Abstract:
A heat dissipation fan includes a housing, a first rotor, a second rotor, a base and a plurality of static blades. The first rotor has a shaft and a plurality of rotor blades. The second rotor is coupled to the first rotor and has a plurality of rotor blades. The base is disposed in the housing for supporting the first and second rotors. The static blades are disposed between the housing and the base, wherein a rear portion of each static blade extends along an axial line of the heat dissipation fan for improving the working efficiency of the second rotor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a heat dissipation fan, and more particularly to a heat dissipation fan with improved efficiency. 
     2. Description of the Related Art 
     Currently, with increased heat generation in electronic elements, conventional convection methods are unable to dissipate heat sufficiently. Thus, heat dissipation fans are required. 
     Conventional heat dissipation fans provide dissipation efficiency of about 15˜30%. However, this efficiency is too low. Additionally, conventional heat dissipation fans generate additional heat into the system, thereby decreasing dissipation efficiency thereof. A high-power heat dissipation fan is thus required, and more energy is in turn wasted. 
       FIG. 1  shows a conventional fan, including a housing  10 , a motor  12 , a base  15  and a rotor. The base  15  is connected to the housing  10  via ribs  14  to support the motor  12 . Conventionally, the heat of the fan is dissipated via an exposed metal shell  11  of the rotor. However, when the volume of the motor  12  decreases, the heat cannot be sufficiently dissipated. 
     Additionally, in theory, blades  13  of the rotor can provide dissipation efficiency of about 75˜85%. However, conventional heat dissipation fans only provide the total dissipation efficiency of about 15˜30%. Eliminating efficiency loss of the motor, in practice, blades  13  only provide dissipation efficiency of about 20˜45%. Thus, conventional heat dissipation fans must be modified to achieve improved dissipation efficiency. 
     BRIEF SUMMARY OF THE INVENTION 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     The invention provides a heat dissipation fan, the heat dissipation efficiency and space utilization of which are optimized by the height ratio of the rotor blades to the static blades, rotor and static blade numbers, and improved static blade design. 
     In an embodiment of the invention, the heat dissipation fan includes a housing, a first rotor, a second rotor, a base, and a plurality of static blades. The first rotor comprises a shaft and a plurality of rotor blades. The second rotor couples to the first rotor and comprises a plurality of rotor blades. The base is disposed in the housing for supporting the first and second rotors. The static blades are disposed between the housing and the base, wherein a rear portion of each static blade extends along an axial line of the heat dissipation fan, improving efficiency of the second rotor. 
     In a modified embodiment, a length of the rear portion is ⅓ to ⅕ of that of the static blade. 
     The second rotor is disposed on the lee side of the first rotor. An end of the shaft passes through a top surface of a hub of the second rotor to be fixed thereon by riveting, screwing, adhesion or other equivalent means. The first rotor and the second rotor rotate at the same speed. 
     The heat dissipation fan includes a first air-guiding shroud disposed on a side of the housing and a second air-guiding shroud disposed on another side of the housing. The first or second air-guiding shroud includes a plurality of static blades disposed therein. The first air-guiding shroud or the second air-guiding shroud expands outward in a flared shape. The first air-guiding shroud and the second air-guiding shroud are connected to the housing by wngaging, riveting, screwing, adhesion, or other equivalent means. 
     The first rotor and the second rotor include a hub, and the rotor blades disposed around the hub. The hub of the first rotor is conical or tapered, or has an inclined surface. Each of the hubs of the first and second rotors comprises a plurality of heat dissipation holes for allowing airflow to pass therethrough so as to dissipate an internal heat of the fan. An inner surface of each heat dissipation hole is inclined. The hub of the second rotor is cup-shaped. 
     In a modified embodiment, the number of rotor blades of the first rotor is different from that of the second rotor. The number of rotor blades of the first rotor is 9, and the number of rotor blades of the second rotor is 8 or 5. The number of rotor blades of the first rotor is 8, and the number of rotor blades of the second rotor is 9 or 5. The number of static blades is 7. 
     In a modified embodiment, a height ratio of the rotor blades to the static blades ranges from 1:1.1 to 1:1.4. A height ratio of the rotor blades to the static blades ranges from 1:1.6 to 1:2.2. 
     The housing further comprises a plurality of connecting portions, and the heat dissipation fan is fixed on an external system frame via holes thereof. 
     The heat dissipation fan further comprises a driving device, disposed through the base to actuate the first and second rotors. 
     In another embodiment of the invention, a heat dissipation fan is provided, comprising a housing, a first rotor, a second rotor, a base and a plurality of static blades. The first rotor comprises a shaft and a plurality of rotor blades. The second rotor couples to the first rotor and comprises a plurality of rotor blades. The base is disposed in the housing supporting the first and second rotors. The static blades are disposed between the housing and the base, wherein a height ratio of the rotor blades to the static blades ranges from 1:1.1 to 1:2.2. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a sectional view of a conventional fan; and 
         FIG. 2  is a sectional view of a heat dissipation fan of a first embodiment of the invention; 
         FIGS. 3A-3C  are top views of the first rotor, the static blades and the second rotor; 
         FIG. 4  is a schematic diagram of rotor blades of first rotor, static blades and rotor blades of second rotor; 
         FIG. 5  is an exploded view of a heat dissipation fan of a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 2  shows a first embodiment of a heat dissipation fan of the invention. The fan includes a housing  21 , a base  22  disposed in the housing  21 , a plurality of static blades  23  disposed between the base  22  and the housing  21 , a first rotor  24 , a driving device  25  (for example, a motor) disposed through the base  22  and supported thereby, a shaft  26 , and a second rotor  27 . The second rotor  27  is disposed on a rear end (lee side) of the first rotor  24 . An end of the shaft  26  passes a top surface of a hub  271  of the second rotor  27  and is fixed thereon. The inner portion of the hub  271  of the second rotor  27  is cup-shpaed. The shaft  26  is fixed to the second rotor  27  by riveting, screwing, adhesion, or other equivalent means. The driving device  25  can drive the first rotor  24  and the second rotor  27  via the shaft  26  to rotate the first rotor  24  and the second rotor  27  at the same speed. 
     A plurality of heat dissipation holes  242  are formed on the top surface of the hub  241  of the first rotor  24 . A plurality of heat dissipation holes  272  are formed on the top surface of the hub  271  of the second rotor  27 . When the first rotor  24  and the second rotor  27  are rotated by the driving device  25 , airflow through the heat dissipation holes  242  and the heat dissipation holes  272  (as shown by the dotted lines) dissipates heat generated by the driving device  25  to elongate the used life thereof. The first rotor  24  includes a plurality of rotor blades  243 . The second rotor  27  includes a plurality of rotor blades  273 . The rotor blades  243  of the first rotor  24  incline upward. A windward side of the housing  21  includes an expanding portion  211  to increase intake airflow. 
     In terms of hydrodynamics, the rotation of the rotor blades will generate a pressure difference so as to generate airflow. However, when the air flow is discharged from the fan, it has an angle speed at the flow direction, thereby resulting in energy loss and decreasing heat dissipation efficiency. Further, in terms of flow field analysis, it will cause energy loss due to the generation of eddy on the heat dissipation fan. Moreover, when the airflow pass through the surface of rigid body, a shearing force is generated by friction, thereby causing energy loss. The gap between the tip of the rotor blades and the inner wall of the housing will also cause energy exhaust. The invention utilizes the Taguchi Method to obtain the optimum height ratio between the rotor and static blades. The static blades  23  guide airflow to reduce eddies, modify the angle speed to axial work, and improve the heat dissipation efficiency of the fan. When a ratio of a height h 2  of the rotor blades  243  to a height h 1  of the static blades  23  ranges from 1:1.6 to 1:2.2, the heat dissipation fan has the best efficiency and usage rate of space. The efficiency of the heat dissipation fan of the invention can be enhanced up to 45%. Eliminating the efficiency loss of the motor, the efficiency of the blades is thus about 60%. Alternatively, the ratio of the height h 2  of the rotor blades  243  to the height h 1  of the static blades  23  can also range from 1:1.1 to 1:1.4. 
     The number of rotor blades  243  of the first rotor  24  is different from that of the second rotor  27 . For example, the number of rotor blades of the first rotor  24  can be 8, and the number of rotor blades  273  of the second rotor  27  is 9 or 5. In this embodiment, as shown in  FIGS. 3A to 3C , the number of the static blades  23  is 7, and noise of the heat dissipation fan is thus reduced. Alternatively, the number of rotor blades of the first rotor is 9, and the number of rotor blades of the second rotor is 8 or 5. 
     Static blades  23  in the housing  21  can improve working efficiency of the second rotor  27 , and increase the airflow pressure. As shown in  FIG. 4 , the tail ends of the static blades  23  are vertical design; in other word, the front portion  23   a  is curved, and the rear portion  23   b  is vertical and extends parallel to a center axis of the heat dissipation fan. Thus, the working efficiency of the second rotor  27  can be greatly improved. Preferably, the length of the rear portion  23   b  is about ⅓ to ¼ of that of the static blade  23 . The rear portion  23   b  is vertical and parallel to the center axis of the heat dissipation fan. Thus, the efficiency of the rear portion  23   b  is enhanced and the performance of the heat dissipation fan is optimized. 
       FIG. 5  shows a heat dissipation fan of the second embodiment of the invention, the structure of which is similar to that of the above-described embodiment except that the hub  241  of the first rotor  24  is conical or tapered, or has an inclined surface, and the inner walls of the heat dissipation holes  242  are inclined. Additionally, the heat dissipation fan further includes a first air-guiding shroud  3  and a second air-guiding shroud  4  respectively disposed on opposite sides of the housing  21 . The second air-guiding shroud  4  further includes a plurality of static blades  41  to increase airflow pressure and improve heat dissipation efficiency. The first air-guiding shroud  3  can further include a plurality of static blades. The first air-guiding shroud  3  and the second air-guiding shroud  4  expand outward or are flared, and coupled to the housing  21  by engaging, riveting, screwing, adhesion, or other equivalent means. The housing  21  further includes a plurality of connecting portions  211 , and the heat dissipation fan is fixed on an external system frame via holes formed on the connecting portions  211 . 
     The invention provides a heat dissipation fan with optimum heat dissipating efficiency, which is achieved by adjusting the height ratio of the rotor blades to static blades, the collocating numbers of the rotor and static blades, and the shaped design of static blades. Thus, the heat dissipation efficiency and usage rate of space are optimized. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.