## Gravity feed to bottom of a lake (very much a newbie)

Forum about flow calculators available on pipeflowcalculations.com and how to find solution for your fluid flow problem.
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Joined: Mon Feb 08, 2010 7:47 pm

### Re: Gravity feed to bottom of a lake (very much a newbie)

Flow rate through pipe is established based on the energy (mainly pressure) difference from start to the end of pipe. If you have bigger pressure difference flow rate will be higher. If you have same pressure difference flow will be higher when resistances are lower.
When you have the end of pipe under the zero water level, it is the same effect as if you have counter pressure on pipe exit. So for p2 in calculator you should enter pressure due to water depth which is p2=rho * g * h. On the other hand, as you have start of pipe above the zero water level you should use that elevation as inlet pressure, which is p1 = rho * g * (H + h).
h - the depth of pipe exit in the water
H - height of pipe entrance above the water.
So in the end you will have pressure difference of p1 - p2 = rho * g * H - that is the energy that you have for water to flow. That energy will be used to create water flow in pipe. Losses due to friction are depending on flow velocity, pipe roughness, pipe length, flow regime.
Of course if you have trapped air in pipeline, you will have possible loss of flow, at the end.
Pipe flow calculations - since 2000