Re: ATM Beyond the fan

["Ken Hunter" <kb7h@onemain.com>]

Somewhere in the archives is a post I made about Peltier devices...
The same info is true today. A 2 inch square Peltier cooler/heater
operated at 12 volts (13.6 vehicle battery) will draw between 2 and 4
amps (24 to 48 watts if using the 12 volt figure). This amount of
energy must be applied to EACH device and the resulting heat sent
somewhere out of the optical path. So far I've seen a lot of
daydreaming about cooling mirrors etc with Peltier devices but not
much thought given to hauling the power source or dissipating the
waste heat.

If I can jog your collective memory... ATM's are making thin mirrors
and lightweight scopes to save a pound or two for ease of transporting
our scopes then, adding hundreds of pounds of support equipment to
make up for the compromises made.

Some of this doesn't make sense to me!

Ken Hunter

----- Original Message -----
From: "Steve JB Bouton" <sjbbouton@juno.com>
To: <atm@shore.net>
Sent: Monday, February 25, 2002 10:08 PM
Subject: Re: ATM Beyond the fan


>
> Well, it looks like that I'm not the only one that's thought of
this.
> The biggest stumbling block to me was how to mount these devices to
the
> mirror.  Glue them to the mirror?  I think that they (and the
related
> heatsinks, fans, etc.) would get in the way of the mirror cell.  And
the
> waste heat could be a problem.
>
> So, I came up with this idea: use a fan blowing past an array of
Peltier
> devices with heatsinks on the cold side.  The hot side is mounted to
a
> heat exchanger, similar to that of the Cookbook Camera design.
> Circulating coolant pulls the heat clear of the main mirror.  How
much
> cooler will the air be past the devices?  Until a protoype is built,
I
> have no idea how effective it would be.  But if it works, there
would be
> nothing to mount to the mirror, and no worry about the heat rising
and
> creating turbulence above the mirror.
>
> On Thu, 21 Feb 2002 09:15:38 -0700 "Chuck Hards"
> <chuckh@companionsystems.com> writes:
> >
> > Has anyone tried attaching a Peltier heat-pump to the back of a
> > mirror, or
> > an array of them?  The heat produced by the "hot" side could be
> > pulled away
> > by a rear-mounted fan blowing backwards, straight out of the tube.
> > The
> > "cold" side can get SO cold that it may be able to cool a mirror
> > much faster
> > than a fan alone.  It doesn't address immediate boundary-layer
> > problems on
> > the mirror's face, a small fan may still be needed if you're in a
> > hurry, but
> > it may shorten appreciably the total cool-down time required.  I
can
> > tell by
> > recent posts that some people still aren't convinced that active
> > cooling is
> > good insurance.
> >
> > You know, you could even use one in an opposite configuration to
> > heat an
> > eyepiece, kind of a high-tech "eyepiece cozy".
> > (Sticking your tongue to the flagpole in winter is nothing
compared
> > to
> > getting your eyeball stuck on a Plossl......just eliminating the
> > "brain
> > freeze" is a step in the right direction!)
> >
> > Just an idea, perhaps more practical than a "levitating
secondary"!
> >
> > C'mon, Richard, let's hear it.  Dig into this one!
> >
> > Chuck
> >
> >
>
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