Multi-pass heat exchanger having finned conduits of polygonal configuration in cross-section

A multi-pass heat exchanger comprising:

• a. a shell having a first inlet opening and a first outlet opening to respectively receive a first fluid and pass said first fluid from the heat exchanger;
• b. at least one tube bank disposed in said shell;
• c. said tube bank consisting of a plurality of conduits disposed in side-by-side relationship to each other;
• d. each of said conduits having a rectangular shape in cross-section and having contiguous surfaces consisting of two opposite large sized surfaces and two opposite small sized surfaces;
• e. a plurality of spaced, parallel fins extending from each of the large sized surfaces of each of said conduits;
• f. each of the conduits being formed into a flattened helical configuration consisting of at least three substantially straight portions so arranged that alternate straight portions extend in substantial parallelism with each other and U-bend portions interconnecting next adjacent straight portions so as to provide series flow of a second fluid therethrough and at least three passes in indirect heat exchange with said first fluid flowing exteriorly of the conduit;
• g. inlet header and outlet header;
• h. each of said conduits having their opposite end portions connected to communicate with said inlet and outlet headers to provide for flow of a second fluid through each of said conduits;
• and
• i. each of said conduits being disposed in said shell between said first inlet and outlet openings with the small sized surfaces of the conduits lying in planes generally normal to the direction of first fluid flow so that the first fluid successively passes the straight portions of said conduits.