A heat transfer device comprising: at least one planar fin having first and second opposed faces (16, 17) and a heat receiving portion at an edge of the planar fin; and at least one thermosiphon component physically and thermally connected to the at least one planar fin and adapted to transfer heat from the heat receiving portion to other areas of the fin, the heat transfer device optionally comprising a plurality of fins with thermosiphon components spatially arranged to form a vertical or horizontal array and further optionally with an air gap or space between said individual fins with thermosiphon devices, wherein: the at least one thermosiphon component includes at least one tube forming a continuous, closed loop and optionally containing a working fluid, the at least one tube being physically and thermally connected to the first face and/or the second face of the planar fin, and the at least one tube and working fluid adapted to operate as a two-phase thermosiphon in which working fluid is evaporated in an evaporation portion of the at least one tube adjacent the heat receiving portion of the planar fin, and working fluid vapor flows in the at least one tube away from the evaporation portion for condensing; characterised in that the at least one tube includes a multiport tube having multiple flow channels; the multiport tube includes a manifold portion that fluidly connects the multiple flow channels with each other; the manifold portion is defined by a coupling that joins ends of the at least one tube to each other and is formed by a sleeve-type coupling, and the manifold portion includes a sealable port for evacuating and/or providing a working fluid to the continuous, closed loop. at least one planar fin having first and second opposed faces (16, 17) and a heat receiving portion at an edge of the planar fin; and at least one thermosiphon component physically and thermally connected to the at least one planar fin and adapted to transfer heat from the heat receiving portion to other areas of the fin, the heat transfer device optionally comprising a plurality of fins with thermosiphon components spatially arranged to form a vertical or horizontal array and further optionally with an air gap or space between said individual fins with thermosiphon devices, wherein: the at least one thermosiphon component includes at least one tube forming a continuous, closed loop and optionally containing a working fluid, the at least one tube being physically and thermally connected to the first face and/or the second face of the planar fin, and the at least one tube and working fluid adapted to operate as a two-phase thermosiphon in which working fluid is evaporated in an evaporation portion of the at least one tube adjacent the heat receiving portion of the planar fin, and working fluid vapor flows in the at least one tube away from the evaporation portion for condensing; characterised in that the at least one tube includes a multiport tube having multiple flow channels; the multiport tube includes a manifold portion that fluidly connects the multiple flow channels with each other; the manifold portion is defined by a coupling that joins ends of the at least one tube to each other and is formed by a sleeve-type coupling, and the manifold portion includes a sealable port for evacuating and/or providing a working fluid to the continuous, closed loop. the at least one thermosiphon component includes at least one tube forming a continuous, closed loop and optionally containing a working fluid, the at least one tube being physically and thermally connected to the first face and/or the second face of the planar fin, and the at least one tube and working fluid adapted to operate as a two-phase thermosiphon in which working fluid is evaporated in an evaporation portion of the at least one tube adjacent the heat receiving portion of the planar fin, and working fluid vapor flows in the at least one tube away from the evaporation portion for condensing; characterised in that the at least one tube includes a multiport tube having multiple flow channels; the multiport tube includes a manifold portion that fluidly connects the multiple flow channels with each other; the manifold portion is defined by a coupling that joins ends of the at least one tube to each other and is formed by a sleeve-type coupling, and the manifold portion includes a sealable port for evacuating and/or providing a working fluid to the continuous, closed loop. the manifold portion is defined by a coupling that joins ends of the at least one tube to each other and is formed by a sleeve-type coupling, and the manifold portion includes a sealable port for evacuating and/or providing a working fluid to the continuous, closed loop.