That and some of the current high power transistors are being designed
to be directly mounted to a heat sink without an intervening insulator.
On 5/1/12 8:17 AM, Sam Carpenter wrote:
> 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@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Paul Christensen
> Sent: Tuesday, May 01, 2012 10:59 AM
> To: amps@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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