A blade heat exchanger includes blades that extend axially with respect to an axis of rotation and are elongated in the radial direction. The blades are arranged about the axis such that, when they are disposed in a housing, they form composite condensation and evaporation chambers that are isolated from each other. The interiors of at least some of the blades form the composite condensation chamber. The exteriors of the blades and the inner surface of the housing cooperate to form the composite evaporation chamber.