Abstract: Disclosed herein is a once-through evaporator comprising an inlet manifold; one or more inlet headers in fluid communication with the inlet manifold; one or more tube stacks, where each tube stack comprises one or more inclined evaporator tubes; the one or more tube stacks being in fluid communication with the one or more inlet headers; where the inclined tubes are inclined at an angle of less than 90 degrees or greater than 90 degrees to a vertical; one or more outlet headers in fluid communication with one or more tube stacks; and an outlet manifold in fluid communication with the one or more outlet headers.