Bill Davidsen wrote:
Robert Myers wrote:

It's misleading for me to say that the CPU has no fan. The case fan
draws air in such a way that the predominant flow is through the many
horizontally stacked, spaced plates of the heat sink. It wouldn't
seem that it would matter so much where the air comes from, but
apparently it does. The heat sink stack is so tall it extends nearly
to the edge of the case, so that air entering through the side holes
(highly turbulent because it is a collection of small jets) encounters
the top of the heat sink almost immediately. I suspect that those
holes behave more like vorticity generators than like a duct. Take
the cover off, and the relatively laminar flow through the heat sink
doesn't create enough heat transfer.

Possible, but I think having the coolest outside air coming to the CPU
first is probably the key.

The short circuit to the air flow with the cover off is just a few
inches between the heat sink stack and the exhausting case fan, which
exhausts much greater heat than the power supply. A piece of cardboard
or plastic that blocked that short circuit would be an interesting test.
There are actually holes upstream of the CPU to cool the disk drive,
and that air has to get through/around the CPU heat sink to exit the case.

My problem has been running high ambient temperatures. With a 90F
building temp keeping CPU and disk cool is an issue. I looked for a
Peltier cooler, but didn't come up with one I really liked. And they
draw a ton of power.

These boxes have run without air conditioning in summer weather. I
don't think 90F ambient should be a problem.

Robert.