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Ludwik Kowalski wrote:
On Friday, May 30, 2003 Pentcho Valev wrote:
This is just one of the numerous myths in thermodynamics,
Ludwik. When a gas pushes a piston, isothermally, it converts
heat into work without creating disorder elsewhere.
Please keep in mind that thermodynamics is not my specialty.
You are talking about an engine, a cyclic device delivering net
work. I know how to calculate the p*dv work, done on an agent,
when an ideal gas is allowed to expand very slowly, at constant
temperature. The same work must be done by the agent, to
compress the gas slowly to the initial state at constant
temperature. The net work in each cycle is zero.
Yes, your constant-temperature electrostatic engine
(presumably performing net work in each cycle) works
differently. You allow the plates to come closer to each other
in a vacuum, (work done on the agent) and you separate
the plates in a liquid dielectric, such as pure water. You argue
that work done by the agent (in separating plates inside the
liquid dielectric) is smaller than work done on the agent,
during each constant-temperature cycle.
Is this a correct description of your proposal? In my mind you
are describing a perpetual motion machine of the second
kind. Please show me what is wrong with this "accusation."
Nothing, except that the perpetual motion machine of the second kind is
just one of the two possible solutions to the problem. You refer to two
steps of the four step cycle - when the plates come closer in vacuum
and
then when they are separated in the liquid dielectric (steps 1 and 3).
The net work extracted from THESE TWO steps is positive - there can be
no doubt about that. The reason is that the attraction between the
plates in the dielectric is experimentally shown to be lower than the
attraction in vacuum. But we should take into account the other two
steps - when the capacitor is immersed in the dielectric and then when
it is withdrawn (steps 2 and 4). It may happen that we SPEND net work
in
these two steps, and the work spent counterbalances the net work gained
from steps 1 and 3. Then there is no perpetual motion machine of the
second kind. However there is a second possibility. As we let the
capacitor down and immerse it into the pool (step 2), the capacitor,
through a pulley, lifts some (maximum) weight. Then, as we withdraw the
capacitor from the pool (step 4), the same maximum weight is used for
withdrawal. If so, we do not spend any net work in steps 2 and 4 and
the
net work gained as the plates get closer in vacuum and are separated in
the dielectric (steps 1 and 3) becomes NET WORK EXTRACTED FROM THE
CYCLE. This can of course be called perpetual motion machine of the
second kind.
As far as I know the rules are as follows. We must accept
data coming from real reproducible experiments, no matter
how many theories they disagree with. But gedanken
experiments are different in that respect; we accept their
conclusions only when these conclusions do not conflict
with accepted theories. Do you agree with these rules?
It depends on what you mean by "theory". Is the statement "perpetual
motion machine of the second kind is impossible" the result of a
theory?
I am afraid it is not even an experimentally tested proposition.
Rather,
it has been advanced to show that those who attempt to test it are just
as mad as those who try to extract energy out of nothing.
In my view, gedanken experiments should not differ essentially
from
real experiments - there can only be inessential reasons for not
performing them in practice. In the present case, the easiest thing to
do is to partially immerse the capacitor in the pool, punch a hole in
one of the plates, near the pool's surface, and see if water would leak
through the hole. That is extremely easy but I am unable to do any
experiment - I hardly survive. I have been asking physicists to do this
experiment for several years - no effect. This shows how efficient the
curse "perpetuum mobile of the second kind" is.