[AMPS] 3CV1500A7; what is vapor cooling?
Alan D. Gray
agray@VOICENET.COM
Tue, 04 Aug 1998 17:15:40 -0400
Specifically, Jack Quinn's (W6MJG) article, "The Stanley Steamer", appeared
in the May 1966 issue of QST, page 19.
Alan, W3BV
At 02:14 PM 8/4/1998 -0600, Richard W. Ehrhorn wrote:
>
>Hi Jon & all...
>
>Concerning your question, Jon, the best readily-available explanation of
>vapor-phase cooling that I know of was a construction article by Jack Quinn
>(of Eimac) in QST around 1968 give or take a year. Think its title was "The
>Stanley Steamer." In a nutshell, more or less, this is why & how vapor
>cooling is used:
>
>Vapor-phase cooling is commonly used in very high power amps because the
>heat absorbed in converting water to steam is 540 cal/gm (of water
>vaporized, if I remember correctly), while in conventional liquid water
>cooling the water absorbs only 1cal/gm/degreeC of temp rise. Physically,
>the vapor- cooled tube's anode is surrounded by a small tank, or boiler, in
>which pure water is vaporized into steam by anode heat. The steam is
>condensed and the water recycles repetitively.
>
>In typical closed-loop liquid-water-cooled systems, the maximum outlet
>(hot) water temp must be held well below 100 degC to avoid hot-spot boiling
>on the anode surface, which can and does create steam bubbles, which in
>turn "insulate" the hot spot from the water so the hot spot gets even
>hotter. This typically creates a temperature runaway and may lead to
>destruction of tube and/or cooling components. Typical inlet (cool) water
>from the chiller may be specified as </= say, 45 degC, and maximum outlet
>water temp as 80 degC to avoid spot boiling. (I'm sure John Lyles can speak
>with more experience on these issues.)
>
>Anyway, in this example each gram of cooling water passing through the
>tube's water jacket can absorb not more than (80-45) = 35 calories of heat.
>Conversely, each gram of 45 degC water entering a vapor-cooled tube's
>boiler absorbs approximately [540 + (100-45)] = 595 cal/gm while
>vaporizing.
>So vapor cooling requires passing only about 35/595 = 1/17 as much water
>volume through the system as does water cooling.
>
>Steam emanating from the boiler is converted back to water just as vapor is
>condensed in a Kentucky still - generally with a copper condenser strongly
>resembling an automobile radiator. The water returns to the reservoir and
>continues to recycle by convection. At least in small systems like the
>ALPHA SEVENTY, no pump is needed. Better yet, with the 6x10x1.5" condenser
>used in the ALPHA 70V, to about 600W plate dissipation no FAN is needed to
>cool the condenser - convection air does the job. If maximum power is run
>for extended periods, all the steam can't be condensed by air convection
>alone. Escaping steam is detected by a thermostat on the vent tube and
>activates a "whisper fan," which supplies plenty of air to condense the
>steam created by at least 1.5 kW of plate dissipation.
>
>Vapor cooling is a joy to use for ham radio 'cuz it's virtually silent.
>Downside is that the water supply must be very clean to keep leakage
>current through the water in the supply tube (the anode is at +HV, the
>reservoir at chassis ground) low enough to avoid heating to the boiling
>point. If water in the supply tube boils, steam bubbles form & tend to
>interrupt the water supply. Also, the water reservoir must be topped-off
>occasionally, as a small amount of water is lost due to evaporation from
>the vent.
>
>Small impurities collect in the boiler, and at perhaps yearly intervals the
>system must be taken down and cleaned. This isn't hard to do, and a
>considerable number of ALPHA 70Vs (built in 1970-71) evidently are still
>receiving regular TLC and use. But in a time when many of us never check
>our cars' oil or water between 3000-5000 mile shop service intervals... air
>cooling is the more practical approach for 1.5 to a few kW amps in today's
>run-it-until-it-quits society!
>
>Sorry to make this so long & rambling, guys, but maybe a few others besides
>Jon will be interested enough to look up Jack Quinn's article.
>
>73, Dick W0ID
>
>-----Original Message-----
>From: Jon Ogden [SMTP:jono@enteract.com]
>Sent: Monday, August 03, 1998 3:36 PM
>To: Richard W. Ehrhorn
>Subject: RE: [AMPS] 3CV1500A7
>
>>To the best of my recollection, Eimac decided to discontinue making the
>>3CV1500A7 (actually a 3CX1000A7 with a boiler instead of air fins) some
>>time in the late 70's.
>
>Dick,
>
>What is meant by "vapor" cooled as opposed to air cooled. And what do
>you mean by a "boiler"?
>
>Just curious as I was just a little knee biter in 1972 and don't know
>much about tubes from back then.
>
>73,
>
>Jon
>KE9NA
>
>
>--------------------------------------------------------------------------
>Jon Ogden
>
>jono@enteract.com
>www.qsl.net/ke9na
>
>"A life lived in fear is a life half lived."
>
>
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>
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