Bad experience with evacuated tubes.

[inetdog]

Using a vacuum pump you suck on the empty tube and then let the vacuum suck your measured amount of alcohol in. No need to pump on the acetone-filled tube.

[Chipper5783]

Recharging heat pipes

You could try installing 1/4 refrigeration access stubs on your tubes, you could then evacuate the tubes with a vacuem pump to remove the air and then suck the acetone into the tubes.
With the access fittings it will be easier to adjust the amount of fluid, or change fluid to alcohol & water to determine which works better.

Hi LucMan,

Thank you for the suggestion on charging the tubes. I don't know about these "access stubs". I saw mkel's experience with "Refrigerant Access Valves" (Dec. 2011), so went straight to crimping and S-solder. I notice that you replied to him, so I'm guessing these "stubs" must be something else? I do not have a vacuum pump (I do have a hot air gun and can simply add a couple cc's extra acetone and let it boil off), but if I did get a vacuum pump, I don't know how I would monitor if it was pulling air or acetone vapours. There isn't very much liquid acetone to work with, it would be easy to flash it all off.

Using alcohol (methanol?) - I didn't try it. Others recommended acetone, which seemed to make sense. At room temperature and pressure, methanol vapor is lighter than air, so with the procedure I'm using to get the air out, I wasn't so sure of being successful. Acetone vapors are nice and heavy, I think that would make it safer (I'm pretty comfortable knowing that the oxygen is out of the tube).

I think it is a pretty suret that water would be better in nearly every aspect - except for the freezing temperature. Certainly the original water filled tubes (even ones that have been in service for several years) heat faster and to a higher temperature than the acetone charged ones when subjected to the "pot of boiling water test" I described earlier. I thought that since I'm only trying to pull about 30 watts of equivalent energy out of a given tube, the reduced transport capability of condensing acetone compared to condensing water will be made up for with a little higher temperature in the evacuated tube (and likely a bit longer initial start time in the morning).

Always glad to hear other ideas.

Regards, David

[LucMan]

You could try installing 1/4 refrigeration access stubs on your tubes, you could then evacuate the tubes with a vacuem pump to remove the air and then suck the acetone into the tubes.
With the access fittings it will be easier to adjust the amount of fluid, or change fluid to alcohol & water to determine which works better.

[inetdog]

Maybe it is just me? I'm finding it a bit tricky to get a decent re-charge on the heat pipe. The first attempt I charged 7 pipes, only one passed the test and heated the bulb up top. I improved my pinch/clamp arrangement and the second attempt I charged 6 pipes, and had two that would pass the boiling water test I described earlier. When the heat pipe is in the hot water, you can hear the acetone boiling like everything, you can also feel the heat progressing up the tube, the good ones will heat right up to the bulb, the not good ones, the heat never gets to the top. I assume the explaination is that there is some sort of non-condensable drawn into the tube (most likely air, perhaps combustion products off the torch).

Yup, that is likely the explanation. Whatever it is must have a lower molecular weight than acetone, otherwise the hot vapor would rise through the contaminant to the top and the tube would work, just not as well.

[Chipper5783]

Heat pipe clamp - trying again with the pictures

DSCF4168 - smaller.jpg DSCF4166 - smaller.jpg DSCF4167 - smaller.jpg

[Chipper5783]

Recharging the copper heat pipes - still learning

Maybe it is just me? I'm finding it a bit tricky to get a decent re-charge on the heat pipe. The first attempt I charged 7 pipes, only one passed the test and heated the bulb up top. I improved my pinch/clamp arrangement and the second attempt I charged 6 pipes, and had two that would pass the boiling water test I described earlier. When the heat pipe is in the hot water, you can hear the acetone boiling like everything, you can also feel the heat progressing up the tube, the good ones will heat right up to the bulb, the not good ones, the heat never gets to the top. I assume the explaination is that there is some sort of non-condensable drawn into the tube (most likely air, perhaps combustion products off the torch).

I made up a better clamp arrangement, in the third attempt, I succeeded in 3 out of 3. Attempted to attache photos. Next step is a larger sample size. The better clamp reduces the excitement level. I was previously trying to manage the hot air gun that was heating the bulb (my "boil off stage") with a foot controlled switch, since the clamps/vise grip did not completely shut off the acetone vapors. With this latest attempt I get the clamp set up, start the boil off, the boil off is easy to monitor as the heat comes up the pipe - and start pinching off the pipe. The approach I have taken, once the pipe is filled with acetone vapors - and mostly pinched off, is to light off the acetone (then I'm not breathing it as much), which makes it easy to confirm the pipe is filled and validate the pinch is good (pinch it off hard, until the flame goes out). Next step is to remove the heat at the bulb and silver solder the open end (I've chosen to do the actual pinch about 3/8" from the end).

I would be glad to upload pictures. The image upload feature seems to be very limited! The clamp is nothing special: two pieces of bar stock with a couple clamping bolts to squeeze. One piece of the bar stock is long enough to hold in the vise (Obviously the clamp needs to be able to tolerate getting pretty hot during the soldering step).

In my efforts to date, the original heat pipes still heat faster and to a higher temperature, compared to the ones recharged with acetone - when the lower end is in a pot of boiling water.

[Chipper5783]

Recharging the heat pipes

This is certainly a very helpful thread. My location is western Canada (cold country) I have a 120 tube system – the first 60 about 5 years ago, the second set I picked up used and am in the process of cleaning up and installing. I discovered the issue of split tubes as I was cleaning up this used set – finding 47 split tubes! I started looking at the existing set and stopped after checking two tubes – both were split. I’m still getting a bit of heat out of the original set of 60 tubes, but not like it used to be.

Per the guidelines in this thread, I am starting to refurbish split tubes. I have a few additional thoughts and learnings. I agree that acetone is likely a good choice for the working fluid. I do not doubt that there are other liquids that would work, but for ease of obtaining, ease of handling and properties like the boiling / freezing point and vapor density – I think acetone is better than methanol, propanol, propane or toluene. A freeze protected water would also probably be pretty good. I went with acetone.

Getting the air out (displaced by acetone vapors) is critical for the function of the heat pipe and to minimize the risk while soldering. The approach I took was to:
• cut the very end off the tube
• deburred and cleaned the tube ID (must be bright copper for the flux to work and the solder to stick)
• flushed the entire tube with methanol
• blew the tube out with compressed air (ran a small air line all the way to the top end)
• I then tipped the tube up & squirted 10.5 mils of acetone in (the intent being there will be ~8 mils of acetone when done)
• Heated the bulb with a hot air gun, with a latex glove tight over the top end of the tube like a balloon (it takes a good minute to drive off enough acetone). I let it flow pretty steady
• Pinched the tube (difficult to get a real tight squeeze). Not quite at the end, so there is room for the silver solder to form a nice little plug. I agree with the recommendation of others that soft solder is probably not a good idea.
• Keep the heat on the bulb until there is liquid solder over the end, then pull the hot air gun away (I think the acetone must condense quickly and the vacuum will suck in air very easily)
• Use a torch that is hot and focused (I used oxygen/propane and a brazing tip – basically an oxy/acetylene unit but I’ve been using propane for fuel). I think oxy/acetylene with a fine tip would work fine.

I found that I ended up using about 2.5 ml of acetone for the boil off (displacing out the air). I learned this because on the first several I recharged, most did not function. I cut them apart again, and measured the acetone that came out.

Once the heat pipe is recharged, test it by standing it up at an angle (the same orientation it would be in the panel) with just the bottom 6 inches in a pot of boiling hot water. The bulb at the top end should very quickly get hot. I tried this with a tube that was not split - the bulb was hot to the touch in about 20 seconds.

It probably goes without saying, but: Think it through, be careful – flame soldering in the presence boiling acetone could get exciting.

[mkel]

Mikel, I am replacing my bad tubes....Sunmaxxsolar has told me there going to ship new tubes to replace my bad ones under warranty. Unfortunately there on a slow boat from China. I don't think I want to put the new tubes in service if they are still using water as their gas medium. Anyway, as I pull them down and cut the swollen end off I plan on putting 7cc of acetone and braising with silver solder. I wanted to ask you about the felt? wool? gasket? they use for insulating up by the end of tube that goes into the manifold. Mine are falling apart as I take apart the tubes. Did you experience that and what did you use if anything. Also did you use any of the silver paste that they sent to use coating the bulb end that goes into the manifold?

The tubes I repaired I brazed with silver but I am not satisfied that I can get a good enough vacuum inside them as it takes longer to braze them shut and I think I loose a lot over that time.. they do not seem to work as well as my original repairs .. however the original didn't hold up over time.
As far as the felt ... I don't have that on mine ( must be a sunmaxx thing... and I am not using any paste on my bulbs.

I recently contacted my supplier and he knew I had past issues so he sent me 60 new heat tubes and 20 complete glass tubes with heat tubes.
Damn this is a great guy ... didn't charge me a thing...
I haven't installed them yet but this will give me a bunch of old tubes to do some serious experimenting with over the next year.
I am like you as I wonder if the medium is the same and I will have a repeat of this problem after the next polar vortex.
I think I am going to take a heat tube to work and put it in the kitchen freezer which runs at -10 degrees. That should answer that question.

These things are awesome when they work but I am starting to think "flat panel" if I do a future system.
mike

[eddy6053]

Yes I have been able to get the tubes out.....I take the glass off, then slide the aluminum collector off the copper tube, then put a c-clamp on the end of copper pipe and tap on the c-clamp and drive out the stuck ones. There not all that hard to do and you have better luck when everything is cool.

[MikeSolar]

Eddy, have you been able to pull out the tube from the header yet? Some times it nearly welded into it. Very difficult to get out.

The upshot of all this is that, with the exception of a couple of controller failures, all my flat collector systems are in great shape. This kind of experience is why I seldom put in tubes any more.

[eddy6053]

Mikel, I am replacing my bad tubes....Sunmaxxsolar has told me there going to ship new tubes to replace my bad ones under warranty. Unfortunately there on a slow boat from China. I don't think I want to put the new tubes in service if they are still using water as their gas medium. Anyway, as I pull them down and cut the swollen end off I plan on putting 7cc of acetone and braising with silver solder. I wanted to ask you about the felt? wool? gasket? they use for insulating up by the end of tube that goes into the manifold. Mine are falling apart as I take apart the tubes. Did you experience that and what did you use if anything. Also did you use any of the silver paste that they sent to use coating the bulb end that goes into the manifold?

[mkel]

Any ideas why some tubes feel warm and others cool to the touch? I pulled the glass off one of the warm ones and the bottom, looked swelled but was to hot to handle. I wonder if the copper is getting hot but not transferring heat to manifold and just sits there and get warm....where the cool tubes are still transferring heat to manifold. any ideas? I have contacted Sunmaxx and there going to get back to me.

BINGO ! .... that is exactly what is going on ... when the heat tube fails the copper gets super hot but because there is no fluid it can't transfer the heat to the manifold.
The copper may be black in color if it's been failed for a while.
Sometimes you can tell by putting your hand on the glass tube like you talked about.... cool = probably working warm = most likely failed.
I have found that using this method seems to work better on a mild sunny day and it is more difficult to tell on a super warm sunny day.... why? don't know... might be radiant heat off roof.

BTW .... out of my 80 tubes I have had freeze failures in all of them over the last 5 years ...
However I have had only one glass tube failure .... maybe I've been lucky but the vacuum glass tubes seem to hold up fine even when super hot.
mike

[eddy6053]

Any ideas why some tubes feel warm and others cool to the touch? I pulled the glass off one of the warm ones and the bottom, looked swelled but was to hot to handle. I wonder if the copper is getting hot but not transferring heat to manifold and just sits there and get warm....where the cool tubes are still transferring heat to manifold. any ideas? I have contacted Sunmaxx and there going to get back to me.

[mkel]

I have two 20 tube banks of evacuated tubes put in 09 [sunmaxx} and after the terrible winter we had in MN this year my output has really dropped. Up on the roof I went....was a cloudy day, as I felt the glass tubes with bare hand some were cool and some were warm.... 9 warm in one bank and 13 in the other. Pulling the glass off one tube the copper bottom was enlarged or swelled but not split. Copper was black..from high heat I presume. I haven't really noticed any foggy bottom of glass tubes like the vacuum had been comprised. Comments?? any ideas?

yep those tubes froze. The glass tubes are fine but with the expansion of the bottom of the copper heat tubes somehow the fluid has leaked out. if it was still in there they would make some heat at the top even on a light cloudy day. The chinese are selling heat tubes on ebay now... but they ask a lot for them. I would contact sunmaxx and see if they will replace them for you.
Over the last few years of frigid winters I don't have any working original tubes left in mine. It sucks but we've been screwed. If you read this entire thread you will find where I've been fixing them... (with some failures) .... I still haven't nailed down a perfect amount of fluid... 7cc seems to be the winner .. and they must be brazed with 15% silver or they will fail again if the system stagnates. Good luck with this.
mk

[eddy6053]

tube failure

I have two 20 tube banks of evacuated tubes put in 09 [sunmaxx} and after the terrible winter we had in MN this year my output has really dropped. Up on the roof I went....was a cloudy day, as I felt the glass tubes with bare hand some were cool and some were warm.... 9 warm in one bank and 13 in the other. Pulling the glass off one tube the copper bottom was enlarged or swelled but not split. Copper was black..from high heat I presume. I haven't really noticed any foggy bottom of glass tubes like the vacuum had been comprised. Comments?? any ideas?