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Old 09-14-09, 11:20 AM   #1
cdig
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Default DIY evacuated tubes?

Stupid question, but has anyone seen or heard of anyone building their own evacuated tubes for a solar collector? Could it really be that hard?

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Old 09-14-09, 11:26 AM   #2
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I've never seen a DIY evacuated tube collector made. However, I'm sure it is possible. The harder part would be making your own heat pipe and the glass tubing I'd imagine.

I also doubt it would be cheaper than a flat plate collector since flat plates are so cheap to make.

It would be really cool to see someone do it though.
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Old 06-15-10, 03:08 AM   #3
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Thought I would Start my first post with something that might help out this link is from
a guy i found a year ago think you might like it check out his other videos

I tried to post a link i cant yet do a search with this on you tube (DIY SOLAR TUBES EVACUATED VACUUM TUBE SOLAR HOT WATER Boil water with the power of the SUN) the guys name is dan rojahs his sight is GREENPOWERSCIENCE hope this helps

Have a great day
Jerry in wv
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Old 06-15-10, 11:38 PM   #4
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I saw a Youtube how-to for making DIY evacuated PVC pipes for moving hotwater from point A to point B.

I guess the idea was to have close to zero heat loss when moving coolant..


It looks like there are a lot of vids on youtube about this stuff.


Those tubes are impressive!

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Old 06-16-10, 11:23 PM   #5
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Heat pipes are easy, evacuated Pyrex tubes are the hard part.
I wonder how the heat pipes would work in a normal flat plate collector frame.
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Old 06-17-10, 07:59 PM   #6
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Quote:
Originally Posted by Ryland View Post
Heat pipes are easy, evacuated Pyrex tubes are the hard part.
I wonder how the heat pipes would work in a normal flat plate collector frame.
Heat pipes would work very well clamped or soldered to the fins of a flat panel collector, I have been doing quite a lot of experimenting building heat pipes of various sorts over the past 6 months for extracting waste heat from gray water (shower drain).

A 2.4m heat pipe soldered to a copper fin 160mm wide would be extremely efficient at conducting the heat collected by the fin to the condensing end of the pipe, pipe dia would be only have to be 8 - 10mm, evacuated to 50 microns and using approx 1cc of water inside the tube. To do this the water is placed in the tube, frozen, then evacuated. This setup would be immune from frost but with a lot of added complexity, just to save a bit of copper with water flowing through it and you require specialist vacuum pump to get the pressure low enough to use water. I have used R22 refrigerant gas quite successfully in heat pipes when extracting heat from lower temperature surfaces.

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Old 07-01-10, 10:03 AM   #7
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Quote:
Originally Posted by Solar Mike View Post
Heat pipes would work very well clamped or soldered to the fins of a flat panel collector, I have been doing quite a lot of experimenting building heat pipes of various sorts over the past 6 months for extracting waste heat from gray water (shower drain).

A 2.4m heat pipe soldered to a copper fin 160mm wide would be extremely efficient at conducting the heat collected by the fin to the condensing end of the pipe, pipe dia would be only have to be 8 - 10mm, evacuated to 50 microns and using approx 1cc of water inside the tube. To do this the water is placed in the tube, frozen, then evacuated. This setup would be immune from frost but with a lot of added complexity, just to save a bit of copper with water flowing through it and you require specialist vacuum pump to get the pressure low enough to use water. I have used R22 refrigerant gas quite successfully in heat pipes when extracting heat from lower temperature surfaces.

Cheers
Mike

Do you use silver solder on those pipes?
What are the steps for make the R22 heat pipe?

I'm wondering if an R22 (lower temp extractor) heat pipe could be used
to fabricate a compact water-to-water heat scavenger to recover the
heat in waste Shower water.?. Luke warm water..
http://ecorenovator.org/forum/conser...ater-heat.html

A smaller exchanger might be just the thing for my shower..


Thanks,
Rich
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Old 07-02-10, 05:49 AM   #8
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You can use silver solder for quick testing, I generally braise with silphos, a lot more reliable than any soft solder, you require an oxy acetylene torch or similar, I have a Multiplaz 3500 plasma welder which doesn't require any bottled gas to run.

To use R22, make a small delivery tank about 1-2% volume of the heat pipe, evacuate it and the heat pipe, fill the delivery tank then use it to gas the heat pipe.

As a coincidence I'm also using heat pipes for extracting heat from the shower drain water, pre-heating the incoming cold water to the shower mixer.

You can use water in the pipes rather than R22, at 50 microns water boils at -40c, so at waste water temp 28 c should work quite well. Still experimenting with this. Have just bought a new vacuum pump and a digital vac gauge as borrowed items had to be returned. A digital gauge is a must, its impossible to work out what is happening with a mechanical gauge. You have to use boiled water, I found after a few days dissolved gasses come out of the water and kill the vacuum enough to stop the pipe working at low temperatures.

Current heat exchanger is a drain pipe with 6m 12mm soft copper tube wound in a spiral, sitting inside; the waste water flows over the coils carrying the cold water to the mixer, sort of illegal but works very well. You have to make a filter for it that easily cleaned of especially hair, it gets caught in the coils and after 6 months stops working.

Cheers
Mike
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Old 06-17-10, 08:03 AM   #9
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These things are new (to me), so I might well not fully understand them..
But, it seems like they work so well, because of the vacuum around them, inside the 'evacuated Pyrex tube'.

That vacuum keeps the heat from being re-radiated..
You couldn't pull much of a vacuum on a flat-plate, before it collapsed in on itself.

That impressive video (above) seems to show the copper just keeps on
accumulating heat and not re-radiating much of it. (Just on the bare end).
Getting up to over 212F seems surprising, since the light capture area is so small.. But, if no heat is escaping..


It might be an interesting experiment, to suspend a solid copper tube inside a clear vacuum bottle.
Sit it out in the sun a few hours and see of it starts glowing cherry red..?..
If no heat could escape, then maybe the copper might just want to melt into a puddle?? LOL!
There must be some frequencies of light (IR?) that will be re-radiated,
(losses) otherwise it would get infinitely hot.. All gain: No loss..

Last edited by Xringer; 06-17-10 at 08:25 AM.. Reason: ideas just keep popping up
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Old 06-17-10, 09:29 PM   #10
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I knew that heatpipes worked real well, since I've been using an 'AC' cooler
on my graphics board (the fan was going bad) for years Arctic Cooling
It was easy to install and doesn't make any noise.. (Like that)!

But, I didn't know how they really worked.. Had to read about it, just now..
Heat pipe - Wikipedia, the free encyclopedia

Pretty neat stuff.. Now I found another use for my vacuum pump!

50 microns is a pretty hard vacuum. I've done some tests with water using my pump, and
the water went to vapor kinda fast. http://ecorenovator.org/forum/projec....html#post4519

It's interesting that ice will keep the water from going into vapor and prevent it from being sucked out by the pump..

I would be very interested in seeing some pics and diagrams of your shower water heat recovery project(s)..

Last edited by Xringer; 06-17-10 at 09:45 PM..
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