Locally inverted fin for an air conditioner

In a finned heat exchanger unit, wherein heat transfer takes place between a first fluid flowing through a plurality of spaced-apart finned tubes and a second fluid flowing outside the finned tubes, a plurality of fins, each fin comprising:

• a thin sheet of a heat conductive material formed into corrugations of predetermined pitch L and height H, comprising a plurality of crests peaked in a first direction alternating with a plurality of troughs peaked in a second direction opposite said first direction;
• said thin sheet being also formed to have a plurality of substantially cylindrical collars therethrough, with the centers of said collars aligned with said troughs, each collar having a shape and size to closely fit around one of said plurality of heat exchanger tubes for conductive heat exchange therewith;
• and
• within a local element of said fin, extending between the centers of a streamwise neighboring pair of said plurality of collars, said thin sheet being further provided with a plurality of parallel first and second cuts, between each pair comprised of a crest and an adjacent trough, whereby a strip of said thin sheet is defined between each pair of said first and second cuts between each pair comprised of a local crest and an adjacent local trough, with each one of said crests and troughs between adjacent strips being locally inverted such that a portion of each crest is locally inverted into a local trough and a portion of each trough is locally inverted into a local crest, said strips being formed into louvers each having a substantial portion thereof formed intermediate to and aligned parallel with the closest portions of said adjacent inverted local crest and local trough, respectively.