I'm interested in channeling air into an underground condenser to generate water. Which of these approaches would be most appropriate, and is there a better approach I haven't considered?

A: A wind-powered turbine, which mechanically drives a fan. I would most likely use a HAWT, with a gear to change the spin direction from horizontal to vertical. HAWTs seem to be the most efficient tested wind power system, although there are pure-vertical alternatives, which would eliminate some moving parts. However, the efficiency claims I've read refer to electricity-generation, where shaft work is the desired output, rather than air flow.

B: A funnel-type intake that faces into the wind, or is omni-directional. It would channel air downwards into the system without moving parts, other than its wind-orientation. This seems like it would avoid efficiency losses in A caused by converting moving air to shaft work, then back to moving air. However, the wind may be largely diverted around the intake, since it would act as a blockage.

C: Use a static airfoil, or other surface to direct air into the system, without acting as a blockage.

  • $\begingroup$ It almost sounds like an electric wind-turbine and an electric fan are, for small to medium sized applications, at least, the best alternatives. From a physics point of view all forms of energy are identical, so it doesn't really matter that electricity is involved. $\endgroup$ – CuriousOne May 3 '15 at 5:37
  • $\begingroup$ Wouldn't converting to, and from electricity introduce efficiency losses? It would provide a benefit of having more control over the fan speed, and the ability to introduce a battery to store energy. $\endgroup$ – Turtles Are Cute May 3 '15 at 10:13
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    $\begingroup$ Converting to electricity does cause losses, probably in the 40%-50% range for a small system, but that can probably be made up for by being able to mount the turbine without limitations by a mechanical drive shaft and, as you said by being able to control the fan speed as well as store energy. Wind is intermittent, but electrical storage can reduce that significantly. In the end you have to make a judgement call what's important for the system performance. $\endgroup$ – CuriousOne May 3 '15 at 10:17

It's a good question, and I would be inclined toward B or C.

You are worried about blockage, but I view that as an issue of aerodynamics, like the difference between a lifting airfoil and a stalled airfoil. If you are not asking the air to follow sharp turns, so the flow doesn't separate, you should be good to go.

If you do need to make the air follow sharp turns, you can put vanes in the tube, to direct the air around the bend. This is what's done in closed-loop wind tunnels.


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