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Testing Evacuated tube heat pipes ? FROSTING

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  • Testing Evacuated tube heat pipes ? FROSTING

    This is sort of an extension to the thread http://www.solarpaneltalk.com/showth...d-tubes/page12

    In this other thread, there is quite a bit of discussion about recharging the heat pipes and a number of posts about insitu evaluation of the condition of the heat pipe in the center of the glass tube (what I loosely refer to as the "thermos bottle"). I do not have one of those non-contact (IR?) thermometer units so I cannot comment on the method discussed in that thread.

    No doubt my observation here is old news to the experts, but it was news to me (so perhaps it will help others struggling with split heat pipes).

    In my efforts to recover capacity in my evacuated tube panels, I have simply been disassembling and inspecting all the tubes (the failure rate is about 80%). I still have some of the original "water" filled tubes (interesting that even with many freeze cycles, some of the heat pipes look good as new) and likely some of my recharged tubes will fail (just because it is hard to get the lower end perfectly sealed with out compromising the lower end - I'm a rookie, I'm still working out the method, I've only successfully recharged 59 tubes to date).

    Anyway, it seems that observing the tube condition as the daily heating cycle kicks in, after a frosting event - really points to which tube are good (the frosted ones) and which tubes are most likely to have a failed heat pipe (the ones that come frost free first). Obviously one must consider shading of the panel if that is effecting which ones remain frosted up longer than others.

    Attached is an annotated picture, where I am at on working through my panels (some have been changed out, still quite a few to go).

    DSCF4222 - reduced2.jpg

    What do others think?

    If one gets quite a few just below freezing frost events then this may be a super easy way to assess good/failed heat pipes – monitor the extent of frost on the tubes as the heating cycle kicks in. Those tubes which tend to being frost free first (without some other explanation, such as shade) are candidates for inspection. If frost events are common, then photograph a few of them and compare results – if the results are repeatable, then pull the tube and check it out.

    Regards, David
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