Immersion-tube heat exchanger

A heat exchanger of the immersion-tube type comprising an outer vessel fitted with a duct for the supply of a primary fluid, a duct for the discharge of said primary fluid after circulation within the vessel, a partition plate for dividing the interior of the vessel into two regions consisting of a lower region at the pressure of the primary fluid and an upper region at the pressure of a secondary fluid to be vaporized by heat transfer with the primary fluid, said partition plate being pierced by holes for the insertion of vertical immersion tubes carried by the plate and reserved for the circulation of the secondary fluid, said immersion tubes being each provided with a pressure tube which is open at the upper end of providing a communication with the region in which the vaporized secondary fluid is collected and closed at the lower end which penetrates into the primary fluid region, in which each immersion tube is provided with an axial duct for supplying secondary fluid in liquid phase within the interior of the pressure tube, wherein said heat exchanger comprises an intermediate tube which is coaxial with the admission duct and a screen mounted within the annular space delimited between the intermediate tube and the pressure tube, said screen being constituted by a sleeve which is coaxial with the two tubes, the upper end of said sleeve being rigidly fixed to the intermediate tube and the lower end of said sleeve being open so as to delimit up to the full height of the sleeve with the intermediate tube an annular zone filled with stagnant vapor which forms a thermal insulation, said coaxial sleeve which forms a screen having in the vicinity of its lower end a projecting annular flange centering said sleeve by bearing on the external surface of the intermediate tube.