1. A thermosiphon, comprising:a condenser;
an evaporator that comprises a fluid channel and a heat transfer surface, the heat transfer surface comprising a plurality of fins or ridges that form a plurality of fluid pathways in the fluid channel that extend through the fluid channel, the evaporator configured to thermally couple to one or more heat-generating electronic devices; and
a transport member that fluidly couples the condenser and the evaporator, the transport member comprising a liquid conduit that extends through the transport member, the liquid conduit comprising an elongated slot aligned with a center of the evaporator to deliver a liquid phase of a working fluid into the fluid pathways, the transport member further comprising a bottom surface to contact a top of the heat transfer surface and vertically enclose the plurality of fluid pathways at the top of the heat transfer surface such that each of the plurality of fluid pathways comprises sidewalls formed by adjacent fins or ridges, a top barrier formed by the bottom surface of the transport member, and a bottom formed by a floor of the fluid channel,
wherein the fluid pathways are configured to transfer heat from the heat-generating electronic devices to the working fluid to change the working fluid from the liquid phase at inlets of the fluid pathways, as the working fluid flows in the fluid pathways, to a vapor phase or mixed-phase at outlets of the fluid pathways, the inlets of the fluid pathways comprising apertures defined by the sidewalls and top of the fluid pathways, and the outlets of the fluid pathways comprising apertures defined by a vertical plane perpendicular to the floor of the fluid channel, and
each of the inlets and outlets are oriented in a direction axially parallel to the sidewalls, and the working fluid flows from the inlets, in a direction transverse to the height of the fins or ridges and across at least a portion of the evaporator, to the outlets, the vapor phase or mixed-phase of the working fluid being vertically enclosed within the fluid pathways as the working fluid flows to the outlets of the fluid pathways.