Patent Publication Number: US-11043876-B2

Title: Electric motor having conformal heat pipe assemblies

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 16/203,161, which was filed on 28 Nov. 2018, which claims priority to U.S. Provisional Application No. 62/670,460, which was filed on 11 May 2018. The entire disclosures of these applications are incorporated herein by reference. 
    
    
     FIELD 
     The subject matter described herein relates to electric motors having heat pipes. 
     BACKGROUND 
     Electromagnetic (EM) power conversion devices generate heat during operation due to Joule heating. Examples of these types of devices include electric machines such as motors and generators, inductors, and transformers. The effectiveness of thermal management approach can restrict the power density, the power per unit volume, and/or the power per unit weight that can be achieved in these devices. Improving the thermal management approach can allow for increased amounts of electric current in the conductors of the devices, without exceeding safe operating temperature limits. Increasing the amount of current that can be conducted in the conductors of the devices can allow for improvements in the power densities of the devices. 
     One way to manage heat generated in devices are heat pipes. Some known heat pipes are made from a conductive material, such as copper. This conductive material generates additional heat when in the presence of high-frequency electromagnetic fields. As a result, the very heat pipes that should operate to carry heat away from the devices (e.g., away from conductive windings or coils of the devices) can generate additional heat due to the changing electromagnetic fields near the heat pipes, leading to drop in power conversion efficiency, in addition to potentially increasing the temperatures. 
     BRIEF DESCRIPTION 
     In one embodiment, a heat pipe assembly includes plural connected walls having porous wick linings along the walls, an insulating layer coupled with at least one of the walls on a side of the at least one wall that is opposite of the porous wick lining of the at least one wall, and an interior chamber disposed inside and sealed by the walls. The porous wick linings of the walls are configured to hold a liquid phase of a working fluid in the interior chamber. The insulating layer of the at least one wall is directly against a conductive component of an electromagnetic power conversion device such that heat from the conductive component vaporizes the working fluid in the porous wick lining of the at least one wall and the working fluid condenses at or within the porous wick lining of at least one other wall to cool the conductive component of the electromagnetic power conversion device. The assembly can be placed in direct contact with the device while the device is operating and/or experiencing time-varying magnetic fields that cause the device to operate. 
     In one embodiment, a heat pipe system includes plural heat pipe assemblies configured to be disposed directly against conductive windings of an electric motor to cool the windings. Each of the heat pipe assemblies includes plural connected walls having porous wick linings along the walls. The walls include at least an interior wall, an outer wall, and a connecting wall that couples the interior wall with the outer wall. Each of the heat pipe assemblies also includes an interior chamber disposed inside and sealed by the walls. The porous wick linings of the walls are configured to hold a liquid phase of a working fluid in the interior chamber. The interior walls of the heat pipe assemblies are configured to be located directly against the conductive windings of the motor such that heat from the conductive windings vaporizes the working fluid in the porous wick linings of the interior walls of the heat pipe assemblies. The working fluid condenses at or within the porous wick linings of the outer walls of the heat pipe assemblies to cool the conductive windings of the motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present inventive subject matter will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below: 
         FIG. 1  illustrates one example of a cross-sectional view of a heat pipe assembly; 
         FIG. 2  illustrates a perspective view of conductive coils of a motor with one embodiment of conformal heat pipe assemblies; 
         FIG. 3  is a perspective view of a portion of the conductive coils and heat pipe assemblies shown in  FIG. 2 ; 
         FIG. 4  is a front view of a portion of the conductive coils and heat pipe assemblies shown in  FIG. 2 ; 
         FIG. 5  illustrates a perspective view of the conductive coils of the motor shown in  FIG. 2  with another embodiment of conformal heat pipe assemblies; 
         FIG. 6  is a perspective view of a portion of the conductive coils and heat pipe assemblies shown in  FIG. 5 ; 
         FIG. 7  is a front view of a portion of the conductive coils and heat pipe assemblies shown in  FIG. 5 ; 
         FIG. 8  illustrates a perspective view of the conductive coils of the motor shown in  FIG. 2  with another embodiment of conformal heat pipe assemblies; 
         FIG. 9  is a perspective view of a portion of the conductive coils and heat pipe assemblies shown in  FIG. 8 ; 
         FIG. 10  is a front view of a portion of the conductive coils and heat pipe assemblies shown in  FIG. 8 ; 
         FIG. 11  is another perspective view of a portion of the conductive coils and heat pipe assemblies shown in  FIG. 8 ; 
         FIG. 12  illustrates a cross-sectional view of a coil of the motor shown in  FIG. 2  and one embodiment of a heat pipe assembly; 
         FIG. 13  illustrates a cross-sectional view of a coil of the motor shown in  FIG. 2  and another embodiment of a heat pipe assembly; 
         FIG. 14  illustrates a cross-sectional view of a coil of the motor shown in  FIG. 2  and another embodiment of a heat pipe assembly; 
         FIG. 15  illustrates one embodiment of an end bell conformal heat pipe assembly; 
         FIG. 16  illustrates a first cross-sectional view of one embodiment of a motor housing heat pipe assembly; 
         FIG. 17  illustrates a second cross-sectional view of the motor housing heat pipe assembly shown in  FIG. 16 ; 
         FIG. 18  illustrates a first cross-sectional view of one embodiment of a rotor sleeve heat pipe assembly; 
         FIG. 19  illustrates a second cross-sectional view of the rotor sleeve heat pipe assembly shown in  FIG. 18 ; 
         FIG. 20  illustrates a cross-sectional view of one embodiment of a rotor heat pipe assembly for an interior permanent magnet motor; 
         FIG. 21  illustrates a cross-sectional view of one embodiment of a rotor heat pipe assembly for an induction motor of a field wound motor; 
         FIG. 22  illustrates a cross-sectional view of one embodiment of a transformer windings or inductor windings heat pipe assembly; 
         FIG. 23  illustrates operation of one or more of the heat pipe assemblies shown in  FIG. 8  in the motor shown in  FIG. 2  that is disposed on a moving system; 
         FIG. 24  also illustrates operation of one or more of the heat pipe assemblies shown in  FIG. 8  in the motor shown in  FIG. 2  that is disposed on the moving system; 
         FIG. 25  also illustrates operation of one or more of the heat pipe assemblies shown in  FIG. 8  in the motor shown in  FIG. 2  that is disposed on the moving system; 
         FIG. 26  illustrates a flowchart of one embodiment of a method for forming a heat pipe assembly for cooling an electric machine; 
         FIG. 27  illustrates an aircraft having propulsion systems; and 
         FIG. 28  illustrates a power supply system. 
     
    
    
     DETAILED DESCRIPTION 
     The subject matter described herein relates to heat pipes formed from one or more materials having lower electrical conductivity than known heat pipes (e.g., significantly lower than copper). For example, the conductivity of the material(s) used to form the heat pipes described herein can be at least one, and may be two or more orders of magnitude smaller than copper (in one embodiment). One or more embodiments of the heat pipes described herein can be formed from titanium, which has a significantly lower electrical conductivity than copper. The heat pipes can be coated conformally with high thermal conductivity ceramic insulation materials via electrophoretic deposition (EPD) for electrical isolation, which can maintain the thermal performance of the heat pipes while enhancing insulation properties of the heat pipes. 
     One embodiment of the inventive subject matter described herein provides a method involving coating a surface of the heat pipe with a ceramic material including a nitride, via an electrophoretic process, to form a first coating. The method further includes contacting the first coating deposited by the electrophoretic process with a thermoset resin to form a second coating; and curing the second coating to form the electrically insulating coating including the ceramic material dispersed in a polymer matrix. A suitable thermally conductive ceramic material includes aluminum nitride, boron nitride, diamond, aluminum oxide, or combinations thereof. A suitable thermoset resin in the ceramic matrix include an epoxy, a siloxane, polyester, polyurethane, cyanate ester, polyimide, polyamide, polyamideimide, polyesterimide, polyvinyl ester, or combinations thereof. Additionally, with additive manufacturing, conformal heat pipes can be form-fitted to practically any winding or coil shape of a machine. Finally, making the heat pipes out of high-strength titanium allows for the replacement of structural elements in heat pipes, such as slot wedges, end-bells, and/or motor housings, leading to dual-purpose thermal-mechanical structures with enhanced performance at reduced weight. 
     Thermal management in electrical machines typically involves heat extraction outside the magnetically active zones, by employing approaches such as liquid or air-cooled heat sinks. This approach may be termed ‘remote cooling’. That is, the heat generated in the machine is conducted across several zones from the source to the sink, before the heat can be extracted. In an electric motor, for example, the heat generated in the copper conductors may be conducted through strand insulation, turn insulation, potting resin, ground-wall insulation, winding-core interface, core laminations, core-housing interface and fins, before the heat can be rejected to the surrounding working fluid. These various zones have limited thermal conductivities (e.g., windings ˜0.5 W/m-K, insulation layers ˜0.15 W/m-K, potting resin ˜0.2 W/m-K, laminations ˜25 W/m-K). Therefore, this approach limits the amount of heat that can be extracted and consequently limits the current that can be sustained in the devices. 
     Improvements to the above approach are also employed when higher performance and power densities are desired, such as by bringing the working fluid closer to the conductors when feasible (e.g., using hollow conductors and flowing the heat-extracting working fluid directly near the heat generating conductors in the devices). This approach, termed ‘embedded cooling’ or ‘direct conductor cooling,’ currently is employed in high voltage machines, where the insulation layers are significantly thicker and severely limit heat extraction via conventional approaches. This approach relies on clean, dielectric working fluids and needs additional infrastructure such as flow distribution manifolds, hoses and filters, for accomplishing the flow, adding to the overall cost and complexity of the design and reducing the overall power density. 
     Heat pipes or interior chambers are seeing increasing use to address similar heat extraction challenges in other applications such as electronics cooling. These devices operate on the principle of phase-change heat transfer in sealed tubes or enclosures, and when properly designed, efficiently carry heat from remote, hard to reach heat sources to the nearby, convenient heat sinks where the heat can be more easily extracted with minimal or reduced temperature drops. Properly designed heat pipes therefore operate as “thermal superconductors” in a thermal management system. The employment and acceptance of heat pipes in EM power conversion applications, however, has been limited for several reasons, such as commercially available heat pipes are typically made up of copper. When such heat pipes are used close to high frequency EM fields, significant eddy current induced heat generation results, causing an overall drop in efficiency and performance. Additionally, the area available for the windings or coils in these devices is compact and the winding profiles are non-standard (i.e., the windings are not always circular or rectangular). 
     Some known heat pipes or interior chambers may only be available in either rectangular or cylindrical tube configurations, further limiting use of these types of heat pipes or interior chambers in these applications. Additionally, owing to the voltage difference between the windings which are at the designed electrical potential, and the heat pipes which are at ground potential, electrical insulation may need to be employed. Typical electrical insulation materials such as NOMEX, KAPTON, mica and fiberglass, are also thermally insulating, cutting down the overall effectiveness of the heat pipes when used near the windings. 
     One or more embodiments of the inventive subject matter described herein address many, if not all, of the shortcomings of copper heat pipes described above. Additionally, form fitted, structural-thermal dual purpose mechanical elements can be formed for further improving the thermal performance of the heat pipes, along with overall weight reduction. The inventive heat pipe assemblies described herein can be used as heat pipes and interior chambers for cooling conductive coils of electric motors (including motors having concentrated windings and/or distributed windings). The assemblies can be conformal interior chamber end-bell assemblies used in motors to cool end-turns of motor windings of the motors. The assemblies can be conformal in that the assemblies have an exterior shape and/or size that conforms to (e.g., is complementary to or matches) the shape of at least a portion of an electrical machine, e.g. the end windings. 
     The assemblies can form housings of electrical machines, with the housing having interior chambers that conform to shapes of the electrical machines. One embodiment of the assemblies includes a sleeve or endplate of a rotor in a motor that includes a conformal interior chamber that cools the rotor. The assemblies can provide for rotor cooling for internal permanent magnets (IPM), surface permanent magnets (SPM), for induction machines (IM) which are singly or doubly excited, switched reluctance machines (SRM), synchronous reluctance machines (SynRM), or for field wound machines (FWM). The assemblies can provide for cooling of transformer and/or inductor windings with a heat pipe or interior chamber built or formed into a bobbin of the transformer, with an optional extension to a heat sink of the heat pipe that assists in drawing heat out and away from the windings. 
     While many examples of the uses of the heat pipe assemblies are described herein, not all uses of the heat pipe assemblies are limited to these examples. The heat pipe assemblies may be used to cool other magnetic devices, machines, or applications. 
     In one embodiment, the heat pipe assemblies are formed from titanium or titanium alloys. The heat pipe assemblies can be formed by additively manufacturing the shapes of the assemblies to conform with the shapes of the devices that are cooled by the assemblies. For example, the assemblies can be created using three-dimensional (3D) printing, rapid prototyping (RP), direct digital manufacturing (DDM), selective laser melting (SLM), electron beam melting (EBM), direct metal laser melting (DMLM), or the like. 
     The heat pipe assemblies can be formed from another material in place of or in addition to titanium. For example, the heat pipe assemblies can be formed from another material that is thermally conductive yet electrically resistive, such as stainless steel. 
     The heat pipe assemblies can be placed or formed in direct contact with the conductive windings of the magnetic devices described herein. This contrasts with some known heat pipe assemblies, which can require that insulation be placed between the exterior surface(s) of the heat pipe assemblies and the conductive windings of the magnetic devices. The heat pipe assemblies can be placed within the time-varying electro-magnetic fields that are generated to cause the devices to operate, in contrast with some known heat pipe assemblies, which are positioned outside of these fields. By applying the heat pipe assemblies directly to the source of heat in these devices, a significant thermal performance advantage may be realized relative to some known heat pipe assemblies. 
     One or more embodiments of the inventive subject matter described herein relates to integrated thermal and mechanical assemblies that can be used in devices for cooling conductive windings of the devices, including three-dimensional printed conformal interior chambers. 
       FIG. 1  illustrates one example of a cross-sectional view of a heat pipe assembly  100 . The assembly  100  is shown in  FIG. 1  to describe the basic operation of how the conformal heat pipe assemblies described herein remove thermal energy from an electrical and/or mechanical heat source (e.g., the conductive windings of an electro-magnetic device, such as a motor, inductor, transformer, induction heating coil, or the like) in steady and/or unsteady cooling conditions. 
     The assembly  100  includes a vapor housing  102  with low thermal resistance. The housing  102  can be formed using additive manufacturing (e.g., three-dimensional printing) and/or can be formed from a material having low thermal resistance and low electric conductivity (e.g., titanium, stainless steel, etc.). The vapor housing  102  defines and encloses an interior chamber  104 . This chamber  104  may be hermetically sealed from the outside environment so that working fluid inside the chamber  104  (e.g., water) is not able to pass out of the chamber  104  through the housing  102  and/or is not able to enter the chamber  104  through the housing  102 . 
     The housing  102  is defined by several walls  106 ,  108 ,  110 ,  112  that extend around and enclose the chamber  104 . The walls  106 ,  108 ,  110 ,  112  are provided merely as one example of how the various heat pipe assemblies described herein can operate to remove heat from an electro-magnetic device. The number, size, and/or arrangement of the walls  106 ,  108 ,  110 ,  112  can change based on the shape of the electro-magnetic device to which the heat pipe assembly is to conform. Additionally, using additive manufacturing support walls may be built in specific places within the vapor space  104  if needed, to mechanically support the outer housing  102  and provide additional rigidity to the structure. The support walls can be configured to allow for the continuous flow of the vapor to offer minimal or reduced blockage. 
     Optionally, one or more of the exterior surfaces of the wall  106 ,  108 ,  110 , and/or  112  can include or be coupled with an insulation layer  116 . This insulation layer  116  can be formed from a dielectric material, a material that is not thermally conductive (or that is less thermally conductive than the wall  106 ,  108 ,  110 , and/or  112 ), and/or a material that is not electrically conductive (or that is less electrically conductive than the wall  106 ,  108 ,  110 , and/or  112 ). Examples of materials that the insulation layer  116  can be formed from include a polyamide, KAPTON, or NOMEX. In one embodiment, the insulation layer  116  is formed on one or more of the walls  106 ,  108 ,  110 , and/or  112  using electrophoretic deposition. Alternatively, another deposition technique is used. 
     In one embodiment, the interior surfaces of one or more of the walls  106 ,  108 ,  110 , and/or  112  include, are formed from, or are lined with a porous wick structure or lining  114 . The porous wick structure  114  can be formed using additive manufacturing and may be formed from sintered powder. Alternatively, the porous wick structure  114  can be formed using another technique and/or from another material. The porous wick structure  114  can line the entire interior surfaces of the chamber  104  and can hold liquid working fluid. Optionally, not all walls may include the insulating layer  116  and/or the porous wick structure  114 . For example, one or more of the walls may not include the wick structure  114 , or a portion of at least one wall may not include the wick structure  114 . As another example, one or more of the walls may not include the insulating layer  116 , or a portion of at least one wall may not include the insulating layer  116 . Optionally, one or more interior support columns or posts may extend from one wall to an opposite wall to mechanically support the walls away from each other. 
     The housing  102  conducts thermal energy from an electro-magnetic device through the walls  106 ,  108 ,  110 , and/or  112 , depending on which wall is next to the device. In some embodiments, multiple walls  106 ,  108 ,  110 ,  112  may be in contact with the same or different devices at the same time. In one example of operation of the assembly  100 , the wall  108  may be in direct contact with a source of heat, such as the conductive windings of the device. 
     As the wall  108  absorbs thermal energy, the wall  108  transfers the thermal energy to a working fluid (e.g., water, ammonia, etc.) that is held within the chamber  104  and/or within pores of the porous wick structure  114  along the wall  108 . This working fluid may be in a liquid state in the porous wicking structure  114 . As the working fluid absorbs the thermal energy, the fluid changes phase from a liquid phase to a vapor phase and moves into the interior chamber  104 . As the working fluid moves into the chamber  104  and/or toward the cooler walls  106 ,  110 , and/or  112 , the working fluid cools and condenses (e.g., changes from a vapor phase into a liquid phase). The liquid phase of the fluid then recirculates back into to the chamber  104  through gravity and/or capillary forces, where the fluid again absorbs thermal energy from the wall  108 , thereby continuing the evaporation-condensation cycle. 
     For example, the sealed chamber  104  can hold the liquid phase of the working fluid and the gaseous phase of the working fluid in thermodynamic equilibrium. When heat is introduced into the chamber  104  (e.g., at one or more walls  106 ,  108 ,  110 ,  112 ) and heat is removed from the chamber  104  (e.g., at one or more other walls  106 ,  108 ,  110 ,  112  located farther from the heat source), a very efficient heat transfer process occurs. This process involves the heat entering the wall  106 ,  108 ,  110 , or  112  and reaching the liquid working fluid in the porous wick lining  114  of the wall  106 ,  108 ,  110 , or  112 . The liquid working fluid is at least partially vaporized by the heat, and the vapor moves to where the vapor can condense, such as the interior of the chamber  104  and/or another wall  106 ,  108 ,  110 ,  112  located farther from the heat source. The vapor condenses back into a liquid phase and, upon doing so, releases heat back into the wall(s)  106 ,  108 ,  110 ,  112  located farther from the heat source. The liquid working fluid enters back into the porous wick lining  114  and can be drawn back toward the interior chamber  104  by capillary action (e.g., capillary wicking forces). 
       FIG. 2  illustrates a perspective view of conductive coils  200  of a motor  202  with one embodiment of conformal heat pipe assemblies  204 .  FIG. 3  is a perspective view of a portion of the conductive coils  200  and heat pipe assemblies  204 .  FIG. 4  is a front view of a portion of the conductive coils  200  and heat pipe assemblies  204 . The motor  202  is one example of an electro-magnetic power conversion device described herein. Only a ring portion  206  of a stator of the motor  202  is shown in  FIG. 2 , and the motor  202  may include additional components. The ring portion  206  can represent a portion of the inside or inner diameter of the stator. The ring  206  includes several conductive coils or windings  200  that when passing current through, produce magnetic fields which interact with the rotor (not shown), causing it to move. 
     The coils  200  can generate heat during operation of the motor  202 . This heat can be dissipated or otherwise removed from the coils  200  by the heat pipe assemblies  204 . The heat pipe assemblies  204  are L-shaped bodies in the illustrated embodiment. The heat pipe assemblies  204  include interior portions  210  that extend between neighboring coils  200  of the motor  202  and exterior portions  208  that are disposed outside of the coils  200  (e.g., are not located between the coils  200 ). The interior portions  210  are elongated in axial directions that are parallel to a center axis or axis of rotation  216  of the motor  202 . The exterior portions  208  are elongated in radial directions that are perpendicular to the center axis or axis of rotation  216  of the motor  202 . In the illustrated embodiment, the exterior portions  208  of the heat pipe assemblies  204  all are located on one side of the ring portion  206  of the stator of the motor  202 . Additionally, the exterior portions of the heat pipe assemblies  204  all extend radially outward (e.g., away from the center axis or axis of rotation  216  of the motor  202 ) in the illustrated embodiment. 
     The heat pipe assemblies  204  can include interior chambers  104  having porous wick linings  114  with working fluid therein, as shown in  FIG. 1 . The heat pipe assemblies  204  can help to rapidly cool the coils  200  by removing heat from the coils  200 , as described above in connection with the heat pipe assembly  100  shown in  FIG. 1 . For example, opposing walls  106 ,  108  in the interior portions  210  of the heat pipe assemblies  204  can be in direct contact with neighboring coils  200 . Heat from the coils  200  vaporizes working fluid held in the porous wick linings  114  of the walls  106 ,  108 , and the vapor working fluid then can move within the interior chambers  104  of the heat pipe assemblies  204  into the exterior portions  208  of the heat pipe assemblies  204  where there is less heat. The vapor working fluid can then condense back into the liquid working fluid (as described below), which then flows or is pulled (e.g., via capillary action) back into the porous wick linings  114  of the interior portions  210 . 
     The walls  106 ,  108  of the interior portion  210  of each of the heat pipe assemblies  204  are in direct contact with the coils  200  that are on opposite sides of the heat pipe assembly  204 , as shown in  FIG. 4 . For example, no additional material other than the material that forms the walls  106 ,  108  may be disposed between the wall  106  and/or  108  and the nearest coil  200 . 
     The exterior portions  208  of the heat pipe assemblies  204  include several fins  212 . These fins  212  may be hollow, elongated extensions that outwardly project from the interior chambers  104  of the exterior portions  208  of the heat pipe assemblies  204 . This can allow for the working fluid working fluid in the interior chambers  104  of the heat pipe assemblies  204  to flow into the fins  212 . In operation, heat from the coils  200  can vaporize the liquid phase of the working fluid in the porous wick lining  114  in the plates  208  of the interior portion  210  of the heat pipe assembly  204  that are adjacent to or otherwise in contact with the coils  200 . The vaporized coolant can move in the portion of the interior chamber  104  that is in the interior portion  210  of the heat pipe assembly  204  to the portion of the interior chamber  104  that is in the exterior portion  208  of the heat pipe assembly  204 . 
     The vaporized working fluid can condense in the portion of the interior chamber  104  that is in the exterior portion  208  of the heat pipe assembly  204 . At least some of the vaporized working fluid can flow into the hollow fins  212  of the exterior portion  208  of the heat pipe assembly  204  to reduce the time needed for the vaporized working fluid to condense. This can rapidly cool the heat generated by the coils  200 . The condensed working fluid can then flow back into the porous wick lining  114  in the interior portion  210  of the heat pipe assembly  204 . As depicted, the heat pipe assembly  204  interfaces with the fins  212  consistent with an air-cooled arrangement. Optionally, the heat pipe assemblies  204  can interface with a liquid heat exchanger consistent with a liquid-cooled arrangement instead. In an alternative embodiment, the fins  212  can be separate entities and are attached to the heat pipe using epoxy, solder or a similar bonding operation ensuring thermal communication between the heat pipe body and fins. 
       FIG. 5  illustrates a perspective view of the conductive coils  200  of the motor  202  with another embodiment of conformal heat pipe assemblies  504 .  FIG. 6  is a perspective view of a portion of the conductive coils  200  and heat pipe assemblies  504 .  FIG. 7  is a front view of a portion of the conductive coils  200  and heat pipe assemblies  504 . 
     The heat pipe assemblies  504  are L-shaped bodies in the illustrated embodiment. The heat pipe assemblies  504  include interior portions  510  that extend between neighboring coils  200  of the motor  202  and exterior portions  508  that are disposed outside of the coils  200  (e.g., are not located between the coils  200 ). The interior portions  510  are elongated in axial directions that are parallel to a center axis or axis of rotation  216  of the motor  502 . The exterior portions  508  are elongated in radial directions that are perpendicular to the center axis or axis of rotation  216  of the motor  202 . In the illustrated embodiment, the exterior portions  508  of the heat pipe assemblies  504  all are located on one side of the ring portion  206  of the stator of the motor  202 . Additionally, the exterior portions of the heat pipe assemblies  504  all extend radially inward (e.g., toward the center axis or axis of rotation  216  of the motor  202 ) in the illustrated embodiment, in contrast to the heat pipe assemblies  204  shown in  FIGS. 2 through 4 . 
     The heat pipe assemblies  504  can include interior chambers  104  having porous wick linings  114  with working fluid therein, as shown in  FIG. 1 . The heat pipe assemblies  504  can help to rapidly cool the coils  200  by removing heat from the coils  200 , as described above. For example, opposing walls  106 ,  108  in the interior portions  510  of the heat pipe assemblies  504  can be in direct contact with neighboring coils  200 . Heat from the coils  200  vaporizes working fluid held in the porous wick linings  114  of the walls  106 ,  108 , and the vapor working fluid then can move within the interior chambers  104  of the heat pipe assemblies  504  into the exterior portions  508  of the heat pipe assemblies  504  where there is less heat. At least some of the vapor working fluid can enter the fins  212  of the exterior portion  508  of the heat pipe assemblies  504 , as described above. The vapor working fluid can then condense back into the liquid working fluid, which then flows or is pulled (e.g., via capillary action) back into the porous wick linings  114  of the interior portions  510 . 
     The walls  106 ,  108  of the interior portion  510  of each of the heat pipe assemblies  504  are in direct contact with the coils  200  that are on opposite sides of the heat pipe assembly  504 , as shown in  FIG. 8 . For example, no additional material other than the material that forms the walls  106 ,  108  may be disposed between the wall  106  and/or  108  and the nearest coil  200 . 
       FIG. 8  illustrates a perspective view of the conductive coils  200  of the motor  202  with another embodiment of conformal heat pipe assemblies  804 .  FIG. 9  is a perspective view of a portion of the conductive coils  200  and heat pipe assemblies  804 .  FIG. 10  is a front view of a portion of the conductive coils  200  and heat pipe assemblies  804 .  FIG. 11  is another perspective view of a portion of the conductive coils  200  and heat pipe assemblies  804 . 
     The heat pipe assemblies  804  are L-shaped bodies in the illustrated embodiment. The heat pipe assemblies  804  include interior portions  810  that extend between neighboring coils  200  of the motor  202  and exterior portions  808  that are disposed outside of the coils  200  (e.g., are not located between the coils  200 ). The interior portions  810  are elongated in axial directions that are parallel to a center axis or axis of rotation  216  of the motor  502 . The exterior portions  808  are elongated in radial directions that are perpendicular to the center axis or axis of rotation  216  of the motor  202 . In the illustrated embodiment, the exterior portions  808  of the heat pipe assemblies  804  are located on opposite sides of the ring portion  206  of the stator of the motor  202 . For example, the exterior portions  808  can alternate between the sides of the ring portion  206  such that heat pipe assemblies  804  that neighbor each other have exterior portions  808  on opposite sides of the ring portion  206 . The heat pipe assemblies  804  that neighbor each other can have interior portions  810  that contact opposite sides of the same coil  200 . Additionally, the exterior portions of the heat pipe assemblies  804  all extend radially outward (e.g., away from the center axis or axis of rotation  216  of the motor  202 ). 
     The heat pipe assemblies  804  can include interior chambers  104  having porous wick linings  114  with working fluid therein, as shown in  FIG. 1 . The heat pipe assemblies  804  can help to rapidly cool the coils  200  by removing heat from the coils  200 , as described above. For example, opposing walls  106 ,  108  in the interior portions  810  of the heat pipe assemblies  804  can be in direct contact with neighboring coils  200 . Heat from the coils  200  vaporizes working fluid held in the porous wick linings  114  of the walls  106 ,  108 , and the vapor working fluid then can move within the interior chambers  104  of the heat pipe assemblies  804  into the exterior portions  808  of the heat pipe assemblies  804  where there is less heat. At least some of the vapor working fluid can enter the fins  212  of the exterior portion  808  of the heat pipe assemblies  804 , as described above. The vapor working fluid can then condense back into the liquid working fluid, which then flows or is pulled (e.g., via capillary action) back into the porous wick linings  114  of the interior portions  810 . 
     The walls  106 ,  108  of the interior portion  810  of each of the heat pipe assemblies  804  are in direct contact with the coils  200  that are on opposite sides of the heat pipe assembly  804 , as shown in  FIGS. 9, 10, and 11 . For example, no additional material other than the material that forms the walls  106 ,  108  may be disposed between the wall  106  and/or  108  and the nearest coil  200 . 
       FIG. 12  illustrates a cross-sectional view of a coil  200  of the motor  202  and one embodiment of a heat pipe assembly  1204 . The cross-sectional view can represent a two-dimensional plane that is oriented perpendicular to the axis of rotation  216  of the motor  202 . The motor  202  has the coils  200  arranged as concentrated windings in the illustrated embodiment. The heat pipe assembly  1204  can represent one or more of the heat sink assemblies  204 ,  504 ,  804  described above. The cross-sectional view of FIG.  12  only shows a cross-section of the interior portion of the heat pipe assembly  1204 . As shown, the heat pipe assembly  1204  has the hollow interior chamber  104 , with the walls  106 ,  108  being adjacent to and/or in contact with the coil  200 . The interior portion of the heat pipe assembly  1204  has a rectangular cross-sectional shape in the illustrated embodiment. The ring portion  206  of the stator of the motor  202  optionally can include a topstick  1200 , which can be magnetic or non-magnetic in different embodiments. 
       FIG. 13  illustrates a cross-sectional view of a coil  200  of the motor  202  and another embodiment of a heat pipe assembly  1304 . The cross-sectional view can represent a two-dimensional plane that is oriented perpendicular to the axis of rotation  216  of the motor  202 . The motor  202  has the coils  200  arranged as concentrated windings in the illustrated embodiment. The heat pipe assembly  1304  can represent one or more of the heat sink assemblies  204 ,  504 ,  804  described above. The cross-sectional view of  FIG. 13  only shows a cross-section of the interior portion of the heat pipe assembly  1304 . As shown, the heat pipe assembly  1304  has the hollow interior chamber  104 , with walls of the assembly  1304  being adjacent to and/or in contact with the coil  200 . The interior portion of the heat pipe assembly  1304  has a T-shaped cross-sectional shape in the illustrated embodiment. This shape provides for a radial portion  1300  of the interior chamber  104  being elongated in a direction that is perpendicular to the axis of rotation  216  and a circumferential portion  1302  of the interior chamber  104  being elongated in a direction that encircles or that otherwise does not intersect the axis of rotation  216 . For example, the interior chamber  104  can be elongated in an orthogonal direction to the axis of rotation  216 . This shape of the heat pipe assembly  1304  can provide for more contact between the coil  200  and the heat pipe assembly  1304  relative to the embodiment shown in  FIG. 12 . This can result in heat being more rapidly transferred from the coil  200  to the heat pipe assembly  1304  to more rapidly cool the coil  200 . Optionally, the heat pipe assembly  1304  can operate as an integrated topstick of the motor. 
       FIG. 14  illustrates a cross-sectional view of a coil  200  of the motor  202  and another embodiment of a heat pipe assembly  1404 . The cross-sectional view can represent a two-dimensional plane that is oriented perpendicular to the axis of rotation  216  of the motor  202 . The motor  202  has the coils  200  arranged as distributed windings in the illustrated embodiment. The ring portion  206  of the stator of the motor  202  optionally can include the topstick  1200  described above. 
     The heat pipe assembly  1404  can represent one or more of the heat sink assemblies  204 ,  504 ,  804  described above. The cross-sectional view of  FIG. 14  only shows a cross-section of the interior portion of the heat pipe assembly  1404 . As shown, the heat pipe assembly  1404  has the hollow interior chamber  104 , with the walls  106 ,  108  of the assembly  1404  being adjacent to and/or in contact with the coil  200 . The interior portion of the heat pipe assembly  1404  has a rectangular cross-sectional shape in the illustrated embodiment. While the interior portion of the heat pipe assembly  1204  shown in  FIG. 12  is elongated in a direction that radially extends toward or away from the axis of rotation  216  of the motor  202 , the interior portion of the heat pipe assembly  1404  is elongated in a circumferential direction that encircles the axis  216 . 
       FIG. 15  illustrates one embodiment of an end bell conformal heat pipe assembly  1500 . The heat pipe assembly  1500  is formed into or is formed as an end bell  1502  that couples with the motor  202 . The end bell  1502  couples with a stator housing  1504  of a stator  1506  of the motor  202 . The end bell  1502  includes recesses  1508  having shapes that conform to the shapes of the coils  200  of the motor  202 . For example, the recesses  1508  may have U-shapes or other concave shapes that separately receive the separate coils  200  of the motor  202 . 
     The end bell  1502  can be formed (e.g., using additive manufacturing) to include heat sink assemblies  1510  in the end bell  1502 . The assemblies  1510  can be shaped to match the curved shape of the coils  200 , as shown in  FIG. 15 . For example, the convex shapes of the coils  200  can extend into the concave shapes of the assemblies  1510 . These assemblies  1510  include the interior chamber  104  that is defined and enclosed by the interior porous wick linings described above. For example, one curved wall  1512  of the assembly  1510  can be an evaporator wall of the assembly  1510  that includes a porous wick lining and an opposite curved or flat wall  1514  of the assembly  1510  can be a condenser wall that includes another porous wick lining. The end bell  1502  optionally can include a gap pad  1516 , which can be a flexible, thermally conductive material that engages the coils  200 . This gap pad  1516  can engage the coils  200  without imparting mechanical damage to the end turns of the coils  200  (e.g., the visible portions of the coils  200  in  FIG. 15 ), while also thermally conducting heat from the coils  200  to the assembly  1510 . 
     In operation, heat from the end turns of the coils  200  is received by the evaporator walls  1512  of the assemblies  1510 . This heat evaporates liquid working fluid in the porous wick linings of the evaporator walls  1512 . The vaporized working fluid moves toward the condenser wall  1514 , where the working fluid condenses to form liquid working fluid. Heat from the end turns of the coils  200  is drawn out from the coils  200  by this evaporation and condensation. The heat pipe assembly  1500  that is formed into the end bell  1502  of the motor  202  can be used alone or in combination with one or more other heat pipe assemblies described herein to rapidly cool the conductive coils of a motor. 
       FIG. 16  illustrates a first cross-sectional view of one embodiment of a motor housing heat pipe assembly  1600 .  FIG. 17  illustrates a second cross-sectional view of the motor housing heat pipe assembly  1600 . The view shown in  FIG. 16  is along a two-dimensional plane that is parallel to or that includes the axis of rotation  216  of the motor  202 . The view shown in  FIG. 17  is along another two-dimensional plane that is perpendicular to the axis of rotation  216 . As shown, the motor  202  can include the end bell  1502 . Optionally, this end bell  1502  can be formed as the end bell conformal heat pipe assembly  1500  described above. 
     The heat pipe assembly  1600  is formed into or is formed as an outer housing  1602  of the motor  202 . The heat pipe assembly  1600  can be formed using additive manufacturing. The heat pipe assembly  1600  can be used to cool the motor  202 , and can be used in combination with one or more of the other heat pipe assemblies described herein. The housing  1602  includes an interior wall  1604  and an opposite wall  1606  with a sealed interior chamber  1608  between the walls  1604 ,  1606 . The walls  1604 ,  1606  can include the porous wick linings described herein. A working fluid can be disposed inside the chamber  1608  and/or the pores of the walls  1604 ,  1606 . 
     The interior wall  1604  can be directly adjacent to the stator housing  1504  to cool the stator housing  1504 . The opposite wall  1606  optionally includes elongated fins  1610  that outwardly project away from the stator housing  1504 . The fins  1610  can be hollow extensions of the interior chamber  1608  such that the working fluid can flow inside the fins  1610 . In operation, the heat from the stator housing  1504  evaporates liquid working fluid in the pores of the porous lining of the wall  1604 . The vaporized working fluid radially flows away from the wall  1604  inward into the interior chamber  1608  and optionally toward the portions of the interior chamber  1608  that are inside the fins  1610 . The fins  1610  permit the vaporized working fluid to move farther away from the source of heat (e.g., the motor), and providing several fins  1610  allows smaller portions of the vaporized working fluid to be separately cooled. These features can permit the vaporized working fluid to rapidly condense by transferring the heat from the motor  202  outside of the assembly  1600 , and thereby rapidly cool the motor  202 . 
     As shown in  FIG. 17 , the heat pipe assembly  1600  optionally can include one or more support posts  1700 . The posts  1700  are structural members that assist in separating the walls  1604 ,  1606  from each other by mechanically supporting the wall  1606  outside of the wall  1604 . The posts  1700  can be formed from the same materials and/or formed using additive manufacturing. Optionally, the posts  1700  can divide the interior chamber  1608  up into several, smaller chambers  1608 . The posts  1700  can include a porous wick lining  114  to aid in moving the condensed working fluid back from the side where the fluid condenses to the side where the fluid evaporates upon exposure to heat. 
       FIG. 18  illustrates a first cross-sectional view of one embodiment of a rotor sleeve heat pipe assembly  1800 .  FIG. 19  illustrates a second cross-sectional view of the rotor sleeve heat pipe assembly  1800 . The view shown in  FIG. 18  is along a two-dimensional plane that is parallel to or that includes the axis of rotation  216  of the motor  202 . The view shown in  FIG. 19  is along another two-dimensional plane that is perpendicular to the axis of rotation  216 . A rotor  1802  of the motor  202  (shown in  FIG. 16 ) is disposed inside the stator  1506  (shown in  FIG. 15 ). The rotor  1802  is coupled with an elongated shaft  1804 , and both the rotor  1802  and the shaft  1804  rotate around or about the axis of rotation  216 . 
     The heat pipe assembly  1800  can be formed as a sleeve and/or end plate on the rotor  1802 . The heat pipe assembly  1800  can be disposed between the rotor  1802  and the stator  1506  to cool the rotor  1802  and optionally the stator  1506 . The heat pipe assembly  1800  includes a sleeve portion  1808  and an end plate portion  1806 . The sleeve portion  1808  is elongated in directions that are parallel to the axis  216 , while the end plate portion  1806  is elongated in directions that are perpendicular to the axis  216 . The end plate portion  1806  can be formed as a circular plate with an opening through which the shaft  1804  extends. In  FIG. 18 , only one half of the sleeve and end plate portions  1808 ,  1806  is shown. 
     The heat pipe assembly  1800  can be formed using additive manufacturing. The heat pipe assembly  1800  can be used to cool the rotor  1802 , and can be used in combination with one or more of the other heat pipe assemblies described herein. The portions  1806 ,  1808  of the heat pipe assembly  1800  include an interior wall  1810  and an opposite wall  1812  with a sealed interior chamber  1814  between the walls  1810 ,  1812 . The walls  1810 ,  1812  can include the porous wick linings described herein. A working fluid can be disposed inside the chamber  1814  and/or the pores of the walls  1810 ,  1812 . 
     The interior wall  1810  can be directly adjacent to the exterior surfaces of the rotor  1802 , as shown in  FIG. 18 . The end plate portion  1806  optionally includes elongated fins  1610  that outwardly project away from the outer wall  1812  of the end plate portion  1806 . As described above, the fins  1610  can be hollow extensions of the interior chamber  1814  such that the working fluid can flow inside the fins  1610 . In operation, the heat from the rotor  1802  evaporates liquid working fluid in the pores of the porous lining of the wall  1810 . The vaporized working fluid radially flows (in the sleeve portion  1808 ) and axially flows (in the end plate portion  1806 ) away from the wall  1810  toward the portions of the interior chamber  1814  and optionally toward the portions of the interior chamber  1814  that are inside the fins  1610 . The vaporized working fluid can then condense and return to the pores in the wall  1810 . In one embodiment, centrifugal forces can assist in returning the working fluid to the side of the heat pipe assembly where evaporation of the working fluid occurs. 
     As shown in  FIG. 19 , the heat pipe assembly  1800  optionally can include one or more support posts  1700 . As described above, the posts  1700  are structural members that assist in separating the walls  1810 ,  1812  from each other by mechanically supporting the wall  1812  outside of the wall  1810 . The posts  1700  can be formed from the same materials and/or formed using additive manufacturing. Optionally, the posts  1700  can divide the interior chamber  1814  up into several, smaller chambers  1814 . 
       FIG. 20  illustrates a cross-sectional view of one embodiment of a rotor heat pipe assembly  2000  for an interior permanent magnet motor. The view shown in  FIG. 20  is along a two-dimensional plane that is perpendicular to the axis of rotation of the rotor of the interior permanent magnet motor. Only a portion of a rotor  2001  and shaft  2003  of the interior permanent magnet motor is shown in  FIG. 20 . 
     The heat pipe assembly  2000  is formed as a rectangular box in which a permanent magnet  2006  of the interior permanent magnet motor is placed. Several heat pipe assemblies  2000  can be provided, such as one assembly  2000  for each permanent magnet in the interior permanent magnet motor. The heat pipe assembly  2000  can be formed using additive manufacturing. The heat pipe assembly  2000  can be used to cool the magnets  2006 . The heat pipe assembly  2000  includes an interior wall  2002  and an opposite wall  2004  with a sealed interior chamber  2006  between the walls  2002 ,  2004 . The walls  2002 ,  2004  can include the porous wick linings described herein. A working fluid can be disposed inside the chamber  2006  and/or the pores of the walls  2002 ,  2004 . 
     The interior wall  2002  can be directly adjacent to the exterior surfaces of the magnet  2006 . In operation, the heat from the magnet  2006  evaporates liquid working fluid in the pores of the porous lining of the interior wall  2002 . The vaporized working fluid radially flows away from the interior wall  2002  toward the interior chamber  2008  and the outer wall  2004 . This can help draw heat away from and cool the magnet  2006 . The vaporized working fluid can condense and return to the interior wall  2002 , as described herein. 
       FIG. 21  illustrates a cross-sectional view of one embodiment of a rotor heat pipe assembly  2100  for an induction motor of a field wound motor. The view shown in  FIG. 21  is along a two-dimensional plane that is perpendicular to an axis of rotation  2126  of the rotor  2102  of the induction motor. Only a portion of a rotor  2102  is shown in  FIG. 21 . 
     The rotor  2102  includes several conductive rods or bars  2104  that are elongated in directions that are parallel to the axis of rotation  2126  of the rotor  2102 . This axis  2126  is oriented perpendicular to the view of  FIG. 21  (e.g., into and out of the page of  FIG. 21 ). These bars  2104  are placed in openings in the rotor  2102 . Several heat pipe assemblies  2100  can be formed around the bars  2104 . The heat pipe assemblies  2100  can be in direct contact with the bars  2104 . For example, each heat pipe assembly  2100  can be formed as a cylindrical sleeve in which one of the bars  2104  are positioned, with the heat pipe assembly  2100  and the bar  2104  placed into an opening in the rotor  2102 , as shown in  FIG. 21 . 
     The heat pipe assemblies  2100  can be formed using additive manufacturing. The heat pipe assemblies  2100  can be used to cool the bars  2104 , which can heat up during operation due to the changing magnetic field to which the bars  2104  are exposed to rotate the rotor  2102 . Although only five of the bars  2104  are shown as including a heat pipe assembly  2100 , optionally, a different number or all the bars  2104  can be provided with a heat pipe assembly  2100 . 
     Each of the heat pipe assemblies  2100  can include an interior wall  2106  and an opposite outer wall  2108  with a sealed interior chamber  2110  between the walls  2106 ,  2108 . The walls  2106 ,  2108  can include the porous wick linings described herein. A working fluid can be disposed inside the chamber  2110  and/or the pores of the walls  2106 ,  2108 . The interior wall  2106  can be directly adjacent to the exterior surfaces of the bar  2104 . In operation, the heat from the bar  2104  evaporates liquid working fluid in the pores of the porous lining of the interior wall  2106 . The vaporized working fluid radially flows away from the interior wall  2106  toward the interior chamber  2110  and the outer wall  2108 . This can help draw heat away from and cool the bar  2104 . The vaporized working fluid can condense and return to the interior wall  2106 , as described herein. 
       FIG. 22  illustrates a cross-sectional view of one embodiment of a transformer windings or inductor windings heat pipe assembly  2200 . The heat pipe assembly  2200  can be used to cool conductive windings  2202  of a transformer or inductor device  2204 . The windings  2202  can be helically wrapped around a bobbin  2206 , and the heat pipe assembly  2200  can be at least partially located between the windings  2202  and the bobbin  2206 . A magnetic core  2208  of the device  2204  is positioned such that the windings  2202  extend around opposing sections of the magnetic core  2208  that are separated by an insulative gap. Alternatively, the heat pipe assembly  2200  can form the bobbin  2206 . For example, the heat pipe assembly  2200  can be formed as a cylindrical body about which the windings  2202  are wrapped. 
     As shown, the heat pipe assembly  2200  can be formed to include ridges  2201  that radially extend away from a center axis of the heat pipe assembly  2200  or bobbin  2206 . These ridges can be sized and positioned to receive different windings  2202 . The ridges increase the surface area where the windings  2202  engage the heat pipe assembly  2200 , which can increase the rate at which heat is thermally transferred from the windings  2202  to the heat pipe assembly  2200 . The ridges optionally can provide a guide for where the windings  2202  are to be positioned during manufacture of the transformer. 
     In operation, the windings  2202  can become heated due to the varying magnetic field that is generated around the core  2208  from the passage of current through the windings  2202 . The heat pipe assembly  2200  can help to cool these windings  2202 . The heat pipe assembly  2200  can wrap around the bobbin  2206  between the windings  2202  and the bobbin  2206 . The heat pipe assembly  2200  includes opposing inner and outer walls  2210 ,  2212 , with a sealed interior chamber  2214  located between the walls  2210 ,  2212 . The walls  2210 ,  2212  can include the porous wick linings  114 , as described herein, with a working fluid in the pores of the linings  114  and the chamber  2214 . The walls  2212  may be in direct contact with the windings  2202 . For example, there may not be any other material between the walls  2212  and the windings  2202 . 
     The heat pipe assembly  2200  also can include a chamber extension  2216 , which is an extension of the interior chamber  2214  that is not disposed between the windings  2202  and the bobbin  2206 . In the illustrated embodiment, this extension  2216  is formed by portions of the walls  2210 ,  2212  and the chamber  2214  that extend along the length of the bobbin  2206  outside of the windings  2202 , as shown in  FIG. 22 . The walls  2210 ,  2212  can encircle the bobbin  2206  such that the heat pipe assembly  2200  forms a cylindrical sleeve in which the bobbin  2206  is disposed. The chamber extension  2216  can be part of this cylindrical sleeve that extends outside of the windings  2202 . 
     The heat pipe assemblies  2200  can be formed using additive manufacturing. The heat pipe assemblies  2200  can be used to cool the windings  2202 , which can heat up during operation of the device  2204 . In operation, the heat from the windings  2202  evaporates liquid working fluid in the pores of the porous lining of the wall  2212  and potentially in the pores of the wall  2210 . The vaporized working fluid axially flows in the chamber  2214  in directions along the length of the bobbin  2206  toward the chamber extension  2216 . For example, the vaporized working fluid increases the gas pressure inside the chamber  2214  in locations between the windings  2202  and the bobbin  2206 . This increased pressure can cause the vaporized working fluid to flow in the chamber  2214  along the length of the bobbin  2206  toward the chamber extension  2216 . 
     The temperature inside the chamber extension  2216  may be reduced relative to the temperature inside the chamber  2214  between the windings  2202  and the bobbin  2206 . This can be due to the heated windings  2202  being farther from the chamber extension  2216 . The cooler temperatures in the chamber extension  2216  can cause the vaporized working fluid to condense, which transfers thermal energy out of the heat pipe assembly  2200  and helps to cool the windings  2202 . The liquid working fluid can then flow back into the pores of the walls  2210 ,  2212  and into the chamber  2214  in locations between the windings  2202  and the bobbin  2206  to continue cooling the windings  2202 . 
       FIGS. 23 through 25  illustrate operation of one or more of the heat pipe assemblies  804  in the motor  202  that is disposed on a moving system. While the description and illustration focuses on the heat pipe assemblies  804 , the description also can apply to other heat pipe assemblies described herein. The motor  202  may be onboard a moving system, such as a vehicle (e.g., an aircraft such as a fixed wing airplane or a helicopter) that experiences different gravitational and other forces due to acceleration of the vehicle. For example, during takeoff of an aircraft (shown in  FIG. 23 ) from the ground, the motor  202  can experience acceleration forces a+g due to both the pull of gravity toward the ground (e.g., g) and acceleration of the aircraft away from the ground (e.g., a). These forces can cause the working fluid in the heat pipe assemblies  804  to be drawn to one wall or side of the interior chambers inside the assemblies  804  than another. 
     For example, the heat pipe assemblies  804  below the motor  202  (relative to the direction in which the vehicle is acceleration, or below the motor  202  in  FIG. 23 ) can have the working fluid pulled away from locations that are between the conductive coils  200  of the motor  202 . This can result in decreased cooling of the coils  200  by the heat pipe assemblies  804  located below the motor  202  (relative to the heat pipe assemblies  804  operating without the acceleration forces a and/or gravity forces g acting on the working fluid). But, the heat pipe assemblies  804  above the motor  202  (relative to the direction in which the vehicle is acceleration, or above the motor  202  in  FIG. 23 ) can have the working fluid pulled into locations that are between the conductive coils  200  of the motor  202 . This can result in increased cooling of the coils  200  by the heat pipe assemblies  804  located above the motor  202  (relative to the heat pipe assemblies  804  operating without the acceleration forces a and/or gravity forces g acting on the working fluid). 
     The net effect of the decreased cooling of half of the heat pipe assemblies  804  and the increased cooling of the other half of the heat pipe assemblies  804  can result in the coils  200  being cooled at the same rate and/or by the same amount that the coils  200  would have been cooled without the influence of the acceleration forces a and/or gravity forces g acting on the working fluid. For example, the increased cooling by the heat pipe assemblies  804  above the motor  202  can counteract and cancel out the decreased by the heat pipe assemblies  804  below the motor  202 . 
     As another example, during constant velocity cruising of the aircraft (shown in  FIG. 24 ), the aircraft may be moving in directions that are more parallel to the ground than away from the ground (e.g., takeoff) or toward the ground (e.g., landing). The motor  202  can experience gravity forces g due to the pull of gravity toward the ground. These forces can cause the working fluid in the heat pipe assemblies  804  on the lower half of the motor  202  (e.g., below a bisecting plane  2400 ) to be drawn to one wall or side of the interior chambers inside the assemblies  804  than another. For example, the heat pipe assemblies  804  below the plane  2400  can have the working fluid pulled away from locations that are between the conductive coils  200  of the motor  202 . This can result in decreased cooling of the coils  200  by the heat pipe assemblies  804  located below the motor  202  (relative to the heat pipe assemblies  804  operating without the gravity forces g acting on the working fluid). But, the heat pipe assemblies  804  above the plane  2400  can have the working fluid pulled into locations that are between the conductive coils  200  of the motor  202 . This can result in increased cooling of the coils  200  by the heat pipe assemblies  804  located below the plane  2400  (relative to the heat pipe assemblies  804  operating without the gravity forces g acting on the working fluid). 
     The coils of the motor can be wound with parallel paths such that the top half of the motor forms one parallel path and the lower half of the motor forms a second parallel path. By adding parallel winding paths to the motor, the net effect of the decreased cooling of half of the heat pipe assemblies  804  and the increased cooling of the other half of the heat pipe assemblies  804  can result in the coils  200  being cooled at the same rate and/or by the same amount that the coils  200  would have been cooled without the influence of the gravity forces g acting on the working fluid. For example, the increased cooling by the heat pipe assemblies  804  above the plane  2400  can counteract and cancel out the decreased by the heat pipe assemblies  804  below the plane  2400 . This leveling of temperature occurs due to the positive temperature coefficient on the electrical resistivity of copper as a function of temperature. 
     If the coils on the top half of the motor were at a lower temperature than those in the lower half of the motor, the electric currents being conducted in the coils are redistributed in that the amount of current conducted in the coils in the top half of the motor increases while decreasing the amount of current conducted in the coils in the lower half of the motor. This occurs because the current is conducted more easily in the lower temperature half of the motor than in the hotter lower half of the motor. This would result in the temperature of the cooler coils on the top half of the motor increasing (due to more current being conducted in these coils) and the temperature of the warming coils on the bottom half of the motor decreasing (due to less current being conducted in these coils). In effect, the combination of parallel winding paths and heat-pipe cooling forms a “self-leveling” process which cancels out the increased or decreased cooling (as applicable) due to the orientation of the heat pipe assemblies. 
     While only two parallel winding paths of coils are shown and described (e.g., top and bottom half coils), the motor windings may be segmented into a different number of parallel winding paths up to and including where each motor winding is in parallel with all others. For example, the windings on the top half of the motor may be one parallel conductive path and the windings in the bottom half of the motor may be another, different parallel conductive path. Alternatively, more than two parallel paths may be provided. 
     As another example, during cruising of the aircraft, the aircraft may accelerate in a direction that is parallel to the ground (shown in  FIG. 25 ). During this lateral or horizontal acceleration, the motor  202  can experience acceleration forces a and gravitational forces g in different directions. The acceleration forces a can pull on the working fluid in one direction (e.g., opposite of the Accelerating Cruise arrow shown in  FIG. 25 ) while the gravity forces g pull on the working fluid in a perpendicular direction (e.g., toward the ground). These forces can cause the working fluid in the heat pipe assemblies  804  to be drawn in different directions. 
     For example, the heat pipe assemblies  804  that are along a leading side of the motor  202  (e.g., the right side of the motor  202  in  FIG. 25 ) and that are above the bisecting plane  2400  can have both the acceleration forces a and the gravity forces g pull the working fluid in these assemblies  804  to locations between the coils  200 . This can result in significantly improved cooling of the coils  200  relative to other heat pipe assemblies  804 . Conversely, the heat pipe assemblies  804  that are along the opposite, trailing side of the motor  202  (e.g., the left side of the motor  202  in  FIG. 25 ) and that are below the bisecting plane  2400  can have both the acceleration forces a and the gravity forces g pull the working fluid in these assemblies  804  to locations away from the coils  200 . This can result in significantly decreased cooling of the coils  200  relative to other heat pipe assemblies  804 . 
     The heat pipe assemblies  804  that are along the leading side of the motor  202  and that are below the bisecting plane  2400  can have the acceleration forces a pull the working fluid in these assemblies  804  to locations between the coils  200 , but the gravity forces g pull the working fluid away from locations between the coils  200 . This can result in improved cooling of the coils  200  relative to other heat pipe assemblies  804  other than the heat pipe assemblies  804  that are above the plane  2400  and along the leading side of the motor  202 . The heat pipe assemblies  804  that are along the trailing side of the motor  202  and that are above the bisecting plane  2400  can have the gravity forces g pull the working fluid in these assemblies  804  to locations between the coils  200 , but also can have the acceleration forces a pull the working fluid in these assemblies  804  to locations that are not between the coils  200 . This can result in improved cooling of the coils  200  relative to heat pipe assemblies  804  other than the heat pipe assemblies  804  that are above the plane  2400  and along the leading side of the motor  202 . 
     The net effect of the different amounts of cooling different quadrants of the heat pipe assemblies  804  can result in the coils  200  being cooled at the same rate and/or by the same amount that the coils  200  would have been cooled without the influence of the acceleration forces a and/or gravity forces g acting on the working fluid. 
       FIG. 26  illustrates a flowchart of one embodiment of a method  2600  for forming a heat pipe assembly for cooling an electric machine. The method  2600  can be used to create one or more of the heat pipe assemblies shown and/or described herein. Two or more of the operations described in connection with the method  2600  can be performed at the same time (e.g., concurrently or simultaneously), or may be performed sequentially. 
     At  2602 , an interior portion of a heat pipe assembly is formed. The interior portion of the heat pipe assembly can define part of a vapor chamber that is shaped to be positioned against or close to conductive portions of an electric machine. For example, the interior portion can be sized to fit between coils of a stator, can be sized as an end bell to fit against the coils of the stator, can be sized to be placed outside of the stator of the motor, can be sized to be placed between the rotor and the stator of the motor, can be sized to be placed around or between magnets inserted in the rotor and the surrounding portion of the rotor in the motor, can be sized to be placed around or between conductive rods inserted in the rotor and the surrounding portion of the rotor in the motor, can be sized to be placed around or against conductive coils of a transformer, or the like. The interior portion can be formed to have a porous wick structure on one or more interior surfaces of the interior portion. As described above, this wick structure can hold a working fluid to help cool the electric machine. The interior portion of the heat pipe assembly can be created using additive manufacturing in one embodiment. 
     Optionally, the interior portion can be formed to have one or more interior support posts. As described above, these posts can mechanically support opposite sides of the heat pipe assembly from moving toward each other during operation of the electric machine. 
     At  2604 , an exterior portion of the heat pipe assembly is formed. The exterior portion can be formed with the interior portion, such as by additively manufacturing the interior and exterior portions at the same time or during the same printing session. Alternatively, the interior and exterior portions can be formed at different times. The exterior portion also can include the interior porous wick structure to hold or help condense the working fluid described above. 
     The exterior portion may be formed to be away from the source of heat that vaporizes the working fluid in the interior portion of the heat pipe assembly. For example, the interior and exterior portions can be formed in an L-shape, with the interior portion shaped to fit between neighboring coils of the stator of the motor and the exterior portion disposed outside of (e.g., not between) the coils. As another example, the exterior portion can be a portion of the heat pipe assembly that is farther from the coils in the end bell heat pipe assembly, that is farther from the magnets or conductive rods in the rotor than the interior portion, that is farther from the rotor that the interior portion, or the like. In one embodiment, the exterior portion can be formed as an extension of a transformer bobbin to allow the working fluid to move away from the coils of the transformer and cool in the exterior portion of the heat pipe assembly. 
     In one embodiment, a heat pipe assembly includes plural connected walls having porous wick linings along the walls, an insulating layer coupled with at least one of the walls on a side of the at least one wall that is opposite of the porous wick lining of the at least one wall, and an interior chamber disposed inside and sealed by the walls. The porous wick linings of the walls are configured to hold a liquid phase of a working fluid in the interior chamber. The insulating layer of the at least one wall is directly against a conductive component of an electromagnetic power conversion device such that heat from the conductive component vaporizes the working fluid in the porous wick lining of the at least one wall and the working fluid condenses at or within the porous wick lining of at least one other wall to cool the conductive component of the electromagnetic power conversion device. 
     Optionally, the conductive component includes one or more conductive windings of the electromagnetic power conversion device such that the heat from the one or more conductive windings vaporizes the working fluid in the porous wick lining of the interior wall and the working fluid condenses at or within the porous wick lining of the outer wall to cool the one or more conductive windings of the electromagnetic power conversion device. 
     Optionally, the walls form an elongated interior portion of the interior chamber that is located between and directly adjacent to neighboring conductive coils of the one or more conductive windings. 
     Optionally, the interior portion of the interior chamber is elongated along an axis of rotation of the electromagnetic power conversion device. 
     Optionally, the walls also form an elongated exterior portion of the interior chamber that is located outside of the conductive coils. 
     Optionally, the exterior portion of the interior chamber is elongated in directions that are perpendicular to an axis of rotation of the electromagnetic power conversion device. 
     Optionally, the assembly also includes elongated fins outwardly extending from the exterior portion. 
     Optionally, the elongated exterior portion of the interior chamber is elongated in a direction radially oriented toward an axis of rotation of the electromagnetic power conversion device. 
     Optionally, the elongated exterior portion of the interior chamber is elongated in a direction radially oriented away from an axis of rotation of the electromagnetic power conversion device. 
     Optionally, the interior portion of the interior chamber has a rectangular cross-sectional shape in locations between the neighboring conductive coils. 
     Optionally, the interior portion of the interior chamber extends between and contacts the neighboring conductive coils on multiple different planes of the conductive coils. 
     Optionally, the interior portion of the interior chamber has a T-shaped cross-sectional shape. 
     Optionally, the interior portion of the interior chamber is located between and contacts opposing surfaces of the neighboring conductive coils that are concentrated windings of an electric motor. 
     Optionally, the interior portion of the interior chamber is located between and contacts opposing surfaces of the neighboring conductive coils that are distributed windings of an electric motor. 
     Optionally, the interior portion of the interior chamber has an H-shaped cross-sectional shape. 
     Optionally, the assembly also includes an end bell that couples with conductive windings of a motor as the electromagnetic power conversion device. The walls and the interior chamber can be located within the end bell. 
     Optionally, the walls are located outside of and directly contact a stator of a motor that is the electromagnetic power conversion device. 
     Optionally, the walls form elongated fins that radially project away from an axis of rotation of the motor, and wherein the interior chamber extends into the fins. 
     Optionally, the assembly also includes support posts located between the walls to structurally support the walls away from each other. 
     Optionally, the walls form a rotor sleeve and end plate in which a rotor of a motor is located as the electromagnetic power conversion device. 
     Optionally, the rotor sleeve formed by the walls encircles the rotor around an axis of rotation of the rotor. 
     Optionally, the end plate formed by the walls is oriented perpendicular to an axis of rotation of the rotor. 
     Optionally, the end plate includes elongated fins that axially project away from the end plate in directions parallel to the axis of rotation. The interior chamber can extend into the elongated fins. 
     Optionally, the walls extend around a permanent magnet in an interior permanent magnet motor as the electromagnetic power conversion device. 
     Optionally, the walls extend around a magnet in an induction motor of a field wound motor as the electromagnetic power conversion device. 
     Optionally, the walls extend around a bobbin of a transformer as the electromagnetic power conversion device, with the walls and interior chamber disposed between conductive windings of the transformer and the bobbin. 
     Optionally, the walls form an extension of the interior chamber that extends along a length of the bobbin but is not located between the bobbin and the conductive windings of the transformer. 
     In one embodiment, a heat pipe system includes plural heat pipe assemblies configured to be disposed directly against conductive windings of an electric motor to cool the windings. Each of the heat pipe assemblies includes plural connected walls having porous wick linings along the walls. The walls include at least an interior wall, an outer wall, and a connecting wall that couples the interior wall with the outer wall. Each of the heat pipe assemblies also includes an interior chamber disposed inside and sealed by the walls. The porous wick linings of the walls are configured to hold a liquid phase of a working fluid in the interior chamber. The interior walls of the heat pipe assemblies are configured to be located directly against the conductive windings of the motor such that heat from the conductive windings vaporizes the working fluids in the porous wick linings of the interior walls of the heat pipe assemblies. The working fluid condenses at or within the porous wick linings of the outer walls of the heat pipe assemblies to cool the conductive windings of the motor. 
     Optionally, the walls of the heat pipe assemblies form elongated interior portions of the interior chambers that are located between and directly adjacent to neighboring conductive windings of the one or more conductive windings. The walls of the heat pipe assemblies also can form elongated exterior portions of the interior chambers that are located outside of the conductive windings of the motor. 
     Optionally, the interior portions of the interior chambers are elongated in directions that are parallel to an axis of rotation of the motor. 
     Optionally, the exterior portions of the interior chambers are elongated in directions that are perpendicular to an axis of rotation of the motor. 
     Optionally, at least one of the heat pipe assemblies also includes elongated fins outwardly extending from the exterior portions of the heat pipe assemblies. 
     Optionally, the conductive windings of the motor extend along a circular ring around an axis of rotation of the motor. The exterior portions of the heat pipe assemblies all can be located on a single side of the ring. 
     Optionally, the conductive windings of the motor extend along a circular ring around an axis of rotation of the motor. The exterior portions of a first group of the heat pipe assemblies can be located on a first side of the ring and the exterior portions of a second, non-overlapping group of the heat pipe assemblies can be located on an opposite second side of the ring. 
     Optionally, the exterior portions of the heat pipe assemblies are elongated in directions that are oriented radially inward toward an axis of rotation of the motor. 
     Optionally, the exterior portions of the heat pipe assemblies are elongated in directions that are oriented radially outward from an axis of rotation of the motor. 
     Optionally, the heat pipe assemblies assist in self-leveling a temperature differential of the conductive windings of the electric motor during operation of the electric motor by receiving more electric current in a first set of the conductive windings that are cooler due to the working fluid in a corresponding first set of the heat pipe assemblies being directed to locations closer to the conductive windings in the first set of the conductive windings due to one or more of gravitational forces or acceleration forces, and by a different, second set of the conductive windings of the electric motor that are hotter receiving less electric current due to the working fluid in a corresponding second set of the heat pipe assemblies being directed to locations farther from the conductive windings in the second set of the conductive windings due to the one or more of gravitational forces or acceleration forces. 
       FIG. 27  illustrates an aircraft  2700  having propulsion systems  2702 ,  2704 . The aircraft  2700  includes two propulsion systems  2702 ,  2704 , but optionally may have a single propulsion system  2702  or  2704 , or may have more than two propulsion systems  2702 ,  2704 . Each of the propulsion systems  2702 ,  2704  can include an electric motor  2706  that is powered by electric current received from the same or different power sources  2708 . These power sources  2708  can include batteries, fuel cells, alternators, generators, or the like. The motor  2706  includes a rotor  2710  that rotates within or relative to a stator  2712  during operation. The rotor  2710  is coupled with a shaft  2714  to rotate the shaft  2714 . The shaft  2714  is coupled with several airfoils  2716  of an aircraft propeller  2718 . Rotation of the shaft  2714  by the rotor  2710  also rotates the airfoils  2716 , which can generate propulsion to move the aircraft  2700 . 
     One or more of the motors  2706  can include a heat pipe assembly  2716  that represents one or more embodiments of the heat pipe assemblies described herein. For example, the motor  2706  can represent the motor  202  having the conductive coils  200  with the heat pipe assemblies  204 ,  504 ,  804 ,  1204 ,  1304 , and/or  1404 . Optionally, the motor  2706  can represent the motor  202  having the stator  1506  with the heat pipe assembly  1504 . Optionally, the motor  2706  can represent the motor  202  having the housing heat pipe assembly  1600 . In another embodiment, the motor  2706  can represent the motor  202  having the sleeve heat pipe assembly  1800 . Optionally, the motor  2706  can include the rotor heat pipe assembly  2000 . In another embodiment, the motor  2706  can be an induction motor having the rotor heat pipe assembly  2100 . As described herein, the heat pipe assemblies can operate to cool the motors  2706  of the aircraft  2700  during operation of the motors  2706 . 
       FIG. 28  illustrates a power supply system  2800 . The power supply system  2800  includes a power source  2802  that provides mechanical energy to a power conversion device  2804 . The power source  2802  can represent an engine, turbine, or the like that rotates a shaft that is coupled with the power conversion device  2804 . The power conversion device  2804  can convert this mechanical energy into electric energy, such as electric current. For example, the power conversion device  2804  can represent an alternator, generator, or the like, having a rotor that is coupled with the shaft and is rotated by the power source  2802 . The rotation of the rotor within a stator of the power conversion device  2804  creates electric current that can be supplied to one or more loads  2806 . The loads  2806  can be auxiliary loads, such as heating systems, cooling systems, entertainment systems, navigation systems, or the like, on the aircraft  2700 . 
     The power conversion device  2804  can include one or more embodiments of the heat pipe assemblies described herein. For example, the power conversion device  2804  can include the conductive coils  200  with the heat pipe assemblies  204 ,  504 ,  804 ,  1204 ,  1304 , and/or  1404 . Optionally, the power conversion device  2804  can include the stator  1506  with the heat pipe assembly  1504 . Optionally, the power conversion device  2804  can include the housing heat pipe assembly  1600 . In another embodiment, the power conversion device  2804  can include the sleeve heat pipe assembly  1800 . Optionally, the power conversion device  2804  can include the rotor heat pipe assembly  2000 . In another embodiment, the power conversion device  2804  can include the rotor heat pipe assembly  2100 . The heat pipe assemblies can operate to cool the power conversion device  2804  during operation. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the inventive subject matter without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the inventive subject matter, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to one of ordinary skill in the art upon reviewing the above description. The scope of the inventive subject matter should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112(f), unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. 
     This written description uses examples to disclose several embodiments of the inventive subject matter, including the best mode, and also to enable one of ordinary skill in the art to practice the embodiments of inventive subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the inventive subject matter is defined by the claims, and may include other examples that occur to one of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 
     The foregoing description of certain embodiments of the present inventive subject matter will be better understood when read in conjunction with the appended drawings. The various embodiments are not limited to the arrangements and instrumentality shown in the drawings. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising,” “comprises,” “including,” “includes,” “having,” or “has” an element or a plurality of elements having a particular property may include additional such elements not having that property.