|
|
re: parabola formula
18 apr 2000
zamboni wrote:
>...the problem was to determine the surface area of a parabolic mirror...
the crc math handbook gives the length of a 2-sided parabola as
s = sqrt(4x^2+y^2)+y^2/(2x)ln((2x+sqrt(4x^2+y^2))/y), so a linear
concentrator, eg a 1-sided solar trough with focal length f and
y^2 = 4fx has length l = sqrt(x^2+fx)+fln((x+sqrt(x^2+fx))/sqrt(fx)).
this is a bit more than the triangular length, 1.48 vs sqrt(2) = 1.414,
if x=y=1 and y^2=4(1/4)x. a 12' tall x 24' wide attic with a central peak
and a transparent south wall and a parabolic reflective north wall has
f = 12^2/(4x12) = 3' and needs l = 17.75' = 16.97' of reflective length.
nick
|
|
