----- Original Message -----
From: "Curt Nixon" <[email protected]>
To: "mike bryce" <[email protected]>
Cc: <[email protected]>
Sent: Thursday, December 16, 2010 10:47 AM
Subject: Re: [Drakelist] AC4 heat Fan Summary
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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