DIY Tube collectors

[meow2222]

DIY Tube collectors

There are some unanswered questions here, and I've never tried doing this, but since I couldn't help noticing one could possibly make concentrating tube collectors for 1/10th of Navitron's prices, I thought I'd float this uncertain idea out here and see where it goes.

1. Take some 1.5" fluorescent tubes, and cut off each end, leaving you with lots of glass tubes.

1. Unsharpen the cut ends.

2. Pull a rag thru each tube on the end of a wire to rub the phosphors off. They come off easily.

1. Cut strips of silvered mylar, and string each strip of greased mylar out between 2 wires with circles of wood on the end, so you get a gutter-like shape. Apply a grease that wont melt at 100C.

2. Thread a glass tube over each mylar strip, and press the mylar into place against the glass.

1. Fab some end stops for the glass tubes. These wont be airtight, the tubes wont be vacuum insulated, just glazed. Flat discs of plastic would probably do.

2. Mount tubes onto your wall or roof, horizontally, using pipe clips to hold the 10mm pipe inside, and bigger pipe clips to hold the glass tubes. Turn the tubes to face the sun. Mount them above each other, all horizontally. The 10mm microbore can be bent rather than jointed at each end. Insulate the metal tubing bends.

We now have a single glazed concentrating collector, with roughly

10mm:32mm concentration factor, or 3:1. Cost is 10mm pipe, pipe clips, a glass cutter, some pipe insulation and time.

Concentration will be similar to commercial vac tubes, insulation as standard flat plate collectors, and price would be a small fraction of Navitrons, and probably cheaper than flat plates. This means for much less money you can have twice the panel area and a lot more output.

Your turn to tell me all the problems with this untried idea.

NT

[dennis]

8< over complicated mechanics.

Watch the phosphors they can be dangerous.

Why not do it the easy way?

Take some triple wall polycarbonate and set it up so you can trickle water down through the rear channels. Mount it on some insulation on a south facing wall and collect the heat.

You should be able to preheat loads of water for much less than commercial panels.

[John Stumbles]

I've seen black single wall polycarbonate sheet with channels fitting the top and bottom edges to feed water through. They were for heating water for a swimming pool so I guess they should be available somewhere. A shaeet of clear polycarb over the top to give double glazing would probably increase efficiency quite cheaply.

[Bob Mannix]

I would say the major problem would be the fragility of the tubes, both with regard to removing the ends and in the manufacture and subsequent use with no ends to add strength YMMV

[Mike Harrison]

Probably much easier to just buy glass tube from chem lab suppliers...

[Mike Halmarack]

Looks like great fun! If it works that would be a big bonus. I can see how buying the tubes from a supplier might be preferable especially if they are thicker walled and clean. Assuming that a vacuum would be helpful, do the tubes you can buy have sealable caps with a valve to allow a vacuum to be caused?

[Grunff]

Deffo - glass tube is extremely cheap, not worth messing with fluorescent tubes.

[Terry]

Is it not true that fluorescents contain a very minute amount of mercury? Which vapourizes and starts conduction through the tube? Also that the powder coating contains chemical phosphors. Do know I have been warned that although quantities are small not to allow kids to break up tubes or inhale the dust etc. If one were dealing with many tubes that could require precautions. But right-on mate for thinking up a possible recycling/reuse! Terry M

[Grumpy owd man]

You can have my old flu' tubes if you want them! Hundreds of 'em!

50 tubes a week suit you? Costs a Government Minister's Spouse's bribe to get rid of them!!!!!!!!!!!!!!!!!!

[meow2222]

From: dennis@home

I understand there were some nasties in historic tubes from the 40s, but that todays materials are not a worry. However someone else might know more detail.

The question is, how do you make a watertight robust seal along the edge of the multiwall sheet? Also those sheets aint cheap.

that isnt hard :)

From: Bob Mannix

I suspect youre right there, outdoor fl tubes would be subject to breakage. Is it poss to apply a film or coating to keep them together if they crack? And is it cost effective? I expect not.

Then again if theyre out of reach?

From: Grunff

Mike Harris>> Probably much easier to just buy glass tube from chem lab suppliers...

do you know what it costs?

From: Terry

yup. This is released into the environment either way. Tooth fillings are a much bigger source of mercury exposure.

basis of the fear of encountering a 1940s tube, some of which used quite toxic coatings.

From: Mike Halmarack

I suppose you might be able to make and weld on glass end caps, make a flexible seal to the copper, evacuate and seal the tubes, but its a lot more work, and they should work ok without that.

I might have a solution to the thinness of the fl tube walls: add a sheet of wired glass over the whole assembly to keep impacting objects off. Still far cheaper than navitrons.

And that raises the optional extra of putting a frame round the top glazing. If you do, you've got double glazed tube collectors, still at much lower cost than Nav.

NT

[Guy King]

The message from "Terry" contains these words:

It's already a vapour before the lamp's switched on.

[Guy King]

The message from [e-mail] contains these words:

Some of them act as anticoagulants - cuts can take some time to stop bleeding.

[Owain]

I'm sorry, I thought this was a cunning plan for receiving satellite signals without using a dish in a conservation area :-)

Owain

[Roly]

I'm intrigued, it sounds promising. Have you done this yourself ?

How do you seal it so that the water doesn't leak out ?

[dennis]

But I have just aqquired 3 off 2.4m lengths of secondhand 10mm polycarb to play with.

I would expect some aquarium tubing and silicon sealant should work fine.

[meow2222]

that might be adequate for ground level use but I cant see it being robust and reliable enough to go onto the roof. It'll be interesting to hear how you get on with it.

NT

[dennis]

I was thinking of putting it on the gable end as it faces SSE and I think I should get enough convection flow to avoid using a pump. I just have to convince the wife it will look OK and wont do any damage.

[Nick]

I have lots of black twinwall Corflute. It wouldn't last long enough but it's very cheap. Why not just use clear corrugated polycarbonate with spiral coils of black plastic pipe under it? I envisage using a small pump, so circulation is not a problem. I have a 50 square metre almost flat roof available, so efficiency doesn't matter. The most heat output for the money is what matters.