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re: parabolic trough concentrators
21 sep 2001
chris hallman(?) wrote:
>what i did was determine the focal point of the sun rays as they reflect
>off a trough on to a pipe -- on paper. i followed j.d. wolfe's method.
>i got a protractor, and compass. i found that only about a quarter of
>the circle could be focused on a pipe, unless you got a big pipe.
i suppose you were modeling a 6" diameter reflector with a 0.5" pipe:
~~~
ray wrote in message
> bill roosa has stated that he uses half circles with .5" pipe for his
> collectors. ~6" edge to edge. the simplicity of using half circles is
> apparent.
~~~
yes, it also seems to me that the reflective parts near the edge of the
half-cylinder wouldn't focus much solar power onto the pipe when the sun
is shining directly into the trough, perpendicular to the reflector
opening, since those parts would only reflect at a grazing angle. but
bill seems to be saying that circles have an advantage over parabolas
at other times of day when the sun is at different off-axis angles, with
no tracking, when circles can focus better (from a smaller area.)
but non-imaging "compound parabolic reflectors" (as used at cern) are
made with parabolas vs circles. and as you suggest, using a bigger pipe
may be a better non-tracking option. or moving the pipe vs reflector.
paavo kousa's recent patent describes systems like these ("directing
and concentrating solar energy collectors," us patent no. 5,851,309,
12/22/98, about 100 pages with lots of diagrams and computer flow charts
for a mere $3 from the commissioner of patents and trademarks, washington,
dc 20231.) some large radio telescopes work this way.
>i'm 17 years old and don't have the money to build a trough but
>someday i will. right not i've got to study and get ready for college
>next year. i'm thinking about studying to become an engineer.
you might check out some of the downsides to engineering as a career:
o lots of unpaid overtime,
o weird non-verbal colleagues,
o being misunderstood by most of the world,
o seasonal mass hirings and layoffs,
o salary compression (engineers with 20 years of experience
often make about the same as those with 5 years of experience), and
o success is often defined as getting out of engineering, into management.
nick
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