Jim,
Tap water has long been used as a coolant in high-power loads, like the
Altronic Omegaline models. In college, I used a 25KW Omegaline water-cooled
load with a Harris FM-25K FM broadcast transmitter. These loads are very
compact in relation to their ability to dissipate heat through running
water. With 25KW being dissipated, you can hold the load in your hand and
it stays cool. However, touch the water on the output and of course it's
very hot but nowhere near boiling. All one needs is a household faucet,
garden hose, and a water drain. For shacks in a basement with a utility
sink, it's ideal.
Flow sensor switches are commonly available that open the transmitter's
interlock in the event water flow stops or become impeded below a
pre-determined cubic volume per unit of time. The Omegaline loads can be
found on the used market although it takes a hawk to find one at a
reasonably inexpensive price - but they're out there. These loads offer
incredibly good return-loss specs. Typically one can expect -30 dB
return-loss up to near 1 GHz.
So, I see no reason why water cannot be used, but I would sweep the load in
water with a VNA and plot return-loss as a function of frequency. You may
find that the Z changes substantially as it's immersed in water. Z may also
change with temperature, and that's something that may be part of the
commercial designs. It may be helpful to call the folks at Altronic for
their input. They're the world's experts with H2O-cooled loads.
Paul, W9AC
----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Tuesday, November 29, 2011 9:05 AM
Subject: [Amps] Can distilled water be used for a dummy load ??
> My hb 50 ohm dummy load consists of 4 x 200 ohm globars in parallel
> [type SP, glass bodied
> and suitable for oil immersion]. Each resistor is 1" diam x 12" long.
> [275 W CCS in air]
> Each resistor resides inside it's own 2.875" OD x sched 40 Aluminum
> tube.
> All 4 x thick walled AL tubes are heliarc welded.
>
> I heard some place that instead of xfmr oil, that distilled water can be
> used instead?
> The same glass bodied type SP resistors, [50 ohm, high wattage] are used
> in water cooled loads,
> the type that has the garden hose on one end, etc.
>
> Seems to me that distilled water will conduct heat a lot better than xfmr
> oil. The question is,
> will the use of distilled water in a 7 gallon metal container, with
> resistors immersed present any
> swr problems ? If I remember correctly, swr was high on heath cantenna
> loads if no oil used at all,
> and dropped to dead flat once the oil was poured in. There was also a
> similar 50 ohm load in the
> old arrl books, same resistor as I'm using but it was a single 50 ohm
> unit, and not 4 x 200 ohms in parallel.
>
> I would prefer not to use xfmr oil if at all possible. It's a little
> tougher to get a hold of these days..and not cheap.
> My main concern however is something leaks. Water on the concrete floor in
> the shop is one thing, but 7 x
> gals of xfmr oil is a disaster. Can you add rust inhibitor's or glycol
> to the distilled water ??
> Do I even have to use distilled water, or will clean tap water work ?
>
> A 50/50 mix of water/glycol will result in a 265 deg F boiling
> point..BUT the heat transfer is no
> where as good. I'm using a new 7 x gal paint can for this project, the 4
> x resistors and the welded AL
> tube assy, hang from the top lid.
>
> Thanks... Jim VE7RF
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