Bad experience with evacuated tubes.

[tandrews]

I must add to this since I have enlightened myself since my last post.
Truth be told, solder can be overcome by the heat generated in a evac tube setup.
I have had a couple of my soldered heat pipes desolder themselves and turn into rockets.

This in itself is not a huge surprise, but the failure mode is rather surprising.
In both cases, the tubes desoldered themselves ON THE BOTTOM.
They effectively became bottle rockets at that point, no splits, nice clean desolder on the bottom end.
One tried to punch through the roof of my thermal shed, then mired itself in the plastic foil bubble wrap I've encased the room in.

I should note this occurred prior to installing the heat removal manifold on top, and likely would not have occurred with that heat removed.
Those tubes that failed had an excess of copper scrub pad wrapped around them and I suspect it insulated and removed airflow up the evac tube. In the absence of a heat draining manifold, heat built up to over the 460 melting temp of my chosen solder.

So, while unlikely and no reason to avoid using solder for DIY, one must make sure they are pulling the heat off the pipe toot sweet or risk bottle rocket heat tubes.
There, I said it.

[russ]

I have had a couple of my soldered heat pipes desolder themselves and turn into rockets.

Maybe we should nickname you Mr Excitement? Sounds like too much fun!

[mkel]

wow ... I'm surprised ... experimentation can be exciting !

I haven't had any of my repaired tubes fail... I guess I'll put one out in the yard without a header and leave it for a few weeks to see what happens.

I would guess all your liquid turned to vapor and with no way to get rid of the heat it wasn't condensing back to the bottom of the tube... that would explain the pressure.

Did it break your glass tube when it blew?
Glad nobody got hurt... good thing you weren't standing by it.
mike

I must add to this since I have enlightened myself since my last post.
Truth be told, solder can be overcome by the heat generated in a evac tube setup.
I have had a couple of my soldered heat pipes desolder themselves and turn into rockets.

This in itself is not a huge surprise, but the failure mode is rather surprising.
In both cases, the tubes desoldered themselves ON THE BOTTOM.
They effectively became bottle rockets at that point, no splits, nice clean desolder on the bottom end.
One tried to punch through the roof of my thermal shed, then mired itself in the plastic foil bubble wrap I've encased the room in.

I should note this occurred prior to installing the heat removal manifold on top, and likely would not have occurred with that heat removed.
Those tubes that failed had an excess of copper scrub pad wrapped around them and I suspect it insulated and removed airflow up the evac tube. In the absence of a heat draining manifold, heat built up to over the 460 melting temp of my chosen solder.

So, while unlikely and no reason to avoid using solder for DIY, one must make sure they are pulling the heat off the pipe toot sweet or risk bottle rocket heat tubes.
There, I said it.

[tandrews]

Let me be clear that I attribute these failures to planning over equipment malfunction or failed engineering.
While I'll never know if there was any liquid form acetone left in my 3/8" pressure vessel, that point is rather moot at the instant the cap comes off anyway.
I do think the inner glass tube bottom has cracked, as the silvered bottom now has a bluish discoloration. I have spares and an inner tubing crack is less bothersome as it vents inside the building. Provided the heat absorbent coating does not oxidize immediately it will continue to serve.

As I noted, I had wrapped my heat pipes with a spiral of copper scrub pad material. In the tubes that failed I had used more then others.
This suggests the copper wrap does indeed work as intended and more is better.
It also raises the recorded by failure temperature evac tubes can manifest (450C).
I just wish I had a manifold installed sooner to avoid losing a tube to unintentional rocketeering.

It was not exciting. I heard what I thought was snow leaving the eves and discovered the result later.
Less exciting still to repair something not yet in service.

[LucMan]

This is Houston to tandrews, prepare for rentry.
You have been reported to NASA for practicing rocketry without with proper clearance.

[russ]

NASA is also a bit pissed about the satellite you shot down

[biosolar]

Some photos here: http://biosolar.hu/stuff/uploads/DSC00760_resize.JPG

[Art VanDelay]

Awesome Learnings!!

Let me be clear that I attribute these failures to planning over equipment malfunction or failed engineering.

Nope, Murphy's Law ALWAYS rules. Even if you had the header on, the pump or controller can fail, or the fluid might leak out of the whole system, or if you go on vacation, your controller might shut off the pump on tank high limit, etc. Or some other failure mode we can't even think of right now.
(phos-cop brazing is actually easier than soldering because it's self fluxing and you don't need a cap. Just pinch the end.)

[biosolar]

fearful type

I am wondering how dangerous the acetone and air mix is. I mean a fire on the roof that could ignite the series of rockets. What do you think?

[tandrews]

I agree Art that brazing would have been preferred.
I simply didn't have facility to do so, nor funds to farm it out and all the digging I did suggested 315

[Art VanDelay]

I'm confused by your temperatures

"It also raises the recorded by failure temperature evac tubes can manifest (450C)." - Tandrews

Most of the readily available plumbing-type tin soft solders will melt at under 240C (464F). (95/5 tin/antimony)

So I'm thinking that you may have mixed up F & C in the above observation, and that your joint melted at 240C. Are you sure about that solder melting point?

[tandrews]

Valid point Art, but I did make a point of getting a roll that had 460C written on it.
I shall locate said roll to confirm as I too have shared your thought and an unplanned explosion of any kind can make one second guess themselves...

Still, wouldn't you expect a failure at the top of the tube in any case since the bottom should have any fluid last?
If I did choose waxy solder, I'd expect this to happen:

http://www.youtube.com/watch?v=5m5BqXR4YJE

Rather then just two.

[Art VanDelay]

The top is cooler in your case

If you hadn't yet assembled the header, I would think that the top is the coolest spot on the heat pipe. It's losing heat to the air while the bottom tip has more insulation around it.

[Art VanDelay]

"It's a serious problem - but rather a shame - that Apricus was't able to supply quality heat-pipes. The heat-pipe replacement under warranty caused extra cost that we couldn't accept."

"Air diffuse through copper? Not gonna happen under these conditions - that 'theory' hasn't checked in with science or practical knowledge - if air does diffuse through copper does then cancel all refrigeration units -heat pumps etc."

Well, now we know Apricus has had an unacceptable number of dead heat pipes. If I were forced to reach a conclusion, I'd blame leakage, not diffusion. According to Refrigeraton Technologies, "all joints leak":

http://www.refrigtech.com/Product/Manuals/LeakDetectionManual.pdf

[russ]

All joints leak is a generalization but not far off. Over the years I worked with the direct reduction process (of iron ore) we tried to minimize hydrogen leaks to an acceptable point. Trying to stop all leaks was a fools game - a lot of work with no success.

Of course the plants were outside so if anything leaked it went up-up and away. In a confined space H2 can cause exciting moments. You have to consider that static electricity is more than enough to ignite hydrogen - not every time but often.