Inner-grooved aluminium tube is a thin-wall round tube with fine helical or straight fins formed on its bore. The grooves enlarge the inner surface and stir the refrigerant, raising heat transfer in fin-and-tube condensers and evaporators. It lets manufacturers build all-aluminium coils that are lighter, cheaper and free of copper–aluminium galvanic corrosion.
In a round-tube plate-fin (RTPF) heat exchanger, refrigerant flows inside the tubes while air passes over thin fins pressed onto them. Most of the thermal resistance on the refrigerant side sits in a thin liquid film on the tube wall. Grooves on the inside break up that film, increase wetted area and promote mixing, so the same tube carries more heat during condensation and evaporation.
Copper inner-grooved tube has been the industry norm for room air conditioners and heat pumps for decades. Aluminium versions have grown as manufacturers look to cut material cost and weight, avoid copper price swings, and make coils from a single metal. An all-aluminium coil has aluminium fins on aluminium tubes, so there is no galvanic couple between dissimilar metals, and aluminium tubes are not attacked by the formicary ("ant-nest") corrosion that affects copper tubes in some indoor environments.
The trade-off is that aluminium is softer and weaker than copper, more sensitive to groove damage during expansion, and harder to join. A successful switch depends on the tube geometry, the alloy, the expansion tooling and the brazing method being designed together, not on substituting one tube for another.
An inner-grooved tube is defined by more than its outside diameter. Each parameter below affects heat transfer, pressure drop, burst strength and how the tube behaves when it is expanded into the fin collars. Agree a drawing that shows all of them, with tolerances.
| Parameter | What it is | Why it matters |
|---|---|---|
| Outside diameter (OD) | Commonly 5, 7, 7.94 (5/16 in) or 9.52 mm (3/8 in) to match fin collar sizes | Must suit the fin die and the expansion bullet |
| Bottom wall thickness | Wall measured at the groove root | Sets burst pressure; aluminium needs more wall than copper for the same pressure |
| Groove (fin) height | Height of the internal fins above the root | Higher fins add area but are more easily flattened during expansion |
| Number of grooves | Count of internal fins around the bore | More fins add area and increase pressure drop |
| Helix angle | Angle of the grooves to the tube axis; zero for straight grooves | Helical grooves swirl the flow and improve heat transfer; straight grooves are easier to make in aluminium |
| Fin apex angle and profile | Shape of each internal fin | Affects drainage of condensate film and resistance to deformation |
Aluminium grooved tube is produced either by extruding the grooves directly with a profiled mandrel or by drawing over a grooved plug; helical grooves may be added by twisting. The route affects achievable geometry, so confirm it with us at enquiry stage.
Tube alloys need high formability in the annealed state, good brazeability and adequate corrosion resistance. Manganese-bearing 3xxx alloys are the most common; leaner 3102 extrudes more easily into fine internal detail. Long-life alloys, which are 3xxx variants with tuned copper, manganese and zinc, are also used to shift corrosion into a lateral, non-perforating mode.
| Element | 3003 | 3102 | 1100 |
|---|---|---|---|
| Silicon (Si) | ≤ 0.60 | ≤ 0.40 | Si + Fe ≤ 0.95 |
| Iron (Fe) | ≤ 0.70 | ≤ 0.70 | (see Si) |
| Copper (Cu) | 0.05 – 0.20 | ≤ 0.10 | 0.05 – 0.20 |
| Manganese (Mn) | 1.0 – 1.5 | 0.05 – 0.40 | ≤ 0.05 |
| Zinc (Zn) | ≤ 0.10 | ≤ 0.30 | ≤ 0.10 |
| Titanium (Ti) | — | ≤ 0.10 | — |
| Aluminium | Remainder | Remainder | ≥ 99.00 |
| Alloy / temper | Typical tensile strength | Typical yield strength | Typical elongation |
|---|---|---|---|
| 3003-O | 110 MPa | 40 MPa | 30 – 40 % |
| 1100-O | 90 MPa | 35 MPa | 35 – 45 % |
Typical values for annealed tube; 3102-O sits close to 1100-O in strength and ductility. The governing limits are those agreed in the tube specification and reported on the certificate for each lot.
Modern refrigerants such as R32 and R410A run at high condensing pressures. Size the bottom wall so the tube meets the burst and fatigue requirements of your safety standard with margin, allowing for the lower strength of annealed aluminium.
Tubes are expanded into fin collars with a bullet. Aluminium grooves flatten more easily than copper ones, so bullet size, expansion ratio and lubricant must be tuned to keep groove height after expansion.
Hairpins are bent from O-temper tube. Tight bends can thin the outer wall and collapse grooves; tooling designed for aluminium and correct bend radius are essential.
Return bends and headers are flame or induction brazed with Al-Si filler and a non-corrosive flux, or joined with brazing ring preforms. Copper-to-aluminium transition joints, where needed, require careful design and protection.
Fins are usually made slightly anodic to the tube so they corrode first. A zinc layer on the tube outside or a long-life alloy gives further sacrificial protection in aggressive air.
Residual drawing oil and particles inside the tube can contaminate the refrigerant circuit. Agree an internal cleanliness limit and a dehydrated, capped delivery condition.
Grooved tube for refrigerant circuits is checked more closely than general-purpose tube, because a single pinhole means a field leak.
| Factor | Aluminium grooved tube (RTPF) | Copper grooved tube (RTPF) | Micro-channel (MCHX) |
|---|---|---|---|
| Material cost | Low | High and volatile | Low |
| Weight | Light | Heavy | Lightest |
| Refrigerant charge | Similar to copper RTPF | Reference | Much lower |
| Production line change | Moderate: same RTPF process, retuned tooling and brazing | None | Major: new brazing furnace and coil design |
| Galvanic risk with Al fins | None | Present at tube–fin contact | None |
| Field repair | Harder; aluminium brazing skills needed | Easy | Harder |
Aluminium grooved tube is attractive for manufacturers who want to keep their existing fin-and-tube lines. Micro-channel coils give larger gains in charge and compactness but require a full redesign; see our micro-channel tube page and folded vs extruded micro-channel comparison.
Yes, in many round-tube plate-fin designs, but not as a straight swap. Wall thickness, groove geometry, expansion tooling and the brazing of return bends must be redesigned for aluminium. Prototype coils should be tested for capacity, pressure and corrosion before production.
Mostly 3xxx alloys such as 3003 and 3102, plus 1100 and proprietary long-life alloys. All are supplied in the annealed O temper so they can be bent into hairpins and expanded into the fins.
Aluminium is softer than copper, so the internal fins flatten more easily when a bullet expands the tube into the fin collars. Bullet size, expansion ratio and lubrication must be tuned to preserve groove height and heat transfer.
No. Formicary or ant-nest corrosion is a copper problem caused by organic acids in indoor air. Aluminium tubes are not attacked this way, which is one reason all-aluminium coils are used for indoor units.
Return bends and headers are brazed with aluminium-silicon filler, by flame or induction, using non-corrosive flux or flux-containing ring preforms. Where a copper line must connect, a purpose-made copper–aluminium transition joint is used.
Usually as level-wound coils that feed hairpin benders directly, or as pancake coils, straight lengths or pre-bent hairpins, cleaned and end-capped. Metline supplies these formats with certificates to customers worldwide.
Send your tube drawing, alloy and volumes. We will reply with geometry feasibility, test plan, packing and a delivered price.
