[Amps] Can distilled water be used for a dummy load ??

[Roger]

On 11/29/2011 9:05 AM, Jim Thomson wrote:
> 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'd try it and see. As long as it's either distilled or Deionized it 
should work. As this is a new system you have not used with oil, you 
don't have to worry about cleaning it.   I'd check it with and analyzer 
and with no fluid, then add water and check again to see how it 
changed.  If it changes for the worse then I'd try the mineral oil.

Yes, water is about the best thing going for heat transfer (calories per 
unit weight) at atmospheric pressure.  Oil, although not as good is 
probably good enough.

Water may need to be changed maybe once a year.  DI is ion hungry so I 
don't know how it'd work with the solder joints or metal in the circuit.
Tap water?  It definitely will lower the resistance of the dummy load.  
Whether it will adversely affect the SWR, only a test will show.

73

Roger (K8RI)

>
> 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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