GA Mike:
Sure, as far as the air movement is concerned, I don't think there is
anything wrong with that thinking. But the relative amount of air
movement from the natural convection is very small compared to the
amount created by the fan. I think the controlling issue, in this case
is the efficiency of the fan. As Richard explained, by creating a small
negative pressure (suction) with the fan, air will enter the Tx from
everywhere. More from the areas of least restriction..like the vent
holes around the tube sockets and screen over large hole beneath the
finals compartment...and move up and out thru the fan. This small but
widely distributed exchange of air is the best situation for the rig as
a whole. It is not necessary to blow air across these tubes to cool
them..just endeaver to keep the ambient air surrounding them at some
lower nominal temperature...the glass tube can conduct the internal heat
away pretty well as long as the air is not totally stagnant.
If appearance was no issue, I would put the fan, drawing out, right on
top of the final cage. But since the cage is perforated, placing it on
the back is nearly as effective and looks better :)
The fan easily overcomes the normal convection path that would be
straight up and the bonus is you exchange air pretty much throughout the
rig.
BTW..these fans are EXTREMELY sensitive to the smallest backpressure.
They pressureize a compartment..that is the whole point. If they could,
it wouldn't make any difference to the rig, as Richard explained. It
doesn't care which direction the air goes, just that it is exchanged for
cooler air. The fan DOES care tho. Even the perforated cages present a
significant back pressure to one of these fans.
Try it...use an incense stick and put the fan right against the cage
blowing in...smoke stick on opposite side. Now try it with fan pulling
air thru the perf panel. You will see the difference.
When I played with the R4 fan install, I did some very interesting flow
experiments using incense sticks for smoke and watched where the air was
going. It is very easy to tell the difference in pressure v suction
when doing this.
Will they work blowing in? sure..they worked 40 years w no fan. m They
just work better pulling air out (thru).
BTW. This is all out the window when considering tube components that
require forced air cooling. Different situation entirely--and most use
blowers not fans.
FWIW
Curt
mike bryce wrote:
thought I'd toss my .02 in with a question
on the tr series, a fan mounted to the rear of the pa compartment,
should it blow in
or suck out?
since we're not trying to pressurize a compartment, there's plenty of
holes in the cage and top cover, and since heat rises,
it would seem to me that one would mount the fan so it would blow into
and onto the final tubes
To me, it seems a fan sucking air out of the pa compartment would have
to compete with the natural convention of heat raising
so, what's the word from the thermal gods?
Mike, WB8VGE
SunLight Energy Systems
The Heathkit Shop
http://www.theheathkitshop.com/
J e e p
o|||||||o
"If the facts don't fit the theory, change the facts."
Albert Einstein
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