Heat exchanger

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, an assembly of a plurality of heat exchanger tubes connected to said inlet and outlet ducts for receiving said first fluid from the inlet duct to convey said first fluid through said tubes for discharge into said outlet duct, said heat exchanger tubes being of U-shape, each including first and second straight leg portions respectively connected to said inlet and outlet ducts and a curved bend region connecting said straight leg portions for reversing the direction of flow of said first fluid from said first leg portion to said second leg portion, said assembly of heat exchanger tubes projecting laterally of said ducts into the path of travel of a second fluid which flows around said tubes in a passage area, said assembly of heat exchanger tubes being arranged in a matrix of rows and columns, the tubes in said columns being disposed in common planes extending parallel to one another and perpendicular to said ducts, said straight leg portions in said common planes being spaced apart equal distances, the curved bend regions of said tubes in said common planes being arranged from an innermost tube of smallest radius of curvature to an outermost tube of largest radius of curvature, the curved bend regions of adjacent tubes having a spacing in each common plane which is greater between the curved bend regions closer to the innermost tube as compared to the spacing between the curved bend regions of adjacent tubes closer to the outermost tube to provide a throttle region for flow of the second fluid at the curved bend regions of the tubes closer to the outermost tube and thereby obtain substantially undisturbed homogenous flow of said second fluid through the tube matrix.