S&JY wrote:
I am interested in your educated thoughts regarding polarity reversal
of constant current DC being supplied to the electrodes.
Specifically, how would one optimize the frequency of polarity
reversals, given brew the time (and possibly the current), to minimize
the buildup of crud on the electrodes? If the reversals are too fast
(e.g. many reversals per second), the ions will not have time to get
from one electrode to the other, and brew time will go up
substantially. On the other hand, if the reversals are too slow e.g.
a few times per brew time), then I suppose this might defeat the
advantage of less crud buildup on the electrodes.
In my case, I use 5.5 inch electrodes spaced about 2 inches apart,
with a constant current of 0.25 ma for 24 hours. This makes a very
good product with very small particles. Based on your experience,
what would be the recommended range of time between reversals, and
what is the basis for your recommendation?
Thanks,
Steve Y.
Optimum time between reversals is a function of the voltage gradient in
the liquid and the distance between the electrodes. It is also a
function of agitation or stirring. For 10,000 Volts it is about 120
reversals per second, and for 20 volts and 1 inch spacing with stirring
it is about 1one per minute. Obviously it is not linear, if you double
the voltage, you can more than halve the time. Quite likely the reason
for this is that with high voltage the electrode size is very small and
have a much higher voltage gradient than between flat plates facing each
other. If we are using 14 gauge wire, the gradient near the wire end
will be about 10 to 20 times what it would be if we were using plates.
Thus if you consider that, it appears to be rather linear, and works out
to about:
F = V/2400l Hz
So if you have l = 1 inch between plates, and 20 volts, frequency is
equal to 20/2400 = 1/120 Hz = 120 second cycle, or 60 seconds per
reversal.
The distance between the electrodes comes into play if there is
sufficient time for the ions to travel to the other electrode during the
cycle. If electrodes are kept sufficiently far apart, and good stirring
is practiced, this should not be a significant factor.
Marshall
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