[ATM] Fan locations & function for a 32

[Bob Drew]

I accept the concept of sweeping away the boundary layer from the primary 
mirror surface.  And I’ll  use some fans under the mirror back.

I’m doing final design of the aluminum tube mirror box for my 32” alt-az.  
So it’s a good time to block in the space needed  for the fans/vents. Plan 
to use 3 or so fans to blow across, and same to draw out and vent the air on 
opposite side.

My questions to you expert, particularly those who use them, are:

1. Should the flow be across the mirror front  be from one side to the other 
side?  Or should it be vertically? (From the lower side of mirror box, 
exiting on the top? or vice versa? )   The scope will have a full shroud as 
a minimum or possibly a rigid tube later.

2. Since its operating in conjunction with the above (and without starting a 
debate) should the fans (imbedded in the cell underneath the mirror)  suck 
or draw the air down and vent out the back of the box,  or blow on the back 
of the mirror.

3.Are there  3” diameter fans that would be able to maintain flow across a 
box about 40” wide, or would a 4” be nec.?  Brand names and models also 
appreciated

The mirror is a 32”  f4, 3” thick weighing about 200 lbs.  Its Corning ULE,  
so thermal deformation won’t be an issue.   But I observe in an area with 
rapidly dropping temperatures, I’d like to exploit the best current 
knowledge we have on optimizing and managing tube currents and minimize 
image degradation.

Would really appreciate your advice real soon, as I’d like to cut some 
metal.
( email privately if you prefer) Thanks

Bob

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