PURPOSE: To form an evaporation heat exchanger to transfer a medium to be evaporated actually completely to a vapor phase.

CONSTITUTION: The evaporation heat exchanger comprises at least one active liquid cooling circuit for discharging a heat in a spacecraft under a gravity-free operating condition and under different acceleration conditions, a space provided with at least one inlet valve for a medium to be evaporated, and cooling liquid passages isolated from each other. The medium to be evaporated can be guided between the passages. The passages are formed of a bundle of small tubes provided perpendicular to a main flow direction of the medium to be evaporated and parallel to each other. The two small tubes front and rear of the medium in a main flowing direction are interconnected to one another to form a zigzag pattern. An interval of the two tubes 4 to 13 front and rear of the medium is changed as separating from inlet tubes 16, 17.