Aluminium Tubes for Heat Exchangers: Types, Alloys and Selection

Why heat exchangers use aluminium tube

For decades copper tube with aluminium fins was the default for air conditioning and refrigeration coils. Since the 2000s, all-aluminium designs have taken over automotive radiators, condensers and evaporators almost completely, and they are now common in residential and commercial HVAC, data-centre cooling and battery thermal management.

The reasons are practical. An all-aluminium coil weighs much less than a copper-tube coil of the same duty, the metal costs less per unit of heat transferred, and a single-metal design eliminates galvanic corrosion between tube and fin. Aluminium also extrudes into shapes copper cannot easily match, such as the multi-port flat tubes of a microchannel condenser, which pack more surface into less volume and need less refrigerant charge.

Aluminium is less conductive than copper, but in an air-side heat exchanger the dominant thermal resistance is on the air side, not in the tube wall. A thin aluminium wall adds very little resistance, so the conductivity difference matters far less than its weight and geometry advantages.

Heat exchanger tube types compared

Choosing between them usually follows from the exchanger concept. A fin-and-tube coil that is expanded mechanically into collared fins needs round tube. A brazed parallel-flow core needs flat tube, either extruded microchannel or welded clad tube. An air-cooled process exchanger handling hot fluids at higher pressure typically uses finned tube.

Precision drawn and inner-grooved round tube

Drawn round tube is the workhorse of fin-and-tube coils. The tube is extruded, then drawn through dies over a mandrel to produce a bright surface, close OD and wall tolerances and the temper required for bending into hairpins and expanding into the fin collars.

Inner-grooved tube adds fine internal ridges that break up the refrigerant boundary layer and increase internal surface area, improving evaporation and condensation coefficients. Aluminium grooved tube is the direct replacement for copper grooved tube in room air conditioners and heat pumps, and it uses the same coil-making equipment with adjusted expansion settings.

Aluminium grooved tube is softer than copper, so expansion bullets, hairpin bending and brazing of return bends must be set up for aluminium. Wall thickness is usually slightly heavier than the copper tube it replaces to keep burst and handling margins.

Microchannel (multi-port extruded) tube

Microchannel tube is a flat extrusion with a row of small parallel ports. Brazed between louvred fins and into header pipes, it forms the parallel-flow cores used in nearly all automotive condensers and a growing share of HVAC condensers, evaporators and CO₂ gas coolers.

Zinc applied to the outside of the tube diffuses into the surface during brazing and creates a sacrificial layer. If corrosion starts, it spreads sideways through that layer instead of pitting through the thin wall. Pre-flux and silicon-flux coatings put the brazing flux, and in the Si-flux case the filler metal, directly on the tube so the fins can be bare, simplifying the brazing line.

HF-welded clad flat tube and folded tube

Radiators, heater cores, charge-air coolers and many oil coolers use flat or oval tube roll-formed from clad brazing strip and welded by high-frequency induction. Production is fast, wall thickness can be very thin, and the cladding provides the brazing filler for the tube-to-fin and tube-to-header joints.

Clad ratio is typically around 10 % of thickness per side for the braze layer. The 4343 filler melts at about 577 – 613 °C and 4045 at about 577 – 591 °C, below the core alloy, which is why controlled-atmosphere brazing (CAB) runs close to 600 °C. Welded tube is also supplied in round, D-shaped and multi-cavity forms for EV battery cooling and solar thermal collectors. See our guide to HF-welded aluminium pipe for size ranges.

Aluminium finned tube

Finned tube multiplies the outside surface of a tube many times, which is essential when the outside fluid is air. Aluminium is the standard fin material because it is light, conductive and easy to form.

Common finned-tube parameters are fin pitch from about 1.5 mm (closer pitch adds surface but raises air-side pressure drop and fouling), fin height up to about 16 mm and average fin thickness around 0.4 mm on base tubes up to about 50 mm OD. Base tubes for process service are often carbon or stainless steel; Metline supplies the aluminium fin material and aluminium finned tube, while non-aluminium base tubes are specified and supplied by the exchanger builder.

How to choose the tube alloy

Magnesium above roughly 0.3 – 0.5 % interferes with fluoride (NOCOLOK-type) flux in CAB brazing, which is why 5xxx and most 6xxx alloys are kept out of flux-brazed cores or brazed in vacuum. For refrigerant pressures in CO₂ systems, wall thickness and alloy strength need checking against burst requirements of the relevant pressure-equipment code.

Standards, tests and documents

• Mill test certificate (EN 10204 3.1) with chemistry, temper and mechanical properties
• Dimensional inspection of OD, wall, port geometry and straightness
• Eddy-current or pressure leak testing of tube as specified
• Flare, flattening, expansion and burst tests where the order calls for them
• Coating weight reports for zinc and flux-coated microchannel tube
• Internal cleanliness and residual oil limits for refrigerant tube

Related heat exchanger materials

Tube products in more detail:

Fins, brazing sheet and fillers:

Aluminium (aluminum) heat exchanger tube: frequently asked questions