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re: a 16' cube
7 mar 2001
chuck simmons wrote:
>the parabolic reflector bothers me. the problem is that if the parabola
>is accurate at all, there will be quite high temperatures if an
>efficient absorber is placed at the focus...
it's a linear parabola made with a dozen line segments softly focusing
sun onto a 4'x16' 160 f water cooled target in a 70 f room. i figured
the target would lose 8,640 btu/h to the room air by all means. perhaps
we should figure 0.1714x10^-8((460+160)^4-(460+70)^4)4'x16' = 7550 btu/h
for radiation plus 0.27((160-70)/4')^0.25(160-70)4'x16' = 3387 btu/h for
convection, which reduces the solar collection efficiency from 81% to
100(45.3k-10.9k)/45.3k = 76%.
nick
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