On 8/11/2013 12:35 PM, Roger wrote:
On 8/11/2013 10:40 AM, Chris Wilson wrote:
Water makes a good heat sink
Water is about the best conductor (most effective) of heat you can
find. There is a table listing water Vs various other compounds
although I've forgotten the URL. I do know that water takes 1 calorie
to heat 1 CC 1 degree. I did a fair amount of work helping to develop
a coolant for solar panels.
As did I back in the 70's. We tried silicone fluids (mainly 200 fluid)
The only drawback to water is it requites anti-freeze in the North
and tends to leach metals.
Antifreeze is usually not much of a problem if it's not conduvctive and
it may even mitigate DI or distilled water's affinity for metal ions.
Particularly those in brass. The copper in tube jackets seems to hold
up quite well. At amateur power levels, heat capacity, and water
pressure, plastic hose fittings work quite well.
With RF generators, running close to 24 X 7, the brass fittings tended
to last 2 or three years. OTOH when one let go, it was something you
couldn't ignore.
One problem with water is it easily evaporates and you do not want
condensation inside an amp, or around a dummy load.
For a dummy load, you can use the appropriate resistors mounted on heat
spreaders that are water cooled. In that case, you can use tap water.
The resistors are a bit pricey, but not bad and are readily available in
a conflagration ready to bolt down along with heat-sink compound to the
spreader.
73
Roger (K8RI)
It depends of the construction and whether the dielectric constant
plays a part. If so, you might have to add some compensation, but
that's not uncommon even in commercial loads.
73
Roger (K8RI)
I built a dummy load consisting of 4 x 200 ohm globars in parallel.
Each resistor is 12 inchs long x 1 inch OD.
Each resistor resides in its own 3 inch od x 12 inch long AL pipe.
All 4 x AL pipes are heliarc welded together.
The entire mess will sit in a 7 gal new paint can. A 5 gal can +
top part of a 2nd can were brazed together.
A 7-16 DIN was installed dead center in the top lid....along with a
pressure relief tube, off to one side.
Instead of xfmr oil, can distilled water be used instead ??
It will only be used on 160-10m..and maybe 6m.
If something goes terribly wrong, Id rather have water all over the
basement floor vs oil. Distilled water is
an insulator. Heck, Bird + CD have water loads that use tap
water. AG6K depicts a hb water load...with a
single 500W resistor inside some pvc tube and a garden hose fitting
on one end....and coax connector on the
other end.
I realize water boils at 212 F. Has anybody tried distilled water
in a 1 gal dummy load ? Is it still 50 ohms ?
Jim VE7RF
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11/08/2013 15:38
My 10kW Bird 8738 water cooled load has tap water which I believe si
in direct contact with the resistive element, and is still working
fine so I don't see why not.
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