Abstract: In one general aspect, a microelectronics cooling device can include a microchannel heat exchanger within an enclosure that houses the device at a heat absorbing end and another heat exchanger which is optionally also a microchannel heat exchanger at a heat sink end outside the enclosure. One or more pipes flowably connect the two ends for transporting liquid working fluid to the heat absorber and vaporized working fluid to the heat sink. The heat pipes may also be used to transfer heat outside a room that contains the electronic devices.

Abstract: In one general aspect, a microchannel heat exchanger is disclosed. It includes a cover, a base, and thermally conductive sheets between the cover and the base that each define a series of side-by-side lanes aligned with a flow direction. The lanes each include aligned slots that define microchannel segments and are separated by cross ribs. The sheets are stacked between the base and cover so as to cause at least some of the ribs to be offset from each other and allow the microchannel segments in the same lane in adjacent sheets to communicate with each other along the flow direction to define a plurality of microchannels in the heat exchanger.

Abstract: In one general aspect, a converging split-flow microchannel evaporator is disclosed. It includes a conductive contact surface to mate to a surface to be cooled, with a core mounted in thermal connection with the conductive surface that defines at least one layer of microchannels. Within the core, one inlet restriction restricts the flow into each microchannel in a first group of the microchannels, and another restricts the flow into each microchannel in a second group. A centrally located fluid outlet receives the flows from opposite ends of the microchannels in the two groups. A check valve can be provided to help ensure ready startup without reverse flow.

Abstract: A heat pipe can include a microchannel heat exchanger at the heat absorbing end and another heat exchanger which is optionally also a microchannel heat exchanger at the heat sink end, with one or more pipes flowably connecting the two ends for transporting liquid working fluid to the head absorber and vaporized working fluid to the heat sink. The heat pipes may be used to cool electronic devices with rejection of heat outside an enclosure, and optionally outside a room, containing the electronic devices. The heat pipes may be used to cool photovoltaic or solar collection devices with rejection of heat to ambient air at a distance removed from the photovoltaic devices. Heat pipe systems are disclosed wherein the working fluid is a hydrofluorocarbon or a mono-chlorinated hydrofluoroalkene having a normal boiling point in a range from 10° C. to 80° C.