An evaporator includes an enclosure having a fluid inlet manifold and a vapor outlet manifold. At least one blind passageway is arranged within the enclosure so as to open into a portion of the vapor outlet manifold. The interior surface of the enclosure that defines each passageway is covered with a capillary wick. A porous valve is arranged in fluid communication between the fluid inlet manifold and a blind end of the at least one blind passageway.