PURPOSE: To provide an evaporation heat exchanger by which the deformation of both shell plates caused by the increase of the internal pressure of a ring gap formed by both shell plates can be surely prevented, and which can be easily manufactured and has a heat of liquid heat transfer cycle usuful for cooling a space craft.

CONSTITUTION: In an evaporation heat exchanger comprising a cylindrical container formed by two shell plates 1, 2, the cooling liquid is guided through a ring gap surrounding a processing chamber, and on the other hand a medium to be evaporated is injected into the processing chamber. In the ring gap, a spiral body formed by ribs 4 is arranged, and these ribs are connected with both of an inner cylinder 1 partitioning the processing chamber and an outer cylinder 2. The ribs are firmly arranged on one of the cylinders, and comprise the recesses 16 on the outer faces adjacent to the second cylinder, and the projections 17 to be engaged with the recesses are arranged on the second cylinder for forming the radial frictional coupling.