Solar cookers can break your heart, but not the laws of thermodynamics.
Consider this elementary fact, my dear Dr. Watson. The insolation on earth
near the equator is about 800 W/m2, it is less at the end of the day, and
much less after sunset. For an aperture of 0.1 m2, you getting about 80 W
black body, ignoring losses. Concentrators have nuttin to do with it! This
amounts to about 270 BTU/hr from which you could boil a bit less than 2
pints of water in an hour, assuming no losses.
BTW, you can, with care and ceremony, make ice in the Egyptian deserts
every cloudless night, by exploiting radiation to the stars from shallow
water trays, and careful control of nucleation, convection and vaporization.
In fact, the temple priests used to do it on the flat roofs of the temples
to impress the unwashed on the bounty of whatever God they were scamming
that week. Much hoopla, involving sanctified water brought up from the
basement (where it had got pretty cool, mixed with yesterday's ice),
throwing holy dust on the surface (to provide nucleation particles) and
wafting the surface at just the right time and rate with magic ostrich
featherwands to actually control heat transfer due to convection and vapors.
It's just thermodynamics, Nefertiti! And if sometimes the ice didn't form,
it was because someone's mother-in-law was a witch! It's amazing what them
religious guys know!!
I usedta teach elementary courses in thermo in CA and the conversion
constants are from memory and only roughly correct.
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