Concentric tube heat exchange assembly with improved internal fin structure

In an evaporative heat exchange unit comprising at least one tube assembly formed by a pair of concentrically positioned tubes defining a substantially annular boiling fluid heat exchange chamber therebetween and which is connected at its ends for the flow of a boiling heat exchange fluid therethrough, an internal metallic fin assembly within said annular chamber comprising a strip of corrugated sheet metal extending spirally within said annular chamber with the corrugations being substantially straight and non-distortable and extending longitudinally of said annular chamber and bridging the space between said tubes to divide said annular chamber into a plurality of substantially parallel longitudinal passages each extending between the side edges of the strip of corrugated sheet metal, the adjacent turns of the spirally formed strip of corrugated sheet metal being spaced from each other to provide a spiral passage between the side edges of the adjacent turns and to thereby reduce the effective length of each of the longitudinal passages to that of a single corrugation of the strip and to permit arcuate fluid flow of the heat exchange fluid between the serially related longitudinal passages along said annular chamber and wherein the distance between the tubes is such that the inner and outer peripheries of the internal metallic fins of the corrugated sheet metal strip have radial compression forces exerted upon them such that the corrugations are placed under radial compression and are subjected to sufficient force to insure a good heat transfer relationship between each of said tubes and said internal metallic fin of corrugated sheet metal strip, the improvement wherein said corrugated sheet metal strip bears a multiplicity of small holes to cause points where localized bubbles of vapor are formed to improve the boiling heat transfer coefficient of the heat exchange unit corrugated sheet metal strip for said boiling fluid flowing between the tubes and passing over the corrugated sheet metal strip surfaces.