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Bad experience with evacuated tubes.

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  • Repairing heat pipes - status update. The acetone recharge has been working pretty well (nearly 2 winters and 1 summer). The system performance was significantly better than it had ever been.

    - Occasionally through the winter, the tubes will frost up, but then the frost melts off during the day. Sometimes, the frost will melt only on certain tubes (not a shade effect). The tubes which melt free significantly faster than the others have always had a failed heat pipe. This is my monitoring strategy for identifying failed heat pipes (not a real fast method, but so far 100% accurate).

    - I only had 16 of the original tubes in service (?water? filled). Several more of those failed. I've lost track of how many originals are still in service - probably fewer than 10 out of 120 tubes.

    - I had about 15 of the acetone tubes fail. When looking closely at the failures, it was generally possible to see that there was an issue with the sealing (silver solder) of the tube end.

    - I recharged all the failed tubes. Needless to say, the system performance is again better than ever. Even with February sunshine (better than December sun, but still well down from summer time) - I am able to get over 10°C temperature rise from panel inlet to panel outlet. Granted it is only about a 1gpm pump - but it is the same pump for the past 5 years.

    It seems using acetone is somewhat controversial. Perhaps my tubes will all quit working? All I can say is that so far I am pleased with the repair results (not happy that I needed to repair them, but that's all history now). I won't be surprised if I get a few more failures (it is hard to really get the seal perfect). My hunch is this will work out just fine.