C44300 Admiralty Brass Tubing for Evaporative Coolers and Wet Air Coolers

C44300 admiralty brass tubing is the standard inhibited copper alloy tube for evaporative coolers, swamp coolers, desert coolers and wet air cooler units. The alloy is a 71 % copper, 28 % zinc brass with about 1 % tin and 0.02 - 0.06 % arsenic, and it is produced as seamless tube to ASTM B111/B111M and the matching ASME SB111 specification. Because evaporative cooling equipment operates with a permanently wet air side and a continuously wetted water circuit, the tube alloy has to resist both corrosion and biological fouling, and admiralty brass does both. This article sets out the alloy details, the cooling principle, the composition and dimensions of the tubing and the reasons it remains the reference material for this duty.

Alloy Identity: Admiralty Brass, Not Naval Brass

The two names are often used interchangeably in catalogue text, but they describe different alloys. Admiralty brass is C44300, a copper-zinc alloy inhibited with tin and a trace of arsenic and used almost exclusively for tubes and tube plates. Naval brass is a separate family, typically C46400 and C46500, in which tin is added to a hot-working brass without arsenic. Both resist seawater, but their compositions, tempers and fabrication routes differ, so a tube specification written for an evaporative cooler should name C44300 and cite ASTM B111 rather than relying on the trade description alone. In the European system the same alloy appears as CW706R or CuZn28Sn1As, in Germany as 2.0470, in Britain as CZ111, in Japan as C4430 and in China as HSn70-1.

The Evaporative Cooling Principle

An evaporative cooler lowers air temperature by bringing air into contact with water and allowing part of that water to evaporate. The process is driven by the enthalpy of vaporisation: water absorbs a large quantity of heat as it changes phase, and that heat is drawn from the air stream, which leaves the unit cooler and more humid. This is fundamentally different from vapour-compression refrigeration, where a refrigerant is compressed, condensed and expanded in a closed circuit, or from absorption refrigeration, which uses a heat-driven sorption cycle. Because evaporative cooling depends on evaporation rather than on a compressor, the exchanger surface stays wet for long periods, and the tubing has to tolerate a continuously damp, aerated environment plus the water chemistry of the recirculating circuit.

Production Standards for C44300 Tubing

Tube is cold drawn from extruded or cast shell, annealed between drawing passes, then finished and straightened. The finished product is inspected for dimensions, surface quality and mechanical properties, and pressure testing or eddy current testing is applied to the tube in accordance with the ordering specification.

Chemical Composition and Dimensions

Long single-length tube is valuable in coil manufacture because it reduces the number of brazed or welded joints inside a wet air stream, and every joint removed is a potential leak path. Where a coil is bent, the tube is supplied in a temper that has enough elongation for the bend radius required by the fin block.

Why Admiralty Brass Suits Wet Air Coolers

Thermal conductivity: about 111 W/(m·K), which keeps the tube wall from dominating the overall heat transfer resistance of a finned coil.

Corrosion resistance: tin and arsenic together resist dezincification in the fresh and brackish water that recirculating coolers use, and the alloy tolerates the alternating wet and dry cycles typical of seasonal operation.

Resistance to biofouling: copper alloy surfaces suppress the settlement and growth of algae and bacteria, which matters where the tube surface is permanently damp.

Mechanical properties: adequate tensile strength and pressure containment, good fatigue behaviour under vibration and thermal cycling, and enough ductility for bending, coiling, flaring and rolling into headers.

Fabrication: the alloy solders, brazes and welds and can be expanded into tube plates without special procedures.

Installation and Maintenance Notes

Evaporative cooler tubing fails for reasons that are usually operational rather than metallurgical. Water treatment is the first control: scale, biological slime and high chloride levels all shorten tube life, so blowdown rates, filtration and biocide dosing belong to the same specification as the coil. The second control is air quality, since dust and debris drawn through a wet coil form deposits that hold moisture against the tube surface. The third is mechanical, because vibration and thermal cycling on long unsupported tube runs cause fatigue cracking, which is avoided by correct fin collar support and by restraint of the coil within its casing. Where the water is consistently aggressive or the unit is expected to run for several decades, a copper-nickel tube alloy is often specified instead of admiralty brass.

Typical Applications

Evaporative condensers and closed-circuit fluid coolers

Swamp coolers, swamp boxes and desert coolers

Wet air coolers and humidification coils

Cooling coils for refrigeration, HVAC and industrial process air

Tube bundles for oilfield pumping units, precision instruments and refrigeration circuits

Frequently Asked Questions

Q: Is C44300 tubing the same as naval brass tubing?
No. C44300 is admiralty brass, an arsenical copper-zinc alloy with tin used for tubes and tube plates. Naval brass is a separate family such as C46400 or C46500, where tin is added to a hot-working brass without arsenic.

Q: Why does evaporative cooling need a corrosion resistant tube alloy?
Because the tube surface stays wetted and aerated for long periods while the recirculating water concentrates dissolved solids. A copper alloy that resists dezincification and biological fouling keeps the heat transfer surface intact.

Q: What sizes of C44300 tubing are available for coolers?
Outside diameters from 5 mm to 110 mm with wall thickness from 0.3 mm to 10 mm, supplied straight in lengths up to 24 m or bent and coiled to a coil drawing.

Q: How does evaporative cooling differ from refrigerated cooling?
An evaporative cooler relies on the enthalpy of vaporisation of water, so air leaves the unit cooler and more humid. Refrigeration instead uses a vapour-compression or absorption cycle to move heat from the load to the outside air.

Q: Which standard governs the tube?
ASTM B111/B111M or the identical ASME SB111 specification for seamless copper alloy tube, with EN 12451 or EN 12449 used on European projects and C4430 or HSn70-1 available where Japanese or Chinese grade designations are required.

Q: What commonly limits the life of cooler tubing?
Water treatment, scale and deposits, vibration and thermal fatigue rather than the alloy itself. Correct blowdown, filtration and coil support usually extend tube life more than any change of material.