A heat exchanger includes: a housing; a working fluid inlet and a working fluid outlet in the housing through which a working fluid enters and exits the housing, respectively, wherein a working fluid flow path connects the working fluid inlet and the working fluid outlet; and a heat transfer medium inlet and a heat transfer medium outlet in the housing through which a heat transfer medium enters and exits the housing, respectively; wherein a heat transfer medium flow path connects the heat transfer medium inlet and the heat transfer medium outlet; further wherein the heat transfer medium flow path includes at least two distinct zones of operation including a radiation dominant zone and a conduction dominant zone.