19 Apr
2016
19 Apr
'16
9:29 a.m.
On Apr 19, 2016, at 10:52 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu> 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