Re: re Mineral Spirits (water conductivity)

To: tesla-at-pupman-dot-com
Subject: Re: re Mineral Spirits (water conductivity)
From: "Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Sun, 28 Feb 1999 18:35:39 -0700
Approved: twf-at-verinet-dot-com

> Jim:
> Are you certain of this? That D.I. Water will actually conduct enough to
> be a problem? The fact that the water will attack and ionize any metal to
> become conductive being put aside, I thought DI water had resistances on
the
> order of megaohms?

Typically 2 Megohm-cm.. which is a lot, but not a perfect insulator.. Fine
for AC and fast pulse apps though, but no good if you want to charge it up
over a period of seconds. 


> Methinks the problem is that the water refuses to remain DI. We deal with
> this all the time on our synchrotron and related beam transport systems.
> We use DI water to cool our buss lines,power supplies and magnets - the
> water
> ciruculates in the windings - but it takes constant work to keep it that
> way,
> and our resin modules are treated as toxic waste (Lots of dissolved
copper
> from
> the buss bars.) This is DC at low V (usually under 50) but high I (on the
> order of 2500A) Perhaps this is why we get away with it..
> Just a comment from the peanut gallery.

I've used DI water to cool HV vacuum tubes and it works just fine. As you
say, the conductivity gradually rises and the leakage current grows, until
you redeionize it or replace it with new water (generally the latter for
me, it is cheaper).

However, if you wanted to use it as a capacitor dielectric, for instance,
you'd probably have a hard time circulating it within the close plate
spacing.  

And, for other large systems (like a Marx Bank that I was building), I
found that the cost of the tanks to contain it was high enough, that it the
cost of oil to insulate it instead was insignificant.

Another interesting insulating liquid is Liquid Nitrogen. half the density
of water, and a coolant, which greatly reduces the resistance of those
copper conductors. However, as a capacitor or transmission line dielectric,
it isn't as wonderful (water is awfully attractive in that application,
gotta love that epsilon of 80 when you're trying to make a 1 ohm impedance
transmission line.