> Headaches of vapor cooling include basically operating a water distillery
> in your coolant circuit, so that you must start with very clean water, and
> keep dissolved oxygen low (ppm) to prevent copper oxides from occuring and
> ruining the heat transfer efficiency of the inside of the water
> jacket/anode. If long life is important to your operation, you will need
> to stay on top of ph, oxygen, and other factors which aren't as important
> in conventional water cooling, and not at all with air cooling.
I own an original Alpha 70V and it's been one of the more
maintenance-friendly amps I've ever owned. While it is true that one must
start with purified or distilled water, the ph and oxygenation issues are
completely manageable -- at least for amps in the amateur class of service.
I change my distilled water supply at annual intervals and the process takes
about 30 minutes. It gives me a chance to tighten, inspect and lubricate
components, and to look for other potential problems while I'm in there.
The vapor-phase cooling system in the Alpha 70V is extremely simple. In
fact, the total parts count consists of three Polypropylene plumbing
connectors, 10-inches of tubing, a Polypropylene "bellows" section, a
condenser, and a pair of copper vent pipes. That's it. Larger amps may
require pumps for added circulation. The Alpha 70V and the original
"Stanley Steamer" used no more than gravity and convection to dissipate heat
from the condenser, although the 70V gets a boost from an internal "whisper
fan."
Compared to pure-liquid water cooling, vapor-phase cooling is approximately
17 times more efficient in passing water volume: each gram of water
converted into steam absorbs heat at the rate of ~ 600 cal/gm compared to ~
35 cal/gm with liquid water cooling.
That said, I can completely understand why a manufacturer today would not
want to produce an amateur amp with vapor-phase cooling. The mere fact that
water and high voltage are brought together wreaks of liability issues where
back in the '60s, that may have been a lesser issue. If the user isn't
careful with the water expungement process (even as simple as it actually
is), there's a lot that can go wrong. But for someone who is cognizant of
safety and correct maintenance procedures, vapor-phase cooling is quiet,
efficient, and still "way cool" in the 21st century.
Paul, W9AC
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