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RE: NFC: [Fwd: Peltier Junctions]

> -----Original Message-----
> From: owner-nfc at actwin_com [mailto:owner-nfc at actwin_com]On Behalf Of
> David A Zitnik
> Sent: Tuesday, July 27, 1999 11:43 AM
> To: nfc at actwin_com
> Subject: Re: NFC: [Fwd: Peltier Junctions]
> What about sticking a couple to a piece of aluminum and then attaching it
> with thermal grease to the bottom of the tank?  The sheet of aluminum
> could then be insulated with a piece of foam or something to prevent heat
> loss from the sheet of aluminum to the air, in essence, "forcing the cold
> into the tank". Heat sinks could then be attached to the bottom "hot side"
> of the peltiers with a couple fans to remove the heat.

This might work on the side of the tank, but I doubt that it would work on
the bottom.  Because of the substrate, any heat passing through the bottom
of the tank must travel by conduction alone, as opposed to the more rapid
convective transfer that occurs at the sides of the tank.  To make matters
worse, cold water has a natural tendency to stay near the bottom of the
tank.  You would be in danger of forming ice in the gravel, which would
reduce the rate of heat transfer even further.

The obvious exception to this would be a tank equipped with an undergravel

Overall, letting the heat transfer occur through the glass is by far the
simplest design, but there is a possibility that it may not work.  Glass is
not a very good conductor of heat, so it requires a relatively steep
temperature gradient for a given rate of heat transfer.  Your best bet would
be to use a large number of low-capacity Peltier junctions side by side,
rather than one high-capacity circuit.  This would greatly increase the area
of heat transfer, and therefore reduce the magnitude of the temperature
gradient necessary to remove the desired amount of heat.  This would put
less mechanical stress on the glass too.

Andrew Dalton