Abstract: An evaporator having a vertically mounted elongated tubular chamber, a pair of upper and lower tube sheets mounted near the ends of said tubular chamber, each tube sheet having a plurality of openings therein with a plurality of vertical evaporator tubes mounted between the pair of tube sheets, tangentially mounted inlet tubes between the upper tube sheet and a top cover for the tubular chamber, and an inverted cone mounted as a filler piece on the underside of the top cover and having its apex just slightly spaced from the upper tube sheet and its circumferential edge substantially spaced therefrom for effecting a uniform and even flow and distribution to the evaporator tubes of a liquid/solid mixture inputted into the tangential inlet tubes. The elongated tubular chamber is also provided with lateral inlet and outlet openings for inputting/outputting heated and subsequently cooled fluid to flow externally past the evaporator tubes.