Suck or Blow! cooling Fan

[Charic]

Q: A fan fitted to the base of a Newtonian reflector will quicken the cooling process prior to observing ( due to the scope moving from a warm to cold environment  at short notice)  is the direction of airflow important?  If it blows directly onto the rear of the  mirror and up the OTA will it cause a `centralised` cooling spot that travels towards to edge of the mirror, and then up the OTA (Optical Tube assembly)  possibly  keeping dust off the mirror, or should it draw air down the OTA to give a more `even` cooling flow of air over the entire surface of the mirror, and potentially sucking in any impurities that may land on the mirror surface?

[emadmoussa]

Your title is very suggestive

Anyway, I think it blows air helping circulate the current inside, creating thermal equilibrium. 

[cotterless45]

Never bothered, the one supplied with the Lightbridge has just the right pitch to sound like nails drawn across a blackboard at high speed , ouch !

Nick.

[SnakeyJ]

I can remember my father joking about a solicitors partnership in Stubbington, Hampshire - 'Blow, Blow, Suck & Blow'.   I suspect some exageration/license on this, but the subject title took me right back to Stubbington in the mid 70s!

Aside from this diversion, Emad has already hit the nail on the head!

[Macavity]

For greater cooling fans should blow. I spent a lot of time trying to get balanced "laminar flow" through PC cases. Almost invariably cooling was much greater (better!) with direct (turbulent) airflow, directed at the hot-spots

P.S. If it's noisy or you feel the draught, you can supply the fan

with 7V... 5V (via variable / fixed resistor) as often used in PCs. 

[emadmoussa]

From what I have heard the attached fans dont really accelerate the cooling time by a noticeable margin. And the whirring is sometimes annoying

[Charic]

I`d only use the fan for a short while. I`m aware of the side affects, More weight (with battery) fitted to the end of  the scope, Noise, Vibration (if not damped) ect. The end of my scope is bare to the mirror surface, so was intending to fit some sort of cover, which will reduce the flow of any existing passages, hence the idea to insert a fan, or just go with my lmetal grill (Isopon Aluminium Mesh) although that looks like it would be more decorative than protective!