ATM Re: Faster Mirror Cooling and Thermal Regualtion - HOT/COLD chips

[Bill Gillespie <bgillespie@pcrs.net>]

Hot soup or cold tea? Just reverse polarity! 

So what about those circuits designed to give off heat under one
polarity and to remove heat at the opposite polarity ( I forget the
chips name - they use them in 12 volt coolers/heaters by Coleman and
others - space technology on the citizen level : ) 

If a person coupled some of these small heating/cooling chips in a
double array <one for heat - one for cooling> on a conductive material
like aluminum ( or even just one array for cooling - provided the
cooling rate was not to fast to jeopardize the mirror ) - and then used
this for the primary mirror plate - with temperature regulating feed
back circuitry to 

A) cause the mirror to arrive at ambient temp and 

B) maintain the mirror at ambient temp - 

why would this idea not be an effective remedy to get our mirrors cooled
and to keep them at ambient?

Bill



"Raymond A. Desmarais Jr." wrote:
> 
> Hi All,
> tom said
> >
> >However, a thinner mirror has less material to cool...so all other things
> >being equal...it will cool faster than a thicker blank...and give you good
> >images sooner than a thicker blank.  (Also, the warm mirror produces tube
> >currents, in addition to the distorted figure from a non-uniform temp
> >profile in the mirror.)
> >
> >My advice still stands:  Strive for the lowest thermal mass, the highest
> >thermal conductivity, and the best use of active cooling (fans) so that your
> >telescope has the "fastest thermal response time" possible.  That way, less
> >time will be spent having the image spoiled by a warped figure or tube
> >currents.
> 
> Having used mirrors that cool almost instantly and knowing about figuring
> and testing.
> The less material to cool the better.
> The air layer above a mirror, when the mirror is not cooled off to ambient
> is much worse than all other things .
> 
> Getting the optic to ambient temperature is the key, fans and good cell
> design help .
> When a mirror is in a transition of changing temp, the thick areas are slower
> to respond.
> Any area on the mirror that is not at ambient temp. will create turbulance
> on the air layer above the mirror. This is bad for what is often called seeing.
> One night in texas a 18" lightweight plate glass mirror was being used at
> over 1000 power under great seeing. All of the other telescope users in the
> field said the seeing was bad.
> The optics they used were not cooled to ambient, some were 7 deg F or more
> from ambient.
> How many of you have measured to keep track of the temp. of various sections
> of your mirror in relationship to ambient temp.?
> Everyone can make a difference with your scope.
> Try to cool off your mirror as soon as possible, anyway you can.
> The focal length is stable at any soaked temp.
> don't wait for the movie
> RAY