Altair Fan

[Dwight K. Elvey]

>From: "Pete Turnbull" <pete at dunnington.u-net.com>
>
>On Jun 17 2005,  7:47, Cini, Richard wrote:
>
>> 	Rules-of-thumb like this are great to know. The fan, I'm sure,
>was
>> installed (like the IMSAI) blowing IN because the inside was caked
>with
>> dust. So, I made it an exhaust fan (no filter).
>>
>> 	As I work on the IMSAI, which has no filter either, I will swap
>it
>> around, too.
>
>Don't do that.  If it's designed to blow in, changing the direction to
>blowing out will alter and probably reduce the cooling.  Why?  Because
>turbulent air is lots better at cooling than a laminar flow, and will
>reach more parts of the case.  You get turbulent air from the "blow"
>side of a fan, but laminar flow towards the inlet side.  You may also
>be directing the airflow away fom some component that previously was
>cooled, eg a PSU.  Moreover, if you alter the flow direction so that
>air is being sucked in through all the other orifices, it will be
>entering via the fronts of disk drives etc (well, probably not on this
>machine but I'm thinking of the general case).  That's the last place
>you want the dust.  Far better it drops on the motherboard where you
>can vacuum it out.  Better still, fit a filter.
>

Hi Pete
 You have to remember, these machines were designed
by electrical engineers, not an air flow expert. Yes,
the original used in blowing air.
 I did a quick check of the temperatures of the boards
in my IMSAI with the in blowing air and some boards
seemed to get no flow at all. Reversing the flow made
a big difference. The powersupply in the IMSAI, at least
is large enough to need little more than some air flow.
The only parts that might get uncomfortable are the
filter caps. Any additional heat here is harder on them.
Still, after many hours of use, with almost a full
boat of 8K boards, I find the caps to be mildly warm.
 While not specifically schooled in air flow, I did
work for a company that made burnin ovens. I learned
a lot about air flow there. We would often get request
from customers to fix the airflow in in-house designed
chambers that had really poor temperature distribution.
Mil spec states how uniform the chamber should be.
 Like I said, many of these were designed by electrical
engineers.
Dwight