Abstract: A heat transfer tube assembly comprising a pair of fluid circulation tubes disposed co-axially one within the other, the inner tube being held substantially concentric within the outer tube by a plurality of pairs of diametrally opposed depressions or dimples formed in the peripheral surface of the outer tube at regular intervals. Each depression or dimple projects inwardly such as to engage and indent the peripheral surface of the inner tube and to cause a corresponding portion of the inner tube to bulge inwardly during forming of the dimples in the periphery of the outer tube by forming punches or, preferably, by two pairs of diametrally opposed rolls, each provided with an appropriate dome-shaped protuberance on its peripheral surface for roll forming the dimples as a result of longitudinally feeding the outer tube, with the inner tube disposed within the outer tube, between the rotating rolls.

Abstract: A heat transfer tube assembly comprising a pair of fluid circulation tubes disposed co-axially one within the other, the inner tube being held substantially concentric within the outer tube by a plurality of pairs of diametrally opposed depressions or dimples formed in the peripheral surface of the outer tube at regular intervals. Each depression or dimple projects inwardly such as to engage and indent the peripheral surface of the inner tube and to cause a corresponding portion of the inner tube to bulge inwardly during forming of the dimples in the periphery of the outer tube by forming punches or, preferably, by two pairs of diametrally opposed rolls, each provided with an appropriate dome-shaped protuberance on its peripheral surface for roll forming the dimples as a result of longitudinally feeding the outer tube, with the inner tube disposed within the outer tube, between the rotating rolls.

Abstract: A fluid flow assembly for solar heat absorbers, radiators and the like formed of a pair of tubular headers, defining respectively an inlet header and an outlet header, and placed in fluid flow communication by a plurality of tubular members disposed substantially coplanar and parallel, and connected at each end to one of the headers. The end portions of the tubular members project into the headers through a collective slot disposed in the sidewall of each header. The lengths of the tubular member projecting end portions progressively increase in the direction of fluid flow through the inlet header, the shortest projecting end portion being disposed upstream, and the lengths of the tubular member projecting end portions progressively decrease in the direction of fluid flow through the outlet header, the shortest projecting end portion being disposed downstream.

Abstract: A solar heat absorber for solar heat collector panels, formed of a pair of tubular headers, defining respectively an inlet and outlet header, and a plurality of flat tubular members disposed substantially coplanar, parallel and mutually adjoining, and connected at each end to one of the headers. In use, the absorbers of the invention are disposed as heat collector units in appropriate areas exposed to sun rays, and a fluid to be heated is circulated from one header to the other, the heat being soaked by the tubular members exposed to the sun rays being transmitted to the circulating fluid which is progressively heated as it flows from one header to the other.