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A exhibit developer/designer tried having the fan external to the main chamber, and a filtered set of holes near the top of the cylindrical chamber that would allow the air to recirculate to the fan. The air was then directed with a paddle. It didn't work very well. If something sealed tight on the area with the fan (external to the cylindrical chamber but inside the exhibit), then the glass top would actually float on a layer of air. If everything was tight so that didn't happen then the airspeed would drop significantly, and the paddles didn't work to direct the air flow. I ended up first replacing the paddles with a hose, then connecting all of the filtered areas directly to the fan via tubing. Then I needed to remove most of the filtration media. Eventually we took the exhibit out of service prior to the end of most exhibits. The original worked *much* better. It very well may be possible to design a chamber that allows air to escape without much air pressure loss or sand loss - but it's definitely difficult! I could envision a series of baffles to slow down the air (but then they would have to be cleaned as they would collect sand - and this would also necessarily reduce the air inflow somewhat).
On Nov 24, 2011, at 6:51 AM, Ian Russell wrote:
> ISEN-ASTC-L is a service of the Association of Science-Technology Centers
> Incorporated, a worldwide network of science museums and related institutions.
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>
> I confess I've no practical experience of this exhibit, but surely it must
> be possible to make it work with an external fan, operating in clean air. If
> the air then spins round inside a cylindrical display case, it would just be
> a matter of designing a large-area, low-resistance, non-clogging filter to
> allow air to escape from the top.
>
> I wonder if this has been tried and found impractical? Or has everybody only
> followed the original approach, as often happens with interactives?
>
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