Abstract:
Devices for removing heat from electronic components. A device includes a heat sink for attachment to an electronic component and multiple miniature fans. Each miniature fan includes an elongated, generally tubular outer housing member adapted to receive end closure plugs or caps at each end, a miniature electric motor mounted within one of the end caps, and a generally cylindrical shaped rotor/impeller disposed within the tubular housing and extending along the length thereof between the end caps, one end thereof being coupled to the motor. The housing member is provided with openings that extend longitudinally along one side thereof to provide an entrance port, and openings that extend along another side to provide an outlet or exit port. With the exception of the motor, all other parts can be made of an injection molded plastic, metal, or a combination of plastic and metal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 11/314,873, entitled “Miniature Fan for High Energy Consuming Circuit Board Devices” by Han, Tai Sheng, filed on Dec. 20, 2005, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     It is well known that some types of electronic circuit card or board devices consume relatively large amounts of electrical power and generate substantial amounts of thermal energy (heat) that must be removed if the device is to continue to operate as intended. For example, in modern computer products, heat dissipation is a problem that unless properly dealt with can cause the computer to malfunction or become inoperative due to overheating. This is of particular importance in the case of high performance computer devices used to rapidly process graphics and game technology. Thus, heat dissipation has become a critical issue that vendors have spent large effort to resolve. In PC units used for graphics and games, add-on units generally referred to as “graphics cards” or “VGA cards” are often installed in the computers. Such cards include a separate processor, called a GPU, one or more memory chips, and other required circuitry, all mounted to an ancillary circuit board having an edge connector that is adapted to plug into an available slot in the mother board of the principal computing device. Such cards often have extremely large computing power and, as a consequence, generate substantial heat that, if not dissipated, will adversely affect operation of the graphics card and/or PC.  
         [0003]     Heretofore, various approaches have been tried to dissipate or otherwise remove heat from the thermal energy generating processor units and normally include some type of thermal mass capable of sinking the heat generated, as well as some type of fan for blowing air across the sink and active components.  
         [0004]     Conventional heat dissipation heat sinks usually include a thick metal plate having a plurality of metal fins located on one side thereof to disperse the heat over a large surface area. Some sinking applications do not need additional airflow to disperse heat, and simply dissipate the energy by, in effect, increasing the radiation area of the heat generating unit. The commonly used basic heat sink is thus passive and cools by convection. However, while the simple heat sink can increase the radiation area, heat energy still has to be discharged by airflow into the surrounding area.  
         [0005]     Means for circulating cooling air by use of a fan has been the most commonly used method for removing thermal energy from a heat source and its associated sinking device. In the usual case, outside air is taken into an apertured heat dissipation device attached to a heat source, passed through the interior of the heat dissipation device, and then discharged to the outside of the device. However, since in most applications the fan or air induction device is a simple multi-bladed rotary fan, or a short axis squirrel cage type blower, itself having a reduced thickness, cooling air does not always flow smoothly through the interior of the heat dissipation device. And since the non-smooth flow of cooling air decreases the cooling efficiency of a radiation device, heat from the thermal source cannot be effectively gathered and carried to the outside. In addition, typical squirrel cage type fans are noisy.  
         [0006]     It is known that cooling performance can be improved by an increase in the flow rate of cooling air. However, since this measure typically requires an increase in the size of a fan or a decrease in the cross section of the flow path, it is problematic since the overall thickness of the heat radiation device usually cannot be increased and the dimensions of the data processing apparatus cannot be decreased. Furthermore, from a practical standpoint, space for accommodating a larger fan is not available in a thin heat radiation device, and the thickness of the data processing apparatus cannot be reduced.  
         [0007]     There is thus a need for a new type of fan or blower that can be readily attached to a card or heat sink without requiring extra flow directing means for interfacing the fan effluent to the heat sink or device to be cooled.  
         [0008]     High performance notebook computers are extremely compact devices that require high performance central processing units (CPUs), and as do the graphics processors, such high performance electronic components also generate a significant amount of heat during operation. Unless removed, such heat also degrades the processing speed and/or performance of the device. For this reason, high temperature, heat generating CPUs are normally provided with some type of cooling means designed in response to the temperature generated by the component. Specifically, when the heat generating unit generates low heat, it can simply be air-cooled using a heat sink or a heat pipe. But when the heat generating unit generates a significant amount of heat, it must be forcibly cooled using a fan, or perhaps both an active cooler, such as a Peltier device, and a fan. For example, in today&#39;s high performance notebook PCs, it is very difficult to simply air-cool a CPU that generates a large amount of heat. Accordingly, almost all high-performance notebook PCs are forcibly cooled using an active cooling system including a fan and a custom engineered heat sink assembly  
         [0009]     However, as laptop computers and other consumer, commercial, and military electronics, are continuously reduced in size, the space available for mounting a conventional multi-blade fan or squirrel cage type blower is also reduced. There is thus a need for a smaller and improved air moving mechanism, which can be added to a standard graphics card to efficiently remove thermal energy generated thereby.  
       SUMMARY OF THE INVENTION  
       [0010]     According to one embodiment of the present invention, a means for removing heat from electronic components includes: a heat sink for attachment to an electronic component, adapted to form at least one flow channel, and including means for directing a stream of heat removing fluid over at least one surface thereof; and a plurality of fans for attachment to the heat sink and adapted to generate stream of heat removing fluid through the channel. Each fan includes: an elongated housing open along its length and at both ends to form a rotor receiving chamber, the housing having an inlet port formed in one side thereof and an outlet port formed in another side thereof; an elongated rotor disposed within the chamber and rotatable about a longitudinal axis thereof, the rotor having a plurality of impeller components extending along its length; a first end cap affixed to the housing and closing one end of the chamber, and a second end cap affixed to the housing and closing an opposite end thereof; a motor disposed at the one end of the chamber and adapted to cause the rotor to rotate about the longitudinal axis whereby ambient fluid is drawn through the inlet port into the chamber by said impeller components and expelled therefrom through the outlet port; and means for mounting the fan to the heat sink. 
     
    
     IN THE DRAWING  
       [0011]      FIG. 1  is a perspective view illustrating miniature fans in accordance with the present invention affixed to two sides of a flow directing heat sink mounted to a graphics card assembly or the like;  
         [0012]      FIG. 2  is an enlarged perspective view more clearly illustrating the exterior details of the miniature fan of  FIG. 1  showing the inlet opening side thereof;  
         [0013]      FIG. 3  is an enlarged perspective view more clearly illustrating the exterior details of the miniature fan of  FIG. 1  showing the outlet opening side thereof;  
         [0014]      FIG. 4  is an exploded perspective view illustrating the principal component parts of the miniature fan of  FIG. 1 , the main housing member part thereof being broken to show the inlet opening in the remote side thereof;  
         [0015]      FIG. 5  is a perspective view showing the housing member and end caps broken along a plane passing through the longitudinal axis of the impeller to illustrate certain interior details of the miniature fan of  FIG. 1 ;  
         [0016]      FIG. 6  is a stylized transverse sectional view schematically showing the air flow characteristics of the miniature fan of  FIG. 1 ;  
         [0017]      FIGS. 7-12  are schematic perspective views of various embodiments of a heat sink that might be used in a graphic card assembly or the like in accordance with the present invention;  
         [0018]      FIG. 13  is a schematic cross sectional view of the heat sink of  FIG. 12 , taken along the line XIII-XIII;  
         [0019]      FIG. 14  is a schematic perspective view of another embodiment of a heat sink that might be used in a graphic card assembly or the like in accordance with the present invention;  
         [0020]      FIG. 15  is a schematic cross sectional view of the heat sink of  FIG. 14 , taken along the line XV-XV;  
         [0021]      FIG. 16  is a schematic perspective view of yet another embodiment of a heat sink that might be used in a graphic card assembly or the like in accordance with the present invention;  
         [0022]      FIG. 17  is a schematic cross sectional view of the heat sink of  FIG. 16 , taken along the line XVII-XVII;  
         [0023]      FIG. 18  is a schematic perspective view of still another embodiment of a heat sink that might be used in a graphic card assembly or the like in accordance with the present invention;  
         [0024]      FIG. 19  is a schematic cross sectional view of the heat sink of  FIG. 18 , taken along the line XIX-XIX; and  
         [0025]      FIG. 20  is a schematic perspective view of a further embodiment of a heat sink that might be used in a graphic card assembly or the like in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]     Referring now to  FIG. 1  of the drawing there is shown at  10  a typical example of a graphics card of the type that might be installed in a PC by inserting the edge connectors  12  into an available slot on the motherboard (not shown). Shown mounted to the top of the card  10  is a heat sink assembly (or, shortly heat sink)  13  that might include a metal bottom plate having a plurality of upstanding ribs formed integral therewith as depicted at  14 . Affixed to the top of the ribs is a metal upper plate  16  having its upper left corner broken away to reveal the ribbed lower part  14 . Note that the bottom and top plates are separated by the ribs and that the ribs are generally curved strips and arranged to fan out from the central portion of the assembly  13 . The ribs define a plurality of air flow passageways extending along the heat sink towards the space where the air flow is discharged to.  
         [0027]     Affixed to the foreground and side edges of heat sink  13  are embodiments of fans or blower devices  20   a,    20   b  in accordance with the present invention. Each of the devices  20   a,    20   b  is generally in the form of an elongated right rectangular structure having its long dimension extending along the rightmost or foreground edge of card  13 . Fans  20   a,    20   b  are affixed to card  13  by any suitable means, such as tabs and screws or bolts (not shown), an adhesive, or tack welds. A single, pair or other plurality of inlet slots  22   a  (or  22   b ) is/are provided on the front side face of each device. Air is drawn in through these slots for expulsion through one or more exit slots (not shown) on the back side thereof for introduction by the fans into the heat sink  13 .  
         [0028]     As the fans  20   a,    20   b  have the same structure, only one fan  20   a  is described hereinafter. The exterior construction of the fan  20   a  is shown in enlarged detail in  FIGS. 2 and 3  wherein the front face including the air flow inlet slots  22   a  is depicted in  FIG. 2 , and the rear face, including the plurality of air flow outlet slots  34 , is depicted in  FIG. 3 . As shown in these figures, the exterior housing of fan  20  is formed by a generally tubular housing member  24  having a rectangular (square) transverse cross section defined by a first pair of parallel opposing front and rear walls  30  and  32 , and a second pair of opposing parallel side walls  36  and  38 . The otherwise open ends of the tubular housing member  24  are closed by a pair of end caps  40  and  42  to form a rotor receiving internal chamber (not shown). Alternatively, the cross section could be formed in other geometric shapes including oval or partially oval, or of any other suitable transverse sectional configuration capable of cooperating with an impeller and inlet and outlet openings to form a blower device. The device can be made in almost any desired size and length. For example, in one small size embodiment, the device has external dimensions of 1.2×1.2×5 centimeters.  
         [0029]     As will be further explained below, the inlet slot or slots  22   a  are arrayed or positioned on one side of the front wall  30  to extend across substantially the entire longitudinal length of the housing member  24 , while the outlet slot or slots  34  are arrayed or positioned on the opposite side of the housing member  24  and occupy a larger area of the rear face  32 . Preferably, the inlet openings or slots  22   a  are disposed on one side of a plane (not shown) intersecting the housing  24  normal to front wall  30 , and passing through the longitudinal axis of the device. The outlet openings or slots  34  are symmetrically positioned on both sides of the same plane as it extends through and out of the opposite side of the device. Hereinafter, the term inlet port is used interchangeably with inlet slots  22   a  and the term outlet port is used interchangeably with outlet slots  34 . In this embodiment, the end caps  40  and  42  are of slightly different size, with the cap  40  serving as a bearing support member, and the cap  42  serving as a drive motor housing as well as bearing support. Suitable flanges, tabs or other means such as those suggested by the dashed lines  37  in  FIGS. 2 and 3 , may be provided for fastening the fan device to a PC board, heat sink or other supporting structure. Such fastening means may be affixed to or molded integral with the tubular housing  24  and/or the end caps  40 ,  42 . Alternatively, the fan could be attached to a supporting structure by one or more straps (not shown).  
         [0030]     Turning now to  FIG. 4 , the fan device is shown with the end caps  40  and  42  exploded axially outwardly from their mating engagement with the tubular housing  24 . Also shown removed axially from the tubular housing  24  is an impeller or rotor  44  having a supporting shaft extending axially from each end at  46  and  50 . A suitable annular bearing member  48  is coaxially disposed on the upper end  46  as depicted. A similar bearing member  52  is provided on shaft end  50  at the opposite end of rotor  44 . Although not shown in this figure, the end cap  40  includes a receptacle for receiving the bearing  48  and shaft end  46  such that the end  46  of rotor  44  is journalled to end cap  40 .  
         [0031]     As depicted in this figure, the rotor  44  is formed of an elongated, solid or hollow, cylindrically shaped body having a plurality of elongated vanes  53  extending along the length thereof. The vanes  53  may be parallel and continuous or segmented along the length of the rotor, and may be straight, helical or serpentine relative to the axis of the rotor. Furthermore, the planes of the vanes may extend radially, at an angle to radial (as depicted in  FIG. 6 ), be segmented and cup-shaped, or have any other suitable configuration designed to move fluid from the entrance side of the housing to the other side for exit.  
         [0032]     At the bottom of  FIG. 4 , the lower end cap  42  is shown to include a receptacle  57  for receiving the bearing  52  and shaft end  50  such that the end  50  of rotor  44  is journalled to end cap  42 . End cap  42  also has a pocket in which a small electric motor  54  is nested. The motor may be AC or DC, but is typically a DC motor operated at a voltage of between 4-24 volts conveniently available from a computer power supply. Motor  54  is provided with a drive shaft  56  having a square shaped, hex-shaped or other suitable cross section that can be mating engaged within a similarly configured female socket  56  ( FIG. 6 ) formed in the end of shaft  50  so as to provide direct drive to rotor  44 .  
         [0033]     The four parts shown separate in  FIG. 4  are assembled by collapsing the several components axially, with rotor  44  moving downwardly to engage the bearing  52  and motor  54 , and housing  24  slipping over rotor  44  so that its lower end engages and seats within the shoulder  59  in lower cap  42 . The assembly is completed by mating the shaft end  46  and bearing  48  with the corresponding receptacles (not shown) formed in the lower side of end cap  40 , and seating the upper end of housing  24  in the shoulder  59  formed around the lower perimeter of the upper end cap  40 . The caps  40  and  42  may be designed to snap fittingly engage the ends of member  24  or they may be retained by the use of glue or epoxy or the like. The assembled engagement is shown in  FIG. 5 , wherein the housing  24 , end caps  40  and  42 , and motor  54  are, for clarity, shown split along the longitudinal axis of the fan to illustrate the assembled configuration of the several previously described component parts.  
         [0034]      FIG. 6  is a stylized, transverse sectional view taken in the plane  6 - 6  of  FIG. 5  and shows how the vanes  53  “drag” or “draw” ambient air (represented by the dashed lines  60 ) in through inlet slots  22   a,  “carry” it across the lower portion of the housing  24  (as suggested by the dashed lines  62 ), and then centrifugally “throw” it out through the outlet slots  34  (as suggested by the dashed lines  64 ). It is believed that with the rotor rotating about its longitudinal axis, the vanes  53  in effect scoop the ambient air at the low pressure inlet slots  22  and cause it to move with the rotor around the inside of the housing. As the moving air experiences centrifugal acceleration tangentially and radially outwardly relative to the axis of rotation of the rotor, it also experiences an increase in pressure and momentum that causes it to exit the housing via the outlet slots  34 . As a consequence, the device acts to draw air into one side thereof and blow it out the other side thereby functioning as a fan.  
         [0035]     As suggested above, with the exception of the motor  54 , all of the several device components can be made using small, structurally simple, injection molded metal, plastic or ceramic parts that can be snap-fit or glued together during assembly to form elongated fluid pumping devices of various sizes having substantial utility for the particular application described above as well as other applications having similar requirements. Furthermore, whereas the “pumping” efficiency of the fan device could perhaps be improved by “streamlining” the interior walls of the housing  30  to eliminate corners and enhance laminar flow within the housing, such streamlining is not deemed necessary to provide a device capable of creating an air flow useful for the suggested applications.  
         [0036]      FIG. 7  is a schematic perspective view of another embodiment of a heat sink  80  of the type to be used in a graphic card assembly or the like in accordance with the present invention. For the purpose of illustration, the metal upper plate  86  is partially broken away to reveal the ribs  84  affixed thereto. The fans  82   a,    82   b  have the similar structure and operational mechanisms as the fan  22   a  depicted in  FIGS. 1-6 . As depicted, the heat sink  80  is similar to the assembly  16  in  FIG. 1 , with the differences that two fans  82   a,    82   b  are affixed to the foreground edge of heat sink in series (i.e., the top end cap of the fan  82   b  is in contact with the bottom end cap of the fan  82   a ) and the ribs  84  are disposed in a parallel array. Two side plates  87  and the top upper plate  86  form a channel and the fans  82   a,    82   b  direct ambient air into one end of the channel. The ambient air directed by the fans  82   a,    82   b  flows through the channel and exits at the opposite end of the channel. As a variation, two or more fans may be affixed to the rightmost edge of a heat sink with ribs extending toward the leftmost edge of the heat sink such that the air is drawn in by the fans at the rightmost edge of the heat sink and discharged at the left side of the heat sink. It is noted that only two fans are shown in  FIG. 7 , even though other suitable number of fans may be affixed in series to the foreground or rightmost side of the heat sink. Likewise, the heat sink  16  in  FIG. 1  may have other suitable number of fans affixed to the foreground and rightmost sides of the heat sink.  
         [0037]      FIG. 8  is a schematic perspective view of yet another embodiment of a heat sink  90  of the type to be used in a graphic card assembly or the like in accordance with the present invention. As in  FIG. 7 , for the purpose of illustration, the metal upper plate  96  is partially broken away to reveal the ribs  84  affixed thereto. The four fans  92   a - 92   d  have the similar structure and operational mechanisms as the fan  22   a  depicted in  FIGS. 1-6 . As depicted, the heat sink  90  is similar to the heat sink  80  in  FIG. 7 , with the difference that four fans  92   a - 92   d  are affixed to the foreground edge of the heat sink in a two-dimensional array. The upper plate  96  and two side plates  95  form a channel, wherein the four fans  92   a - 92   d  are disposed at one end of the channel and generate flow that proceeds toward the opposite end of the channel. The outlet ports of the four fans  92   a - 92   d  face the opposite end of the channel (or, equivalently, the background edge of the heat sink  90 ). As a variation, the four fans disposed in a two-dimensional array may be affixed to the rightmost edge of a heat sink with ribs extending toward the leftmost edge of the heat sink such that the air is drawn in by the fans at the rightmost edge of the heat sink and discharged at the left side of the heat sink.  
         [0038]      FIG. 9  is a schematic perspective view of still another embodiment of a heat sink  100  of the type to be used in a graphic card assembly or the like in accordance with the present invention. The two fans  102 ,  104  have the similar structure and operational mechanisms as the fan  22   a  depicted in  FIGS. 1-6  and respectively disposed at the foreground and background edges of the heat sink  100 . The outlet port of the fan  102  faces the inlet port of the fan  104  such that the flow drawn in by the fan  102  is discharged by the fan  104 . In this embodiment, the two fans are respectively disposed at the two ends of the channel formed by the upper plate  106  and two side plates  107 . It is noted that the heat sink may include ribs affixed to the upper plate  106  in a parallel array. As a variation, the two fans may be affixed to the rightmost and leftmost edges of the heat sink such that the air is drawn in by the fan at the rightmost edge of the sink and discharged by the fan at the leftmost edge of the sink.  
         [0039]      FIG. 10  is a schematic perspective view of a further embodiment of a heat sink  110  of the type to be used in a graphic card assembly or the like in accordance with the present invention. For the purpose of illustration, the metal upper plate  116  is partially broken away to reveal the ribs  113  affixed thereto. The channel formed by the upper plate  116  and side plates  117  is separated into upper and lower channels by the middle plate  115  affixed to the ribs  113 . The two fans  112 ,  114  have the similar structure and operational mechanisms as the fan  22   a  depicted in  FIGS. 1-6 . The upper fan  112  is disposed at one end of the upper channel, while the lower fan  114  is disposed at the opposite end of the lower channel. The upper flow generated by the upper fan  112  proceeds through the upper channel in a direction opposite to the lower flow generated by the lower fan  114 .  
         [0040]     As a variation, the two fans may be respectively affixed to the upper portion of the rightmost edge and lower portion of the leftmost edges of the heat sink with ribs extending in a direction substantially normal to the longitudinal axes of the fans. In this variation, a middle plate separates the channel into upper and lower channels such that the air drawn by the fan at the rightmost edge of the heat sink flows in the upper channel while the air drawn by the fan at the leftmost edge of the heat sink flows in the lower channel. Also, the flow in the upper channel proceeds in a direction opposite to the flow in the lower channel.  
         [0041]      FIG. 11  is a schematic perspective view of another further embodiment of a heat sink  120  of the type to be used in a graphic card assembly or the like in accordance with the present invention. For the purpose of illustration, the metal upper plate  126  is partially broken away to reveal the ribs  124  affixed thereto. The channel formed by the upper plate  126  and side plates  127  is separated into right and left channels by the middle plate  125  affixed to the upper plate. Two fans  121 ,  122  have the similar structure and operational mechanisms as the fan  22   a  depicted in  FIGS. 1-6 . The fan  121  is disposed at one end of the right channel, while the fan  122  is disposed at the opposite end of the left channel. The flow generated by the fan  121  proceeds through the right channel in a direction opposite to the flow generated by the fan  122  in the left channel.  
         [0042]     As a variation, a middle plate extends from the rightmost edge to the leftmost edge of the heat sink, dividing the channel into front and rear channels. In this variation, a first fan is disposed at the one end of the front channel while a second fan is disposed at the opposite end of the rear channel. The flow in the front channel proceeds in a direction opposite to the flow in the rear channel.  
         [0043]      FIG. 12  is a schematic perspective view of another further embodiment of a heat sink  130  of the type to be used in a graphic card assembly or the like in accordance with the present invention.  FIG. 13  is a schematic cross sectional view of the heat sink  130 , taken along the line XIII-XIII. The heat sink  130  includes two fans  132 ,  134  that have the similar structure and operational mechanisms as the fan  22   a  depicted in  FIGS. 1-6 . As depicted in  FIGS. 12-13 , a first fan  132  is disposed at foreground edge of the heat sink, while a second fan  134  is disposed at the background edge of the heat sink. In this embodiment, the upper plate  136  and two side plates  137  form a flow channel. Ambient air is directed into the channel by the fans  132 ,  134  that are respectively disposed at the two ends of the channel and sent toward the center of the heat sink. The upper plate  136  includes an elongated exit port  144  through which the air is discharged. The exit port  144  extends transverse to the flow in the channel and, in one exemplary embodiment, may spans almost the entire width of the upper plate  136 . The heat sink also includes a flow deflector  142  disposed in the heat sink to direct the air flow toward the nozzle  144 . The flow deflector  142  may be mounted on a heat generating component  140 , such as GPU, which is positioned on a graphic card assembly  138  or the like and disposed under the exit port  144 . As a variation, the two fans may be affixed to the rightmost and leftmost edges of the heat sink and the exit port  144  extends substantially transverse to the flow in the channel.  
         [0044]      FIG. 14  is a schematic perspective view of another embodiment of a heat sink  150  of the type to be used in a graphic card assembly or the like in accordance with the present invention.  FIG. 15  is a schematic cross sectional view of the heat sink  150 , taken along the line XV-XV. As depicted, the heat sink  150  is similar to the heat sink  130  in  FIGS. 12-13 , with the difference that the heat sink  150  includes an elongated scoop or deflector  157  attached to the bottom surface of the upper plate  156  and positioned under the exit port  158 . The deflector  157  includes a pair of elongated plates that are arranged in a spaced-apart relationship with the exit port  158  and direct the flow toward the exit port, aiding the ventilation of flow. As a variation, the two fans may be affixed to the rightmost and leftmost edges of the heat sink while the exit port and deflector extend substantially transverse to the flow in the channel.  
         [0045]      FIG. 16  is a schematic perspective view of another embodiment of a heat sink  160  of the type to be used in a graphic card assembly or the like in accordance with the present invention.  FIG. 17  is a schematic cross sectional view of the heat sink  160 , taken along the line XVII-XVII. As depicted, the heat sink  160  is similar to the heat sink  130  in  FIGS. 12-13 , with the differences that the upper plate  166  includes an elongated opening or slit  168  formed therein and that the air drawn through the opening is discharged from the heat sink  160  by two fans  162 ,  164 . The opening  168  extends transverse to the flow in the channel. In this embodiment, two fans  162 ,  164  are respectively disposed at the two ends of the channel formed by the upper plate  166  and two side plates  167  and direct ambient fluid into the channel through the opening  168 . As a variation, the two fans may be affixed to the rightmost and leftmost edges of the heat sink and the opening  168  extends in a direction substantially parallel to the longitudinal axes of the fans.  
         [0046]      FIG. 18  is a schematic perspective view of another embodiment of a heat sink  170  of the type to be used in a graphic card assembly or the like in accordance with the present invention.  FIG. 19  is a schematic cross sectional view of the heat sink  170 , taken along the line XIX-XIX. As depicted, the heat sink  170  is similar to the heat sink  160  in  FIGS. 16-17 , with the differences that the heat sink includes an elongated cover  180  disposed over an elongated opening or slit  178 . The cover  180  covers the opening  178  to prevent foreign particles from entering through the opening  178  and/or directly hitting the surface of the graphic card assembly  138  or the like.  
         [0047]     It is noted that the fans in  FIGS. 12-15  can be arranged to have the outlet ports face away from the channel, i.e., the fans discharge ambient fluid from the channel through the outlet ports. Likewise, the fans in  FIGS. 16-19  can be arranged to have the outlet ports face the channel, i.e., the fans direct ambient fluid into the channel toward the openings formed in the upper plate.  
         [0048]      FIG. 20  is a schematic perspective view of another embodiment of a heat sink  190  of the type to be used in a graphic card assembly or the like in accordance with the present invention. As depicted, the heat sink includes a fan  192  disposed at the foreground side of the rightmost edge thereof and another fan  194  disposed at the background side of the leftmost edge thereof. In this embodiment, the upper plate (or wall)  196  and four side plates (or walls)  198  form a flow channel. Ambient fluid is drawn into the heat sink through two openings or slits  200 ,  202  formed in the upper plate  196 , while the drawn fluid is discharged from the heat sink by the two fans  192 ,  194  through the outlet ports of the fans. The fan  192  draws the ambient fluid through the opening  200 , while the fan  19 =draws the ambient fluid through the opening  202  such that the flow near the foreground side of the heat sink generated by the fan  192  proceeds in a direction opposite to the flow near the background side of the heat sink generated by the fan  194 . A portion of the flow near the foreground side is mixed with a portion of the flow near the background side such that a vortex or swirl  198  may be induced at the central portion of the heat sink, enhancing the heat extraction efficiency.  
         [0049]     Although the present invention has been described above in terms of a single preferred embodiment, it is understood that various modifications in size, relative dimensions, inlet and outlet configurations, rotor vane configuration, construction methods and materials, etc., will no doubt become apparent to those skilled in the art after having read this disclosure. Accordingly, it is intended that the above disclosure be interpreted as exemplary rather than limiting, and that the appended claims be interpreted broadly, and limited only by the true spirit and scope of the invention.