On Apr 19, 2016, at 10:52 AM, Noel Chiappa <[email protected]> wrote:
> Speaking of orientation, though: these fans, like most PDP-11 fans, send air
> downwards. I was thinking of flipping them, to send the heat upwards (its
> 'natural' direction), but after pondering a bit, I'm not sure this is a good
> idea: the air-flow on the intake side is diffuse, whereas on the output, it's
> a concentrated, directed blast - better for cooling boards, etc.
I share the sentiment. However, in many cases thermal engineers actually had
something to do with the original design and they also know about heat rising.
I would be careful about second-guessing the design, at least on
well-engineered systems.
I reversed the fan on my NeXT 040 Cube a long time ago. That way air goes out
through the Optical drive port, and does not pull dust into it. Shortly
thereafter, I started getting very occasional read errors on the SCSI bus. I
thought through the air pathway, and sure enough the SCSI chip was now
*down*stream of the power supply. I put the fan back to its original
orientation, and no problems since. (The optical drive doesn’t work anyway,
but I understand that is not a rare problem and in this case I don’t believe it
is related to dust.)
- Mark
