Heat exchanger and associated method

A heat exchanger comprising an inlet duct for admission of a first fluid to be heated, an outlet duct for discharge of said first fluid after heating thereof, said ducts being arranged in substantially parallel relation, a matrix assembly of a plurality of U-shaped heat exchanger tubes connected to said inlet and outlet ducts for receiving said first fluid from said inlet duct to convey said first fluid through said tubes for discharge into said outlet duct, said heat exchanger tubes extending transversely from said inlet and said outlet duct into the path of flow of a second fluid, said tubes of the matrix assembly forming first and second straight line matrix sections extending into a common curved bend matrix section in which reversal of flow of said first fluid is effected, said tubes of said first and second matrix sections each providing flow fields and respective through flow areas for said second fluid differing from the flow field and respective through flow areas of said tubes in said curved bend matrix section, said matrix assembly being divided into a plurality of separate groups adjacent to one another lengthwise of said ducts, each group of tubes having a central longitudinal plane extending perpendicularly to said ducts, said curved bend sections of said tubes in each group converging uniformly towards said central longitudinal plane, to locally reduce the flow areas between said tubes in said curved bend matrix section the curved bend sections of the tubes in each group on opposite sides of said central longitudinal plane being of opposite curvature.