A fluid heat exchanger for cooling an electronic device can have a plurality of walls. The walls can define a corresponding plurality of microchannels. Each microchannel can extend from a first end to a second end. The plurality of microchannels can define at least two opposed outer microchannels and a centrally located microchannel positioned between the opposed outer microchannels. A fluid inlet passage can be configured to deliver a heat-exchange fluid to each microchannel between the corresponding first end and the corresponding second end of the respective microchannel. A fluid outlet passage can have an enlarged outlet region from the centrally located microchannel compared to a corresponding outlet region from one or both of the opposed outer microchannels. Related methods are disclosed.