Bad experience with evacuated tubes.

[Art VanDelay]

freezing and water heat pipes

Heat pipes use very little fluid. About 2-4 ml of water, acetone or whatever.

The mechanics of pipe damage due to water freezing are as follows:

1. Water in the bottom of a mostly empty tube tends to freeze from the top of the water down. That's because the coldest water becomes buoyant at 39F and rises up to freeze (that's why we can skate on partially frozen lakes)

2. The freeze plug that forms on the top surface of the water sticks hard to the sides of the pipe.

3. As the freeze plug expands downward, it pushes on the incompressible liquid water, which splits the pipe.

So, if you can coax the water into freezing at the bottom tip of the tube first, and expanding upward, there is no split.

The Chinese solution is: a small amount of water mixed with a coarse copper powder.

As I say, I haven't seen any documentation on this. I just tore apart a few heat pipes to see what was inside. I also put them in a freezer to see if the tip diameter increased when frozen. It didn't.

Don't get me wrong, I'm not against acetone, I'm just reporting what is in millions of Chinese heat pipes (SunRain)

[tandrews]

Water is safer, cheaper and transports the most energy per gram of just about any fluid.
Freezing is an issue that is being solved by using very little water, and they add a coarse copper powder to the water. I haven't really found the official reason for the powder. But it apparently causes the to water to freeze in the tip before making an ice plug. If it freezes bottom first and expands upward, no damage will occur.

Safer for installation, transport and install agreed. For troublefree use in Northern climates, not so much as is evident by known failures.
Perhaps the copper powder is intended to manage crystal formation and diffuse lateral pressures at the bottom of a heat tube? As long as the amount of water covers the bottom of the capped end, there remains risk of a split in the event of freezing. While I agree that water would be preferred for heat transfer, it's properties alone also add risk to freeze failure. I'd love to read some reasoning for copper powder additive if someone can speak to it directly. For now I'm sticking with Acetone, but reserve the right to flip my opinion if sufficiently informed otherwise.

I'm not sure how copper powder would cause freezing to occur in the tip first (If by tip, you mean upper manifold end?).
If it freezes bottom first, damage may very likely occur. Why do you say it wouldn't?

In a failed evac tube freezing might occur anywhere in the water based heat pipe, but in a good tube exposure to temps is limited to those areas exposed to weather or poorly insulated from it (grommets, flashings etc). They're not perfect insulators, but they're not perfect vacuum either. The chances of Acetone freezing are well past -78C directly exposed. We see -35C on occasion here, so water = bad in my part of the world. Your mileage will vary.

[Gonsh]

heat pipe siezing in header

GRRRR, My manifold has cracked somewhere and to fix it i attempted to remove my tubes from the header assembly. The glass slips out just fine but the heat pipe is stuck in the manifold!! I have already broken one heat pipe trying to remove it. Please can anyone help me. It does look green up in there and i cant even remove the bulb nwith much force from the one i already broke!! Help me please. I have it covered so it will cool off and i hope it will disengage when it does.

[Art VanDelay]

Chinese heat pipes use water and Cu powder

This is how I made my heat tubes:

https://www.youtube.com/watch?v=LU4eynU6R-8

Why a manufacturer would use water eludes me. Regulations perhaps.

Water is safer, cheaper and transports the most energy per gram of just about any fluid.

Freezing is an issue that is being solved by using very little water, and they add a coarse copper powder to the water. I haven't really found the official reason for the powder. But it apparently causes the to water to freeze in the tip before making an ice plug. If it freezes bottom first and expands upward, no damage will occur.

[tandrews]

The fellow in the video is merely my inspiration for using acetone as transfer medium.
I am a humble self educating newb working toward some less processed energy for heating and perhaps TEG generation next summer.
Like many here, it's something I must do.

[Mike90250]

This is how I made my heat tubes:

https://www.youtube.com/watch?v=LU4eynU6R-8

In the absence of timed heating machines for ensuring vapor evacuation of air and perfect seal when soldered, it is indeed an art form.
I didn't use the plumbing riser bit, just an end cap with a center punch dot in the middle to trigger the condensate return to liquid.
I soldered rather then brazed. Sufficient melting temp buffer there anyway.
Acetone works great and it's volatility ensures a rapid gas/liquid heat exchange.
Because they're isolated mechanically from the collection loop, there is no danger of potable (should one choose to use it) contamination.

The biggest difficulty is timing the solder application and heat removal to get an effective solder seal whilst acetone tube pressure swings by zero bar.
Cooling does the vaccuum for you afterwards.

Why a manufacturer would use water eludes me. Regulations perhaps.

Very cool. Do you have a blog or web site covering collectors and building them?

I've heard of using propane as a replacement working fluid in air conditioners, as long as we're talking about "out of the box" thermal fluids.

[tandrews]

This is how I made my heat tubes:

https://www.youtube.com/watch?v=LU4eynU6R-8

In the absence of timed heating machines for ensuring vapor evacuation of air and perfect seal when soldered, it is indeed an art form.
I didn't use the plumbing riser bit, just an end cap with a center punch dot in the middle to trigger the condensate return to liquid.
I soldered rather then brazed. Sufficient melting temp buffer there anyway.
Acetone works great and it's volatility ensures a rapid gas/liquid heat exchange.
Because they're isolated mechanically from the collection loop, there is no danger of potable (should one choose to use it) contamination.

The biggest difficulty is timing the solder application and heat removal to get an effective solder seal whilst acetone tube pressure swings by zero bar.
Cooling does the vaccuum for you afterwards.

Why a manufacturer would use water eludes me. Regulations perhaps.

[Frank@Apricus]

Under warranty

RJ Randall,

Your Apricus collectors are still very much within their warranty period. Please contact me personally or our main office to discuss your issues and ensure that you get the appropriate replacement parts to get your system up and running properly. We're not happy until you're happy.

[Naptown]

Don't do service and mostly flat plate thermal (Sorry) but I will run this by the Service Dept.

[Naptown]

I would hope I know a little about this as I also do this for a living (Sales now installs way back.
And where did the heat pipes in fridges come from I never mentioned low temp ones.

[russ]

Russ
They can be evacuated by heating the entire pipe which will expel most of the air as it is heated along with the pipe and then sealed. This is pretty much the way incandescent light bulbs are evacuated.

Agreed but that is not simply welding.

It would be interesting to know more about heat pipes - solutions, degree of vacuum etc but it is difficult to find - at least what I have read from various manufacturers hasn't said much.

[Naptown]

[QUOTE=russ;27212]From your wikipedia article - [I]The vast majority of heat pipes for low temperature applications use some combination of ammonia (213

[russ]

From your wikipedia article - [I]The vast majority of heat pipes for low temperature applications use some combination of ammonia (213

[solar guru]

Link to Heat Pipes

As requested here is a link to heat pipes http://en.wikipedia.org/wiki/Heat_pipe and if you scroll down that page it clearly says Solar Thermal and a couple of sentences later...distilled water. There are many different uses for heat pipes and depending on the application may use different fluids. There are heat pipes used for cooling a lap top which may use different fluids. Acetone is actually on of the top picks for replacing water but because of it's volitile nature is not allowed.

[solar guru]

Heat Pipes

My knowledge might be lacking in spelling but I wouldn't try brazing a top on my fuel tank (don't forget the bomb crap Russ). If you don't believe that sealing something that is hot and cooling it creates a vacume try the old grade one test of filling a plastic bottle half full with hot water, sealing it and then cooling it. A heat pipe that is not sealed for what ever reason will not function as the distilled water soon leaks out of the heat pipe and then there is nothing to make steam. Ethylene glycol doesn't work either as it can't withstand +300c. and breaks down. The steam rising into the condensor and changing state from a gas to a liquid is how such high temperatures are reached in evacuated tube systems unlike flat panels. If you would like to learn more right from the horses mouth you should take a course from a manufacturer the way I have and then go out and install a couple thousand tubes. I posted a testing method for heat pipes that works because WE do it....don't just talk about it. I didn't come on here for a spelling lesson just to help people check their systems without taking every tube out which only creates allot of work, broken glass and frustration.