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My Parabolic Trough Water Heater | 27 comments (27 topical, editorial)

Re: My Parabolic Trough Water Heater (3.00 / 0) (#11)
by BigBreaker on Wed Sep 3rd, 2008 at 10:08:22 AM MST
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The math of a parabola is pretty easy, y = a * x * x. To find the focus just put 2 units (inches, feet, whatever) in for "x", find y and then the reciprocal, IE 1 divided by "y". That's your focal length. Alternatively the take your desired focal length, take the reciprocal and multiply by 4 to find "a" and plot your curve.

http://en.wikipedia.org/wiki/Parabola

I think graph paper and a hand calculator would be plenty to draw a near perfect template. Also there are drafting aids like "soft" rulers that you can use to fit a curve to multiple points.

I wonder if there is a mechanical method of drawing it like there is for an ellipse, and obviously a circle. A parabola is a conic section like an ellipse and a hyperbola, so there is definitely a good shot. Ok there is a method but it isn't very practical. You'd need some very inelastic string as a parabola is basically an ellipse with one focus out in infinity.

[ Parent ]

Re: My Parabolic Trough Water Heater (3.00 / 0) (#12)
by TomW on Wed Sep 3rd, 2008 at 12:37:37 PM MST
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BB;

I wonder if there is a mechanical method of drawing it like there is for an ellipse, and obviously a circle. A parabola is a conic section like an ellipse and a hyperbola, so there is definitely a good shot.

mkseps posted this link above in #9 I think:

http://home.germany.net/100-441770/amsi-model.html

It looks easy just a T square, string, a pencil and a couple pins. No math just draw it.

Tom

"Education consists mainly of what we have unlearned."--Mark Twain
[ Parent ]

Re: My Parabolic Trough Water Heater (3.00 / 0) (#13)
by BigBreaker on Thu Sep 4th, 2008 at 07:36:40 AM MST
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Very neat link - thank you. I was going to suggest approximating a parabola with a very eccentric ellipse. You can use just a string to make an ellipse so it requires very little in the way of equpiment.

Adding in a t-square is no great burden and using it in the way suggested on that website looks easy and accurate - no approximations. I like it.

[ Parent ]

My Parabolic Trough Water Heater | 27 comments (27 topical, 0 editorial)

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