Calculating Flow Dynamics

[Tripspike]

Trying to determine flow rate from one tank to another via a 3" SCH 80 PVC pipe. The tanks are exact same size and the 3" pipe is an equalization pipe between the two tanks. I would like to determine the flow from one tank to the other with a 1" solution differential.

Thanks

Mike

 

[LittleInch]

And your problem is?

There are many simple charts showing this. 1" differential is very low. Any length will result in very low flow

Why is this important?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Latexman]

Do. Or, do not. There is no try.

I recommend you refer to Crane Technical Paper No. 410. If you don't have it, buy it. It'll be the best $60 you ever spent. Crane TP410

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[Tripspike]

We have varying volumes of fluid coming into each tank from other sources. This pipe is used to equalize the two tanks. There is a point where the pipe will not be able to equalize the two tanks. We are trying to maintain the 1" differential and want to know how much flow there is between the tanks with 1" differential. In other words, if we pump too much too quickly into one tank to where the equalization pipe does not keep up it will overflow the tank.The equalization pipe is very short only about 18" long.

Perhaps you could point me to a chart. I would appreciate it.

Thanks,

Mike

 

[katmar]

With such a short pipe you can get a good estimate ignoring the friction in the pipe itself. All that is consuming your 1" of head is the resistance to getting the fluid into the pipe (i.e. the entrance loss) and accelerating the fluid to whatever velocity is achieved (i.e. the exit loss). These losses are expressed as Resistance Coefficients, commonly called K values. The Crane manual referred to above describes this in detail, or you can get a summary here.

The formula is h = KV²/(2g), or V=√(2hg/K)

h is the head, which you would have to express as 1/12 ft if the velocity is in ft/s
V is velocity in ft/s
g is acceleration of gravity = 32.2 ft/s²

If your pipe is welded flush to the tank wall then the entrance loss is K=0.5 and for the exit loss K=1.0, giving a total K of 1.5

This makes V = √(2 x 32.2 / (12 x 1.5)) = 1.89 ft/s
which is 38.8 USgpm in a 2.9" ID pipe. I would take off 15% for friction and safety and assume that the flow is 33 USgpm


Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[LittleInch]

Trip spike, you won't get a better answer than that provided by katmar. At that length you might also be able to estimate flow by using a restriction orifice calculation, there are many online versions available then subtract a but for the pipe run, but the pressure loses are dominated by other things than the pipe friction as katmar says.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Compositepro]

Or measure it and don't worry if you used the right equation. So many engineers love equations because they don't have to leave their desks and they get to use a computer. However, if you do not validate the calculation though some measurement it is basically worthless. Calculations are somewhat useful when designing something to build. Operations after construction will validate the calculations. Your system is apparently already built and operating.