Re: How to make money fast (in science fiction)

Luke Campbell (lwcamp@[EMAIL PROTECTED]
) writes:
> On Apr 8, 9:27 pm, Ric Locke <warlo...@[EMAIL PROTECTED]
> wrote:
> 
>> Thank you very much, by the way, for the (to me) new insight of
treating
>> a solar cell as using the Carnot cycle! It's absolutely true, of
course,
>> but I'd never thought of it that way, and it's a useful way of looking
>> at it.
> 
> I didn't realize this until I was teaching an undergraduate course on
> thermodynamics and statistical mechanics.  When I got to the part of
> what was and was not a heat engine, I tried to come up with various
> well known examples of generators/motors that fell into both cl*****
> (wind turbines, hydroelectric turbines, automotive piston engines,
> methane fired gas turbines, nuclear power plants, etc) for the class
> to consider.  When I considered a solar cell, I realized that sunlight
> (and thermal radiation in general) has entropy, and thus has the same
> limits on turning radiant heat to work as any Carnot engine.  It is
> somewhat curious, though, that the same device can be a heat engine
> when run off of radiant heat, but not a heat engine when run off of,
> say, a laser beam (which has vani****ng entropy).
> 
> I don't think the class really appreciated this point, though, as much
> as I tried to put into their heads that what really defines a heat
> engine is the flow of entropy through the device, rather than any
> particular set of isotherms/isobars/adiabats/whatever.
> 

Very interesting. Have you seen the current thread in sci.physics "Carnot
efficiency and solar cells, etc."?  (The consensus there is that solar
cells are not Carnot heat-engines, but I suspect you've thought about the
matter more than most of the participants.)

	--John Park