[ATM] Thermal Mass - WAS Tees instead of triangles

["Cary Chleborad" <Cary@Chleborads.com>]

This topic has drifted along to thermal issues and I thought it would be
appropriate to follow on with this.
 
Now that people are considering the scale of thermal differentials between
the optic and the ambient air and even seeking active cooling solutions  -
what about cellular structured mirror blanks?
 
There have been a couple of folks in recent years that have been fusing post
and plate structure systems together.  The advantage of such as system is
one can achieve the cross section of a very thick mirror blank at only ~1/3
the mass of an equally thick solid blank.
 
The interesting thing about such a blank is that the amount of heat is
directly proportional to the mass of the blank.  On this basic principle
alone a cellular mirror with 1/3 the mass of a traditional mirror will
thermally equalize three times faster.
 
Now, it gets better!  Heat flows out of a structure at a rate proportional
to the thickness of the material it is flowing from.  The cellular structure
ends up having web thicknesses as much as 1/16 the thickness of a
traditional blank.  The heat can now escape the blank at a rate insanely
faster than our poor old plano solid blanks.
 
To recap, 1/3 the mass = 1/3 the heat. Which can escape the blank 4, 8, 16
times faster than traditional blanks.  You end up seeing thermal
equalization rates that take minutes instead of hours and with no fans.
 
Now, to top it off and make it sound like an infomercial:
 
It still gets better!!!  A cellular blank is not only less massive and cools
much faster; it ends up being much stiffer than and equally thick and solid
blank.  Furthermore if the cellular blank is made by a full casting instead
of fusing plates and posts the cellular structure can be designed to be
totally self supporting.  The mirror then sits right on the collimation
bolts!!  No more fussing with complex mirror cell designs!!
 
Now the catch!!!  No one is commercially producing cellular mirror blanks -
yet....
 
 
 -Cary
 
> > > I'm using this idea to address the thermal problem:
> > >
> > > http://www.balinka.com/portfan.htm
> >
> > You should really consider a front blowing fan.  With the 3 inch thick
> > mirror, getting the air moving on both sides is going to help a lot.
> > Also, perhaps even more important, a rear fan doesn't break up the
> > thermal boundary layer on the front side that causes much of the image
> > distortion.
> >
> >

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