Christopher Tidy wrote:

Oil isn't going to carry much charge, unless you dope it with something,
maybe little particles of some polar stuff. Or, maybe, tiny wire
fragments. Then, the charge has to REACH the particles, THROUGH the oil,
which I think
wrecks the whole idea. You don't want a very good insulator to interfere
with the charge transfer.

Thanks for the thoughts. Why can't oil carry much charge, but a nylon belt
can? I don't doubt your answer, but as more of a mechanical guy, I'm not
sure of the reason.

A couple of days ago I was thinking that it might be possible to mix the
oil with thousands of tiny plastic balls which could carry the charge. Or
hollow metal balls, but they might not go through the pump. The pump can
cope with a maximum particle size of 3 mm and, depending on the head, can
deliver a flow rate up to 60 litres/minute. But charging the balls might
be difficult.
Yes, I think you are on the right track. I'm not a physicist, but it seems
that a liquid just isn't going to carry much charge. i think it is SURFACES
that can carry charge, and these surfaces have to have a distinctly
different polarity than what they are surrounded by. Anything works OK if
surrounded by vacuum (or air, even). The oil would have to be a VERY good
insulator, meaning very clean and dry. The metal balls ought to work, you'd
need a metal brush to break through the oil film to charge them.

Jon