Abstract:
Provided is an impeller of a centrifugal compressor including: a hub fixed to a rotation shaft; and a plurality of blades extending outward from a center portion of the hub on one surface of the hub, wherein a length of the blade is greater than a straight length between an inlet end of the blade and an outlet end thereof. Assuming that an outlet angle formed along a longitudinal direction of the blade at the outlet end of the blade is β and an inclination angle of the blade from the one surface of the hub at the outlet end of the blade is γ, the following equation is satisfied: 1&lt;sin(β−20°)+cos(γ−40°)&lt;1.5.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Korean Patent Application No. 10-2010-0076399, filed on Aug. 9, 2010, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which in its entirety are herein incorporated by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    This disclosure relates to a centrifugal compressor, and more particularly, to an impeller which adds velocity energy to a compressible medium while rotating at high speed. 
         [0004]    2. Description of the Related Art 
         [0005]    A compressor is a device for compressing gas by applying mechanical energy and is necessary for an air-conditioning apparatus such as a refrigerator to compress a cooling medium. There are different kinds of compressors, including a reciprocating compressor, a screw compressor, a centrifugal compressor, and the like. Particularly, the centrifugal compressor rotating at high speed has been widely used since fluctuation of a discharge gas does not occur and reductions in size and weight are easily achieved. 
         [0006]    In general, a centrifugal compressor used in a freezer includes a casing having a cooling medium inlet port on one side, an impeller which is provided inside the casing for compressing a cooling medium flowing therein, a diffuser for converting kinetic energy of the cooling medium compressed by the impeller into pressure energy, and a volute for transferring the cooling medium passing through the diffuser to a discharge duct. The cooling medium flowing through the cooling medium inlet port of the centrifugal compressor is compressed by the impeller and the diffuser, passes through the volute and the discharge duct, and then is transferred to a condenser. 
         [0007]    The impeller which may be considered as the heart of the centrifugal compressor includes a number of blades and applies centrifugal force to the compressible medium (the cooling medium) by rotating at high speed. Thus, there is a problem in that noise occurs. 
       SUMMARY 
       [0008]    This disclosure provides an impeller which has an optimal structure to minimize noise and a centrifugal compressor including the same. 
         [0009]    In one aspect, there is provided an impeller of a centrifugal compressor including: a hub fixed to a rotation shaft; and a plurality of blades extending outward from a center portion of the hub on one surface of the hub, wherein a length of the blade is greater than a straight length between an inlet end of the blade and an outlet end thereof. Assuming that an outlet angle formed along a longitudinal direction of the blade at the outlet end of the blade is β and an inclination angle of the blade from the one surface of the hub at the outlet end of the blade is γ, Equation (1) is satisfied: 
         [0000]      1&lt;sin(β−20°)+cos(γ−40°)&lt;1.5  (1)
 
         [0010]    The outlet angle β may be in a range of 20° to 70°. 
         [0011]    The inclination angle γ may be in a range of 40° to 90°. 
         [0012]    In another aspect, there is provided a centrifugal compressor including: an impeller which is fixed to a rotation shaft to be rotated at high speed; and a diffuser which converts kinetic energy of a compressible medium that is increased by the impeller into pressure energy, wherein the impeller satisfies Equation (1). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above and other aspects, features and advantages of the disclosed exemplary embodiments will be more apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0014]      FIG. 1  is a cross-sectional view illustrating a centrifugal compressor according to an embodiment; 
           [0015]      FIG. 2  is a perspective view of an impeller according to an embodiment; 
           [0016]      FIG. 3  is a front view of the impeller for illustrating an outlet angle of a blade; 
           [0017]      FIG. 4  is a partial side view of the impeller for illustrating an inclination angle of the blade; 
           [0018]      FIG. 5  is a graph showing a change in noise level depending on a value of sin(β−20)°+cos(γ−40°) in regard to the outlet angle β and the inclination angle γ of the blade; 
           [0019]      FIG. 6  is a graph showing a change in noise level depending on the outlet angle of the blade; and 
           [0020]      FIG. 7  is a graph showing a change in noise level depending on the inclination angle of the blade. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Exemplary embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth therein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments. 
         [0022]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the use of the terms a, an, etc. does not denote a limitation of quantity, but rather denotes the presence of at least one of the referenced item. It will be further understood that the terms “comprises” and/or “comprising”, or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
         [0023]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
         [0024]    In the drawings, like reference numerals in the drawings denote like elements. The shape, size and regions, and the like, of the drawing may be exaggerated for clarity. 
         [0025]    Hereinafter, a centrifugal compressor according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. 
         [0026]      FIG. 1  is a cross-sectional view illustrating a centrifugal compressor according to an embodiment.  FIG. 2  is a perspective view of an impeller according to an embodiment.  FIG. 3  is a front view of the impeller for illustrating an outlet angle of a blade.  FIG. 4  is a partial side view of the impeller for illustrating an inclination angle of the blade. And,  FIG. 5  is a graph showing a change in noise level depending on a value of sin(β−20°)+cos(γ−40°) in regard to the outlet angle δ and the inclination angle γ of the blade. 
         [0027]    Referring to  FIG. 1 , the centrifugal compressor  100  according to an embodiment includes a casing  10 , a rotation shaft  20  which penetrates the center of the casing  10  to be connected to a motor, an impeller  30  which is fixed to the rotation shaft  20  to be rotated so as to cause a compressible medium such as a cooing medium to flow therein, and a diffuser  40  which is disposed at a predetermined interval from the impeller  30  to convert kinetic energy of the compressible medium into pressure energy. 
         [0028]    On one side of the casing  10 , there is provided an inlet port  12  through which the compressible medium flows and which is disposed in a longitudinal direction of the rotation shaft  20 . An inlet guide vane (IGV)  50  for controlling an inflow of the cooling medium is provided in the inlet port  12 . A bearing member  60  for supporting the rotation shaft  20  is provided on the rear of the impeller  30 . 
         [0029]    The cooling medium compressed by the impeller  30  and the diffuser  40  is directed to the discharge duct through the volute  70 . 
         [0030]    In the centrifugal compressor  100  having the above-described configuration, the impeller  30  includes, as illustrated in  FIG. 2 , a hub  32  which is directly fixed to the rotation shaft  20 , and blades  34  which protrude from one surface of the hub  32  for inducing a flow of the cooling medium. The hub  32  may have various shapes such as a disk shape or a columnar shape having a width increasing in an axial direction in which the cooling medium flows. 
         [0031]    A plurality of the blades  34  extend outward from the center portion of the hub  32  in a radial direction at predetermined intervals. Each blade  34  may extend in a streamline shape, and accordingly, an actual length (curve length) of the blade  34  may be greater than a straight length between an inlet end  342  and an outlet end  344  of the blade  34 . 
         [0032]    The shape of the blade  34  has a great effect on the flow of the cooling medium. Particularly, the outlet angle β and the inclination angle γ of the blade  34  are factors having a great effect on generation of noise due to the flow of the cooling medium. 
         [0033]    As illustrated in  FIG. 3 , the outlet angle β of the blade  34  refers to an angle between a longitudinal direction (tangential direction) of the blade  34  and a tangential direction of the hub  32  at a point where the outlet end  344  of the blade  34  meets an outermost portion of the hub  32 . As illustrated in  FIG. 4 , the inclination angle γ refers to an angle between a height direction of the blade  34  and a tangential direction of the one surface of the hub  32  at the outlet end  344  of the blade  34 . 
         [0034]    The impeller  30  of the centrifugal compressor  100  according to an embodiment satisfies Equation (1) in regard to the outlet angle β and the inclination angle γ of the blade  34 . 
         [0000]      1&lt;sin(β−20°)+cos(γ−40°)&lt;1.5  (1)
 
         [0035]    The applicant discovered that noise generation by the impeller  30  is minimized when the outlet angle β and the inclination angle γ of the blade  34  satisfy Equation (1). 
         [0036]    As illustrated in  FIG. 5 , in regard to the outlet angle β and the inclination angle γ of the blade  34 , the noise generation is reduced when the value of sin(β− 20 °)+cos(γ−40°) is in the range of 1 to 1.5. 
         [0037]      FIG. 6  is a graph showing a change in noise level depending on the outlet angle of the blade.  FIG. 7  is a graph showing a change in noise level depending on the inclination angle of the blade. 
         [0038]    Referring to  FIG. 6 , when the outlet angle β of the blade  34  approaches 90°, pressure at the outlet end  344  of the blade  34  is increased, and thus the level of noise (blade-passing frequency (BPF) noise) is very high. However, the noise level is sharply reduced when the outlet angle β is 70° and is maintained at a predetermined level. Meanwhile, when the outlet angle β is smaller than 20°, a difference in speed between the cooling medium flowing along the outer surface of the blade  34  and the cooling medium flowing along the inner surface thereof increases rapidly at the outlet end  344  of the blade  34 , and thus the noise level is increased again. Therefore, in the centrifugal compressor  100  according to the embodiment, the outlet angle β may have a value in the range of 20° to 70°. 
         [0039]    Referring to  FIG. 7 , the noise level is maintained at a predetermined level or a smaller level when the inclination angle γ of the blade  34  is in the range of 40° to 90°. However, when the inclination angle γ is smaller than 40°, a difference in speed between the cooling medium flowing along the outer surface of the blade  34  and the cooling medium flowing along the inner surface thereof is increased, so that the noise level increases rapidly. Therefore, in the centrifugal compressor  100  according to the embodiment, the inclination angle γ may have a value in the range of 40° to 90°. 
         [0040]    In the foregoing description, a single-stage centrifugal compressor has been described. However, this disclosure is not limited thereto. The number of the stages of the centrifugal compressor may be changed differently. 
         [0041]    The centrifugal compressor according to the present disclosure includes the impeller which has an optimal shape based on the outlet angle and the inclination angle, so that there are advantages of high reliability in designing and a reduction in noise of the centrifugal compressor. 
         [0042]    While the exemplary embodiments have been shown and described, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the spirit and scope of this disclosure as defined by the appended claims. 
         [0043]    In addition, many modifications can be made to adapt a particular situation or material to the teachings of this disclosure without departing from the essential scope thereof. Therefore, it is intended that this disclosure not be limited to the particular exemplary embodiments disclosed as the best mode contemplated for carrying out this disclosure, but that this disclosure will include all embodiments falling within the scope of the appended claims.