Abstract: A pipe for a cooling unit comprises an outer pipe, and an inner pipe shorter than the outer pipe and located at an evaporating portion in the outer pipe, a circulation gap being defined between the inner wall surface of the outer pipe and the outer wall surface of the inner pipe and leading from one end to the other end of the inner pipe, whereby working liquid is permitted to boil up continuously and stably in the evaporating portion even uder a low temperature flow of working liquid.

Abstract: An apparatus for heating fluid in a storage tank or transport pipe includes a elongated horizontally positioned tubular receiver having a cover plate at one end thereof through which an electric cartridge heater is inserted into a lower portion of the receiver. A vaporizable working fluid partially fills the lower portion of the receiver to a level sufficient to cover the heater and a temperature detector for controlling the heater is inserted through the cover plate into the receiver above the level of the fluid therein. A sealed tubular heat exchanger communicates with the receiver through a single passage through which vaporized working fluid enters the heat exchanger and condensed working fluid's returned to the receiver and the receiver and heat exchanger are evaculated of gasses. The heat exchanger may be disposed whithin a container holding fluid to be heated or constitute a jacket disposed around the container.