[Amps] more - oil bath GS-35b

[Fuqua, Bill L]

  Comparing water cooled engines and oil cooled transmitting tubes does not work.
Coolant in engines is near boiling point which means that there is always a chance of state change, ie steam.
Cavitation is due to a liquid to vapor phase state change, it causes pump volume to drop, and voids in engine
cooling. Oil has a much higher boiling point, in fact you don't want to reach that point. If you get near it
the tube will probably be destroyed anyway.
  More circulation means more turbulence and greater contact of cool oil with hot surfaces to be cooled.
Once the system has reached equilibrium the radiator is doing all it can with  a given air flow. The cooler
you can make the radiator by blowing more air across it the better, or by increasing its surface area.
  The cooler the radiator is the cooler the oil exiting it will be but you still have to have enough flow to
cool the tube. You don't always want to maximize temperature difference, Clearly maximizing the temperature
difference on the tube's anode is not a good idea. 
  Also, I have disassembled several oil cooled aviation transmitters in the past. The all had 
the whole tube in the bath. Both had 4CN15A tubes. They had little heat sinks on the anodes that
were very small and looked larger versions of the ones you press onto TO5 transistors. Also, one had
all the connections to the base soldered and the other in sockets. Never quite understood that one.
73
Bill wa4lav

________________________________________
From: Amps [amps-bounces at contesting.com] on behalf of Jim Thomson [jim.thom at telus.net]
Sent: Wednesday, April 01, 2015 1:35 PM
To: amps at contesting.com
Subject: [Amps] more - oil bath GS-35b

Date: Wed, 1 Apr 2015 16:37:16 +0100
From: Chris Wilson <chris at chriswilson.tv>
To: Bill Turner <dezrat at outlook.com>, amps at contesting.com
Subject: Re: [Amps] more - oil bath GS-35b
Message-ID: <905754433.20150401163716 at chriswilson.tv>
Content-Type: text/plain; charset=us-ascii


There are optimum flow rates based on heat exchanger coolant medium,
be it gaseous, or fluid, the type of liquid, and its viscosity. It
also depends on the surface area of the inside and outside elements of
the exchanger and the device being cooled. For sure faster flow is
*NOT* necessarily better. In automotive racing water (or water mix)
coolant is NOT flowed as fast as possible through the engine, but very
careful design has water flow going at different rates in different
parts of the engine. Those who have replaced a cylinder head gasket
may have noticed the flow restriction hoses of varying sizes in the
head and gasket. Different areas of the engine run at different
temperatures, and flow rate is varied to optimize heat extraction.
Water to air radiators have internal turbulators in high end coolers
to increase internal surface areas, thermostats have restrictor plates
to control water flow rates. Current cooling systems use electronic
water pump drives and electronic thermostats to optimize flow
according to load, blah blah.

Air flow through heat exchangers is similarly regulated for optimum
heat exchange speeds.

I am sure in an oil to air heat exchanger with a submerged valve there
will be an optimal flow rate for the oil and the air, that is far away
from the fastest flow rate, and there are big differences between
convection, conduction and radiation. I am most definitely *NOT* a
heat transfer engineer, but I am a race car engineer and I know a lot
of science and experimentation goes on in the engine world to maximize
heat exchanger performance, and engine coolant flow is a lot slower
than you perhaps imagine.


--
Best regards,
Chris                            mailto:chris at chriswilson.tv

### Us hot rodders  run into this exact same issue with superchargers on V8 engines.
The intercooler is just a small radiator, typ bar + fin type... placed on the hot output
of the supercharger.  Its job is to EXTRACT heat.   A small pump passes the distilled
water /glycol mix to the HE, aka heat exchanger..aka rad # 2.   The HEs job is to DUMP heat.
Mine doesn’t have a fan on the HE,but simply relies on airflow due to vehicle speed.
Some will use  dual fans on the HE, to keep things cooled down a bit at red lights,
and also between runs at the drag strip etc.  For road course folks, the fans don’t provide
any benefit  once above  20-30 mph.   They impede airflow.

##   faster pump speeds will make the intercooler work better..and extract more heat,
BUT the entire assy is one big loop.  Pump the hot water/glycol coolant through the
intercooler-HE loop too fast, and all you end up doing is spinning hot water around,
with no increase in eff at all.  Unless the HE (external radiator in the case of the GS35B)
can dump the heat as fast as its being generated, you are wasting your time with faster pump speeds.

##  1 watt = 3.15 BTU.   1 kw = 3150 BTU    In the case of the proposed  GS35B
setup,  1-2 kw CCS  of heat to extract..then dump is not a big issue.  And with
ssb /cw modes, the heat generated is going to be a lot less.   Beware of advertised GPM
flow rates on pumps.  They are typ for no load.  IE: fire hose connected from 55 gallon
drum of water, to input of pump.... then another big diam hose from output to  the ground.

## Once actually hooked up to the tight bends and puny size fittings, small tubing, and
the restrictions inside the  GS35B tube and the external radiator, the actual measured flow rates
drop like a rock.  Install a much bigger pump, and flow rates  typ increase very little
if any.

##  check out the BTU specs for small radiators...like automatic transmission coolers.
They are typ 8000-20,000 BTU rated..provided airflow of XXX CFM is put through em.
I had to install a 2nd auto tranny cooler in series with my oem cooler, since the tranny temps
climbed way too fast in just a few secs when super charger on..and gas pedal mashed. Like
170-200 F  in just 7 secs.

##  Old style radiators were tube + fin type. Better types are bar + plate.   You can also get em
in single, dual or triple core..and also single and dual pass.   My bar + plate Tranny cooler uses a unique
T stat......operates on viscosity.   The hotter the synthetic  tranny fluid gets, the higher it rides up either side
of the rad.  At that point it makes more and more parallel passes  from one side to the other.

##  The  GS35B, with its low dissipation, will not be an issue.   Perhaps  2-5000 btu at most.
Ultimately... ALL the heat has to be eventually transferred to the air !   BTW, you will have to provide
some cooling to the base seals of the tube, where the fil connections are made.   With Eimac water cooled
tubes, or vapor phase cooled tubes, a small air pump,  is used to cool the fil pins.
Same deal  with a normal air cooled tube which uses anode to base flow.... instead of the usual base to anode flow,
typ 3-5 cfm on a 3CX-3000A7.  But uses anode to base flow ...nobody..its fubar and requires way more cfm.
The additional  air flow to the base will not be required if the entire tube is immersed in oil, like you proposed.

##  A  2-4 GPM  pump  will more than meet your requirements.   Then perhaps a pair of 120 mm square
fans, like the 65 cfm rotron whisper types.. placed in front of the external  rad. They are very quiet, and can be
further lowered in speed with a simple metal finned resistor, variac, variable dc supply etc. Shroud the front of the
rad, where the fans are... other wise you are wasting your time... air will leak like a sieve out the sides.
Un shrouded rads don’t work too well.   IMO, you are better off pushing air through the rad, vs sucking
it through the back end of the rad.  Then you don’t have hot air passing in and out past the fan bearings.

later.... Jim  VE7RF




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