Evacuated Tube Collecter doesn't Heat Up ??

[Art VanDelay]

Glass is Opaque to Infrared thermometer

. If you can borrow an infrared non-contact thermometer you can check the top and bottom temperatures of the inner collector tube. The temps should be high and almost identical between top and bottom?

If the inner tube is hot at the top and the manifold it not, then the thermal connection between the tubes and the manifold is bad.

A standard non-contact thermometer cannot "see" thru the outer glass to the inner absorber surface. But if it could, it wouldn't be a very high temperature in a working tube because the heat pipe/header assembly is quickly sucking most of the heat out of it.

[russ]

A standard non-contact thermometer cannot "see" thru the outer glass to the inner absorber surface. But if it could, it wouldn't be a very high temperature in a working tube because the heat pipe/header assembly is quickly sucking most of the heat out of it.

Wrong - if that was the case a heat tube wouldn't function - temp loss is mainly in the upper manifold where the heat transfer takes place - there will be some cooling of the tube as the condensed liquid returns to the bottom of the pipe.

[Art VanDelay]

Wrong - if that was the case a heat tube wouldn't function - temp loss is mainly in the upper manifold where the heat transfer takes place - there will be some cooling of the tube as the condensed liquid returns to the bottom of the pipe.

Russ,

What's wrong, that IR thermometers can't see through clear glass?

[russ]

Russ,

What's wrong, that IR thermometers can't see through clear glass?

Quote, ''But if it could, it wouldn't be a very high temperature in a working tube because the heat pipe/header assembly is quickly sucking most of the heat out of it.''

[MikeSolar]

Quote, ''But if it could, it wouldn't be a very high temperature in a working tube because the heat pipe/header assembly is quickly sucking most of the heat out of it.''

If you wait till is stops, you could see the difference

[Art VanDelay]

Finding "dead" heat pipes

Sorry Mike and Russ, I don't quite understand your points.

But I think we're trying to explain to the OP how to find dead heat pipes if he has them. Last year, "Solar Guru" posted a good explanation in the thread Bad Experience with Evacuated Tubes

I've edited SG's post because of typos and minor corrections:

"How to test heat pipes without taking the evacuated tubes apart.
(Freeze) burst heat pipes are very common and most consumers don't know until their system is putting out nothing. Apricus, Sunrain, Thermo-max all have their problems. There is suppose to be (2 or so) ml of water in each heat pipe about (1-2 inches) so insulating the neck of the condensor will not help this problem. Apricus (,Sunrain and SunTask) mix a copper compound in the water to (prevent freeze bursting) but if there is too much water or not enough copper they burst. Someone mentioned that some company's use methanol but I doubt it as (as we have never seen it) If you want to test an evacuated tube for performance all you have to do is use an infrared thermometer on the outside of the glass tube. In full sun put the thermometer right against the glass on the bottom of the tube. Your pump must be running for this to work. Check every tube. Tubes with failed heat pipes will register a 3 to 4 deg. celsius higher reading as the heat pipe is not extracting the heat to the manifold the way it should. Faulty heat pipes when pulled out turn completely black and cooked to death (after a few sunny days). If you want to check a heat pipe heat some water to close to boiling and put the bottom end in the water. If you can touch the condensor in 30 seconds it's toast. Good ones will have a natural copper color and cook your hand, 100 celsius. These company's will tell you that they have never, ever seen this, but they are lying. Most companies originally designed these systems for warmer climates so they are playing catch-up on cold weather design. Where I live -20c is just a nice day to go fishing. Hope this helps."

SG's post was mainly about frozen and burst heat pipes. There are other failure modes, but the test method is the same.

[MikeSolar]

Sorry Mike and Russ, I don't quite understand your points.

But I think we're trying to explain to the OP how to find dead heat pipes if he has them. Last year, "Solar Guru" posted a good explanation in the thread Bad Experience with Evacuated Tubes

I've edited SG's post because of typos and minor corrections:

"How to test heat pipes without taking the evacuated tubes apart.
(Freeze) burst heat pipes are very common and most consumers don't know until their system is putting out nothing. Apricus, Sunrain, Thermo-max all have their problems. There is suppose to be (2 or so) ml of water in each heat pipe about (1-2 inches) so insulating the neck of the condensor will not help this problem. Apricus (,Sunrain and SunTask) mix a copper compound in the water to (prevent freeze bursting) but if there is too much water or not enough copper they burst. Someone mentioned that some company's use methanol but I doubt it as (as we have never seen it) If you want to test an evacuated tube for performance all you have to do is use an infrared thermometer on the outside of the glass tube. In full sun put the thermometer right against the glass on the bottom of the tube. Your pump must be running for this to work. Check every tube. Tubes with failed heat pipes will register a 3 to 4 deg. celsius higher reading as the heat pipe is not extracting the heat to the manifold the way it should. Faulty heat pipes when pulled out turn completely black and cooked to death (after a few sunny days). If you want to check a heat pipe heat some water to close to boiling and put the bottom end in the water. If you can touch the condensor in 30 seconds it's toast. Good ones will have a natural copper color and cook your hand, 100 celsius. These company's will tell you that they have never, ever seen this, but they are lying. Most companies originally designed these systems for warmer climates so they are playing catch-up on cold weather design. Where I live -20c is just a nice day to go fishing. Hope this helps."

SG's post was mainly about frozen and burst heat pipes. There are other failure modes, but the test method is the same.

The single biggest issue with vacuum tubes is loss of vacuum heat pipes comes second. Finding the loss of vacuum is easy as the "getter" at the bottom of the tube (within the silver area) evaporates and clouds the bottom part of the tube.

It is a bit harder to test for the failed heat pipe. The liquid is methanol or an alcohol mixture, not generally water and they are a bit secretive about the mixture. IF you can get the heat pipe out of the header which is sometimes impossible, what SG writes is true for temps.

This and many other reasons are why I will, almost always, pick a flat collector over a tube collector.

[Art VanDelay]

I haven't seen any proof of Alcohol in Chinese Heat Pipes

"The liquid is methanol or an alcohol mixture, not generally water and they are a bit secretive about the mixture." That's true, they are secretive. I can't speak Chinese, and that's where they are all made.

I've searched everywhere and cut open heat pipes of all the major manufacturers, and haven't yet seen alcohol. Since I'm trying to understand as much as possible about these collectors, please forward any information you have about what's in these heat pipes. Every one I've cut open only has pure water and that copper powder. We've verified that the powder is what prevents freeze bursting.

Some DIYers in the US have been using acetone, but water is more efficient, cheaper, and safer.
Just compare the specific heat capacities and latent heats of vaporization.
There's a good YouTube video on making them.

[MikeSolar]

"The liquid is methanol or an alcohol mixture, not generally water and they are a bit secretive about the mixture." That's true, they are secretive. I can't speak Chinese, and that's where they are all made.

I've searched everywhere and cut open heat pipes of all the major manufacturers, and haven't yet seen alcohol. Since I'm trying to understand as much as possible about these collectors, please forward any information you have about what's in these heat pipes. Every one I've cut open only has pure water and that copper powder. We've verified that the powder is what prevents freeze bursting.

Some DIYers in the US have been using acetone, but water is more efficient, cheaper, and safer.
Just compare the specific heat capacities and latent heats of vaporization.
There's a good YouTube video on making them.

My experience with heat pipes goes back to the 80s products and I must admit that i am far less knowledgeable about the newer chinese materials. I had refurbished a bunch of Norsun flat panels and also phillips/corning style tubes in the early 90s. Both these were alcohol based or at least had a different refrigerant that would start to boil at a lower temp than 100C. The goal was to get heat transfer from 20C and up, especially the Phillips tubes that were used in the arctic for a number of years. Phillips was the predecessor of Thermomax.

[Art VanDelay]

Water can boil at 80F

When the pressure is 0.5 psi. Therefore I think water started making more sense to these manufacturers.