ATM thoughts on scope temperature

["Arjan te Marvelde (EMN)" <Arjan.te.Marvelde@emn.ericsson.se>]

Hello list,

I've been following the thread on mirror cooling/expansion calculation. Being new in 
telescope making, but with a solid physics education, i have a couple of questions about 
this issue.

What seems to me the main issue here is thermal equilibrium, meaning that temperature at 
any place of interest (the optics including the air column you're looking through) is 
stable in time. For the mirrors this may not be enough: they also should have no internal 
temperature gradients.

Transport of heat can go three ways: conduction, convection and radiation. 
Conduction is the main means of transport within solids, convection takes place in gas 
and fluids and any kind of matter radiates heat in the form of IR. I think that all of 
these mechanisms apply to telescopes; there is conduction of heat from each components' 
inside to the surface, there's convection when cool interior air is replaced with 
exterior air, and there is radiation of heat towards space. 
I read not much about the radiation component. Any object facing void would attempt to 
get into thermal equilibrium with it (i.e. 3 Kelvin?) by means of radiation. The radiated 
heat is replaced by heat from the environment, flowing in mostly through conduction and 
convection. Hwoever, if the object is thermally well enough insulated, it may become many 
degrees cooler than it's environment. I would say that this effect would also apply to a 
scope, so i expect the interior to cool down significantly below ambient air teperature 
(isn't this also causing dew?). 

-1- Wouldn't a fan cause turbulent mixing of warm environment air with cool interior air, 
thus causing 'bad seeing'? I can understand using a fan or whatever means to speed up the 
process, but to reach ultimate equilibrium i would say patience would be the best 
mechanism.

-2- Does anybody know of some mathematical model for heat exchange in a telescope?; this 
would give some more grip on  quantifying the problem, i.e. better means to find out 
which mechanisms matter most.

-3- Isn't the best way of reaching equilibrium very much dependent on the specific scope 
mechanics? I figure that the interior of an open-truss OTA cools down less that a 
conventional tube. Also the tube walls will transport heat from environment to interior,  
causing temperature gradients and air flow.

As said, i have no experience with scope building, so maybe i'm under/over estimating 
some effects. Can anybody comment on this?

Kind regards,
Arjan te Marvelde