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

[Bill Gillespie <bgillespie@pcrs.net>]

This idea could even be used this way.

On bigger dobs - the mirror is already in a "closed box" - so why could
we not just add an insulated temp sensor under the mirror somewhere -
and then have two of the standard large panels like the coolers use -
inside the mirror box on its walls - with a display for the mirror temp
readout outside and a plug in for the 12. volt while we drive to our
site!

Or ....Something like that.........

Bill Gillespie wrote:
> 
> 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