Cooling fans: suck or blow

[traveller (Bo)]

Ok, you get the idea.
Thinking of fitting a cooling fan to the rear end of Schmidt Newtonian OTA, should I get the fan to blow into the rear of the cell holder or extract air from it?
Sucking air from the cell and push it out seems sensible, but will I get more efficient cooling by blowing air onto the cell assembly?
Thanks

[Waxing_Gibbous (Peter)]

Well. Thank goodness that's clarified!
Blow I think. Simply because most manufacturers design them that way.
Suck sounds reasonable if you have an OTA with vents a both ends (Phhhwooooar!), but I suspect you'll get better, or at least faster, cooling by blowing on the mirror.
Could be wrong. Usually am.

[traveller (Bo)]

I thought blow is the way to go, but worried about introducing dust into the OTA (note to self, need to seal the OTA at the bottom end).

[dannat (Daniel)]

blow or suck - can't you do both, some new CAT coolers rely on 2 holes, to circulate

[traveller (Bo)]

Thanks Daniel,
My main concern with through flow is the need to open up a "sealed" SN OTA tube. At this stage, I am keen just to cool the primary mirror and let the steel tube cool the inside temperature passively.
Bo

[AndrewJ]

Gday Bo

Blow is the way to go to reduce possible contamination inside the tube.
Filtering the input for one fan is easy, and by having a slight pressure increase inside the tube, any leaks will let filtered air out vs unfiltered air in.

Andrew

[rustigsmed (Russell)]

how about a peltier setup?
http://www.iceinspace.com.au/forum/s...ad.php?t=43627

[traveller (Bo)]

Originally Posted by AndrewJ

Gday Bo

Blow is the way to go to reduce possible contamination inside the tube.
Filtering the input for one fan is easy, and by having a slight pressure increase inside the tube, any leaks will let filtered air out vs unfiltered air in.

Andrew

Good point!

Originally Posted by rustigsmed

how about a peltier setup?
http://www.iceinspace.com.au/forum/s...ad.php?t=43627

Err, I prefer the under-engineering approach

[multiweb (Marc)]

I'd say suck from a heat sink but blow on a mirror.

[mswhin63 (Malcolm)]

Not really sure but suck maybe better to reduce turbulence within the OTA. Not sure if turbulence is a major factor up close to the mirror.

Could go either way.

[strongmanmike (Michael)]

I asked the same question when deciding on what to have Orion Optics UK do with my 12" AG12 Newt...and got many different answers too Seemed to me that with a completely open tube either method replaces the warm air around the mirror with cooler air at the same rate which was largely determined by the fan blade and speed and number of fans of course, so there is a cooling effect on the mirror with both options. Which method is more efficient..? well I needed someone to show me hard evidence (but no one could ). So I went with dragging air down the tube and out the back as it seemed like the less turbulent option, particularly considering the fans would be left on all night. I imagined the air being gently drawn down the tube and around the edges of the mirror, with the turbulence mostly occurring once the air went around the back of the mirror compared to blowing causing turbulence mostly as the air went around the front of the mirror which, to me at least, seemed likely to be the more problematic? I've tried to see if there is any difference in focus stars with the fans on or off but, at least visually on the screen, there seems to be little difference ....I leave the fans on anyhoo just because it seems right...and the pictures seem ok

Mike

[traveller (Bo)]

Thanks Mike,
Being a sealed tube, Schmidt Newtonian don't get as dirty as the open top Newts. I think I will try the blow method first with a filter over the intake part and see how I go.
Bo

[JethroB76 (Jeff)]

I would blow the outside air onto the mirror, rather than suck air from near the mirror, which will get replaced with other warm air from the OTA

[algwat (Alan)]

Just an opinion.....
the fans at the low end of the scope closer to cooler ground air.( ok away from hot concrete...)

So, pump it in and force warmer higher air out the top.
The mirror cools, and tube air cools so less tube thermals...??

kind regards, Alan.