Apparatus for increasing effective scavenging vent steam within a heat exchanger which condenses vapor inside long tubes

A heat exchanger for transferring heat from a first fluid, which changes state from a vapor to a liquid, to a second fluid, which increases in temperature, said heat exchanger comprising a shell, a tube sheet having a plurality of holes, a head cooperatively associated with said shell and tube sheet, a plurality of U-shaped tubes having their inlet and outlet ends disposed in said holes in said holes in said tube sheet, a dividing plate disposed in said head so as to produce a first chamber and a second chamber and to separate said inlet and outlet ends of all of said tubes, said second chamber being unobstructed allowing the fluid to flow freely therethrough, an inlet nozzle for said first fluid in fluid communication with said first chamber of said head, a manifold disposed within the first chamber of said head, said manifold being so disposed in fluid communication with a plurality of said tubes and to cooperate with said second chamber to cause said first fluid to make four passes through said second fluid, and in such a manner that the first two passes produce a countercurrent cross flow relationship and the last two passes produce a concurrent cross flow relationship with a general up flow in the bends of the U-shaped tubes of said last two passes, said second chamber of said head having a liquid drain nozzle disposed therein and said second chamber being disposed to form a large plenum chamber between said second and third passes, whereby liquid is separated from the first fluid prior to the first fluid entering said third pass, and a vent line in fluid communication with said mainfold, said vent line being disposed to vent vapor from said manifold.