[Amps] Tubes vs. Solid State (was) Expert Amps2K-FA:AnyOpinions?

[Sam Carpenter]

Aren't Vapor Cool and Water Cooling vastly different in efficiency with
Vapor Cooling being much, much better. I think I remember that the Vapor
Cooling thing goes to hell really fast if you allow a boiling condition on
the cooling surface? I did not think the transfer efficiency was even close
in standing or moving water vs vapor. I think I remember too that if things
boil, and has bubbles on the surface that you lose a lot of the
water-to-surface heat transfer for periods of time. Sorry if fuzzy on this
as time has passed since I looked into a 70V. I remember being absolutely in
love with the idea of having that amp and studied it for a while before
giving up on finding enough tube supply to buy one.

I think things will be changing very soon on the SS Devices. I heard a story
of a recent discovery of a near perfect medium for heat transfer that is
only 1 atom thick. There was a story last week on NPR and I think it is
published in something called or something like "The Nature or Materials".
The study involved heat transfer from glass to gold but they said it would
end up translating into semi conductors and would be world changing for
electronics. May be able to find on NPR archives.

N9FUT

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Paul Christensen
Sent: Tuesday, May 01, 2012 10:59 AM
To: amps at contesting.com
Subject: Re: [Amps] Tubes vs. Solid State (was) Expert
Amps2K-FA:AnyOpinions?

> "I doubt that ... the solid state devices would not appreciate the die
temperatures with vapor phase cooling.  However, a small radiator and closed
water system would work very well.  With a suitable pump the
radiator/reservoir/fan could be located outside or in another room for
essentially zero noise."

Joe, good point.  It's an interesting thought exercise...

I looked up the maximum operating temperature for the Motorola MRF150 and
Microsemi ARF1500.  From the datasheets, maximum operating temperature is
between 175-200 degrees C which is > 75 degrees C above the H2O boiling
point.  As I recall, water can never exceed the boiling point temperature
under normal atmospheric pressure.  Additional heat does not raise water
temperature but causes steam and steam too never increases beyond the
boiling temperature at normal atmospheric pressures.  But under pressure,
it's a completely different ball game.  Added pressure raises the boiling
point and the temperature of steam can get extremely high.

Assuming a set of transistors mounted onto a dense copper block (copper, to
avoid water contamination) and immersed in distilled water, it seems to me
that these transistors could operate well under their maximum ratings with a
lot of room to spare.  Worst case is the temperature of the transistor
substrate could never exceed 100 degrees C, at least not very long.  That 
is, until water is boiled out of the reservoir.   This cooling system needs 
a means to monitor water level (as does the Alpha 70V) since it's so
critical to stay under maximum temp ratings.

A normal vapor-phase cooled system is vented to atmospheric pressure so
there's no danger of rising temperatures due to rising boiler temperature. 
But as long as the transistor is immersed, the worst effect is generated
steam that simply moves from the boiler to the condenser where its cooled
and re-circulated in the vented closed loop.  That's the normal cooling
function of a vapor-phase system.  So, if I've got my facts straight, a
solid-state amp using vapor-phase cooling would utilize 1/17th the volume
when compared to a water-cooled system, thereby keeping the system contained
within a desktop size enclosure.

Paul, W9AC




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