Bad experience with evacuated tubes.

[Art VanDelay]

Interlocking Extrusions

Once you remove those end caps, I think you'll find two interlocking extrusions. Maybe you can tap the top one off with a hammer. If urethane foam has them all glued together, it will be really difficult.

Hey, keep me posted, I'm gathering a summary of the failure modes of this type of collector.

[Art VanDelay]

Copper powder

In a six ft. heat pipe, there was about 2 ml of water, and 1ml of powder.

So no, the water level is above the level of the copper powder, by 1-2 cm in the 1/4" tube. The shape of the tube at the bottom end is also probably important to get the water to freeze "correctly".

[hamish]

hi gonsh, apply a mild acid like spirit vinegar to the area around the heat pipe where it meets the
manifold and leave it for a few hours. It will slowly disolve the buildup between the heat pipe and manifold. You could also use a good penitrating oil or brake fluild if its very stuborn, the main thing is you must leave it on for a long time keep reapplying it over night or a day or two and it will come loose.

[SolarHome]

Apricus Heat Pipe Failure

I had multiple heat pipe failures like "Windy." I obtained new heat pipes from my Apricus dealer, but now I am going to check my installation with and infrared camera. I live in Northeastern Maine and the cold temps may have been responsible. The bottom of the pipe was expanded and ruptured. If you remove the tube and the bulb on the pipe is not not, but the heat pipe is, especially after being out in the sun for a few minutes after being removed from the manifold, your heat pipe is bad.

[sunno]

Yes this happened to me also, it is very important I think not to buy those cheap chinese tubes, but make investigation on the web before byuing and building your solar vacuum tube system. Well even if some tubes breaks, it is still very efficient product.

[mkel]

heat tube repair comments

I've been experimenting with evac tubes for a few years now. Have 80 tubes on the roof and last year I started to have heat tube failures. I want to add some comments about my experiences and maybe they will help someone else.... some of these comments are my opinions with no scientific tests.
Please don't rip me if I miss-spell something --

1. I read where a infra-red heat detecter could be used on the glass tubes to determine if a heat tube had failed inside. I did a reading on all 80 tubes and wrote down each reading. there were a number of tubes that read 4+ degrees higher than others (supposedly indicating the heat tube is bad). When I pulled the tubes I found no correlation based on this method.

2. My ratio of failed heat tubes was about 40%. They had split and I do agree with statements in this forum that this was a product of freezing.

3. Found a number of tubes that had NOT split yet were expanded at the bottom.

4. My supplier offered to replace all my heat tubes however I declined because I have no faith that the new tubes will have anything different in them and would just become a future failure. I have repaired all 80 tubes by soldering a refrigerant access valve on the bottom of the tube. Pulling the schrader valve out I can charge the tube with fluid and then replace the valve. Heating the tube I depress the valve until I feel a bit of moisture from the fluid. At that point I close the valve and replace the valve cap.
These tubes work great and because of the valve I was able to experiment with different mixtures and quantities to find the best ratio for my tubes.

5. In this process I cut all the tubes that had not burst. I found that every tube contained a different amount of fluid with a variance of as much as 8cc. Some tubes had almost nothing.. maybe 2cc. The fluid appeared to be dirty water and I suspect the copper dust is not a product of engineering but residue from poor manufacturing of deburing or pipe prep. The amounts of residue went from a trace to quite a bit and some had none.

6. SUMMARY -- I believe the tubes that split had much more fluid (water) in them than the ones that didn't split. the pipes that were expanded had more fluid in them than the ones that looked normal.
It appears the manufacturing process is sloppy at best. The random liquid levels in the heat tubes may explain why the infra-red heat reading didn't work. In experimenting with different amounts of fluid in the tubes I found a wide swing of temperatures depending on the amount. I lined up 8 tubes with different amounts of fluid from 2cc to 14cc. This provided interesting results and I found 7cc to be the perfect amount for my pipes. Less than 7cc worked well in direct sun but at 7cc I got some heat even when it was cloudy... only dropping off when clouds were very thick. Solution of choice turned out to be acetone. Nothing else I tried provided as good of results... and it won't freeze. There is ZERO chance of a failed acetone heat tube contaminating the water circulating in a evacuated tube system. Also for those who are paranoid of explosion... I put one of these acetone heat tubes in my burn barrel and cooked the crap out of it with no explosion.. solder did melt and acetone escaped with no event noted.

Hope some of this info helps others. It is a shame the manufacturing of these tubes has left the customers with this problem. Worst part for me was the huge number of trips up and down from the roof removing and replacing the tubes.

EDIT 3-2014 -- INFO UPDATE -- I had repaired tubes with refrigeration valves on the ends... This was a failure after 1 year ... the refrigeration valves could not take the heat inside the tubes for an extended period of time.
Next try was to crimp and solder the bottoms --- worked great for a long time but then we had a power outage on a sunny day and the system started dropping off on temps and wasn't producing heat like it had. I pulled some tubes and found that under stagnation in direct sun the solders had melted. 460 degrees ... my pressure relief did go off but that didn't prevent the heat tubes from failing.
Last try -- same as before -- crimp tubes but used silver solder this time .. only did 20 tubes about a year ago and they are all still working great. I intend to do the rest this spring. I did see that the suppliers of evac tubes are starting to sell replacement heat tubes on ebay.... could you trust them? My guess is they are filled with water just like the ones that failed in the first place ... and they are asking a lot of $ for them if you are replacing a lot.
END EDIT.


bulb-stop.jpg heat-tube-valve.jpg broken-tubes-opt.jpg
mkel

[russ]

Hi mkel - Welcome to Solar Panel Talk!

Good post and a lot of research it seems!

The IR temp measuring device should show a big temp difference as in many degrees comparing bad tube to good ones. The tube is collecting heat and the vacuum doesn't let it escape.

I generally think the IR devices are useless for measuring temperature but they should be great for a go/no go indicator in a situation like this.

They rely totally on the emissivity setting and that is rarely adjusted correctly by the user.

It seems to make sense to use a liquid with a low melting point rather than water -

[mkel]

reply to Russ

Hi Russ,
While it did give me measurements like you indicate I found that the heat tubes with less fluid transfered less heat to the header and gave me pretty much the same reading as the failed tubes. I found the most acurate way to find out if the tube was failed was to pull the glass tube and pull the heat tube up about a foot. If the heat tube was black in color it was failed. If it is copper or gold in color it is still good. However....... even this method wasn't 100%.
No matter what ... this is great fun playing with these systems.
broken-tubes-opt.jpg

Hi mkel - Welcome to Solar Panel Talk!

Good post and a lot of research it seems!

The IR temp measuring device should show a big temp difference as in many degrees comparing bad tube to good ones. The tube is collecting heat and the vacuum doesn't let it escape.

I generally think the IR devices are useless for measuring temperature but they should be great for a go/no go indicator in a situation like this.

They rely totally on the emissivity setting and that is rarely adjusted correctly by the user.

It seems to make sense to use a liquid with a low melting point rather than water -

[russ]

Hi mkel,

Even more fun when you get it worked out in the end!

Well done!

[hamish]

Hi mkel,
thanks for sharing your experiences and experiments with the heat pipes. I like your idea of fitting a valve to the heat pipe end and being able to manage the heat pipe indefinitely.
Please post some pics, and wellcome to the forum. How low do the temps go where you are.

[mkel]

temp where I live

Hi Hamish,
I added some pics to my post above... not sure why I got a thumbnail of the same pic.
It does get cold at times here in Missouri USA ... last winter we had several nights at -15 and windchill in the area of -30 degrees. Normal winter cold snap would be around 10 degrees.
My system is a total hybrid that I built.. making some changes now but when I have time I'll post pictures of everything.
mike

Hi mkel,
thanks for sharing your experiences and experiments with the heat pipes. I like your idea of fitting a valve to the heat pipe end and being able to manage the heat pipe indefinitely.
Please post some pics, and wellcome to the forum. How low do the temps go where you are.

[Art VanDelay]

Whose Tubes and what year of manufacture?

Mkel,

Great job showing your problem and your solutions.

I think that most of the evacuated tube collectors being imported these days to the US don't have this freeze breaking problem. I've been testing SunMaxx and not had any trouble yet, and I've put them in my chest freezer also.

Hence my question of who made yours and when. Pre 2006 Apricus heat pipes had a high failure rate. This information is tough to find online, which makes these forums the best place to find it.

I don't think solder can handle the dry stagnation temperatures inside the evacuated tube. I've seen temperatures at 400F up at the header, which means the absorber was much higher. That's why the heat pipes are brazed.

[LucMan]

Great post mkel!
I don't think that you will have any failures with the shraeder cores as long as you use the refrigeration type if you leave the cap on. Let us know how the solder holds up.
I think that the US & Canada exporting Chinese companies have rectified the problems with their tubes freezing. Most tubes were originally made for the southern China market, where temperatures are mild. Some offer 2 different tubes, low temp rated and standard. They had no idea how cold it gets here in the US and Canada.
I recently returned from a trip to southern China and was surprised at the amount of thermosyphon systems installed on rooftops. Thousands of installations in the Shanghai area, it seemed as if all the newer buildings had multiple rooftop systems. I was also amazed at the amount of mini split a/c & heatpump systems hanging from the sides of 25 floor apartment houses. I'm still envisioning how the serviceman rappels 15 floors down from the roof to repair a unit!

[mkel]

don't know

Hi Art,
I ran into a guy who lives here in USA but is from china and imports for his business. He wanted to start selling evac collectors here and brought over some in one of his containers. I bought mine from him over a year ago. Unfortunately I don't know who made them as they have his company name on them. They are very well built and until this heat tube problem they really worked well.
I hope I don't have issues with the solder. I have several tubes leaning up outside with no header. To keep rain from getting down the glass tube I taped a soup can over the bulb and glass tube leaving a small opening at the bottom. I wanted to see what would happen if they just cooked. they have been out there about 6 weeks with no issues so far. Thanks for your comments.

PS .. You probably know this but some out there may not ... coiling the tube and putting it in the freezer will not tell you anything unless you absolutely know all of the liquid is concentrated in the bottom of the tube and it is placed vertical or close to the angle it would be in the collector. Coiling the tube allows the fluid to disperse along a longer length of the tube and would never be able to burst the tube ... rendering the test useless.

Mkel,

Great job showing your problem and your solutions.

I think that most of the evacuated tube collectors being imported these days to the US don't have this freeze breaking problem. I've been testing SunMaxx and not had any trouble yet, and I've put them in my chest freezer also.

Hence my question of who made yours and when. Pre 2006 Apricus heat pipes had a high failure rate. This information is tough to find online, which makes these forums the best place to find it.

I don't think solder can handle the dry stagnation temperatures inside the evacuated tube. I've seen temperatures at 400F up at the header, which means the absorber was much higher. That's why the heat pipes are brazed.

[mkel]

thanks

The guy I got mine from is from china and travels back and forth monthly. He told me he is surprised that so many in the USA think these are some new technology. He said they are everywhere in china and have been for many years. Somehow I get calls from people all over that are installing these and want to ask questions. They seem to becoming a rather common installation at resorts in Costa Rico and Panama. I've had several calls from there. BTW .. I'm an experimenter -- not an expert by any means.
mike

Great post mkel!
I don't think that you will have any failures with the shraeder cores as long as you use the refrigeration type if you leave the cap on. Let us know how the solder holds up.
I think that the US & Canada exporting Chinese companies have rectified the problems with their tubes freezing. Most tubes were originally made for the southern China market, where temperatures are mild. Some offer 2 different tubes, low temp rated and standard. They had no idea how cold it gets here in the US and Canada.
I recently returned from a trip to southern China and was surprised at the amount of thermosyphon systems installed on rooftops. Thousands of installations in the Shanghai area, it seemed as if all the newer buildings had multiple rooftop systems. I was also amazed at the amount of mini split a/c & heatpump systems hanging from the sides of 25 floor apartment houses. I'm still envisioning how the serviceman rappels 15 floors down from the roof to repair a unit!