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Discussion Starter #1
If you have a stream on your property, you may be able to use an ancient device know as the Trompe compressor to generate power or provide refrigeration silently, with no moving parts, and with no external energy required.

First used in the early iron age, these devices provided a steady blast of air to the Catalan forges used to produce iron. A large-scale one, built in 1910 on the Montreal River in Northern Ontario, provided all of the power, air circulation, and cooling for the extensive mining operations in the area. Amazingly, it's still in operation today.

A Trompe compressor drops water down a tube. Near the top of this tube, a restriction causes the water to speed up, reducing its pressure. At this point, air is sucked in through small tubes, which are angled upwards to prevent the water from leaking out.

The falling water captures the bubbles. The air is trying to rise, but the water is falling faster, so the bubbles are carried downward and compressed by the weight of the water in the column. When compressed, air usually gets hotter, but the water absorbs this heat, resulting in compressed air that is close to the temperature of the water.

The pipe travels straight down, then turns and moves horizontally into a pressure vessel where the compressed air is now free to rise and fill the chamber. The water continues out, and can be returned to almost the same level from which it started. It should be slightly warmer, but is otherwise unaffected. So now you have a tank of cool, dry, compressed air, yay!

Here's where it gets interesting... when you compress air it gets hot, but when you allow this air to expand, it gets cold. Cold enough to freeze water, cold enough to use for all your refrigeration needs.

If memory serves me, a fall of 32 feet produces 15 psi. That might not be enough to run most air powered tools or generators, but it's more than enough to provide cooling. Hard data on Trompes are hard to come by these days, but I am guessing a fall of 10 or even 5 feet would be enough if you had enough water falling to compress a fair volume of air.

As I said, solid design info is hard to find. The data I have comes from some old books in my eLibrary:

Air Compression and Transmission (1903)
Colliery Engineer (1910)
Compressed Air Information (1903)
 

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Discussion Starter #4
Montana: All of the info I have found online seems to be rehashes of the same general information, and is lacking in the technical details one would need to design a working system. Specifically, venturi design and drop/pressure/flow data. Still, just having what little info is available might be enough if someone wanted to experiment with the idea.

As far as efficiency: it's hard for me to imagine being more efficient than a device with no moving parts. Instead of efficiency, I would be more interested in long term reliability. Anything that turns will eventually fail.

You don't need 50 feet of drop to make these things worth while. I have heard of Trompe systems which use 5 feet of fall to produce usable pressures. Of course, this depends on your intended use. For driving power tools or a generator, a traditional turbine set up might be more realistic if you have a 50 foot elevation change and steady water source. For refrigeration, however, you shouldn't need much of a drop, making Trompe designs applicable to a much wider range of sites. Add that to the no-maintenance angle and it's something worth looking at, I think. :)
 
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