Re: Here it comes

On Nov 17, 3:17 am, Jim Black <fmla...@xxxxxxxxxxxxxxxx> wrote:
On Fri, 16 Nov 2007 23:00:53 -0800 (PST), Willie.Moo...@xxxxxxxxx wrote:
On Nov 17, 12:24 am, Bill Ward <bw...@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Fri, 16 Nov 2007 12:54:27 -0600, jgraber wrote:
For a different concentrator:
Suppose a standard satellite dish parabolic reflector concentrates
sunlight from a 3m diameter to a 1cm diameter, and a synthetic ruby
downward reflector (some other name for it) concentrates the 1cm diameter
to a 1mm diameter; the 1mm focus is reported to be hotter than the sun. Is
this believable? (reported in Pop Science or some such)
If so, then it could theoretically use the sun as the cool end
of a Stirling engine. Does this violate the 2nd law? If not, why?

If you've transferred heat from a cool body (the sun) to a hot body (the
receiver), you've violated the second law. We're still here, so I kind of
doubt that.- Hide quoted text -

- Show quoted text -

You're getting lost in the translation.

Solar pumped lasers have been built.

Take a large parabolic concentrator and focus the light onto a fabrey-
perot cell to produce a solar pumped laser.

Take the laser output and focus it to a very tiny spot not possible to
achieve with the solar image - greater than 40,000x - which is the
limit for the solar image, but not for a nicely built laser..

The laser spot can be hotter than the surface of the sun. No problem.

Does this mean that the 2nd law is violated?

NO!

Why?

Because the total power of the laser is not increased even while the
power per unit surface area increases without bound.

That's the first law.

Let's say the laser is 50% efficient. That means for each 4 watts of
power entering the system from the sun, a 2 watts of laser energy
emerges.

Now, Bill Ward and Jim Black would have us believe such was impossible
because we can run a heat engine on the temperature difference between
the laser target and the solar image - wrongly arguing it would
violate the 2nd law.

Clearly one can see why when you actually run a heat engine in this
way that recovers 50% of the energy difference between the hot side,
and the cold side - and find that for every 4 watts of power entering
the system from the sun, 1 watt shows up in the heat engine.

The laser system is thermodynamically possible if the laser requires a heat
sink cooler than the sun to operate. Does your concentrator design require
a heat sink to operate?

I have a water filled lens whose surface area is far larger than the
PV cell illuminated.

I don't want to go too deeply into this sort of analysis for my
system, at the level it makes sense, but at this level its easy to see
that making hot spots out of cold spots does not violate the 2nd law
if the total power of the hotspot is less than or equal to the total
power in the cool spot.

The rule is that the sum of the heat energies taken out of objects, divided
by their temperatures, must be less than or equal to the sum of the heat
energies put into other objects, divided by their temperatures.

Entropy - I'm familiar with the concept.

Your concentrator can't work unless there's some reason you can't heat the
entire concentrator, with the exception of the target, to 6000K, heat the
target a little hotter, subject the concentrator to 6000K blackbody
radiation, and have it still concentrate light.

None of this applies so clearly your statement that my concentrator
can't work is gratuitously made.

--
Jim E. Black- Hide quoted text -

- Show quoted text -

Obviously each time I take your objections at face value, you shift
the argument around so that you can make dismissive statements about
me for no damn good reason. Plainly I can safely dismiss your
comments on that basis. Clearly, your goal is not to understand, but
to discredit - without having any real basis.

Fact is, I've built arrays of lenses made of sheets of PET filled with
water that illuminate sparse arrays of PV material soldered to copper
foil - all stabilized with EPS. I have quotations from qualified
vendors that show that they can be built for 5 cents per peak watt or
less based on the results of over a dozen years of testing.
..
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