzles leading to a pumps.

A pity that that seems not to be the case in your vessel.

 

 

 

My question: does anyone have a theoretical explanation that supports or disputes the hypothesis that pressurizing a tank (with compressed air) will reduce the depth of the vortex during pumping?

I have never read that pressurizing would reduce vortex, I don't believe it either as I don't see what physical phenomena would explain such effect.

 

Most vessels in process plants are pressurized (by the process gas), usually at higher pressures than that of plant air, so that would mean that in these cases, without a vortex breaker, there is little or no chance on vortex in liquid outlet nozzle? I don't think so.

 

[quote]My colleagues insist that if the tank is pressurized the vortex will be reduced. They ran a test and claim to have confirmed this hypothesis.

How did they determine that the vortex was reduced?

Edited by PingPong, 07 March 2014 - 01:07 PM.