Describes a brazed aluminium heat exchanger developed for air-cooled exchangers used in residential air conditioners and heat pumps. The brazed aluminium design provides high performance per unit weight than currently used designs. Presently used indoor heat exchangers have plate fins on round tubes. The outdoor heat exchanger uses round tubes with either a plate fin of a spine fin geometry. The brazed aluminium heat exchanger is made of extruded aluminium tubes having a 1.0 in. (25.4 mm) major diameter and a 9.16 in. (4.06 mm) minor diameter. The tubes contain 0.031 in. (0.79 mm) thick membranes spaced at 0/194 in. (4.93 mm) to meet the R22, 2,200 psi (15 MPa) design pressure. The air side uses the louvred fin geometry. Wind tunnel tests were made on two fin geometry variants, each having 12, 15, and 18 fins/in. (472, 591, and 709 fins/m). Compared to a 12 fpi (472 fins/m) plain plate fin with 3/8 in. (9.5 mm) diameter tubes, the brazed aluminium design gives a 90% higher heat transfer coefficient for only 25% high pressure drop. Compared to an 18 fpi (709 fins/m) spine fin design with 3/8 in (9.5 mm) diameter tubes, the brazed aluminium design gives a 44% higher heat transfer coefficient and a 10% smaller pressure drop. Burst pressure tests showed that the tube failed at 1,900 psi (13 MPa). Increasing the membrane thickness to 0.036 in. (0.91 mm) will meet the required 2,200 psi (15 MPa) burst pressure.

KEYWORDS: performance, heat exchangers, aluminium, unit air conditioners, heat pumps, tubes, testing, comparing, heat transfer coefficient, heat flow, pressure drop, high pressure, membranes, thickness, geometry, diameter, R22, refrigerants