Altair Fan

[Dwight K. Elvey]

Hi
 One should note that unless the fan is blowing directly onto
some particularly hot item, you'll get really poor air flow
distribution by blowing with a muffin fan. First the fast moving
air tended to stick to the first surface it finds ( Coanda effect ).
Also the air is rotation that tends to cause it to find corners
to travel along.
 When the air is pulls into the fan, it tends to have more
laminar flow from all directions.
 For better all around cooling, I recommend taping or masking
off most of the slots on the power supply side, near the fan
( for a IMSAI or Atair ). These keep the air from cheating by
taking the path of least resistance. More air flows across the
boards and along the power supply.
Dwight

>From: "Dave Dunfield" <dave04a at dunfield.com>
>
>At 21:31 16/06/2005 -0400, you wrote:
>>All:
>>
>>	OK, this is a stupid question. I'm fixing up the 8800b that I got
>>recently and I removed the fan to perform some work on the power supply.
>>Unfortunately I didn't mark which direction the air blows. Can someone tell
>>me if it blows inward or outward?
>>
>>	Thanks.
>>
>>Rich
>
>Hi Rich,
>
>Both of my 8800s have the fan blowing out.
>
>The general rule is:
>
>If the fan has a filter, then it should blow in.:
>
>  By maintaining positive internal pressure, and
>  filtering the air that comes in, you keep dust
>  from entering the box.
>
>If it does not have a filter, it should blow out:
>
>  A fast moving stream of air will carry more dust
>  than a slow one. If you blow the fan in, it will
>  carry dust into the box which will drop out before
>  it exits at slower speed (because of the much larger
>  area of all the vents and other openings) - it also
>  causes dust buildup to concentrate that certain
>  points bacause of sudden changes in airflow (you can
>  often see bands of thick dust in boxes with fans
>  improperly installed). Going the other way reduces
>  the entry speed (same reason) and thus the amount of
>  dust that enters - what does get in tends to settle
>  out in a more uniform distribution.
>
>Regards,
>Dave
>-- 
>dave04a (at)    Dave Dunfield
>dunfield (dot)  Firmware development services & tools: www.dunfield.com
>com             Collector of vintage computing equipment:
>                http://www.parse.com/~ddunfield/museum/index.html
>
>
>