Abstract:
A heat dissipation device includes a heat sink ( 22 ), a first fan ( 24 ) disposed on one part of the heat sink, a second fan ( 26 ) disposed on another part of the heat sink and a cover ( 30 ) disposed to enclose the heat sink, the first fan and the second fan. The second fan draws the air produced by the first fan and flowing through the heat sink to quickly leave the heat sink.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to a heat dissipation device for removing heat from an electronic component, and particularly to a heat dissipation device comprising double fans to enhance an airflow flowing through a heat sink in contact with the electronic component, which is mounted on a periphery card. 
   DESCRIPTION OF RELATED ART 
   With advancement of computer technology, electronic devices operate with high speeds. It is well known that the more rapidly the electronic devices operate, the more heat they generate. If the heat is not dissipated duly, the stability of the operation of the electronic devices will be impacted severely. 
   Generally, in order to ensure the electronic device to run normally, a heat dissipation device is used to dissipate the heat generated by the electronic device. A conventional heat dissipation device includes a heat sink and a fan attached on a top of the heat sink. The heat sink includes a base contacting a heat-generating electronic component like a CPU and a plurality of fins extending upwardly from the base. Most of the heat generated by the heat-generating electronic component is absorbed by the base, and conducted upwardly to the fins. The fan blows air directly to the fins from the top of the heat sink to enhance heat-exchange between the fins and air around the fins. 
   However, when the air flows from the top of the fins to the bottom of the fins, most of the air is heated and the heated air is concentrated on the bottom of the fins. The heated air cannot be quickly and effectively expelled from the bottom of the fins. Thus, heat dissipation efficiency of the fins is poor and the heat transfer efficiency between the base and the bottom of the fins is low. Heat transfer speed from the base to the fins needs improvement greatly. Thus, a heat dissipation device which can quickly remove the heated air from the fins, particularly the bottom of the fins, is needed. Such a heat dissipation device is particularly necessary for a periphery card of a computer, for example, a video graphic array (VGA) card. A periphery card is usually crowded with other periphery cards whereby only a limited space is available for an airflow to flow through a heat sink thereof. Heat accumulated at bottom of the fins of the heat sink of the periphery card is particularly serious, which requires an immediate solution. 
   SUMMARY OF INVENTION 
   A heat dissipation device in accordance with a preferred embodiment of the present invention comprises a heat sink, a first fan disposed on one part of the heat sink, a second fan disposed on another part of the heat sink and a cover disposed to enclose the heat sink, the first fan and the second fan. The second fan helps the airflow produced by the first fan flowing to the heat sink to quickly leave the heat sink so that heat absorbed by the heat sink from a heat-generating electronic component can be quickly and efficiently taken away. The cover defines communicable first and second rooms. The first fan is received in the first room, while the second fan is received in the second room. 
   Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is an isometric view of a heat dissipation device in accordance with a preferred embodiment of the present invention, mounted on a printed circuit board of a VGA card; 
       FIG. 2  is an exploded view of the heat dissipation device of  FIG. 1 ; 
       FIG. 3  is an enlarged bottom view of a cover of  FIG. 1 ; and 
       FIG. 4  is a cross-sectional view taken along line IV-IV in  FIG. 1 , showing airflow flowing paths through the heat dissipation device. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a heat dissipation device in accordance with a preferred embodiment of the present invention, mounted on a printed circuit board  10  of a VGA card. The printed circuit board  10  has a heat-generating electronic component  12  ( FIG. 2 ) attached thereon, which is a graphic processing unit (GPU) in this embodiment. 
   Also referring to  FIGS. 2-3 , the heat dissipation device comprises a heat sink  22 , a first fan  24 , a second fan  26  and a cover  30 . The heat sink  22  has a bottom base (not labeled) contacting with the heat-generating electronic component  12  to receive heat generated by the heat-generating electronic component  12 . A plurality of fins  220  is extended upwardly from the base to dissipate the heat on the base to ambient air. The first fan  24 , which is an axial fan, is disposed on a top of the fins  220  of the heat sink  22  and produces an airflow to directly flow from the top of the fins  220  to a bottom of the fins  220  of the heat sink  22 . The second fan  26 , which is a blower, is also mounted on the top of the heat sink  22  and located near the first fan  24 . The second fan  26  comprises an airflow inlet (not labeled) in a bottom surface thereof and an airflow outlet  260  at a lateral side thereof. The airflow outlet  260  is arranged to be adjacent to and face an exit  14  of the VGA card, which is communicated with a surrounding air of a computer system in which the VGA card is mounted. 
   The cover  30  is disposed on tops of the first and second fans  24 ,  26  to enclose the heat sink  22 , the first and second fans  24 ,  26 . The cover  30  comprises a body  32 , a pair of elongated opposite baffles  34  and a short baffle  36  respectively extending perpendicularly downwards from three sides of the body  32 . The short baffle  36  is located between the baffles  34 . The baffles  34  are arranged to enclose a pair of lateral sides of the heat sink  22 . The baffles  34 ,  36  have bottoms connected to the printed circuit board  10 . The body  32  defines a first hole  320  corresponding to the first fan  24  and a second hole  322  corresponding to the second fan  26 . In a bottom view of the cover  30  in  FIG. 3 , a clapboard  38  is formed inside of the cover  30 . The clapboard  38  divides an inner space of the cover  30  into a first room  340  corresponding to first hole  320  and receiving the first fan  24  therein, and a second room  342  corresponding to the second hole  322  and receiving the second fan  26  therein. The clapboard  38  defines a cutout  380  extending from a bottom to a middle of the clapboard  38 . The cutout  380  provides a communication for allowing the airflow produced by the first fan  24  to enter the second room  342  from the first room  340 . When the cover  30  is mounted to printed circuit board  10 , the heat-generating electronic component  12  is located in the first room  340 . 
   In operation, referring to  FIG. 4 , the heat generated by the heat-generating electronic component  12  is transferred to the bottom base of the heat sink  22  and then to the fins  220 . The first fan  24  drives air to flow toward the top of the fins  220  of the heat sink  22 . The air flows from the top to the bottom of fins  220  to have a heat exchange with the fins  220 , whereby most of the air is heated. The heated air enters the second room  342  from the first room  340  through the cutout  380 . Under the action of the second fan  26 , the heated air enters the second fan  26  and is discharged to the surrounding air via the airflow outlet  260  of the second fan  26  and the exit  14 . When the heated air leaves the bottom of the fins  220 , new cooling air flows to the fins  220  again under the action of the first fan  24  to cool the fins  220  and accordingly the heat-generating electronic component  12 . Since the second fan  260  is operated to draw the air in the second room  342  upwardly, the heated air in the bottom of the fins  220  in the first room  340  is also drawn to flow into the second room  342  via the cutout  380 , whereby the heated air can quickly leave the bottom of the fins  220  to effectively take the heat therefrom. Thus, the heat dissipation efficiency of the bottom of the fins  220  is improved. Heat-transferred speed of the heat dissipation device has a great improvement. 
   It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.