Abstract:
Disclosed is a axial flow fan of an outdoor unit of an air conditioner. The axial flow fan comprises a hub connected with a rotational shaft of a motor; and at least one blade contacting the hub, wherein the blade has a part from the hub to a predetermined portion of the blade among a whole part from the hub to an outer end of the blade, and the other part from the predetermined portion of the blade to the outer end of the blade, the part being equally applied at a predetermined rake angle, and the other part being raised in a direction of a pressure surface of the blade, and wherein a ratio of an inner diameter and an outer diameter of the axial flow fan is between about 0.35 and about 0.4.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an axial flow fan of an air conditioner, in which the number of blades is two, and each blade has a part from the hub to a predetermined portion of the blade among a whole part from the hub to an outer end of the blade which is equally applied at a predetermined rake angle, and the other part from the predetermined portion of the blade to the outer end of the blade which is raised in a direction of a pressure surface of the blade, and a ratio of an inner diameter and an outer diameter of the axial flow fan is between about 0.35 and about 0.4.  
         [0003]     2. Background of the Related Art  
         [0004]     In general, an air conditioner is mounted therein with a refrigerating cycle system composed of a compressor, a condenser, a capillary tube, an evaporator and a heat exchanger. The air conditioner is an apparatus for properly sending cold air formed at the evaporator or warm air generated at the condenser according to an indoor condition, and thus genially maintaining indoor atmosphere.  
         [0005]     The air conditioner may be divided into a window type air conditioner where the refrigerating cycle system is mounted in a single body, a spilt type air conditioner where an indoor unit and an outdoor unit are separated and installed indoors and outdoors respectively, and so forth. Particularly, the spilt type air conditioner is again divided, according to an installation method, into a wall-mounted type, a permanent-mounted type (including a package air conditioner), a ceiling-mounted type, a ceiling-embedded type and so on. Especially, the indoor unit of the spilt type air conditioner may has a structure capable of alternatively using the wall-mounted type and the permanent-mounted type and being simultaneously applied as the ceiling-mounted type according to need of a user, which is referred to as a convertible type indoor unit.  
         [0006]      FIG. 1  schematically shows a general air conditioner.  
         [0007]     Referring to  FIG. 1 , the conventional air conditioner is composed of an outdoor unit  20  which is disposed outdoors and exchanges heat with outdoor air, an indoor unit  10  which is disposed indoors and conditions indoor air, and a connecting line  30  which connects the outdoor unit and the indoor unit with each other.  
         [0008]     To be more specific, the outdoor unit  20  is a means for converting a gas refrigerant of low temperature and low pressure, which is inputted from the indoor unit  10  by exchanging heat with the outdoor air, into a liquid refrigerant of low temperature and low pressure, and is composed of a compressor  11 , a condenser  12  and an expansion valve  13 .  
         [0009]     Further, the compressor  11  is a component for converting the gas refrigerant of low temperature and low pressure, which is inputted from the indoor unit  10 , into the gas refrigerant of high temperature and high pressure, and the condenser  12  is a component for converting the gas refrigerant of high temperature and high pressure into a liquid refrigerant of middle temperature and high pressure, and the expansion valve  13  is a component for converting the liquid refrigerant of middle temperature and high pressure into the liquid refrigerant of low temperature and low pressure.  
         [0010]     Here, the condenser  12  is a component for directly exchanging the heat with the outdoor air, and has a separate fan for introducing the outdoor air.  
         [0011]     Meanwhile, the indoor unit  10  lowers an indoor temperature by means of evaporation, which occurs when the liquid refrigerant of low temperature and low pressure introduced from the outdoor unit  20  is converted into the gas refrigerant of low temperature and low pressure.  
         [0012]     The indoor unit  10  is composed of an evaporator  21  and a fan  21   a , wherein the evaporator  21  converts the liquid refrigerant of low temperature and low pressure into the gas refrigerant of low temperature and low pressure. The connecting line  30  is a component for connecting the indoor unit  10  and the outdoor unit  20  to circulate the refrigerant, and is properly disposed according to a distance between the outdoor unit  10  and the indoor unit  10 .  
         [0013]     As set forth above, the outdoor unit  20  of the split-type air conditioner includes the compressor, the condenser, a cooling fan (hereinafter, referred to as “axial flow fan”) which usually generate many noises, and a driving motor for rotating the axial flow fan. The indoor unit  10  includes the evaporator  21  and the blow fan  21   a , and performs refrigeration and circulation of the indoor air.  
         [0014]      FIG. 2  is a perspective view illustrating a general split type air conditioner.  
         [0015]     As shown in  FIG. 2 , the indoor unit  10  and the outdoor unit  20  are connected to each other by the connecting line  30 .  
         [0016]     Meanwhile, the axial flow fan  40 , as shown in  FIG. 3A , has a hub  42  coupled to a rotational shaft of the driving motor (not shown), and a plurality of blades  44  formed on an outer circumferential surface of the hub  42 , wherein the hub  42  is integrally formed with the blades  44 .  
         [0017]     When the axial flow fan  40  is rotated by the driving motor, a pressure difference is generated between front and rear sides of the plurality of blades  44  formed on the outer circumferential surface of the hub  42 .  
         [0018]     This pressure difference generates a suction force capable of sucking up the air, thus sucking up the outdoor air toward the outdoor unit  20  through the suction. Thus, the outdoor air passes through the condenser  12  provided on an intake side of the outdoor unit. At this point, the outdoor air exchanges the heat with the gas refrigerant flowing through the condenser to condense the gas refrigerant into a liquid state, and then flows out outside the outdoor unit  20  through ventilation of the axial flow fan  40 .  
         [0019]     As for characteristic factors determining a ventilation characteristic of the axial flow fan  40 , they are divided into two types: general factors such as the number of the blades  44 , a (outer) diameter D of the axial flow fan, a (outer) diameter d of the hub and so forth, and so-called blade factors such as a pitch angle β, a peak point of the camber P, a maximum quantity of the camber MC, a length of a chord, a sweep angle α and so forth at the blade, which will be described below with reference to  FIGS. 3A and 3B .  
         [0020]     The pitch angle β of the blade, as in  FIG. 3B , is an angle between a flow direction of the fluid or the air (x-axis in the figure) and a straight line, namely a chord, running from a leading edge (L.E) of the blade  44  and its trailing edge (T.E).  
         [0021]     Here, the quantity of the camber refers to a length joining the camber (a central line across a cross section of the blade) and the chord. The maximum point of the camber quantity, i.e., the maximum quantity of the camber MC, as in  FIG. 3B , refers to the camber quantity between the L.E. of the blade  44  and the camber peak point P on the chord C running from the L.E to the T.E.  
         [0022]     The sweep angle α refers to an angle between two lines that intersect, one of which is one which connects the center of an inner end of the blade  44  or the center of a portion where the blade  44  comes into contact with the hub  42  but goes with a curvature of the blade  44 , and the other is one (Y axis in the figure) which passes through the center (point) of the inner end of the blade  44  and the center (point) of the hub  42 .  
         [0023]     Especially, the sweep angle α is a factor determining a noise of an airflow of the axial flow fan  40 . When the sweep angle α is great, a phase difference of the airflow between the hub  42  and a tip of the blade  44  becomes great. In contrast, when the sweep angle α is great, the phase difference of the airflow becomes small.  
         [0024]     The phase difference of the airflow causes a phase difference between a noise generated at the outer end of the blade  44  and a noise generated at the inner end of the blade  44 . The greater this noise phase difference is, the lower a frequency of the airflow passing through the blade  44  becomes. Hence, the noise becomes lower.  
         [0025]     And, the number of the blades  44  is an important factor determining the airflow noise generated when the axial flow fan  40  is operated.  
         [0026]     One example of this conventional axial flow fan  40  is disclosed in Korean Patent Publication No. 2003-14960, titled AXIAL FLOW FAN OF OUTDOOR UNIT OF AIR CONDITIONER, previously filed by the present applicant and published as of Feb. 20, 2003. As for the disclosed axial flow fan of the outdoor unit of the air conditioner, it includes a hub  42  connected with a rotational shaft of a motor and a plurality of blades  44  integrally formed on an outer circumferential surface of the hub, wherein the number of the blades  44  is set to three, a whole outer diameter of the fan is set to 340±2 mm, and a diameter of the hub  42  is set to 100±2 mm.  
         [0027]     Further, each blade  44  is configured so that the pitch angle β is linearly changed from the hub  42  to the end thereof in a range between 20 degrees and 37 degrees.  
         [0028]     Each blade  44  is also configured so that the peak point of the camber P is formed at a point corresponding to 70% of the chord length in a direction from the L.E thereof to the T.E thereof, and that the maximum quantity of the camber MC is set to 0.5% within each radius from the hub  42  to the end of the blade  44 .  
         [0029]     Further, the sweep angle α of each blade  44  has a range between 47 degrees and 49 degrees when a dimensionless radius coordinate is less than 0.3 and is linearly increased when the dimensionless radius coordinate exceeds 0.3 to have a range between 55 degrees and 57 degrees at the end of the blade.  
         [0030]     For reference, the dimensionless radius coordinate is a factor for taking into consideration of performance of the axial flow fan only by the blades  44  except for the hub  42 , and is determined between 0 and 1 when a position where the blades and the hub come into contact with each other is set to 0, and the end of each blade  44  is set to 1.  
         [0031]     The dimensionless radius coordinate is obtained by the follow formula. r=(R−Rh)/(Rt−Rh), where R is the length from the center of the axial flow fan (i.e. the center of the hub) to a certain position, Rh is the radius of the hub  42 , Rt is the length from the center of the axial flow fan (i.e. the center of the hub) to the end of each blade  44 , namely, the radius of the axial flow fan.  
         [0032]     According to the axial flow fan  40  having three blades  44  in the outdoor unit of the foregoing air conditioner, as shown in  FIGS. 4 and 5 , a pressure coefficient and constant pressure efficiency are enhanced as compared to another conventional axial flow fan having four blades. As a result, the motor for the axial flow fan having three blades can be also enhanced in operation efficiency at an operation point, and can be driven with a size smaller than that for another conventional axial flow fan having four blades. In addition, the motor for the axial flow fan having three blades is reduced by about 22% in consumption electrical power required for operation.  
         [0033]     However, when the axial flow fan  40  is driven, a slip stream or wake component is generated at the L.E and T.E of the leading blade  44 , and a turbulent flow component is generated by separation on a negative pressure surface. These two components have influence on the trailing blade  44 , thus deteriorating the performance of the axial flow fan  40 , and simultaneously generating the noise by a turbulent flow.  
       SUMMARY OF THE INVENTION  
       [0034]     Therefore, an objective of the present invention is to design an axial flow fan within an optimal design range capable of suppressing increase in intensity of a turbulent flow generated from a surface of each blade, increase in thickness of a boundary layer on the surface of each blade and disturbance of an airflow within a region of the hub.  
         [0035]     It is another objective to provide an axial flow fan capable of remarkably reducing a noise within the predetermined frequency range (between about 300 Hz and about 1000 Hz) with respect to the same air volume as the conventional axial flow fan.  
         [0036]     To achieve the above objective, the present invention provides an axial flow fan comprising a hub connected with a rotational shaft of a motor; and at least one blade contacting the hub, wherein the blade has a part from the hub to a predetermined portion of the blade among a whole part from the hub to an outer end of the blade, and the other part from the predetermined portion of the blade to the outer end of the blade, the part being equally applied at a predetermined rake angle, and the other part being raised in a direction of a pressure surface of the blade.  
         [0037]     Further, the axial flow fan has a ratio of an inner diameter and an outer diameter of the axial flow fan between about 0.35 and about 0.4.  
         [0038]     Therefore, according to the present invention, the axial flow fan can reduce the noise as low as possible and increase the pressure coefficient and the constant pressure efficiency compared to the conventional axial flow fan. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0039]     The above objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:  
         [0040]      FIG. 1  schematically shows a general air conditioner;  
         [0041]      FIG. 2  is a perspective view illustrating a general split type air conditioner;  
         [0042]      FIGS. 3A and 3B  are front and side views of a conventional axial flow fan, respectively;  
         [0043]      FIG. 4  is a graph showing comparison of relation between a pressure coefficient and a flow rate coefficient in a conventional axial flow fan with that of another conventional axial flow fan;  
         [0044]      FIG. 5  is a graph showing comparison of relation between constant pressure efficiency and a flow rate coefficient in a conventional axial flow fan with that of another conventional axial flow fan;  
         [0045]      FIGS. 5A and 5B  are front and side views of an axial flow fan according to the present invention, respectively;  
         [0046]      FIGS. 7A and 7B  show a state where blades are tilted on an outer circumferential surface of a hub at a certain rake angle in axial flow fans according to the prior art and the present invention;  
         [0047]      FIG. 8  is a graph showing a state where a noise is changed according to a change of a solidity with respect to axial flow fans of the prior art and the present invention;  
         [0048]      FIG. 9  is a graph showing a state where a noise is changed according to a change of a quantity of a camber with respect to axial flow fans of the prior art and the present invention;  
         [0049]      FIG. 10  is graph showing relation between a (constant) pressure coefficient, a constant pressure efficiency and a flow rate coefficient with respect to axial flow fans of the prior art and the present invention; and  
         [0050]      FIG. 11  is a graph showing comparison of a state where a noise is changed according to a change of a frequency of an axial flow fan of the present invention with that of an axial flow fan of the prior art. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0051]     An exemplary embodiment of the present invention will now be described with reference to the accompanying drawings.  
         [0052]      FIGS. 6A and 6B  are front and side views of an axial flow fan according to the present invention, respectively.  FIGS. 7A and 7B  show a state where blades are tilted on an outer circumferential surface of a hub at a certain rake angle in axial flow fans according to the prior art and the present invention.  
         [0053]     An axial flow fan  140  of an outdoor unit of an air conditioner according to the present invention is composed of a hub  142  connected with a rotational shaft  141  of a motor, and a plurality of blades  144  integrally formed on an outer circumferential surface of the hub  142 .  
         [0054]     The axial flow fan  140  is configured so that the number of the blades is two, that a ratio of an inner diameter to an outer diameter (i.e. a ratio of the outer diameter of the hub and the outer diameter of the fan) is between about 0.35 and about 0.4, that a solidity, a ratio of the whole area of the fan  140  and an area of the blades, has a range of 0.85±0.05, and that a quantity of a camber of the hub  142  has a range of 5.0%±1.0%.  
         [0055]     Hereinafter, a detailed description will be made on the axial flow fan of the outdoor unit of the air conditioner according to the present invention.  
         [0056]     Meanwhile, when the axial flow fan  140  is driven, a slip stream or wake component may be generated at a leading edge (L.E) and a trailing edge (T.E) of the leading blade  144 , and a turbulent flow component may be generated by separation on a negative pressure surface. These two components may have influence on the trailing blade  144 , thus deteriorating performance of the axial flow fan  140 , and simultaneously generating a noise by a turbulent flow. Thus, the present invention aims at preventing the drawbacks of the axial flow fan  140 .  
         [0057]     Further, the present invention is to suppress increase in intensity of the turbulent flow generated from a surface of each blade  144 , increase in thickness of a boundary layer on the surface of each blade  144 , and disturbance of an airflow within a region of the hub  142 .  
         [0058]     In order to accomplish the objectives, the axial flow fan  140  is formed so that the number of the blades  144  is two, that the ratio of the inner diameter to the outer diameter (i.e. the ratio of the outer diameter of the hub and the outer diameter of the axial flow fan) is between about 0.35 and about 0.4, that the solidity, the ratio of the whole area of the fan  140  and the area of the blades, has the range of 0.85±0.05, and that the camber quantity of the hub  142  has the range of 5.0%±1.0%. With regard to this, the detailed configuration of the present invention is as follows.  
         [0059]     The axial flow fan  140  of the outdoor unit of the air conditioner according to the present invention, as shown in  FIG. 6A , is composed of the hub  142  connected with the rotational shaft  141  of the motor, and the plurality of blades  144  integrally formed on the outer circumferential surface of the hub  142 .  
         [0060]     Here, the number of the blades  144  is set to two. The inner and outer diameter ratio of the axial flow fan  140 , i.e. the ratio of the outer diameter of the hub  142  and the outer diameter of the axial flow fan  140 , is set to a range between about 0.35 and about 0.40.  
         [0061]     Further, the ratio of the whole area of the axial flow fan  140  and the area of the blades, i.e. the solidity, has the range of 0.85±0.05, and the camber quantity of the hub  142  has the range of 5.0%±1.0%. The solidity can be expressed by the following formula. 
 
Solidity=(chord× Z )/2 πr  
 
 where 2πr: circumference length when a radius is r, chord: straight line joining the L.E of the blade with the T.E of the blade, Z: the number of blades. 
 
         [0063]     Thus, a value of the solidity presented in the present invention may become a mean value from the hub and a tip, for example, an integral value.  
         [0064]     For the axial flow fan  140 , as shown in  FIGS. 7A and 7B , a rake base line of each blade  144  formed on the outer circumferential surface of the hub  142  is tilted from that formed horizontal to the outer circumferential surface of the conventional hub  42  by a rake angle between about 20 degrees and about 23 degrees. Here, the rake angle refers to an angle determining how much to tilt and form the blades  144  on the circumferential surface of the hub  142 .  
         [0065]     As for a state where the blades  144  are formed on the outer circumferential surface of the hub  142  through the rake angle, as shown in  FIGS. 7A and 7B , among the whole length from the outer circumferential surface of the hub  142  to the outer end (i.e. tip) of each blade  144 , a part from the outer circumferential surface of the hub  142  to a predetermined portion of each blade  144  is tilted at the rake angle, and the other part from the predetermined portion of each blade  144  and the tip of each blade  144  is provided with a bulge  146  protruded toward a pressure surface. The tip of each blade  144  has the same angle as the rake angle from the outer circumferential surface of the hub  142  to the predetermined portion of each blade  144 . In this manner, a profile of the axial flow fan  140  is formed as a whole.  
         [0066]     In other words, when the section from the outer circumferential surface of the hub to the tip of each blade is divided into two sections, the first section performs rotational displacement at the identical angle, and the second section forms a non-linear angle raised toward the pressure surface. The tip (i.e. a section except for the two sections) is adapted to apply an identical value of the first section.  
         [0067]     At this point, the outer diameter D of the axial flow fan is 460±2 mm, and the outer diameter d of the hub  142  is 170±2 mm.  
         [0068]     Here, a pitch angle, a peak point of a camber, and a sweep angle of each blade  144  are the same as the pitch angle β, the peak point of the camber P, the maximum quantity of the camber MC, and the sweep angle α of the conventional blade  44  shown in  FIGS. 3A and 3B . Now, the pitch angle, the peak point of the camber, and the sweep angle of each blade  144  will be described in detail below.  
         [0069]     The pitch angle β of each blade  144  is configured to be linearly changed from the hub  142  to the end of the blade  144  within a range between 37 degrees and 20 degrees.  
         [0070]     Each blade  144  is configured so that the peak point of the camber P is formed at a position corresponding to 70% of a length of a chord in a direction from the front end of the blade to the rear end of the blade, and that the maximum quantity of the camber MC is kept constant at a value of 0.5% within each radius from the hub  142  to the end of the blade  144 .  
         [0071]     Furthermore, the sweep angle α of each blade  144  has a range between about 47 degrees and about 49 degrees when a dimensionless radius coordinate is less than 0.3 and is linearly increased when the dimensionless radius coordinate exceeds 0.3 to have a range between about 55 degrees and about 57 degrees at the end of the blade.  
         [0072]     A change of the noise generated from the axial flow fan configured as set forth above will be described below.  
         [0073]      FIG. 8  is a graph showing a state where a noise is changed according to a change of a solidity with respect to axial flow fans of the prior art and the present invention.  FIG. 9  is a graph showing a state where a noise is changed according to a change of a quantity of a camber with respect to axial flow fans of the prior art and the present invention.  FIG. 10  is graph showing relation between a (constant) pressure coefficient, a constant pressure efficiency and a flow rate coefficient with respect to axial flow fans of the prior art and the present invention.  FIG. 11  is a graph showing comparison of a state where a noise is changed according to a change of a frequency of an axial flow fan of the present invention with that of an axial flow fan of the prior art.  
         [0074]     As seen from the foregoing description and the drawings, the solidity applied to the present invention has a range of 0.85±0.05 and the camber quantity of the hub has a range of 5.0%±1.0%.  
         [0075]     In contrast, the solidity applied to the prior art (Z=3) has a relatively great value compared to that of the present invention, and the camber quantity of the hub has a relatively small value.  
         [0076]     The following description will be made with reference to  FIGS. 10 and 11 .  
         [0077]     In the graph of  FIG. 10 , an upper line shows a comparison of relation of the (constant) pressure coefficient and the flow rate coefficient in the axial flow fan  140  with that of the conventional axial flow fan  40 , while a lower line shows a comparison of relation of the constant pressure efficiency and the flow rate coefficient in the axial flow fan  140  with that of the conventional axial flow fan  40 .  
         [0078]     For the axial flow fan  140  according to the present invention, the noise change was measured depending on the change of the solidity as the ratio of the whole area of the fan  140  to the area of the blades. It was found that as a result of the measurement, as shown in  FIG. 8 , when the ratio of the whole area of the fan  140  to the area of the blades, i.e. the solidity, was about 0.87, the noise was the lowest. Further, the noise change was measured depending on the change of the camber quantity of each blade of the axial flow fan  140 . It was found that as a result of the measurement, as shown in  FIG. 9 , when the camber quantity of the blade  144  was about 0.5%, the noise was lowest.  
         [0079]     For the axial flow fan  140  according to the present invention, it can be seen that as shown in  FIG. 10 , the pressure coefficient and the constant pressure efficiency were enhanced over the conventional axial flow fan  40 , and that the operation efficiency was also enhanced at the operation point according to the enhancement of the pressure coefficient and the constant pressure efficiency of the axial flow fan  140  as set forth above.  
         [0080]     Further,  FIG. 11  is a graph showing comparison of a state where a noise is changed according to a change of a frequency of an axial flow fan of the present invention with that of an axial flow fan of the prior art. As shown in  FIG. 11 , it can be seen that when having an air volume equal to that of the conventional axial flow fan  40 , the axial flow fan  140  was subjected to great reduction of the noise in a range between about 300 Hz and about 1000 Hz.  
         [0081]     As set forth above, the present invention relates to the axial flow fan configured so that the number of the blades is two, that a predetermined rake angle is kept constant in the part from the hub to the predetermined portion of the blade among the whole part from the hub to the outer end of the blade and is increased in the pressure surface direction in the other part from the predetermined portion of the blade to the outer end of the blade, and the ratio of the inner diameter to the outer diameter is between about 0.35 and about 0.4.  
         [0082]     Therefore, the axial flow fan of the present invention is designed within an optimal design range (that the solidity, the ratio of the whole area of the axial flow fan and the area of the blades, is about 0.87 and that the camber quantity of the hub is about 5.0%), for example, capable of suppressing increase in intensity of the turbulent flow generated from the surface of each blade, increase in thickness of the boundary layer on the surface of each blade and disturbance of the airflow within the region of the hub. As a result, the axial flow fan of the present invention can reduce the noise as low as possible and increase the pressure coefficient and the constant pressure efficiency compared to the conventional axial flow fan.  
         [0083]     Further, the axial flow fan of the present invention can remarkably reduce the noise within the predetermined frequency range (e.g. between about 300 Hz and about 1000 Hz) with respect to the same air volume as the conventional axial flow fan.  
         [0084]     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.  
         [0085]     For example, the axial flow fan of the present invention may be applied to a refrigerator or other apparatuses for condensing and evaporating a refrigerant.  
         [0086]     Therefore, the above-mentioned description is simply illustrative but not intended to restrict the invention by limitations of the claims.