PURPOSE: To obtain an evaporator capable of forming a uniform and stable gravity liquid film on the outer surface of a heat transfer pipe, by supplying liquid to be evaporated to the outer surface of the heat transfer pipe via a plurality of through-holes by fixing a support plate to the casing of an evaporator in a liquid-tight manner, and attaching a controller in the form of a crown to the heat transfer pipe extended through the support plate by the intermediary of a packing.

CONSTITUTION: A fluid distributing means 31 consists of a support plate 32 fixed to the casing 23 of an evaporator in a liquid-tight manner and a controller 34 having a packing 33 and disposed on the upper surface of the support plate 32. The controller 34 is shaped in the form of a crown and fitted around a heat transfer pipe 24 in the form of a flange. The controller 34 has a coupling portion 35 at its central portion where the pipe 24 is extended vertically upward and is formed with a fluid passage section 36 under the coupling portion 35. Further, a packing groove is formed at the coupling portion 35 and the packing 33 is fitted therein. On the other hand, the fluid passage section 36 is communicated with the outside of the controller 34 via a plurality of through-holes 37 which are opened in the tangential direction of the heat transfer pipe 24. By selecting the number and diameter of the through-holes 37, a proper amount of fluid to be heated can be supplied to the circumferential portion of the heat transfer pipe 24. Thus, the distance between the controller 34 and the heat transfer pipe 24 is kept uniform over the entire circumference of the pipe 24, and the fluid to be heated is introduced from the through-holes 37 in the form of jet and forms a uniform liquid film on the outer surface of the pipe 24 while causing swirl around the same.