"vairox" wrote in message
oups.com...
lots of replies! I'm trying to distill alcohol without an open flame,

allegedly, your local Customs & Excise office - look under HMCR in the
yellow pages can supply all the advise you'll need.

ethanol boils off at 78.4C (174F) and I don't want a source that is
going to constantly turn on and off because it will lower the temp and
then have to get back to where it was and cycle again and again... I
was hoping there was some sort of heating device that you just turn to
whatever temp you want and it stays there... maybe one of those $800
lab hot plates I don't know.

it doesn't seem like it would be all that hard to have an electric hot
plate that stayed at a certain temp, but then again I'm no electrician.


One of the phenomena of _all_ control systems is called hysterisis:
What you've described as "going to (constantly) turn on and off because it
will lower the temp and then have to get back to where it was and cycle
again and again"

A system will ramp up to a control value, perhaps maintain that value then
fall off to a lower value, perhaps maintain this lower value before ramping
back up to the top value. Any temperature maintaining system will exhibit
hysterisis. 'Tight' control loop systems _might_ achieve 78.4 deg but it'll
be 78.4 +/- a 'bit'. Roughly; the size, and direction, of 'a bit' is going
to become more expensive the smaller 'a 'bit' is.
78.4 (0 / -2) would be cheaper than 78.4 (+0.001/-0.001). You seem to desire
a 'perfect' system with no hysterisis that will heat a fluid to 78.4 +0.000
/-0.000. But as the old saying runs; anything is possible given enough time
and money.

BTW; why?

--

Brian