Abstract:
Ion wind fans produce ozone. In one embodiment, a heat sink used in conjunction with an ion wind fan includes at least one ozone catalyst fin coated with an ozone catalyst, to destroy at least some of the ozone produced by the ion wind fan. In one embodiment, the ozone catalyst fan protrudes from the downstream side of the heat sink towards the ion wind fan.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the priority benefit of U.S. Provisional Patent Application No. 61/233,112, entitled “MITIGATING OZONE IN A DEVICE HAVING AN EHD SOLID STATE FAN”, filed Aug. 11, 2009, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is related to ion wind fans, and in particular to reducing ozone produced by an ion wind fan. 
       BACKGROUND 
       [0003]    It is well known that heat can be a problem in many electronics device environments, and that overheating can lead to failure of components such as integrated circuits (e.g. a central processing unit (CPU) of a computer) and other electronic components, such as light emitting diodes, chips, and so on. Heat sinks are a common device used to prevent overheating. Heat sinks dissipate heat from a heat source using conduction and convection. To increase the heat dissipation of a heat sink, conventional rotary fans have been used to move air across the surface of the heat sink to increase convection. Conventional fans have many disadvantages when used in consumer electronics products, such as noise, weight, size, and failure of moving parts and bearings. A solid-state fan using ion wind, also known as corona wind, to move air addresses the disadvantages of conventional fans. However, providing an ion wind fan that meets the requirements of consumer electronics devices presents numerous challenges not addressed by any currently existing ionic wind device. 
         [0004]    One potential drawback of ion wind devices is that the high electric field that results in ion generation and ultimately ionic wind, also generates ozone (O 3 ). Ground-level ozone—as opposed to ozone found in the ozone layer of the stratosphere—is a considered a pollutant and can be harmful to the lungs if inhaled in large concentrations. In large concentrations, ozone also has an unpleasant odor. 
         [0005]    The problem of ozone production in ion wind fans has been known for some time. For example, U.S. Pat. No. 6,522,536 to Brewer et al., entitled “Electrostatic Cooling of a Computer,” discloses an ion wind device consisting of a high voltage ionization strip that ionizes the air, and a grounded heat sink that attracts the ions creating ionic wind. Brewer et al. describes coating the surface or channels of the heat sink with a catalyst that breaks down ozone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a block diagram illustrating an ion wind fan and a heat sink implemented as part of thermal management of an electronic device; 
           [0007]      FIG. 2  is a frontal view of a heat sink; 
           [0008]      FIG. 3A  is a side view of a heat sink fin according to one embodiment of the present invention; 
           [0009]      FIG. 3B  is a top view of an ozone catalyst fin according to one embodiment of the present invention; 
           [0010]      FIG. 3C  is a side view of a heat sink according to one embodiment of the present invention; 
           [0011]      FIG. 3D  is a frontal view of a heat sink according to one embodiment of the present invention; 
           [0012]      FIG. 4A  is a perspective view of a heat sink according to an embodiment of the present invention; 
           [0013]      FIG. 4B  is a perspective view of a heat sink with ozone catalyst fins according to an embodiment of the present invention; and 
           [0014]      FIG. 5  is a side view of a heat sink and an ion wind fan according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. In the present specification, an embodiment showing a singular component should not necessarily be so limited; rather the principles thereof can be extended to other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration. 
         [0016]    Ion wind or corona wind generally refers to the gas flow that is established between two electrodes, one sharp and the other blunt, when a high voltage is applied between the electrodes. The air is partially ionized in the region of high electric field near the sharp electrode. The ions that are attracted to the more distant blunt electrode collide with neutral (uncharged) molecules en route to the collector electrode and create a pumping action resulting in air movement. The high voltage sharp electrode is generally referred to as the emitter electrode or corona electrode, and the grounded blunt electrode is generally referred to as the counter electrode or collector electrode. 
         [0017]    The general concept of ion wind—also sometimes referred to as ionic wind and corona wind even though these concepts are not entirely synonymous—has been known for some time. For example, U.S. Pat. No. 4,210,847 to Shannon, et al., dated Jul. 1, 1980, titled “Electric Wind Generator” describes a corona wind device using a needle as the sharp corona electrode and a mesh screen as the blunt collector electrode. The concept of ion wind has been implemented in relatively large-scale air filtration devices, such as the Sharper Image Ionic Breeze. 
       Example Ion Wind Fan Thermal Management Solution 
       [0018]      FIG. 1  illustrates an ion wind fan  10  used as part of a thermal management solution for an electronic device. The electronic device may need thermal management for an integrated circuit—such as a chip or a processor—that produces heat, or some other heat source, such as a light emitting diode. Some example systems that can use an ion wind thermal management solution include computers, laptops, gaming devices, projectors, television sets, set-top boxes, servers, NAS devices, memory devices, LED lighting devices, LED display devices, smart-phones, music players and other portable devices, and generally any device having a heat source requiring thermal management. 
         [0019]    The electronic device will include the heat source (not shown), and a heat sink  12  to dissipate heat from the hear source. Since  FIG. 1  is a top view, the heat source is assumed to be under the heat sink  12 . To assist in heat transfer, an ion wind fan  10  is provided in the system to help move air across the surface of the heat sink  12 . The air flow is illustrated by lines A in  FIG. 1 . In other prior art systems, conventional rotary fans with rotating fan blades have been used for this purpose. 
         [0020]    As discussed above, the ion wind fan  10  operates by creating a high electric field around one or more emitter electrodes resulting in the generation of ions, which are then attracted to a collector electrode, thereby creating airflow. The airflow thus created can then be used to move air through the channels of a heat sink, such as the heat sink  12  shown in  FIG. 1  and  FIG. 2 .  FIG. 2  is a frontal view of a fin-type heat sink  12 —a view from the ion wind fan  10  for example. The heat sink  12  is generally made up of a base  14 , fins  16  attached to the base  14 , thereby forming channels  18  for air contact. 
         [0021]    As explained above, some ion wind fans  10  generate ozone. One way to mitigate ozone production described in U.S. Pat. No. 6,522,536 to Brewer et al., entitled “Electrostatic Cooling of a Computer,” is coating the surface and the channels of the heat sink  12  with a catalyst that breaks down ozone. There are several shortcomings of the catalyst-coated heat sink disclosed by the &#39;536 patent. In the &#39;536 patent, the heat sink itself is used as a collector electrode. However, in many embodiments, it is preferable to not electrically ground the heat sink and provide a heat sink that is separate physically from the ion wind fan, as shown in  FIG. 1 . Furthermore, coating the collector electrode (the heat sink in Brewer) with a catalyst can have detrimental effects on fan performance, as the catalyst used in Brewer is not highly conductive. 
         [0022]    As shown in  FIG. 1 , in some embodiments it is desirable to have a gap or plenum between the ion wind fan  10  and the heat sink  12 . A drop in air pressure from the fan can result if the heat sink  12  is positioned right next to the ion wind fan  10 . However, according to research performed by the inventors of the present invention, ozone concentration tends to be highest in the immediate vicinity of the ion wind fan  10 . 
       Protruding Ozone Catalyst Fins 
       [0023]    One embodiment of a heat sink having protruding ozone catalyzing fins is now described with reference to  FIGS. 3A-D .  FIG. 3A  shows a side-view of a heat sink fin  20 . The fin  20  is similar to heat sink fins  16  from  FIG. 2 , except that fin  20  has two slots  22  ( 22   a  and  22   b ). The slots  22  are each adapted to receive and ozone catalyst fin  24 , as shown in top view in  FIG. 3B . The ozone catalyst fin  24  is coated with (or composed of) an ozone catalyst. The heat sink fin  20  may or may not be coated with an ozone catalyst. There are numerous known ozone catalysts, such as manganese oxide and dioxide, activated carbon, platinum, and various other alloys and materials. The embodiments of the present invention are not limited to any particular ozone catalyst; any catalyst whether already known or yet to be discovered can be used. 
         [0024]    In one embodiment, the slots  22  are disposed substantially perpendicular to the side of the fin  20 , however angles other than 90 degrees may be used. In the embodiment illustrated by  FIGS. 3A-D , the perpendicular slots  22  result in the slots  22  being disposed substantially in a horizontal direction when the fin  20  is mounted vertically on a heat sink. The thickness of the slots  22  is approximately the thickness of the ozone catalyst fin  24 , so that the ozone catalyst fin  24  can be inserted into one of the slots  22 . 
         [0025]    In  FIG. 3B , the ozone catalyst fin  24  is shown as being substantially rectangular. However other shapes can be used. For example, the ozone catalyst fin  24  may be substantially oval shaped. In other embodiments, the ozone catalyst fin  24  need not have a regular shape. Any shape slidably insertable into slots  22  can be used. 
         [0026]    A heat sink  30  utilizing the fin  20  having slots  22  and ozone catalyst fins  24  is illustrated in a side-view in  FIG. 3C . The airflow from an ion wind fan is again represented by line A. Multiple heat sink fins  20  are attached to a base  26 , although only the rightmost fin  20  is visible in  FIG. 3C . As shown in  FIG. 3 , ozone catalyst fin  24   a  is inserted into slot  22   a.    
         [0027]    In one embodiment, the width of the ozone catalyst fin  24   a  is greater than the depth of the slot  22   a , causing ozone catalyst fin  24   a  to protrude from the heat sink  30  and from the heat sink fin  20 . In  FIG. 3C , the distance of protrusion is represented by the letter “P” and the depth of the slots  22  is represented by the letter “D.” In one embodiment, P is in the range of 5-25 mm, while D is in the range of 1-5 mm. According to another embodiment, P is in the range of 10-100% of the depth of the heat sink  30 , while D is in the range of 5-100% of the depth of the heat sink. 
         [0028]    These ranges are large, as the optimum sizing of both the heat sink  30  and the ozone catalyst fins  24  is dependent on various application-specific factors such as the size and temperature of the heat source, the power of the ion wind fan, the number of emitter electrodes, the airflow and pressure generated by the ion wind fan, the amount of ozone generated by the ion wind fan, and other such design considerations. The embodiments of the present invention are not limited to any particular size or percentage protrusion. 
         [0029]    In  FIG. 3C  (as well as in  FIG. 5 ), P is shown to be larger than D. However, in other embodiments, D is larger than P, meaning that the ozone catalyst fins  22  extend deeper into the heat sink fins  20  than they protrude from them. According to one embodiment, the ozone catalyst fins  22  can extend the entire depth of the heat sink  30 , meaning that D would be substantially equal to the width of the heat sink fins  20  (and the channels between them.) However, such an embodiment would obstruct airflow more than the embodiment illustrated in  FIGS. 3C and 5 . 
         [0030]    A frontal-view of the heat sink  30  is shown in  FIG. 3D . Form this view, all the heat sink fins  20  of the heat sink  30  are visible the entire width of the heat sink  30 . In one embodiment, the ozone catalyst fin  24   a  is greater in length than the heat sink  30  is wide, resulting in the ozone catalyst fin  24   a  protruding not only towards the front of the heat sink  30  (as shown in  FIG. 3C ), but also protruding from the sides of the heat sink  30 , as is visible on ozone catalyst fin  24   a . The left and right “side” of the heat sink  30  can be though of as the leftmost and rightmost fin  20 . 
         [0031]    In contrast, the lower ozone catalyst fin  24   b  is shown to be flush with the sides of the heat sink  30 . In other embodiments, other ozone catalyst fins  24  can be shorter in length than the heat sink  30  in wide. While the embodiments described with reference to  FIGS. 3A-D  have two ozone catalyst fins  24 , more or fewer such fins can be used. 
         [0032]    For example, a fin-stack type heat sink  40  having three ozone catalyst fins is shown and described with reference to  FIGS. 4A-B .  FIG. 4A  is a perspective view of a stack of fins  42  that snap into each other to form fin stack  40 . Each fin  42  has three slots  44 . The fins  42  shown in  FIG. 4A  are substantially identical. Thus, the slots  44  form grooves that are substantially parallel with the top and bottom of the fin stack  40 . 
         [0033]      FIG. 4B  is a perspective view of the fin stack  40  shown in  FIG. 4A , with ozone catalyst fins  46  inserted into the grooves. In one embodiment, the ozone catalyst fins  46  are simply inserted into the grooves formed by the slots  44  and are held in place by friction. In other embodiments, the ozone catalyst fins can be further attached using glue, soldering or various other mechanical attachment methods, such as crimping and pin insertion. 
         [0034]    One reason it can be advantageous for an ozone catalyst fin to protrude from a heat sink, is that ozone concentrations tend to be highest near the ion wind fan, but positioning a heat sink in the immediate vicinity of an ion wind fan without leaving a gap an result in high airflow restriction.  FIG. 5  is a side-view illustrating a heat sink  50  positioned relative to an ion wind fan  60  according to one embodiment of the invention. 
         [0035]    The heat sink  50  can be similar or even identical to the embodiments described with reference to  FIGS. 3A-D . The base  56  of the heat sink  50  is positioned on a heat source  70  (such as a processor or LED) in a thermally conductive manner. Such positioning is sometimes referred to as thermally coupling the heat source  70  and the heat sink  50 . 
         [0036]    The fins  52  extend substantially perpendicular from the base  56  and form channels for airflow. Ozone catalyst fins  54   a  and  54   b  are provided horizontally across the heat sink  50 , such that the ozone catalyst fins  54  extend substantially perpendicular to both the air flow generated by the ion wind fan  60  and the orientation of the fins  52  and channels. In one embodiment, the ozone catalyst fins  54  are positioned substantially parallel to the base  56 . 
         [0037]    In one embodiment, the ion wind fan  60  is positioned so that the protruding portions of the ozone catalyst fins  54  are very near the collector  64  of the ion wind fan  60 , without actually contacting the collector  64 . In one embodiment, the distance between the collector  64  and the ozone catalyst fins  54  is in the range of 0-1 mm, but larger separations can also be used. 
         [0038]    In one embodiment, the ozone catalyst fins  54  are positioned so that they are as close as possible to the emitter electrodes  62  of the ion wind fan  60 . In some ion wind fans, ozone is generated in the vicinity of the emitter electrodes. In the embodiment shown in  FIG. 5 , there is one ozone catalyst fin  54  for each emitter electrode  62  of the ion wind fan  60 . Namely, emitter electrode  62   a  of the ion wind fan  60  is associated with ozone catalyst fin  54   a  of the heat sink  50 , and similarly, emitter electrode  62   b  of the ion wind fan  60  is associated with ozone catalyst fin  54   b.    
         [0039]    As shown in  FIG. 5 , ozone catalyst fin  54   a  is positioned so that it is approximately at the same horizontal location as emitter electrode  62   a . For example, if the emitter electrode  62   a  is implemented as a wire electrode extending in a horizontal direction (so that it would appear in cross section on  FIG. 5 ), the ozone catalyst fin  54   a  would extend horizontally substantially parallel to the emitter electrode  62   a.    
         [0040]    This is visually demonstrated in  FIG. 5  by the emitter electrode  62   a  and the ozone catalyst fin  54   a  being located along the dotted line A. Similarly, emitter electrode  62   b  and the ozone catalyst fin  54   b  are located along the dotted line B. As explained above, in this manner, the ozone catalyst fins are located as close as possible to the emitter electrodes. 
         [0041]    In other embodiments, there need not be an equal number of emitter electrodes and ozone catalyst fins. For example, the heat sink  50  of  FIG. 5  can have only one ozone catalyst fin located at a position indicated by line A, line B, or somewhere between the two lines. Similarly, the heat sink  50  could contain additional ozone catalyst fins  54 . 
         [0042]    In the descriptions of some of the Figures above, the ozone catalyst fins have been described as being associated an emitter electrode. However, in other embodiments, there need not be a one-to-one association between ozone catalyst fins and emitter electrodes. The invention is not limited to any specific number of ozone catalyst fins or emitter electrodes of the ion wind fan. For example, for an ion wind fan using a pin grid array as emitter electrodes, there are likely to be many more emitter electrodes in the ion wind fan than ozone catalyst fins on the heat sink. 
         [0043]    Furthermore, in  FIG. 3B , and subsequent figures and descriptions, the ozone catalyst fin has been described as approximately rectangular with a flat lengthwise edge that is at perpendicular angles from the top and bottom surfaces of the ozone catalyst fin. However, in other embodiments, the leading and trailing edges of the ozone catalyst tin can be sharpened or otherwise shaped to improve the aerodynamic efficiency of the ozone catalyst fins. 
         [0044]    In the descriptions above, the ion wind fan has not been described in much detail, as embodiments of the present invention can be used with any ion wind device. Furthermore, the ozone catalyst fins described above can be attached or otherwise part of any type of heat sink. The present invention is not limited to vertical-fin-on-base type heat sinks that are used above for purposes of illustration. 
         [0045]    In the descriptions above, the ozone catalyst fins are described as being inserted into slots on heat sink fins to attach the ozone catalyst fins to heat sinks. However, any other means of attachment can be used. Furthermore, the ozone catalyst fins do not need to be separately attached to the heat sink. In some embodiments, the heat sink can be integrally formed with ozone catalyst fins, for example during the molding, pressing, snapping, or other forming process. Furthermore, the heat sink may not be a fin-type heat sink. Embodiments of the present invention can be implemented, for example, in a pin-type heat sink as well. 
         [0046]    In the description above, and in the claims below, the term “substantially” generally mean within a minor variation, based on context. For example, the heat sink fins projecting substantially perpendicular from the base of the heat sink means that the fins can project at angles 80-100 degrees for example, but not 45 degrees. 
         [0047]    In the descriptions above, various functional modules are given descriptive names, such as “ozone catalyst fin,” “ion wind fan,” and “heat sink fin.” These terms are descriptive. For example, fins do not necessarily have to be fin shaped; many shapes can be used.