> "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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