Re: [ATM] Thermal mirror deformation -fan on both sides

["tony gondola" <acgna@comcast.net>]

I don't think it's a matter of how important the work is but is it a useful, 
validated tool? It's interesting but I don't think anyone really knows what 
to do with it. Everyone knows that performance will be degraded while the 
mirror is equalizing to ambient. My personal feeling is that actual field 
measurements would be more useful.

I'm also not sure that I agree with conclusion on fan placement. The most 
common configuration is to blow air out from the back of the tube or mirror 
box. The fan isn't blowing directly on to the glass but is rather setting up 
a flow of air that surrounds the mirror, front back and sides. The actual 
airflow is much more complicated then Jan's simple infinite diameter disk 
model suggests and is also subject to turbulence and dead areas induced by 
various structures in the flow path including the mirror's edge. Even a full 
CFD analysis wouldn't tell the whole story.

Tony



----- Original Message ----- 
From: "Ric Rokosz" <radicell2@yahoo.com>
To: "Jan van Gastel" <jhm.vangastel@wanadoo.nl>; <atm@atmlist.net>; 
<atm_free@yahoo.com>
Sent: Tuesday, August 29, 2006 6:55 AM
Subject: Re: [ATM] Thermal mirror deformation -fan on both sides


>
>
> --- Jan van Gastel <jhm.vangastel@wanadoo.nl> wrote:
>
>
>> >
>> > Inspired by the recent thread on under/over
>> correction of a mirror due to
>> > radiative cooling, I have done some simulations
>> with a PDE solver and
>> > written an article about it. Please have a look at
>> >
>>
> http://home.hetnet.nl/~artm/atm/articles/cooling.html
>> > Iwould very much appreciate any comments: there
>> might be wrong assumptions
>> > or errors.
>
> I'm somewhat surprised more comments haven't been
> advanced on this specific example of the effects of
> mirror cooling,especially the fact that using a fan on
> just the backside of the mirror induces more
> distortion than no fan at all!Kinda sets a new
> standard for atm's that pro's knew about for quite a
> while.
>
> The best solution is to use a fan on both sides.This
> reminds me of the work done by a French optician that
> used a heater wires around the circumference of the
> mirror to both equalize the mirror temp in the blank
> and to distort the mirror's shape to an aspheric
> shape.
>
> Thanks Jan for this important work.
>
> Ric
>
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