Abstract:
A thermal module for dissipating heat generated by a heat source includes a heat pipe and a heat sink. The heat pipe includes a vaporized portion thermally connected to the heat source for collecting the heat, a condensed portion for receiving the heat transmitted from the vaporized portion, and a heat transferring portion connecting the vaporized portion and the condensed portion, cross-sectional areas of a transitional portion for connecting the vaporized portion and the heat transferring portion being gradually changed. The heat sink is thermally connected to the condensed portion for cooling the condensed portion.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a thermal module and, more particularly, to a thermal module incorporating a heat pipe for improving heat dissipating effectiveness thereof.  
       DESCRIPTION OF RELATED ART  
       [0002]     As computer technology continues to advance, electronic elements such as central processing units and chipsets in computers have faster operational speeds and larger functional capabilities. Heat produced within a computer enclosure increases greatly due to the advance in the operational speed. Operational stability of the electronic elements is deteriorated. In order to dissipate heat, various thermal modules are applied.  
         [0003]     Referring to  FIG. 6 , a general thermal module  70  is illustrated. The thermal module  70  includes a heat sink  20 , a fan  30 , a heat receiver  40 , and a heat pipe  50 . Channels  200 ,  400  respectively defined in the heat sink  20  and the heat receiver  40  are applied for extensions of the heat pipe  50 . The fan  30  is mounted on the heat sink  20  to blow heat away therefrom. The heat receiver  40  is attached to a heat source such as an electronic element (not shown) for collecting heat released from the heat source. The heat pipe  50  includes a heat transferring portion  500 , a vaporized portion  502  and a condensed portion  504 . The vaporized portion  502  and the condensed portion  504  are arranged at two opposite ends of the heat transferring portion  500  and are respectively inserted into the channels  200 ,  400 . Working fluid (not shown) in a liquid state at a nonworking temperature, such as water, is filled within the heat pipe  50 . The working fluid circulates in the heat pipe  50  when it is vaporized at the vaporized portion  502  and condensed at the condensed portion  504 . The heat can be conducted away from the heat receiver  40  toward the heat sink  20  due to changing from the liquid state to a gaseous state. The heat sink  20  and the fan  30  dissipate the heat to surrounding atmosphere. Thermal resistance of a thermal junction between the heat pipe  50  and the heat source is increased because the heat pipe  50  is indirectly connected to the heat source via the heat receiver  40 . The high thermal resistance results in lower heat dissipating effectiveness of the thermal module  70 .  
         [0004]     Referring also to  FIG. 7 , another thermal module  80  is developed in order to overcome the above-described shortcoming. The thermal module  80  includes a heat sink  22 , a fan  32 , and a heat pipe  52 . The heat pipe  52  includes a heat transferring portion  520 , a vaporized portion  522  and a condensed portion  524 . The vaporized portion  522  and the condensed portion  624  are arranged at two opposite ends of the heat transferring portion  520 . The vaporized portion  522  marches with the heat transferring portion  520  via a connecting position  526 . The vaporized portion  522  is board-shaped and mounted to an electronic element (not shown) to receive heat. The heat is transmitted from the electronic element to the heat sink  22 , and discharged to surrounding atmosphere by the fan  32 . Thermal resistance of a thermal junction between the electronic element and the heat pipe  52  is lowered because the heat receiver  40  (shown in  FIG. 1 ) is omitted. The heat dissipating effectiveness of the thermal module  80  is improved to some extent. However, areas, an extent of a planar region or of a surface of a solid measured in square units, of cross-sections from the vaporized portion  522  to the heat transferring portion  520  and adjacent to a connecting position  526  are acutely changed. Fluid resistance against the working fluid is heightened, and energy loss of the working fluid is greatly increased. Therefore, the heat dissipating effectiveness of the thermal module  80  is still lower.  
         [0005]     Therefore, a thermal module having an improved heat dissipating effectiveness is needed.  
       SUMMARY OF INVENTION  
       [0006]     A thermal module for dissipating heat generated by a heat source includes a heat pipe and a heat sink. The heat pipe includes a vaporized portion thermally connected to the heat source for collecting the heat, a condensed portion for receiving the heat transmitted from the vaporized portion, and a heat transferring portion connecting the vaporized portion and the condensed portion, cross-sectional areas of a transitional portion for connecting the vaporized portion and the heat transferring portion being gradually changed. The heat sink is thermally connected to the condensed portion for cooling the condensed portion. 
     
    
       [0007]     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  
       [0008]      FIG. 1  is an exploded isometric view of a thermal module in accordance with a preferred embodiment, the thermal module including a heat pipe;  
         [0009]      FIG. 2  is a top view of the heat pipe of  FIG. 1 ;  
         [0010]      FIG. 3  is a schematic view of a theoretic model of the general heat pipe of  FIG. 2 ;  
         [0011]      FIG. 4  is a schematic view of a curve of fluid energy loss index of the heat pipe of  FIG. 2 ;  
         [0012]      FIG. 5  is a schematic view of a theoretic model of the heat pipe of  FIG. 3 ;  
         [0013]      FIG. 6  is an isometric view of a general thermal module with a general heat pipe thereof; and  
         [0014]      FIG. 7  is an isometric view of another general thermal module with another general heat pipe thereof. 
     
    
     DETAILED DESCRIPTION  
       [0015]     Reference will now be made to the drawing figures to describe, at least, the preferred embodiment of the present thermal module incorporating a heat pipe, in detail.  
         [0016]     Referring to  FIGS. 1 and 2 , a thermal module  60  for dissipating heat generated by a heat source such as an electronic element  90  is illustrated. The thermal module  60  includes a heat pipe  10 , a heat sink  24  and a fan  34 . The heat pipe  10  is thermally connected to the electronic element  90  and the heat sink  24 . The fan  34  is attached to the heat sink  24  for cooling the heat sink  24 .  
         [0017]     The heat pipe  10  is an elongated vessel filled with working fluid (not labeled) therein. The heat pipe  10  includes a heat transferring portion  100 , a vaporized portion  102  and a condensed portion  104 . The vaporized portion  102  and the condensed portion  104  are arranged at two ends of the heat transferring portion  100 . The vaporized portion  102  includes an attaching plane  106  conformed to a corresponding upper plane  900  of the electronic element  90 . An area of the attaching plane  106  is substantially equal to that of the upper plane  900 . It is noted that the word “area” means an extent of a planar region or of a surface of a solid measured in square units in all chapters. A width W of the vaporized portion  102  is greater than a width D of the heat transferring portion  100 . A transitional portion  108  interconnects the vaporized portion  102  and the heat transferring portion  100 . Cross-sectional areas of the transitional portion  108  are gradually reduced from the vaporized portion  102  to the heat transferring portion  100 .  
         [0018]     In the preferred embodiment, the vaporized portion  102  is a cuboid, and the heat transferring portion  100  is a tube with a diameter D. The transitional position  108  is convergent from the vaporized portion  102  to the heat transferring portion  100 , and has convergent contours with transitional radii R thereof.  
         [0019]     Referring to  FIGS. 3 and 4 , a theoretic model and an analysis curve for simulating and analyzing fluid energy loss H L1  of the working fluid therein are illustrated. The relationship between the fluid energy loss index C L  and R/D is defined as formula (1):
 
C L =0.5e {−13R/D}   (1)
 
         [0020]     The fluid energy loss H L1  can be defined as formula (2):
 
 H   L1   =C   L ( V   1 - V   2 ) 2 /2 g   (2)
 
         [0021]     S 1 , S 2  are cross-sections and respectively at opposite sides of the transitional position  108 , V 1 , V 2  are respectively velocities of the working fluid passing cross-sections S 1 , S 2 . If R/D fulfills the condition 0.2≦R/D≦1.0, the fluid energy loss index is lowered to 0&lt;C L ≦0.0038. If R/D fulfills the condition R/D&gt;1.0, the fluid energy loss index C L  is continuously and sluggishly decreased. If R/D fulfills the condition R/D&lt;0.2, the fluid energy loss index C L  is exponentially increased. The fluid energy loss H L1  is thus markedly lowered when R/D fulfills the conditions 0.2≦R/D≦1.0 and R/D&gt;1.0. Therefore, the condition R/D≧0.2 is acceptable for lowering the fluid energy loss H L1 .  
         [0022]     Contrastively, referring also to  FIG. 5 , another theoretic model for simulating fluid energy loss H L2  of the working fluid filled in the general heat pipe  80  of  FIG. 2  is illustrated. The fluid energy loss H L2  can be deduced from following formulas (3)˜(8).
 
Q=V 1 A 1 =V e A 1 =V 2 A 2   (3)
 
         [0023]     Q represents flux of the working fluid, V 1 , V e , V 2  represent respectively represent velocities of the working fluid passing a cross-section S 1 , the transitional position  526  (shown in  FIG. 2 ) between cross-sections S 1 , S 2  and the cross-section S 2 , A 1 , A 2  respectively represent cross-sectional areas.
 
( P   e - P   2 ) A   2   =pQ ( V   2 - V   e )  (4)
 
y=pg  (5)
 
         [0024]     y represents specific gravity, p represents density. Supposing P e =P 1 , V e =V 1 , formula (4) is converted to formula (6). P 1 , P e , P 2  respectively represent pressures that the working fluid is received at the cross-section S 1 , the transitional position  526  and the cross-section S 2 .
 
( P   1 - P   2 )/ y=pQ ( V   2 - V   1 )/ pgA   2   =Q ( V   2 - V   1 )/ gA   2   (6)
 
 H   L2 =( P   1 - P   2 )/ y+ ( Z   1 - Z   2 )+( V   1   2 - V   2   2 )/2 g   (7)
 
         [0025]     Z 1 , Z 2  respectively represent heights of the working fluid. Supposing Z 1 =Z 2 , formula (5) is converted to formula (6) as following:
 
 H   L   2   =Q ( V   2 - V   1 )/ gA   2 +( V   1   2 - V   2   2 )/2 g= ( V   1 - V   2 ) 2 /2 g   (8)
 
         [0026]     Comparing formulas (1) to (8), H L1 =C L H L2 . Because 0&lt;C L ≦0.0038, the fluid energy loss H L1  in the heat pipe  90  is much less than the fluid energy loss H L2  in the general heat pipe  80 .  
         [0027]     In use, the vaporized portion  102  of the heat pipe  90  is affixed to the electronic element  60  with thermally conductive grease (not shown) sandwiched therebetween. Thermal resistance of a thermal junction between the heat pipe  90  and the electronic element  60  is lowered. The vaporized portion  102  gains the heat from the electronic element  60 . The heat transferring portion  100  transfers the heat from the vaporized portion  102  to the condensed portion  104  via the working fluid filled in the heat pipe  90 . The heat sink  24  collects the heat from the condensed portion  104 , and discharges the heat to the atmosphere around via a plurality of fins (not labeled) thereof. In order to enhance the cooling performance of the heat sink  24 , the fan  34  may be applied to generate airflow to cool down the heat sink  24  more quickly. The working fluid reflows to the vaporized portion  102  to gain the heat again as soon as it is cooled at the condensed portion  104  by the heat sink  24  and fan  34 .  
         [0028]     In alternative embodiments, the vaporized portion  102  may be configured as other general configurations such as a flat column. The condensed portion  524  may be also configured as the vaporized portion  522 . In addition, the fan  34  may be omitted in case the heat sink  24  is sufficient for cooling the heat pipe  50  quickly. The heat sink  24  may be configured as other general configurations besides the configurations illustrated in the  FIG. 3 .  
         [0029]     The embodiments described herein are merely illustrative of the principles of the present invention. Other arrangements and advantages may be devised by those skilled in the art without departing from the spirit and scope of the present invention. Accordingly, the present invention should be deemed not to be limited to the above detailed description, but rather by the spirit and scope of the claims that follow, and their equivalents.