A heat exchanger is described and which includes a heat exchanger portion defining a multiplicity of internal passageways, and wherein at least one of the passageways is defined in part by a wicking structure; a refrigerant distributor coupled in fluid flowing relation relative to the defined passageways of the heat exchanger portion; and a source of ammonia refrigerant which is supplied to the internal passageways of the heat exchanger portion, and wherein substantial equal amounts of liquid refrigerant are supplied to each of the passageways defined by the heat exchanger portion.