Aluminium vs copper brazed coils

I am interested in how folks feel about the all-aluminium brazed coils. This technology seems to have gradually crept into the high volume, low cost market, as far as I can tell.

Repairability must be tough.
What about corrosion?
Cost?
Reliability?

As far as I understand things, much of the reason for this aluminisation has been performance & cost.

Copper extruded multiport tubes
A great deal of research has gone into extruded copper multiport tube technology over the past years.
1. One process was never fully commercialised, due to tolerance stability issues. I was able to successfully braze coils with this technology, however.
2. A second process has been limping along for some years, but suffers from many difficulties.
3. These tubes anneal during brazing, become very soft - a design issue.

New copper composite multiport tube
I have been developing this technology for some years. Interest has now been shown by a large industry player. If the market volumes are realized, this technology could be in compact, high-performance coils, within 12-18 months. These tubes actually strengthen during the brazing process. Very high pressures can be managed.

It is also possible to create hybrid brazed copper-aluminium coils.

Please let me know your experiences with these modern aluminium brazed coils.

Kind regards,
desA

Attachment 14772

Brazed core matrix. Copper multiport tube, anneal-resistant high-performance fins.

Attachment 14773

Post-braze testing.

Attachment 14774

Section showing tube-fin joints.

A variety of different fin types can be used - optimised for different parameters - heat-transfer, draining, strength.

Sounds interesting desA.

Is the strengthening just from the use of a copper composite (or alloy?) or is it a special brazing process?

Copper strengthening during the brazing process.

This is fairly similar to the age-hardening of some aluminium alloys.

A finely dispersed metal phase of the copper alloy, moves together into larger metallic structures, when the metal is heated during the brazing process. This induces strain in the overall alloy & tends to make it much stiffer and stronger.

These types of coils are incredibly strong. So much so that a single person will not be able to bend them much, at all. Even after twisting a thin core through a few degrees, they spring back. :)

Do they fail in a brittle manner? if your able to overload them.

Is it looking like their going to be much more expensive than Aluminium coils?

Do they fail in a brittle manner?

No, this has not been our experience. The amount of 'strengthening alloy' added, is a fraction of 1%. Copper alloys are usually very forgiving, in general.

With brazed coils, the strength is most-often controlled by the tubes. The fins form a secondary strength role. (This is different to automotive radiators, where the fins provide major structural strength to a very thin tube).

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Cost comparison.

For coils where strength & heat-transfer is important, initial cost is often not the main concern. Life-cycle cost (initial + repair cost + energy saving), is often more important.

For coils where initial price is important, we are developing hybrid brazing technology to allow low-cost aluminium fins to be brazed to copper tubes. The coil then has copper tubes, where important, & aluminium fins where cost is the main driver. There are some technical balancing acts in this. This is an exciting development.

@desA the life of aluminium heat exchanger aka radiators goes upto 10+ years and strength of the radiators, even in cars, assembly is due to tubes and not fins. Fins are fragile. Aluminium brazing to copper is something new and looks promising. Aluminium is cheap, corrosion resistant but has poor heat transfer rate compared to copper.

Thanks desA. It will be interesting to hear how you get on with the hybrid.

vikky1971, I would have to differ with your thoughts on aluminium, in radiator service. Radiators & condensers are different from a strength/corrosion perspective. I will answer assuming you did mean 'radiators' & not 'condensers'. :)

Aluminium radiators are acceptable in regions with little external corrosion attack. In this application, corrosion life is extended with waterside corrosion inhibitors. Fin life can be extended by managing tube-fin galvanic potentials.

In salt-laden regions eg. in winter, the aluminium radiators suffer. For instance, in parts of Russia, aluminium radiators often do not last one full winter season. Holes large-enough to drive a fist through.

The tubes of a modern automotive radiator, are made from aluminium foil. The thickness has been decreasing over time, in order to shave off costs & weight. Some are are thinner than 0.265 mm. Under pulsation load, the fins tend to crack just above the fin-tube braze-joint. After this, the tube swells & ruptures. This is a standard test for each new proposed radiator model. The fins here, act like the lattice structures seen in roof-trusses, bridges.

I hope this sets your mind at rest. If you would like a review of aluminium automotive condensers, please let me know.

Thank you, seanf. Take care. :)

Quote:

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Originally Posted by desA

vikky1971, I would have to differ with your thoughts on aluminium, in radiator service. Radiators & condensers are different from a strength/corrosion perspective. I will answer assuming you did mean 'radiators' & not 'condensers'. :)

Aluminium radiators are acceptable in regions with little external corrosion attack. In this application, corrosion life is extended with waterside corrosion inhibitors. Fin life can be extended by managing tube-fin galvanic potentials.

In salt-laden regions eg. in winter, the aluminium radiators suffer. For instance, in parts of Russia, aluminium radiators often do not last one full winter season. Holes large-enough to drive a fist through.

The tubes of a modern automotive radiator, are made from aluminium foil. The thickness has been decreasing over time, in order to shave off costs & weight. Some are are thinner than 0.265 mm. Under pulsation load, the fins tend to crack just above the fin-tube braze-joint. After this, the tube swells & ruptures. This is a standard test for each new proposed radiator model. The fins here, act like the lattice structures seen in roof-trusses, bridges.

I hope this sets your mind at rest. If you would like a review of aluminium automotive condensers, please let me know.

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With yours 2214plus posts I don't want to get into the argument. Whether you say condenser or radiator they all are heat exchangers. We don't choose the material used but can keep it clean to maintain the heat transfer at utmost efficiency. In pulsating heavy loads fins aren't brazed to the tubes but differential expansion and contraction of tubes and fins will decide the contact area and so will the heat exchange rate. Tubes always remains to provide the strength to the assembly.