Patent Publication Number: US-10767848-B2

Title: Extruded heat sink

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional application No. 62/569,080, filed Oct. 6, 2017, the contents of which are incorporated herein by reference. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX 
     Not Applicable 
     FIELD OF THE TECHNOLOGY 
     The subject technology is in the technical field of heat sinks, particularly for lamps, light heads, fixtures, luminaries, and other situation requiring heat to be drawn away to protect the entity producing heat. 
     BACKGROUND OF THE TECHNOLOGY 
     A light emitting diode (“LED”) produces light by as a result of passing electrical energy through particular solid components. In incandescent lamps, where electrical energy also is passed through a solid component, namely the filament, most of the electrical energy delivered to the lamp is converted to heat. A small portion is converted to light. In an LED lamp, the process is more efficient in several respects, including: 
     a) less electrical energy is consumed, and 
     b) the majority of that energy is converted to light energy as opposed to heat energy. 
     Fluorescent lamps, including compact fluorescent lamps (hereafter the term “CFL” shall refer to both) work differently, in that instead of passing electrical energy through a solid component, the electrical energy is passed through a container holding a gas mixture typically comprising mercury and argon. First, ballast electronic circuitry converts the electrical energy from typically 120 V sinusoidal alternating current and 60 Hz, to full-wave rectification, to square-wave alternating current at much higher frequency, back to sinusoidal wave form at much higher voltage. The ballast causes the required initial “strike” electrical characteristics needed to ignite, and the post-strike characteristics that allow the CFL to operate thereafter. The resulting reaction generates heat as well ultraviolet light. The ultraviolet light, in turn excites fluorescent coating (phosphor) inside the container. That excitation produces visible light. As with the LED, the CFL lamp is more efficient than the incandescent lamp in that less electrical energy is consumed, and the majority of that energy is converted to light energy as opposed to heat energy. However, the efficiency of an LED lamp exceeds that of the CFL lamp. The CFL requires more electrical energy to produce the same amount of light as an LED lamp, and produces more heat per radiated light. 
     In all lamps, some of the heat produced is transferred into the lamp itself and into surrounding components. Particularly for LED and CFL lamps, this heat, although considerably less than generated by incandescent technology, can cause damage: to the LED itself or to the ballast electronics of the CFL. It is essential that this heat is transferred away quickly, sufficiently, and efficiently in order to avoid damaging the lamp. 
     In particular, an LED that has been exposed to high heat will likely lose efficiency, produce less light, and have a greatly reduced service life. Because of increasing efficiencies and lower costs of LED technology, and lingering problems related to mercury and the disposal of CFL lamps, LED technology will likely prevail. Thus, a need exists for high-performance heat sinks capable of removing the heat generated by LEDs. 
     Need for Subject Technology 
     What is needed is a heat sink body which comprises an extruded fixture or light head onto which the lamps are attached. Specially oriented fins and cut outs cause efficient air flow across the heat sink surface area. 
     SUMMARY OF THE TECHNOLOGY 
     The subject technology is an article of manufacture comprising a heat sink to be attached a heat source, being coupled thermally and directly for conductive flow of heat from the heat source to the heat sink. The heat sink is formed via extrusion of material of suitable density and mass to absorb heat from the particular heat source based on design requirements. The extruded heat sink is further configured with specially oriented extruded fins and machined cross cuts to increase surface area available to air flow, and arranged for efficient passage of air flow around the extruded heat sink, thus effecting efficient convection of heat from the extruded heat sink and into the air ambient. Cross cuts and fin are specifically arranged to enhance the so-called “stack effect,” or “chimney effect,” associated with air flow. (Wong, et al., The study of active stack effect to enhance natural ventilation using wind tunnel and computational fluid dynamics (CFD) simulations, Elsevire, Energy and Buildings, Volume 36, Issue 7, July 2004, Pages 668-678). 
     An objective is to maximize air flow across available surface area, and thus to enhance removal of heat into the air ambient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an end profile view of the extruded heat sink. 
         FIG. 2  is a view of the back of the extruded heat sink, before cross cuts are applied. 
         FIG. 3  is a view of the front of the extruded heat sink, before cross cuts are applied. 
         FIG. 4  is a view of the back of the extruded heat sink, with cross cuts applied. 
         FIG. 5  is a view of the front of the extruded heat sink, with cross cuts applied. 
         FIG. 6  is a front view of the extruded heat sink, with cross cuts applied, and also showing an aperture cut revealing an internal extrusion cavity. 
         FIG. 7  is an end profile view showing air flow around the extruded heart sink, oriented with the light directed upward. 
         FIG. 8  is an end profile view showing air flow around the extruded heart sink, oriented with the light directed downward. 
         FIGS. 9A  and B are views showing air flow around the extruded heart sink, oriented with the light directed upward and downward, respectively. 
         FIG. 10  is a view showing air flow around the extruded heart sink, oriented with the light directed orthogonally with respect to gravity. 
         FIG. 11  is an exploded view of the preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE TECHNOLOGY 
     The subject technology will be described more fully with reference to the accompanying drawings, in which a preferred embodiment of the subject technology is shown. However, persons of ordinary skill in the appropriate arts may modify the subject technology described here while still achieving the favorable results. Accordingly, the description which follows is to be understood as being a broad, teaching disclosure directed to persons of ordinary skill in the appropriate arts, and not as limiting upon the subject technology. 
     A heat source, which is typically one or more LED lamps, is thermally and directly coupled to the extruded heat sink inside an interior cavity, so that light is radiated outward through an aperture. The heat source is thermally coupled in series via one or more intermediate thermally conductive materials, which are in series adjacent with the heat source and which are themselves thermally coupled to each other. The thermally conductive materials, although they serve particular purposes, also allow the conductive flow of heat from the LED to the extruded heat sink. The thermally conductive materials include printed circuit boards (“PCB”) onto which the LED is electrically and mechanically coupled, and a thermally conductive pad or paste, bonding the adjacent intermediate thermally coupled material to the extruded heat sink. 
     Certain definitions are stated to assist in interpreting this description and the Figures. 
     A “lamp” is an actual light source, such as an LED, compact fluorescent light (“CFL”) bulb, fluorescent tube, or incandescent bulb. 
     A “light head” receives the lamp, and is generally portable. 
     A “fixture” receives the lamp, and is generally fixed. 
     A “luminaire” is a complete assembly providing illumination. The term used especially in technical contexts. A luminaire may be a fixture or light head. In this case, the luminaire is sealed to prevent intrusion of water, gasses, and dirt. 
     For two entities to be “coupled thermally directly for conductive flow of heat” from one entity to the other means that there is no intermediate entity between the entities that substantially impedes the flow of heat from one entity to the other. Indeed, any intermediate entity is designed or otherwise selected to promote conduction of heat. 
     “Direction of extrusion” refers to the longitudinal direction of extruded material out of an extrusion die. As will be discussed further, pathways for additional air flow created by cross cuts are generally perpendicular to the direction of extrusion. Complementary to the direction of extrusion is a perpendicular in all planes. For example, if the direction of extrusion is along the z axis in conventional terms, then x and y axes in all planes are perpendicular to the direction of extrusion. 
     The terms “extrusion” and “heat sink” may be used interchangeably. The product of extrusion here is a single body that and operates as a heat sink after application of cross cuts. 
     The extruded heat sink comprises generally a cylindrical tube with a machined cut opening along an outside surface, exposing an interior cavity and creating an aperture. Additionally, a grooved feature is machined cut around the aperture opening, creating a pocket for a gasket or adhesive seal. This gasket seal forms a flexible water tight barrier between a transparent glass or polymer window and the extrusion. The extruded heat sink, as a property of extrusion process, is open at two ends. Furthermore, the extruded heat sink provides a platform inside an interior cavity and on an interior side onto which the heat source is thermally and directly coupled. The process of extrusion naturally leaves ends open, revealing the interior cavity. 
       FIG. 1  shows an end profile view of the extruded heat sink  100 . For reference purposes,  FIG. 1  also shows a 3-dimensional coordinate system  120 , with x, y, and z axes. The z-axis represents an axis of extrusion  114 , indicating the direction in which extruded material leaves an extrusion die. As shown, points along the y-axis are positive upward on the page and points along the x-axis are positive to the right of the page. 
     The extruded heat sink  100  is generally tubular, with a cavity  112 , a set of back fins  102 , sets of side fins  106 , and a front surface  110 , all of which being formed as a result of extrusion. The cavity  112  defines a mounting surface  108 . The back fins  102  generally run parallel to the axis of extrusion  114  and generally extend away orthogonally from the axis of extrusion  114 . The side fins  106  generally run parallel to the axis of extrusion  114  and generally extend away obliquely from the axis of extrusion  114  and relative to a perpendicular to the axis of extrusion  114 , angled towards the front surface  110 .  FIG. 1  also shows “T-shaped” adapter fins, as stud ridges, for use in attaching two or more extruded heat sinks  100  together or for attaching various other parts to the extruded heat sink  100 . 
     Extruded material is any material suitable for extrusion and with sufficient thermal conductivity, and most particularly aluminum or aluminum alloys. Although other forms of manufacture are available for producing a desired shape, including forging and casting, extrusion produces superior results for the contemplated embodiments. The superior results include creation on the cavity  112  into which lamps will be deployed, lower costs, and greater thermal conductivity. (Jackson, Steve; Aluminum extrusions match SSL thermal management need in many applications; LEDs Magazine, April 2013). Furthermore, extrusion makes the resulting product very dense and thus very massive, which allows it to absorb more heat away for the heat source. 
       FIG. 2  is a view of the back of the extruded heat sink  100 , before further modification. The axis of extrusion  114  is upward. Back fins and side fins  106  are shown relative to the axis of extrusion  114  and the cavity  112 . 
       FIG. 3  is a view of the front of the extruded heat sink  100 , before further modification. The front surface  110 , shown relative to the axis of extrusion  114  and the cavity  112 , is uncut in this view. 
       FIG. 4  is a view of the extruded heat sink  100 , modified with cross cuts  402  applied to the back fins  102 , side fins  106 , and adaptor fins  104 . Similarly,  FIG. 5  is a front and side view of the extruded heat sink  100 , with cross cuts  402  applied.  FIG. 5  also shows an aperture  502  cut into the front surface  110 , revealing the cavity  112  inside. When the extruded heat sink  100  is fully assembled, source of light  720  would be deployed within the cavity  112 , on the mounting surface  108 , with the light  720  directed outward through the aperture  502 . In both  FIGS. 4 and 5 , the cross cuts  402  are arranged generally orthogonally to the direction of extrusion. 
       FIG. 6  is a front view of the extruded heat sink  100 , with cross cuts  402  applied, and showing the cavity  112  and mounting surface  108  as seen through the aperture  502 . The mounting surface  108  further comprises a heat conduction surface for heat and light producing components mounted on it. 
       FIG. 7  is an end profile view showing air flow around the extruded heat sink  100 , oriented with the light  720  directed upward with respect to gravity. Electrical energy delivered to an LED  708  lamp is primarily converted to light  720  and heat  722 . The light  720  here is in the visible and non-visible light  720  spectrum, radiated outward; and heat  722  retained in and around the LED  708 , but which must be conducted away in order to avoid damage to the LED  708  lamp. A fundamental principle of passive heat sink operation is drawing heat away from an entity, generally by conduction through one or more intermediate thermally conductive, and thermally coupled materials, to the thermally coupled heat sink. The heat sink, being warmed by the heat transferred to it, allows convection via air currents to transfer heat from the heat sink, to the air ambient. It is well-known that warm air is less dense than cooler air, and thus warm air rises opposite of the direction of gravity when it is surrounded by cooler air. As less-dense warm air is drawn away, cooler, denser air takes its place. Thus, the cooler, denser air is in place to receive additional heat from the heat sink. This operation is further shown in  FIG. 7 , where heat  722  from an LED  708  lamp is conducted through a printed circuit board PCB  710  on which the LED  708  is mounted, through a thermally conductive pad  714 , and to the extruded heat sink  100 . The heat  722  propagates through the extruded heat sink  100 , and arrives at the back fins  102  and side fins  106 . Air around the back fins  102  and side fins  106  carry heat  722  away in rising air  702 , and cooler incoming air  712  arrives to replace the rising air  702 . 
       FIG. 7  also shows a lens  718  covering the aperture  502  and the cavity  112 , through which light  720  passes. The lens  718  comprises transparent material which may or may not otherwise modify the light  720 . An o-ring  704  provides a seal between the lens  718  and the body  906  of the heat sink, as protection against moisture and gasses. 
       FIG. 7  also reveals hold down  716  clips configured to hold the lens  718  in place, being attached to adaptor fins  104 . Associated with the LED  708  lamp is a reflector  706  for directing the light  720  outward, through the lens  718 . 
       FIG. 8  is an end profile view showing air flow around the extruded heat sink  100 , oriented with the light  720  directed downward with respect to gravity. The flow of heat  722  is similar to that described with respect to  FIG. 7 , however initial directions of heat  722  and light  720  from the LED  708  lamp are opposite. 
       FIGS. 9A, 9B, and 10  show how cross cuts  402  enhance the flow of air around the extruded heat sink  100 , and thus enhance the extruded heat sink  100  capacity to transfer heat  722  into the air ambient. 
       FIGS. 9A and 9B  are views showing air flow around the extruded heat sink  100 , oriented with the light  720  directed upward and downward, respectively, with respect to gravity. In both  FIGS. 9A and 9B , the flow of cool incoming air  712  onto the extruded heat sink  100 , drawn in by the flow of warm rising air  702 , is channeled by the cooperation and arrangement among back fins  102 , side fins  106 , and cross cuts  402 . The channeling moves the cool incoming air  712  across and around the surface area of the back fins  102  and side fins  106 , and along the length of the extruded heat sink  100 . An objective is to achieve efficient exposure of incoming air  712  to available heated surface area so that the heat may be transferred into the air ambient. 
       FIG. 10  is a view showing air flow around the extruded heat sink  100 , oriented with the light  720  directed orthogonally with respect to gravity. The same operation applies as depicted in  FIGS. 9A and 9B , although the primary effect is the channeling of cooler incoming air  712  along the length of the body of the extruded heat sink  100 , with additional cooler air being drawn in and through the cross cuts  402 . 
     Light directed upward, causing heat initially to be driven downward as in  FIG. 7 , is the most difficult situation. This requires the heat sink to draw heat downward, against nature. Even at that, the extruded heat sink  100  performs well. 
       FIG. 11  is an exploded view of a preferred embodiment of the extruded heat sink  100 . The extruded heat sink  100  is shown with cross cuts  402 , and various additional components and features which, taken together, result in a luminaire. A top cap  902 , followed by a top seal  904 , closes one end of the extruded heat sink  100 . Screws hold the top cap  902  and top seal  904  to the extruded heat sink  100 . 
     An assembly comprises an LED  708  reflector assembly  962  comprising one or more reflector  706   s , further containing individual LED  708  lamps deployed within the reflector  706   s . The reflector  706   s  are configured to collect light  720  from the LED  708  lamps, and to direct the light  720  outward. The LED  708  reflector assembly  962  further comprises a PCB  710 , generally of aluminum and having a front side and a back side, and an internal electrical connector  964  attached to the PCB  710 . The LED  708  reflector assembly  962  is connected to the front side of the PCB  710 . The PCB  710  and internal electrical connector  964  are configured so that electrical energy delivered to the internal electrical connector  964  is delivered to the LED  708  lamps. The assembly further comprises a thermally conductive pad  714  connected to the back side of the PCB  710 . The assembly is attached, via screws  950 , to the mounting surface  108  (not shown in  FIG. 11 ) within the extrusion cavity  112 , with the thermally conductive pad  714  being physically adjacent to the mounting surface  108 . The thermally conductive pad  714  delivers heat generated by the LED  708  lamps to extruded heat sink  100 . 
     The o-ring  704  is deployed at the aperture  502 , between the lens  718  and the extruded heat sink  100 , the o-ring  704  thus providing a seal. Light from the LED  708  lamps passes through the lens  718 . A hold downs  716  secure the lens  718  to the extruded heat sink  100 . 
     A bottom assembly completes the closure and sealing of the extruded heat sink  100 , and provides means for delivering electrical energy to the internal electrical connector  964 . In the order of connection, the bottom assembly comprises: a bottom seal  910 ; a bottom cap  914 , further comprising internal electrical connector  912  which passes through the bottom seal  910 , and an external electrical connector  916 ; an o-ring  920  providing a seal for the external electrical connector  916 ; a thread connector attachment plate  922 , through which the external electrical connecter  916  passes to receive electrical energy; an o-ring  924  for sealing the thread connector and bottom assembly and an external power source (not shown); and screws  950  holding the bottom assembly to the extruded heat sink  100 . The external power source comprises a battery or other source that connects to the external electrical connector  916  which protrudes from the thread connector attachment plate  922 . 
     Finite Element Analysis 
     Finite element analysis shows heat transfer characteristics of the extruded heat sink  100  in several conventional orientations. These orientations include light directed downward, light directed upward, light directed horizontally, and several variations. Finite element analysis was conducted with these initial parameters: 
     air ambient being 33 degrees Celsius 
     3 LED heat sources each producing 24.3 Watts (for a total of 72.9 Watts) 
     0.1 Degree Celsius/Watt thermal resistance of the thermally conductive pad on the mounting surface 
     Results of the analysis, in the light upward configuration of  FIG. 7 , were as follows: 
     maximum air velocity was approximately 0.252 m/s 
     maximum temperature at the heat source (LED) was approximately 74 degrees Celsius 
     temperature of the extruded heat sink  100  at the interface with the air ambient 62 degrees Celsius 
     computed case to ambient thermal resistance 0.563 degrees Celsius/Watt 
     Advantages of the Subject Technology 
     The subject technology delivers several advantages, including: 
     Works well in any orientation relative to gravity and rising air 
     Light weight 
     Totally passive cooling design; no added mechanical systems required for cooling 
     Extrusion is superior to die casting: less expensive and can have variable lengths for manufacturing. Although the extruded aluminum structure is relatively expensive, it is less so than a die cast product. 
     Simple manufacturing: The heat sink is extruded, and then the cross cuts and opening aperture are cut out. 
     The “T-shaped” adapter fins allow for linear length-wise combination and connectivity of several heat sinks or to other mechanical attachment mounts. Extruded heat sink  100   s  may be aligned along the extrusion axis, and connected via clamps at the “T-shaped” adapter fins. 
     Few water leak points, relative to the aperture. An “O” ring around a glass covering (covering the aperture) provides a seal. Other O-rings provide seals where electrical connectors are introduced and at ends. 
     Other control or power electronics, which are outside of the heat sink interior, still benefit from the heat sink if thermally coupled to the heat sink body. The structure is physically strong and can be used as load bearing physical support elements. 
     The extruded heat sink  100  is never hot to the touch when in use. 
     Best Mode of the Preferred Embodiment 
     A preferred embodiment of the subject technology is as a light head, fixture, or luminaire, as show in in  FIG. 11 . The subject technology could be used for other heat sources, instead of LED lamps. 
     While the foregoing written description enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. For example, the arrangement of the second set of fins, may be angled differently or not angled at all. Unless claimed, particular system architecture and algorithms shown are not critical, but represent one or more embodiments.