Calculate the total available energy from a water stream by use of a turbine?
Calculate the total available energy from a water stream by use of a turbine?
(OP)
Had this posted in different forum, think this is more appropriate.
I keep confusing myself on this question, basically i want to know how you would determine the amount of potential energy you could capture by using a turbine, if water is flowing down a pipe into a river.
The change in elevation from the start to end of pipe is 30 meters.
The pipe is 100 meters long.
Water is flowing at a rate of 10 liters per second.
Not assuming the efficiency of the water turbine itself, is the formula just the potential energy minus the friction in the pipe? Thus:
Power = (Mass Flowrate X Gravitational constant X Change in Elevation) - Friction losses
= ((10 L/s X 0.001 m3/L X 1000 kg/m3) X (9.81 m/s2) X (30 m)) - Friction
= (2943 W/s or 2.94 kW/s) - Friction
Also second question, I know how to calculate the friction in a pipe, but the problem i cannot get my head around is that because the pipe is nearly a meter in diameter, the pipe is not full of water, thus i dont know how to calculate Reynolds number etc? Any help here would also be appreciated,
Would all the potential energy from the water elevated 30m be dissipated as it travels down the pipe because the pipe is not full? If this is the case, how does that make sense? Surely flowing down a larger diameter if pipe would reduce friction?
Thanks Guys
I keep confusing myself on this question, basically i want to know how you would determine the amount of potential energy you could capture by using a turbine, if water is flowing down a pipe into a river.
The change in elevation from the start to end of pipe is 30 meters.
The pipe is 100 meters long.
Water is flowing at a rate of 10 liters per second.
Not assuming the efficiency of the water turbine itself, is the formula just the potential energy minus the friction in the pipe? Thus:
Power = (Mass Flowrate X Gravitational constant X Change in Elevation) - Friction losses
= ((10 L/s X 0.001 m3/L X 1000 kg/m3) X (9.81 m/s2) X (30 m)) - Friction
= (2943 W/s or 2.94 kW/s) - Friction
Also second question, I know how to calculate the friction in a pipe, but the problem i cannot get my head around is that because the pipe is nearly a meter in diameter, the pipe is not full of water, thus i dont know how to calculate Reynolds number etc? Any help here would also be appreciated,
Would all the potential energy from the water elevated 30m be dissipated as it travels down the pipe because the pipe is not full? If this is the case, how does that make sense? Surely flowing down a larger diameter if pipe would reduce friction?
Thanks Guys





RE: Calculate the total available energy from a water stream by use of a turbine?
Friction loss will inclue
1) friction in canal,
2) entrance loss to penstock,
3) loss in penstock,
4) loss in scroll case,
5) loss in turbine,
6) loss in draft tube.
RE: Calculate the total available energy from a water stream by use of a turbine?
RE: Calculate the total available energy from a water stream by use of a turbine?
The only issue is that the diameter of the drainage pipe is very large, thus the pipe is not fully contained with water, only partially.
RE: Calculate the total available energy from a water stream by use of a turbine?
RE: Calculate the total available energy from a water stream by use of a turbine?
RE: Calculate the total available energy from a water stream by use of a turbine?
As the drainage is constant at 10 L/s, how would i then ensure that once the pipe is backed up and full of water, that it does not overflor/backflow? If you get what i mean? Without having to install a water tank? Could you ensure that 10 L/s of water travels through the turbine? so that the pipe remains full but does not backlog?
Thanks again
RE: Calculate the total available energy from a water stream by use of a turbine?
RE: Calculate the total available energy from a water stream by use of a turbine?
A fairly simple level sensing arrangement at the upper elevation to keep the penstock full could be used to control a waste valve installed near the bottom of the penstock to bleed off excess water flow when the amount available is greater than what the pump/turbine can pass. This by-pass arrangement should be configured to be capable of wasting the full flow if the pump/turbine should be tripped for any reason, and the penstock could still be kept full for easy return to normal operation. Since the penstock seems to be relatively much greater in diameter than would be normal for a penstock for the expected flow, friction losses in the penstock can probably be ignored for estimating purposes, and the extra flow through the waste valve would probably have a trivial effect on generator output. This waste valve could be a simple, moderately slow opening, slow closing valve that would serve to keep the upper water level within some reasonable range between a "high" limit and a "low" limit.
With this arrangement, a nearly constant amount of power would be generated. For safety and simplicity, it will almost certainly be best to plan to use an induction generator. The use of multiple standard pipe reducer fittings in series would probably be adequate to provide suitably gentle acceleration of the flow into the pump "discharge" combined with similar use of pipe reducer fittings to gently decelerate the flow from the pump "inlet" would be significant in helping to maximize recovery of the available potential energy from the flow.
Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.
RE: Calculate the total available energy from a water stream by use of a turbine?
Also, i just said 10 L/s as a guess, i think it is much larger than that,
Thanks for help
RE: Calculate the total available energy from a water stream by use of a turbine?
Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.
RE: Calculate the total available energy from a water stream by use of a turbine?
RE: Calculate the total available energy from a water stream by use of a turbine?
Back to your issue. My thoughts are that you need to figure out what your average or most common flowrate if it is variable, then do some calcs in excel for various friction losses, say 1,2,3,4,5,6....m in total, work out what size of PE pipe would accommodate these friction losses– search head loss PE pipe on the internet - then see if that pipe would fit inside your existing pipe. Then channel all the water into the end of your new pipe and any excess can then run down the old pipe. PE pipe is cheap, quite smooth and easy to install. Then you can go looking for a turbine with a good idea of flow and head available. 50% overall efficiency is a good number to start with.
If when you try it out the turbine takes too much water, you may need to increase the turbine resistance. Start with a small one and add more if the water in your pipe doesn't start to fall.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Calculate the total available energy from a water stream by use of a turbine?
RE: Calculate the total available energy from a water stream by use of a turbine?
Best to you,
Goober Dave
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