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cdig 09-14-09 11:20 AM

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?

Daox 09-14-09 11:26 AM

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. :)

ccomander 06-15-10 03:08 AM

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

Xringer 06-15-10 11:38 PM

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!

YouTube - Finished evacuated tube heat pipe in the sun

Ryland 06-16-10 11:23 PM

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.

Xringer 06-17-10 08:03 AM

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. :eek:

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..

Solar Mike 06-17-10 07:59 PM


Originally Posted by Ryland (Post 7096)
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.


Xringer 06-17-10 09:29 PM

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.

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)..

Solar Mike 06-17-10 10:32 PM

Yes to get 50 microns you need a double stage pump with fresh oil, I found is quite easy to make heat pipes from soft copper tube, pinch and solder both ends, drill a small hole at one end and solder a short length of 1/8 copper tube for the vacuum pump connection, squirt in the water with a syringe then place in the freezer for a few hours. Connect up the pump using a flexi connection leaving the heat pipe in the freezer, leave pump running for 10 minutes or so, a good vacuum gauge helps as it shows how close to a near vacuum you are getting, any water vapor will prevent a good vacuum and register on the gauge. Crimp the 1/8 pipe, cut and solder to seal.

To see how effective the pipe is dunk one end in luke warm water, listen with an ear to the pipe, you should hear it boiling, place in hot water, the other end gets hot instantly.

The U tube video shows acetone being used as this boils at a lower temp than water, I tried it and works as described, ok for solar where the temps > 40c, but it doesn't work below 40c, would have to evacuate the pipe properly, ...rather difficult when it doesn't freeze.

Heat recovery still being worked on, not enough hours in the day.


Piwoslaw 07-01-10 09:46 AM

Question: Which type of evacuated tube collector is more efficient - heat-pipe or direct-flow? I found this site, but it doesn't compare efficiencies.

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