Re: [Phys-L] work versus mechanical transfer of energy

[Diego Saravia <dsa@unsa.edu.ar>]

> Not quite the same.  There has to be "some" temperature drop
> across each heat exchanger, in order to persuade the energy
> to flow in the desired direction.  The faster the engine goes,
> the greater this drop must be.

of course!,  thats the real world (or a better model), not a simplified one

in that simplified model, the equilibrium thermodinamics, or thermostatics,
nothings moves, or it moves at "constant velocity", no forces. indiferent
equilibrium.

You move the engine "cuasistatically", horrible word.


> Just as you ignored the inner workings of the heat exchangers
> in the Carnot engine,


because I am not interested in irreversibility, in fact in that case I want
to supress it.



> you can ignore the inner workings of
> the filament that carries the heat leak.


In that case you do not have entropy generation, but you have it!, so your
model is inconsistent.

just as happens in the two condersers, one charging the other, if you take
the resistance to cero, your model colapses, if you dont
take in care another stuff like electrons acelerations, or wave emissions.



> The apparatus was
> designed to make such details irrelevant.  If a student
> asks about it, you can say hypotheses_non_fingo, which is
> Latin for "I'm ignoring the question because the answer
> doesn't matter".


the problem you faces is that you have irreversibiliy in the system, but
you are not able to tell where is it!

in the two condersers you loose energy ....  but where its gone?????


>     In case you hadn't noticed, I'm a huge fan of the
>     spiral approach to teaching and learning.
I like it too.

I think is a good idea to teach thermostatics as a first version, then you
can advance to the > problem and  the s+

in a second review you can take in care of heat exchangers, its size,
analize power, see curzon-alhborn machines.
And its remarkable formula 1- sqrt (T/T) for maximum power.