Liquid Height above outlet nozzle
Liquid Height above outlet nozzle
(OP)
I have a system pumping water at 350gpm into an open atmospheric tank. From this tank, the water then flows into a 2nd atmospheric tank and finally into a third. How can I calculate what the height of the liquid is above the outlet nozzle of the final tank?





RE: Liquid Height above outlet nozzle
If the outlet pipe isn't submerged enough, you can get flow limited by vortex or weir effects.
If that last pipe doesn't just dump out somewhere, but goes into a distribution system, you'd either need to assume a pressure at some point or have some means of analyzing the whole system.
RE: Liquid Height above outlet nozzle
RE: Liquid Height above outlet nozzle
RE: Liquid Height above outlet nozzle
This web page should help you figure it all out.
http://www.efunda.com/formulae/fluids/draining_tan...
RE: Liquid Height above outlet nozzle
The equations given are:
Q = C*Aspout*Vjet
Solving for Vjet
Vjet = Q/C*Aspout
Vjet2 = 2g*z
Using:
Q = 350 gpm (0.779 ft3/sec)
Aspout = 0.2007 ft2 (flow area of 6" SCH40 pipe)
Vjet = 3.96 ft/sec
(3.96 ft/sec)2 = 64.4*z
z = 3.96 ft/sec)2/64.4
z = 0.24ft = 2.88in above centerline
Does this seem correct? Also, you mention to do this same calculation for the second tank and the first tank. If those tanks also have 6" connections wouldn't the height above the nozzle be the same (2.88in)?
Thanks.
RE: Liquid Height above outlet nozzle
You would do well to post your attachment/sketches as PDF’s, we can see them and print them much easier in that format. The same applies to your flat plate problem (Struct. forum, thread507-379753: Roark Flat Plate Question), which is far from a flat plate in your latest iteration. You hadn’t addressed the flat plate problem correctly either, before it so radically changed. Maybe you should be asking these questions of your boss, so he knows what you know and what you don’t know, and he can help guide you and keep you out of trouble. That would be good for you and the company. E-Tips is a wonderful place to come for help and discussion on engineering problems, but it shouldn’t be a substitute for material you should have covered in your earlier engineering course work. Dig out you text books and class notes, and do a little self study.
RE: Liquid Height above outlet nozzle
You can use the orifice equation.
Use 0.6 as the Cd coefficient. g = Gravitational constant (9.8 m/s).
There is an online calculator here:
http://www.ajdesigner.com/phporifice/orifice_equat...
The orifice equation will only work for full pipe flow through the orifice. Weird things happen if you have air/water or a vortex situation.
A 6-Inch nozzle should have approximately 6-Inches of headloss
RE: Liquid Height above outlet nozzle
RE: Liquid Height above outlet nozzle
The outlet nozzle does not have to be at the top of the tank. You can pump off the bottom.
If you are using the nozzle to control the level in the tank, then think about putting some type of weir or overflow box. A nozzle on the side of the tank will not do a good job of keeping a constant level in the tank.
There needs to be some thought to prevent air from entering the outlet nozzle. A nozzle at the water surface is not a good idea as it will allow air to enter the discharge pipe.
A nozzle near the surface may also cause a vortex and pull air into the outlet.
RE: Liquid Height above outlet nozzle
you don't say or have included in any of the calcs the friction losses in the interconnecting pipes, valves etc or the friction losses from nozzle A to the centrifugal pump you mention in a post above. In that instance it is highly likely that the pressure at the end of the pipe will fall below atmospheric pressure unless you very carefully match your pump flow to the pipe and hence getting 350 gpm will be quite difficult.
you essentially have two halves to your sytem here from what I can see - the inlet half comprising the incoming flow which appears to be above the water line- OK - and the first 2 1/2 tanks and then the final chamber in the interceptor which is connected to your pump (not shown). The critical item in the last half is the pump and its discharge system and the friction losses in the pipe feeding the pump which will determine what head you need in the final chamber. Then its a matter of whether there is any flow control on your discharge to get it equal to the inlet flow?
Not quite as simple as it looks?
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Liquid Height above outlet nozzle
The chances of getting all these calculations accurate enough to confidently predict the level in the final compartment of the tank are very slim. I would not try to convince anybody that I could do such a calculation. And if the flow rate varies even slightly you could rapidly move from an overflowing tank to sucking air into the pump.
The usual way to handle a flow problem of this nature is to control the level in the final compartment by modulating the valve on the discharge side of the pump. You know 350 gpm is coming in to the tank and the valve will ensure that 350 gpm leaves the tank by enforcing a "conservation of volume" strategy.
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Liquid Height above outlet nozzle