A heat exchanger (120) comprising a core (130) containing inlet manifolds (140), outlet manifold (126) and interconnecting channels (144) and having a heat-transfer surface (128). Each interconnecting channel fluidly communicates at one end with a corresponding inlet manifold and at the other end with the two outlet manifolds located immediately adjacent that inlet manifold. The inlet manifolds are located distal from the heat-transfer surface. The interconnecting channels are configured such that substantially all of the heat collected by a working fluid is collected as the working fluid flows from the inlet manifolds toward the heat-transfer surface in a direction substantially perpendicular to the heat-transfer surface.