Light funnel design

[...]

Right now I am away from an internet connection for my computer, which
has the graphs and other communicative things. Perhaps I'll wrestle
some files onto this computer sometime soon, but otherwise it'll be a
couple weeks. But the light funnle does indeed have interesting
properties. I am no longer skeptical about the usefulness of a well
designed light funnel in solar thermal processes.

My friend, who has built one, has done some research and claims that
the ideal angle of the funnel is 60 degrees. Vinay has been in the
scene for a while. Is this the common thinking about funnels, that 60
degrees is ideal?

If it is, then raytracing and good old algebra have some suggestions.
When I post some more detailed analysis I'll have a design to propose
based on my results.

elliot

[Vinay]

The Brigham Young guys who invented it claim 45 to 60 degrees is
ideal. I think it depends on how often you're willing to turn it. But
they showed no working, so for all I know it was a guess - it'll be
great to actually *know* :-)

Vinay

On Thu, Oct 8, 2009 at 4:38 AM, ... <offonoff...@gmail.com> wrote:
>
> Right now I am away from an internet connection for my computer, which
> has the graphs and other communicative things. Perhaps I'll wrestle
> some files onto this computer sometime soon, but otherwise it'll be a
> couple weeks.  But the light funnle does indeed have interesting
> properties.  I am no longer skeptical about the usefulness of a well

> designed light funnel in solar tThe Bhermal processes.

>
> My friend, who has built one, has done some research and claims that
> the ideal angle of the funnel is 60 degrees.  Vinay has been in the
> scene for a while.  Is this the common thinking about funnels, that 60
> degrees is ideal?
>
> If it is, then raytracing and good old algebra have some suggestions.
> When I post some more detailed analysis I'll have a design to propose
> based on my results.
>
> elliot
>
> >
>

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[...]

I just got back to a decent internet connection and uploaded my report on the solar funnel. 

http://www.permafacture.org/funnel.html

The result is that a tilt of 75 degrees is ideal.  This angle out performs 60 degrees in every way.  I wonder why this has not been brought up before.  I stumbled upon this through ray tracing but regular old geometry could have indicated towards this fact without such extreme measures as numerical simulations.

In a cone type setup, 75 degrees allows for a concentration ratio of about 13, where a 60 degree funnel is limited to 4x.

There is no reason I can see for a shallower angle.  Although 45 degrees behaves differently from the steeper models, a single vertical mirror would easily out perform it in a once a day tracking adjustment situation.  For even once every hour and a half adjustments, 75 degrees is superior to any other design.

I'm really frazled right now from traveling and tackling the dozens of things that were neglected in my absence the past few weeks.  But the report should be enough information for right now.

I have not had opportunity yet to test these numerical results in the real world.  I could be perfectly wrong, But i've been surrounded by my results for long enough that I fully believe them.

later,
elliot

[Vinay]

Elliot, this is beyond wonderful work. I'm still parsing it, so I
wanted to drop you a line to say thank you now, and I'll have thoughts
and feedback in a couple of days.

Fantastic, and well done.

Vinay