non tracking dish collector?

[Kwazai]

I had read some info on solar cookers for fabrication techniques and had run across some on solar steam also-

solar steam- http://www.lightlink.com/francis/stevenhomepage.html

concrete dish fab- http://www.cc.jyu.fi/~hvirtane/cooker/

after playing around with cadd for a while I had drawn up a small hot dog cooker which looked like an oblate spheroid with the top cut off. If filled with water the water could be at a height to acheive TIR at the air-water line. not sure if I cadd'ed it correctly (reflecting equal angles at the normal to the surface).

http://www.glenbrook.k12.il.us/gbssci/phys/Class/refrn/u14l3b.html

any ideas how to put this into a calculable formula- the cadd work is a bunch of disconnected segments.

[Kwazai]

[Kwazai]

maybe this will make more since

[Phil Timmons]

Hey Kwazai,

I think you are working on some very useful ideas here with a fairly clever approach.

Are you still interested in working on this?  (I see this is about a month and a half old).

If so, I would like to help you.  (EE type with some optics design)  Are you mostly interested this as a theoretical concept or actual application?  My bias (enginerd) is more towards application, but theory can be fun, too.

[Kwazai]

don't have the money to pursue it right at the moment- any kind of real heat would mean 10FT diameter or better.  the sides would have a focal point equal to the radius and the bottom would have a focal point just below the surface of the water.

I am in need of a good equation grapher that outputs .dxf files. I can check the reflectance normal to the surface 2-D. Not sure about the math involved for calcing the normal to the surface (integral/derivative..)

[Phil Timmons]

I think I might have some curve fitting software that can do that.  I will ponder it with some other EE type friends, if that is ok with you?

By pursue, I assume you mean actually build one?  Or try some smaller "proof of concept type thing?  Don't know that I could do an economic justification on a 10 foot diameter one, either, but I probably have some surplus, junk, leftovers, etc., we could do something with, if you want?

I admire the use of mixed materials (air/water interface)for the properties, but in application would not the water surrounding the target rapidly dissipate the heat -- or would it be a glass (?) tube?  No biggie, just have more of engineering application bent, rather than physics on this end.

Actually when I first saw your first sketch drawing in this topic thread, I was thinking trough -- rather than round.  Have you considered this for a long trough style design?

[Kwazai]

I had an offlist email conversation in regards to several things- mylar film and fiberglass won't mix very well. got me thinking about white paint(titanium oxide pigment instead). and you might just be right about it being oblong shape (possibly more like a rounded end football with a conic slice out of the top). The water /air interface is what would make it non directional (meaning it could be used without heliosat)-it is the TIR that makes catching low light(morning,evening) possible(-based on the idea anyway..). The water would probably not absorb much heat- the pipe at the foci(focus line?) would be where the heat would come from. I have not tried to plot the foci versions of the horizontal and vertical parabolas so it may actually end up more like a flat top tomato or similar in actuality. the top part of the sketch is a plan view- round for simplicity at this point. The pipe being the heat point- with a large solar-incident-light area would need to be sized hopefully to boil the water inside it- the depth of the pipe in water being the available steam pressure (2 to 5ft of water head of steam-dependent on the temp and depth)- thats why so large (10ft or better). still not sure about the actual shape. a 10ft diameter flat top tomato would be rather impractical to make- but something about hot tub size wouldn't. I had seen recently on the turbine list (posted here a few weeks ago) where one of the tesla turbine guys had put together a "dirt mold" dish about the same size. I can send the link if you need it- its in one of the postings here.

in terms of proof of concept- the 'hot dog cooker' size would probably be big enough to see if it functioned acceptably without having to track (heliosat) the sun.

[Kwazai]

Had you been able to check the curves yet? I got to thinking about this the other day and looking at what kind of junk I have laying around the house. When I can find all the pieces I think I'm going to try a small one. A cardboard box, three pieces of threaded rod & nuts, some wire ties and a box of aluminum foil. If I put the threaded rod thru the ends of the box (with-say- a cardboard disc at the ends) I believe I can 'stretch' the box to somewhat football shaped proportions and then cut part of the top off and line it with aluminum foil. The rod would be attached at the box at the center of the box face and perpindicular to the other two pieces of rod. I have a couple of rectangular boxes, but they open on the wide face instead of just the ends. I will post here when I get one put together.

L8r

Mike

[Phil Timmons]

No. [grumble, grumble] The program I think I have is sort of "nested" on the hard-drives I have copied up on to bigger hard-drives.  I think it is buried a few layers in. After a few hours of looking, I am not so certain.

Anyway, I have copied our stuff up to a friend who does optics to get his point-of-view, too.

However, on the practical end, I do have a bunch of small mirrors that I think I can use to approxiamate the result -- set them up standing on a grid drawn out on a smooth sheet of plywood.  And after I get the data points that creates, we can "curve fit" those data points, to get the underlying equation of the curve.  That should allow us to scale the design to any size.  Kind of bass-ackwards, but it should work.  

Is it is a resonable assumption that the mirror-to-mirror reflection would be the same for an air-to-air surfaces, as your water filled tank?  I am thinking that would be the case, as the incident angle is created only at the air/water interface of your design?

[Kwazai]

that is a reasonable assumption- TIR would occur only at the water-air interface.

as of late I have also been looking at refractive indicies on clear polyethylene sheet. an alternative to the water may be a vertical semi-parabolic cone-shaped piece of clear plastic sheeting (if I only had a brain...) above the spheroid-not sure just yet. The idea being to capture full sun-like a light trap- without having to track the sun.

[Phil Timmons]

Got some comments back from a friend regarding this . . .

(Just so this makes sense, he was thinking a trough design (so the basic reflector design is only two dimension)

=============

Geek friend:

"Interesting.  Guessing it could be made to work, somewhat.  You brought

up one issue, which is the heat transfer back from the working fluid (in the

pipe) to the water needed to get TIR in the trough.  I think you would end up

heating the entire tank rather than adding a lot of heat to the working fluid.  

That said - you might be able to come up with a N-S oriented open trough

that would work in air, and might need adjustment only seasonally to account for

solar elevation."

"There isn't any material that you can apply only to the top of the

trough achieve TIR, as you only get TIR at an interface from a dense to a rare

medium. However, if you filled the trough entirely with a medium denser than

air, but thermally resistive, then you might have something.  But it'd be

something heavy and expensive.

"Things also to consider could be a shaped "lens" atop the trough, or a

series of fresnel lenses.  But I think the design trade would be for making the

maximum use, all the time, of all of your optics versus the mechanically

complexity of focusing the mechanism.

"H'mmm."

==============

Phil (again):

Looks like his perspective matches yours regarding top-side lenses, reflectors, refractors, whatever, to grab more sunlight in.  Dunno if that is entirely valid, as the total exposed surface area is still only the total exposed surface area.  That is where the total energy available comes from?  Again, that is my assumption, and this is new area of pondering for me.

I had considered "wing wall" reflectors -- (e.g., for a North-South trough, the West reflector goes up in the morning, and the East reflector goes up in the afternoon).  

That increases the actual total reflective surface area, and so more energy is collected.   However, it starts to slip away from one of the beauties of your concept -- no mechanical motion required.

But I am going on with the "reflector board" two-dimensional test rig, and we will see where that leads.  

[Kwazai]

thinking as of late is from seeing the anatomy of an eyeball-with a lense at the top (water lens using plastic sheet?- not sure about how to get plano concave lens shape though-tir just above the plastic at the water surface) anyway-still just thinking. L8r

Mike

[Kwazai]

Ok,

after having followed some links to  a hotub heat trap solar cover-I rethought what I was after (hot tub size-cheap from plastic or aluminum,etc.). please comment- I'd like to have something doable small scale (9ft diameter or so). hadn't gotten to the flash steam part yet. see pic below.

[Kwazai]

ran across a good link today and also found the concentric ring version was patented in 1982. anyway her's link

http://www.powerfromthesun.net/book.htm

[ghurd]

Did you see this solar absorbtion refrigeration ice maker?

Not sure if it'll help.

http://homepower.com/files/solarice.pdf

G-

[Kwazai]

I had seen it earlier. The S.T.E.V.E.N. homepage also has a similar setup for low pressure steam (50 psi or so). wish I lived in the country....