A heat exchanger includes a plurality of multi-channel heat exchange tubes extending between spaced inlet and outlet headers. Each heat exchange tube has a plurality of flow channels defining discrete flow paths extending longitudinally in parallel relationship from its inlet end to its outlet end. The inlet header has a channel for receiving a two-phase fluid from a fluid circuit and a chamber for collecting the fluid. The chamber has an inlet in flow communication with the channel and an outlet in flow communication with the plurality of fluid flow paths of the heat exchange tubes. The channel defines a relatively high turbulence flow passage that induces uniform mixing of the liquid phase refrigerant and the vapor phase fluid and reduces potential stratification of the vapor phase and the liquid phase within the fluid passing through the header.