Harness Hydro Power With A Trompe

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One remarkable feature of trompes (the Ragged Chutes plant included) is that the air that comes out of the system is actually cooler and drier than the air that goes in . The air comes out cooler because the cold water flowing through the trompe absorbs the heat that's usually generated by the compression of air. It comes out drier because the atmospheric moisture held in the air bubbles that flow through the system condenses—so to speak—on the bubbles' walls (since those walls are, after all, colder than the air they're surrounding). The result: Compressed air that's [1] the same temperature as the cool water it just left and [2] drier than it was when it entered the trompe. Free air conditioning!

The Ragged Chutes plant employs a battery of 72 14-inch-diameter pipes to mix the air and water as they fall into the inflow shaft, but the builder of a small-scale trompe should be able to achieve the same result with only one or two such tubes. Here are a couple of things to remember if you decide to jury-rig your own hydraulic air compressor:

[1] If you want to be able to switch the air off but leave water running through the device, build a "blowoff" pipe (see diagram), the lower end of which is located slightly below the normal water level in the reservoir. This way, when you block the airflow through the discharge line, the air pressure in the reservoir will increase to the point where the water level drops and surplus air can escape through the blowoff pipe. (At Ragged Chutes, the blowoff sends a mixture of water and air 100 feet into the sky.)

[2] When you first start up your trompe, don't let any air escape through the discharge line until the pressure has had a chance to build. Otherwise you'll end up with a plenum full of water and no compressed air.

The trompe: a mighty old idea . . . and a mighty good one, too.

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