Bad experience with evacuated tubes.

[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.

[russ]

No use in trying to be nice to some people it seems.

Provide links for water in the heat pipe if you can please. I would like to learn more about the things. Not word of mouth.

Your understanding of manufacturing processes seems to be lacking. You drive around a car/pickup using gasoline/diesel and you are OK - right? Forget the bomb crap

Welding creates a vacuum in the heat pipe? Maybe you misunderstood someone. If any is created in that manner it would be so small as to not be noticeable.

[solar guru]

Heat Pipes

You read it Somewhere? I'm sure you'll find it somewhere! A manufacturers name is what I was asking about. Another reason that methanol might not be the best fluid in a heat pipe is that it is flammable and explosive in the right concentrations. The heat pipe must be brazed closed while hot (which is what creates the vacume in the heat pipe) so what you have is a little bomb and a brazing torch....you may have to try this and let me know how it works out. I have been trained by 4 different solar thermal manufacturers who send out the very best tech. people they have....they don't send out grammer teachers. I originally posted to help people find bad heat pipes. I own and work in this business everyday, not just read about...somewhere.

[russ]

The internet and cell phones have made people forget all about spelling or sentence structure. inefficiant?

An IR gun has it's uses for a rough temperature measurement - just forget accuracy with the things. A digital thermometer does the same. Glad you are happy with your method of locating bad tubes.

We are quite aware of the properties and uses of propylene glycol.

Oh gee! Methanol being so toxic - less than most household cleaners? Any chemical is to be treated with respect. Taking a bath in methanol or a few thousand other things is not recommended.

About using methanol in heat pipes - I have read that some where in the past. I have looked for that reference several times as I was wanting to know more but most parties treat the composition of the fluid as a secret.

Why they want to use water is beyond me - lousy selection for cold areas and the claim to fame for vacuum tube type collectors is they work better in colder areas.

[solar guru]

Heat pipes and methanol

If there is a company that uses methanol in their heat pipes please put their name down. I agree the condensor and the manifold create a double wall just haven't found a manufacturer yet that uses methanol. Sorry for my spelling on infrared thermometer (didn't know this was a spelling bee), but we have used this system for finding faulty heat pipes and works flawlessly and saves removing lots of vacume tubes that you wouldn't have too. We build closed loop systems using propylene glycol which is non toxic and actually used in foods and skin creams. Methanol on the other hand can be absorbed through the skin and is very toxic. If you like expense and inefficiant things, then double walled heat exchangers are perfect. In some places they are law because of installers that use methanol and ethylene glycol in their closed loop. My original post was to do with finding faulty heat pipes not the closed loop. We have changed hundreds using this method and it WORKS.

[Naptown]

Even if methanol or ethelyne glycol were used in the heat pipe of an evacuated tube there would be no problem as the header and tube connections are by necessity double walled.