US Patent 11670987 High specific power electrical machine

An electric machine for converting between electrical and rotary mechanical energy includes a rotor that is journalled to rotate about an axis of rotation, and an adjacent stator that magnetically exerts torque upon the rotor across a magnetic airgap in response to applied electric power to air core stator windings that are bonded in thermal contact to a slotless ferromagnetic stator backiron forming the stator surface facing the magnetic airgap, the rotor has a surface that is opposed to, and spaced apart from, the corresponding surface on the stator, the rotor surface and the stator surface define the airgap therebetween. The rotor has permanent magnets that generate magnetic flux across the magnetic airgap and through the air core stator windings. The air core windings are cooled by a physical loop having an evaporator, a remote located condenser and connected by two fluid flow lines filled with two phase fluid comprising liquid and gas both traveling in the same direction around the physical loop. The evaporator is constructed as an annulus co-annular with the rotor and located in thermal contact with the stator backiron and in thermal conduction indirectly with heat across the bond of the air core stator windings and through the stator backiron as heat is generated from the application of electric power; The evaporator transfers heat from the stator backiron to the fluid through phase change energy of the fluid, and the fluid is passively circulated to the condenser where the phase change energy is released remotely by convection of heat to ambient air, wherein the condenser is located at a higher elevation than the stator and the evaporator has two internal parallel fluid paths located on opposite diametral sides of the stator.