Abstract:
An exemplary centrifugal fan includes a housing and an impeller received in the housing. The housing defines an air inlet and an air outlet thereof. Airflow driven by the impeller flows out of the housing via the air outlet. The housing further defines an opening adjacent to one end of the air outlet. The ambient air out of the centrifugal fan enters the housing via the opening, and flows out of the housing via the air outlet.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to centrifugal fans typically used in electronic devices such as computers. 
         [0003]    2. Description of Related Art 
         [0004]    With rapid development of the computer industry, central processing units (CPUs) in computers generate a large amount of heat during operation, and the heat must be dissipated immediately. A typical heat dissipation device for dissipating heat from a CPU includes a centrifugal fan and a heat sink. A cooling airflow generating by the centrifugal fan dissipates the heat rapidly, so that heat remaining in the CPU stays within a safe temperature range. 
         [0005]    One way to improve the heat dissipation performance of the centrifugal fan is to increase the rotation rate of the blades, thereby increasing the air output of the centrifugal fan. However, this may also increase the noise of the centrifugal fan, and annoy or discomfort the user of the computer. 
         [0006]    Therefore, a centrifugal fan which is capable of overcoming the above described shortcomings is desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0008]      FIG. 1  is an exploded, isometric view of a centrifugal fan in accordance with a first embodiment of the present disclosure. 
           [0009]      FIG. 2  is an exploded, isometric view of a centrifugal fan in accordance with a second embodiment of the present disclosure. 
           [0010]      FIG. 3  is an exploded, isometric view of a centrifugal fan in accordance with a third embodiment of the present disclosure. 
           [0011]      FIG. 4  is an exploded, isometric view of a centrifugal fan in accordance with a fourth embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to  FIG. 1 , a centrifugal fan  100  of a first embodiment of the present disclosure includes a housing  10  and an impeller  20 . The housing  10  defines a receiving room  30 , and the impeller  20  is received in the receiving room  30 . The impeller  20  has a plurality of blades  21 . 
         [0013]    The housing  10  includes a base  11 , and a top plate  12  covering the base  11 . The base  11  includes a bottom plate  111 , and a peripheral sidewall  112  perpendicularly and upwardly extending from a periphery of the bottom plate  111 . The top plate  12  connects a top end of the sidewall  112 , and is parallel to the bottom plate  111 . An air inlet  13   a  is defined in a center portion of the top plate  12 , and an air inlet  13   b  is defined in a corresponding center portion of the bottom plate  111 , with both air inlets  13   a ,  13   b  corresponding to a position of the impeller  20 . In the illustrated embodiment, the air inlet  13   a  is different from the air inlet  13   b . In particular, the air inlet  13   a  is a round hole, and the air inlet  13   b  comprises three discrete, elongated, curved cutouts arranged in a circle radially symmetrically. An air outlet  14  is defined in one side of the sidewall  112 . An orientation of an opening of the air outlet  14  is substantially perpendicular to an orientation of an opening of each of the air inlets  13   a ,  13   b . The air outlet  14  is communicated with the air inlets  13   a ,  13   b  via an interior of the housing  10 , i.e., the receiving room  30 . 
         [0014]    In operation of the centrifugal fan  100 , the blades  21  of the rotating impeller  20  drive air to flow along an inner surface of the sidewall  112  and then towards the air outlet  14  of the centrifugal fan  100 . A bulge  17  is formed on the inner surface of the sidewall  112  close to one end of the air outlet  14 . The bulge  17  extends into the interior of the housing  10 . The bulge  17  is used for increasing air pressure of the air flowing into the housing  10  from the air inlets  13   a ,  13   b.    
         [0015]    A protrusion  15  is formed on an outer surface of the sidewall  112  close to the other end of the air outlet  14 . The protrusion  15  extends outwards away from the housing  10 . The protrusion  15  is integrally formed with the sidewall  112  as a single piece. In fact, in the present embodiment, the entire base  11  is a single monolithic body made of the one same material. An oblique opening  16  is defined commonly through the protrusion  15  and the sidewall  112 , and communicates with the external environment of the base  11 . The opening  16  extends obliquely from an outer surface of the protrusion  15  to the inner surface of the sidewall  112 , along a direction substantially consistent with a clockwise direction of rotation of the impeller  20 . In particular, outer extremities of the blades  21  cooperatively define an imaginary circle, and the direction of rotation of the impeller  20  can be considered to coincide with such circle. A tangent can be drawn on the circle at a point thereof nearest to a middle of the opening  16 . The direction of extension of the opening  16  is parallel to or approximately parallel to such tangent. With this configuration, a user of the centrifugal fan  100  cannot see the internal structure of the centrifugal fan  100  from the exterior of the centrifugal fan  100 , and so the internal structure of the centrifugal fan  100  does not adversely affect the aesthetic appearance of the centrifugal fan  100 . In addition, the protrusion  15  can enhance the strength of the sidewall  112  at the opening  16 , and help avoid breakage of the sidewall  12  due to the presence of the opening  16 . 
         [0016]    During operation of the centrifugal fan  100 , the impeller  20  rotates clockwise. The blades  21  drive air to flow into the interior of the housing  10  from the air inlets  13   a ,  13   b ; and the air then passes along the inner surface of the sidewall  112 , and flows towards the air outlet  14 . Due to the configuration of the bulge  17 , and due to flaring of the airflow path as the air flows finally away from the blades  21  and towards the air outlet  14 , the air pressure at the air outlet  14  is reduced. The means that the airflow accelerates as it passes out of the air outlet  14 , and also that the air pressure at the air outlet  14  is lower than the air pressure outside the housing  10  where the opening  16  is located. According to the principle that air flows from areas with high air pressure to areas with low air pressure, the air outside the housing  10  at the opening  16  flows into the housing  10  through the opening  16 , and then flows out from the air outlet  14  together with the original airflow generated by the blades  21 . 
         [0017]    Therefore, firstly, the air output of the centrifugal fan  100  is increased due to the additional airflow generated by the air pressure difference at the opening  16 , and the heat dissipation performance of the centrifugal fan  100  is improved without any need to increase the rotation rate of the blades  21 . Secondly, the airflow generated by the air pressure difference at the opening  16  flows from outside the housing  10  through the opening  16 , and thereby dissipates heat generated by electronic components located close to the opening  16 . Thirdly, the opening  16  extends obliquely in the protrusion  15 , along a direction substantially consistent with the rotation direction of the impeller  20 . This means the airflow generated by the air pressure difference at the opening  16  flows out from the air outlet  14  substantially without changing the direction of the original airflow generated by the blades  21 , i.e., with minimum or no interference caused to the original airflow. Therefore the noise (if any) of the centrifugal fan  100  is not raised by the provision of the opening  16 . 
         [0018]    Referring to  FIG. 2 , a centrifugal fan  100   a  of a second embodiment of the present disclosure is shown. Compared with the centrifugal fan  100  of the first embodiment, no protrusion  15  is formed on the sidewall  112  of the centrifugal fan  100   a , and instead an opening  16   a  is directly defined in the sidewall  112 . The opening  16   a  extends obliquely from the outer surface of the sidewall  112  to the inner surface of the sidewall  112  along a direction toward the air outlet  14 . The centrifugal fan  100   a  has characteristics similar to those of the centrifugal fan  100 , and functions in a manner similar to that of the centrifugal fan  100 . 
         [0019]    Referring to  FIGS. 3 and 4 , centrifugal fans  100   b  and  100   c  of third and fourth embodiments of the present disclosure are shown. The centrifugal fans  100   b  and  100   c  are both similar to the centrifugal fan  100   a . The differences are, a rectangular opening  16   b  of the centrifugal fan  100   b  is defined in the top plate  12 , close to the air outlet  14  and the sidewall  112 . There is no opening defined in the sidewall  112 . A rectangular opening  16   c  of the centrifugal fan  100   c  is defined in the bottom plate  111 , close to the air outlet  14  and the sidewall  112 . There is no opening defined in the sidewall  112 . The centrifugal fans  100   b ,  100   c  each have characteristics similar to those of the centrifugal fan  100 , and function in a manner similar to that of the centrifugal fan  100 . 
         [0020]    It is understood that the shapes and/or quantities of the openings  16 ,  16   a ,  16   b ,  16   c  and the specific structures of the centrifugal fans  100 ,  100   a ,  100   b ,  100   c  are not limited to what is described above and shown in the drawings. Such shapes, quantities and/or specific structures can be altered, adjusted, combined and/or omitted according to actual requirements. 
         [0021]    In addition, the particular embodiments shown and described are provided by way of illustration only. The principles and the features of the present disclosure may be employed in various and numerous embodiments without departing from the scope of the disclosure. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.