Siphon flow over a dam
Siphon flow over a dam
(OP)
We are trying to remove hypolimnetic water from a reservoir and discharge the water downstream using a siphon. The problem is the deep spot in the reservoir is 800 feet away. The maximum head downstream is ~20 feet. We were planning on using 4" HDPE pipe but from my calculations, first using Bernoulli's (frictionless flow) to get the flow rate for various values of Head and pipe diameters. I Then used the Hazen-Williams formulas for flow rate and enter various length of pipe to find the friction loss. The friction loss is just too high with that length/dia. of pipe. I can get it to work if I use an 8" pipe, but it can only be 50 feet long. Am I correct? The friction loss head has to be less than the actual head below the dam in order for the siphon to work?





RE: Siphon flow over a dam
RE: Siphon flow over a dam
RE: Siphon flow over a dam
RE: Siphon flow over a dam
Steve
RE: Siphon flow over a dam
RE: Siphon flow over a dam
Yes, with the added phrase "at the specified flow rate".
In your spreadsheet, at the friction loss calculation, you would simply start reducing the assumed flow rate to find the discharge flow that would satisfy: friction losses < available head. Not clear if the equation you are using accounts for inlet loss at the suction.
RE: Siphon flow over a dam
RE: Siphon flow over a dam
RE: Siphon flow over a dam
RE: Siphon flow over a dam
Keith Cress
kcress - http://www.flaminsystems.com
RE: Siphon flow over a dam
RE: Siphon flow over a dam
RE: Siphon flow over a dam
RE: Siphon flow over a dam
Mike Halloran
Pembroke Pines, FL, USA
RE: Siphon flow over a dam
Instead, you can, e.g., plug the pipe length into the Hazen-Williams equation, and an arbitrary flow, then goal seek, varying the flow to make the friction loss equal the available head. (Modern spreadsheets do Newton's Method pretty well).
Doing that for 800 feet of 4" id pipe and a head loss of 20 ft gives a flow of 0.5 cfs (cell C37).
Knowing that and the area of the reservoir would tell you how patient you have to be while it's draining down.
Expanding the inlet end, e.g. a bellmouth, is probably a good idea to minimize induced circulation in the bottom.
Don't orient the inlet vertically, or it will capture fish. (They will sense and flee from a horizontal current).
Mike Halloran
Pembroke Pines, FL, USA