Trompe Efficiency

http://www.instructables.com/id/Pulser-pump-Model.-A-substitute-for-lots-of-fossel/

and

http://www.viswiki.com/en/Trompe

a bit of light reading

http://espace.library.uq.edu.au/eserv/UQ:9433/coe02_1.pdf

look at this design its basicly the same concept except it has moving parts

http://outlands.tripod.com/farm/rampump.htm

and finally an animated version

http://www.appropedia.org/Pulser_pump#Principle_of_Operation

It is easy to calculate the energy component used to compress the air.(this is only a couple of percent in my case) I have been looking at my pulser pump figures from the late 1980's and I do not remember how I calculated the efficiency of the tromp section! It was a really low head trompe (half meter head) so the compressed air production figures were only about 30%. Someone in England did research that suggested 60% efficiency for trompes or better if head was around 2 meters.

I think what I did was substitution. I was pumping air down to replace water at 3 meters deep so that is more or less the same as pumping the replaced water 3 meters higher. And it is easy to calculate the potential energy of that water, . mass by acceleration due to gravity by height. (I think you substract the mass of the air that is under pressure). It has been decades so I forget how I did it. People are convinced that you need a venturi in a trompe but acceleration as the water falls in the pipe is all you need to entrain air. If YOU were fluid and accelerated headfirst from a horisontal inletpipe to a vertical downpipe, you would stretch as your head accelarates faster than your feet. The stretching would leave room for air. Water does not expand to fill the space!

The effects on the flow of water from the work done by compressing the air are subtle. There is less turbulence in the exit water. (So it will not pick up silt and clay and sand as readily as water exiting from a normal waterfall). That is the main difference. The turbulence is gone. Turbulence is not a very visible thing so it does look much the same.