Patent Publication Number: US-2007095508-A1

Title: Heat dissipation device having louvered heat-dissipating fins

Description:
BACKGROUND  
      1. Field  
      This invention is related to a heat dissipation device, and particularly to a heat dissipation device having louvered heat-dissipating fins for use in removing heat from a heat generating electronic device.  
      2. Related Art  
      It is well known that, during operation of a computer, electronic devices such as central processor units (CPUs) frequently generate large amounts of heat. The heat must be quickly removed from the electronic device to prevent the electronic device from becoming unstable or being damaged. Typically, heat dissipation devices are desired to dissipate heat generated by the electronic devices.  
      Conventionally, a heat dissipation device comprises a heat sink which has a base and a plurality of fins on the base. The fins each being flat sheet are parallel to each other and spaced arranged on the base. Therefore, pluralities of passages are defined between the fins for airflow passing therethrough. Generally, the heat dissipation device further comprises a fan for providing forced airflow to the heat sink. However, due to aerodynamics properties of fluid, a boundary layer is always formed at the interface of the fin and the airflow, which prevents cooling airflow from getting to the fin to have heat exchange with the fin. Additionally, each of the fins is flat; therefore, each of the passages between the fins is straight. Consequently, beyond the boundary layer, the airflow suffers from low resistance at a direction of flowing thereof. Thus, the cooling airflow speedily flows out of the passages without sufficient heat exchange with the fins. As a result, the fins of the heat sink is not fully utilized, the heat dissipation efficiency of the heat dissipation is not perfect. Thus, a new heat dissipation device is needed to meet the heat dissipation demand of the electronic device.  
     SUMMARY  
      Accordingly, what is needed is to provide a heat dissipation device which has a capacity of having sufficient heat exchange with cooling airflow passing through the heat dissipation device.  
      A heat dissipation device in accordance with an embodiment of the present invention comprises a base having a first face and a second face opposite to the first face for contacting a heat generated electronic device, and a fin set arranged on the first face of the base. The fin set comprises a plurality of spaced fins, a first end and a second end opposite to the first end. Pluralities of passages are defined between the fins and extend from the first end to the second end of the fin set. Each of the fins has a plurality of louvers defined therein and a plurality of tabs each extending along a side of each of the louvers from each of the fins. The louvers of the fins communicate with the passages between the fins. The tabs of each of the fins extend toward corresponding louvers of an adjacent fin. The passages communicate with ambient air at the first end and the second end of the fin set. A fan is mounted to the first end of the fin set. When the fan operates, an airflow generated by the fan flows through the passages. The airflow in one passage can flow to an adjacent passage through corresponding louvers in the fin between the two passages.  
      Other advantages and novel features of the present invention will be drawn from the following detailed description of preferred embodiments of the present invention with the attached drawings, in which:  
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is an exploded isometric view of a heat dissipation device in accordance with a preferred embodiment of the present invention;  
       FIG. 2  shows a fin set of  FIG. 1 ;  
       FIG. 3  is a cross-sectional view taken along line III-III of  FIG. 2 ;  
       FIG. 4  is an assembled view of  FIG. 1  with a fan mounted thereon; and  
       FIG. 5  is an assembled view of a heat dissipation device in accordance with an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
      Referring to  FIGS. 1-3 , a heat dissipation device comprises a base  10 , a bottom wall  20  on the base  10 , a fin set  30  on the bottom wall  20 , two sidewalls  40  located at two sides of the fin set  30 , two heat pipes  50  connecting the base  10  and the two sidewalls  40  and a ceiling  60  on the fin set  30 .  
      The base  10  is a substantially rectangular plate having a high heat conductivity. The base  10  has a top face defining two parallel grooves  110  therein and a bottom face opposite to the top face. The grooves  110  are for receiving the heat pipes  50 , and the bottom face is for contacting with a heat generating electronic device, such as a CPU (central processing unit) (not shown).  
      The bottom wall  20  is substantially a rectangular plate arranged on the base  10 . The bottom wall  20  comprises a flat portion  210  thermally contacting with the base  10  and two extension portions  220  integrally extending upwardly from two opposite sides of the flat portion  210 . Each of the two extension portions  220  defines two cutouts  230  communicating with the grooves  110  of the base  10 , respectively.  
      The fin set  30  comprises a plurality of fins  31  vertically stacked one by one. The fin set  30  horizontally rests on the two extension portions  220  above the flat portion  210  of the bottom wall  20 . Each fin  31  is substantial rectangular, and has a body  310  and two flanges  320  perpendicularly and downwardly extending from two opposite edges of the body  310 . The flanges  320  of each fin  31  abut against the body  310  of an adjacent fin  31  therebelow. The flanges  320  of each side of the fins  31  cooperatively form a contacting face for contacting a corresponding sidewall  40 . Pluralities of passages  350  are defined between the fins  31 . The body  310  can be generally divided into right and left portions along a middle thereof, as viewed from  FIG. 2 . Each portion defines a plurality of parallel elongated louvers  330  therein, extending along a direction perpendicular to the flanges  320  of the fins  31 . A plurality of tabs  340  is formed by the body  310  of each fin  31  wherein each tab  340  is located corresponding to a respective louver  330 . The tab  340  extends slantwise upwardly along a lengthwise side of a corresponding louver  330 . The tabs  340  at the two portions incline toward each other. The louvers  330  and the tabs  340  of the two portions of the body  310  are symmetrical to each other. Each louver  330  of each fin  31  communicates adjacent two passages  350  above and below the fin  31 . Each tab  340  of each fin  31  extends toward a corresponding louver  330  of an adjacent fin  30  thereabove.  
      The two sidewalls  40  are respectively disposed on the extension portions  220  of the bottom wall  20  and located at the two opposite sides of the fin set  30 . Each of the sidewalls  40  is substantial rectangular and has an inner face defining two grooves  410  for receiving the heat pipes  50  therein. The two grooves  410  cooperatively form a substantially V-shaped contour. The inner faces of the sidewalls  40  respectively thermally contact the contacting faces of the fin set  30  constituted by the flanges  320 . Therefore, the fin set  30  is sandwiched between the two sidewalls  40 . The two sides of the fin set  30  are sealed by the two sidewalls  40 .  
      Each of the two heat pipes is substantially U-shaped, and comprises working fluid therein. The working fluid has a phase change when a temperature thereof gets to a certain degree. Each heat pipe  50  comprises a first section  510  and two second sections  520  respectively perpendicularly extending from two ends of the first section  510 . A rounder corner is formed at each joint of the sections  510 , 520  of the heat pipe  50 . The first sections  510  of the heat pipe  50  are soldered into the grooves  110  of the base  10 , respectively. The second sections  530  of the heat pipes  50  project upwardly beyond the base  10  and the bottom wall  20  from the cutouts  230  of the bottom wall  20 , and are soldered into the grooves  410  of the sidewalls  40 , respectively.  
      The ceiling  60  hoods on the fin set  30 . The ceiling  60  has two flanges  610  depending from two opposite sides thereof. The two flanges  610  abut against two sides of a top of a top fin  31  of the fin set  30 .  
      Therefore, the fin set  30  is surrounded by the bottom wall  20 , the two sidewalls  40  and the ceiling  60 . As a result, the passages  350  between the fins  31  communicate with ambient air only at two ends of the fin set  30 . Furthermore, a fan  70  is located at one of the two ends of the fin set  30  to provide a forced airflow through the fin set  30 .  
      In use, the heat dissipation device has the bottom face of the base  10  contacting the electronic device to absorb heat generated by the electronic device. Sequentially, the heat in the base  10  is absorbed by the first sections  510  of the heat pipes  50  and by the bottom wall  20 . The first sections  510  are constructed as evaporators for the heat pipes  50 . The heat in the first sections  510  of the heat pipes  50  reaches the sidewalls  40  via the second sections  520  of the heat pipes  50 . The second sections  520  are constructed as condensers for the heat pipes  50 . Also, part of the heat in the bottom wall  20  is conducted to the sidewalls  40  through a direction connection between the bottom wall  20  and the sidewalls  40 . Then, the heat in the sidewalls  40  is transferred to the fin set  30  to be dissipated to the ambient air.  
      According to the first embodiment of the present invention, the louvers  330  of the fins  31  communicate the passages  350  between the fins  31 , and the tabs  340  of the fins  31  extend toward the louvers  330 ; thus, when the fan  70  provides the forced airflow through the fin set  30 , the tabs  340  guide the airflow to flow from one of the passages  350  to the adjacent upper one of the passages  350  via the louvers  330  between the two passages  350 . As a result, the cooling airflow is facilitated to sufficiently contact with the fins  31  and have a full heat exchange with the fins  31 . Therefore, in comparison with the conventional heat dissipation device, heat dissipation capacity of the heat dissipation device of the present invention is improved.  
      Additionally, the fins  31  are surrounded by the bottom wall  20 , the sidewalls  40  and the ceiling  60 ; thus, the airflow between the fins  31  can only flow out of the heat dissipation device via the end opposite to the fan  70 ; by this, the airflow out of the heat dissipation device can cool other electronic devices located near the end of the heat dissipation device opposite the fan  70 ; therefore, the airflow of the fan  70  is fully utilized.  
      Furthermore, the heat dissipation device has two heat pipes  50  connecting the base  10  and the two sidewalls  40  thereof, and the fins  31  thermally contact the two sidewalls  40 ; therefore, the heat absorbed from the electronic device by the base  10  is rapidly transferred to the sidewalls  40  and then to the fins  31  to be dissipated.  
      Referring to  FIG. 5 , a heat dissipation device of an alternative embodiment of the present invention is shown. The heat dissipation device in accordance with this alternative embodiment comprises a bottom wall  20 ′, two side plates  60 ′ and a top wall  40 ′ cooperatively surrounding the fin set  30  therein. The bottom wall  20 ′ has a bottom face thermally contacting the base  10 , and a top face on which the fin set  30  is arranged. The fin set  30  has a plurality of horizontally oriented fins wherein each fin thermally contacts with the top face of the bottom wall  20 ′. The fin set  30  has a structure the same as that of the previous embodiment; however, the fin set  30  of this alternative embodiment is vertically mounted on the bottom wall  20 , rather than horizontally mounted like the previous embodiment. The two side plates  60 ′ each have two flanges at top and bottom sides thereof respectively. The two flanges are located on the two opposite sides of the fin set  30 . The top wall  40 ′ is located on the fin set  30  opposite to the bottom wall  20 ′ and thermally contacts the fin set  30 . Two heat pipes  50 ′ thermally connect the base  10 , the bottom wall  20 ′, the fin set  30  and the top wall  40 ′. Top and bottom of the fin set  30  are sealed by the top and bottom wall  40 ′,  20 ′. Each heat pipe  50 ′ is generally U-shaped with a middle portion and two arms extending from two ends of the middle portion. One of the arms is thermally engaged between the base  10  and the bottom wall  20 ′ and the other of the arms is thermally engaged between the top of the fin set  30  and the top wall  40 ′.  
      It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.