[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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