Abstract:
The present disclosure provides an improved rotor of a centrifugal compressor. The rotor includes a blade arrangement and geometry that increase the overall efficiency of the rotor. In particular, blades within the rotor are curved and inclined in a manner that improves the overall efficiency of the rotor. The present disclosure also provides a method of manufacturing the improved rotor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 60/934,886, filed Jun. 14, 2007, which application is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to an improved rotor of a centrifugal compressor and a method for manufacturing a rotor. 
       BACKGROUND 
       [0003]    A centrifugal compressor utilizes rotors, also known as impellers, to impart to a fluid (typically air) the energy necessary to change the pressure of the fluid. The rotor of a common type of centrifugal compressor includes a number of blades, also known as vanes, disposed radially between a doughnut-shaped cap, also known as a shroud, and a circular base, also known as a hub. The blades, cap, and base of such a rotor are arranged to form fluid flow passages within the rotor that converge towards the center of the rotor. 
         [0004]    When the above-described rotors are rotated at high speeds, they can generate high pressures and temperatures. These rotors preferably have high rotational and structural stability (e.g., strength, balance), high heat resistance, high efficiency, and also are relatively easy to manufacture. These design constraints are particularly significant as the size of the rotors increases, because the stresses on the rotors increase as the size of the rotors increases. 
         [0005]    Attempts have been made to improve the dynamic performance of such rotors by changing the geometry and/or arrangement of the blades within the rotors. For example, U.S. Pat. No. 6,729,845 to Rossi discloses the use of curved blades within the rotor. Attempts have also been made to improve the methods of manufacturing such rotors. For example, U.S. Pat. No. 6,276,899 to Lambert et al. discloses a method of welding together rotor components; U.S. Pat. No. 6,976,828 to Godichon et al. discloses a method of bolting together rotor components; US 2002/0051707 to Takahashi et al. discloses a method of molding a rotor; and U.S. Pat. No. 7,305,762 to Mola and U.S. Pat. No. 6,676,826 to Battistini et al. disclose methods of machining a rotor. Notwithstanding these advances, further improvements in the design, construction, and overall performance of centrifugal compressor rotors are desirable. 
       SUMMARY 
       [0006]    An object of the present disclosure is to provide an improved rotor of a centrifugal compressor. The improved rotor includes a blade arrangement and geometry that increase the overall effectiveness of the rotor. The rotor in some embodiments of the invention includes uniquely shaped curved airfoil blades. In other embodiments the rotor includes a unique arrangement of shorter and longer blades. Another object of the present disclosure is to provide an improved method for production of a rotor involving molding a rotor of a synthetic resin. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0007]      FIG. 1  is a perspective view of an embodiment of a rotor according to the principles of the present invention; 
           [0008]      FIG. 2  is a perspective view of a single-stage centrifugal compressor; 
           [0009]      FIG. 3  is a side view of a multi-stage centrifugal compressor; 
           [0010]      FIG. 4  is a perspective cross-sectional view of  FIG. 2  showing the rotor of  FIG. 1  within the compressor; 
           [0011]      FIG. 5  is a side cross-sectional view of  FIG. 2  showing the rotor of  FIG. 1  within the compressor; 
           [0012]      FIG. 6  is an assembly view of the compressor of  FIG. 2 ; 
           [0013]      FIG. 7  is a side view of the rotor of  FIG. 1 ; 
           [0014]      FIG. 8  is a side cross-sectional view of the rotor of  FIG. 7 ; 
           [0015]      FIG. 9  is a cross-sectional view of the rotor of  FIG. 7  along line B-B; 
           [0016]      FIG. 10  is a cross-sectional view of a primary blade of the rotor of  FIG. 7 ; and 
           [0017]      FIG. 11  is a cross-sectional view of a secondary blade of the rotor of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The principles of the present disclosure are described herein with reference to the figures. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
         [0019]    Referring to  FIG. 1 , a rotor  10  for a centrifugal compressor according to the principles of the present disclosure is shown. The rotor includes a number of blades  12  arranged between a cap  14  and a hub  16 . The cap  14  includes a center aperture, which defines an inlet  18  for receiving fluid (e.g., air). The fluid received through the inlet  18  is accelerated by the rotor and discharged through the outlets  20  located along the periphery of the rotor  10 . 
         [0020]    Referring to  FIGS. 2-7 , the rotor  10  is shown in the context of industrial sized centrifugal compressors  22 ,  24 . Centrifugal compressors have a wide range of applications (e.g., vacuum systems, transporting natural gas through pipelines, pressurizing cabins of aircrafts, turbo charging engines, compressing fluids in refrigeration, etc.). However, for description purposes, the rotor  10  will be described herein in the context of an industrial sized centrifugal compressor that is configured to be used in a pneumatic conveyor. Pneumatic conveyors are machines that are commonly used to unload grain (and other flowable materials) from storage facilities, trucks, rail cars, barges, large ships, and in-plant applications. Pneumatic conveyors are available from http://www.christianson.com/. It should be understood that alternative embodiments of the rotor of the present disclosure and related method can be used in numerous other types of industrial and non-industrial centrifugal compressors. 
         [0021]      FIG. 2  is a perspective view of a single-stage centrifugal compressor  22 . The single stage compressor  22  includes a body  30  with an intake  26  and a discharge  28 . A single rotor  10  is supported within the body  30  of the centrifugal compressor  22 .  FIG. 3  is a side view of a multi-stage centrifugal compressor  24 . The multi-stage centrifugal compressor  24  also includes a body  32  with an intake  34  and a discharge  36 . In the depicted embodiment multi-stage centrifugal compressor  24  is a four-stage centrifugal compressor. In other words, four rotors  10  are housed within the body  32 . The four rotors  10  are arranged such that they work together to compress fluid that passes through the multi-stage compressor  24 . As discussed above, it should be appreciated that many rotor arrangements are possible (e.g., different sizes and geometric configurations). However, for the purposes of this description, the depicted rotor  10  will be described herein with reference to the single-stage centrifugal compressor  22 . 
         [0022]    Referring to  FIGS. 4-6 , the rotor  10  is shown mounted within the single stage centrifugal compressor  22 . The body  30  of the single-stage compressor includes a main housing structure  40  and a base  42 , which are configured to house the rotor  10 . The main housing structure  40  includes an inlet  26  shown attached to an inlet tube  44  which is used to direct fluid into the body  30  of the compressor  22  towards the rotor  10 . The main housing structure  40  also includes the fluid outlet  28  for discharging the pressurized fluid. It should be appreciated that the main housing structure  40  can be constructed of any strong material (e.g., metal or composite material). 
         [0023]    In the depicted embodiment, the main housing structure  40  is shown bolted to the base  42 . The base  42  is configured to support a bearing assembly, which in turn supports the drive shaft  46  that mounts to the rotor  10 . The drive shaft  46  connects the rotor  10  to the motor output  48 . In the depicted embodiment, the drive shaft  46  bolts to the rotor  10  and is supported by a flange bearing  50 , a pillow block bearing  52 , and a coupler  54 . The flange bearing  50  and pillow block bearing  52  are shown directly mounted to the base  42 , and the coupler  54  is supported on the base  42  via a bracket  56 . It should be appreciated that alternative configurations of the single-stage compressor  22  are possible. 
         [0024]    Still referring to  FIGS. 4-6 , when the rotor  10  is rotated within the body  30  in a first direction, the fluid (e.g., air) is moved from the inlet  26  to the outlet  28 . When the rotor  10  is rotated at high speeds (e.g., 5000 rpm) a pressure differential is created between the inlet  26  and the outlet  28 . The pressure differential that can be generated using the rotor  10  of the present disclosure is unexpectedly much greater than the pressure differential that can be generated with prior art rotors driven by a motor with the same horsepower rating. The chart below illustrates the pressures that are generated by the rotor  10  under various conditions. 
         [0000]                                                                              PSIA                   CFM   (pounds-   WC       HP   HG   (cubic   force per   (inches of       (horse   (inches of   feet per   square inch   water       power)   mercury)   minute)   absolute)   column)                                75   23.98   3246   2.92156   325       100   24.12   4458   2.851666   327       150   24.63   7285   2.60255   334       200   25.38   10115   2.23345   344       250   26.38   12942   1.74495   358               1 PSI = 27 Inches in WC       14.7 PSI = 408 Inches in WC = 29.29 HG       HG = (WC/27.68)*2.04       WC = (HG/2.04)*27.68            
Comparable size centrifugal compressors with prior art rotors generate significantly less pressure when driven by the same size motor at similar speeds. In the typical pneumatic conveyor embodiment the rotor  10  has high tail/tip speeds due to its relatively large size. For example, if the diameter of the rotor is 27 inches at 5000 RPM the tail of the blades have a linear velocity of about 589 ft/sec (27 in*1 foot/12 inches*3.14*1 minute/60 sec*5000 rpm). At 4000 rpm the linear velocity of the tails are about 471 ft/sec.
 
         [0025]    Finite element analysis (FEA) was used as a tool in the geometric design process of the rotor  10 . FEA is a computer simulation technique used in engineering analysis that applies a numerical technique called the finite element method (FEM). The FEA tool was used by the inventors to test the geometry and arrangement of unusual shaped and arranged blades. The geometry of an embodiment of the rotor  10  is described below in further detail. 
         [0026]    Referring to  FIGS. 7-9 , the rotor  10  is shown in greater detail.  FIG. 7  is a side view of the rotor  10 . As discussed above, the rotor includes a number of blades  12  arranged between a cap  14  and a hub  16 . The rotor  10  is configured to receive air through the inlet  18  and discharge air through the outlets  20  located along the periphery of the rotor  10 . 
         [0027]    A seal helps to maintain a pressure differential between the input and the output regions of the rotor  10 . More particularly, the cap  14  includes a neck  60  which forms a seal with the intake  26  of the body  30 . The neck  60  includes an annular groove  62  shown in  FIG. 8 , which is a cross-sectional view of the rotor  10  of  FIG. 7 . The hub  16  includes a central drive shaft mount  64  that includes a recess and holes  66  that are configured to receive a portion of the drive shaft  46 . In the depicted embodiment the blades  12  include a set of longer primary blades  68  and shorter secondary blades  70 . 
         [0028]    In the depicted embodiment, the primary blades  68  are interspersed with secondary blades  70 . Both the primary blades  68  and secondary blades  70  generally extend from the periphery edge of the rotor  10  towards the center of the rotor  10 . In the depicted embodiment the diameter of the rotor  10  is about 27 inches (R1=13.5 inches) and the diameter of the inlet  18  is about 10 to 11 inches (R2=5 to 5.5 inches). The primary blades  68  extend from the periphery edge to about 5-7 inches from the center of the hub  16 , and the secondary blades  70  extend from the periphery edge to about 8-10 inches to the center of the hub  16 . More particularly, the twelve secondary blades  70  extend to line DD, which is about 8-9 inches (e.g., 8.5 inches) from the center of the hub  16 , and the twelve primary blades  68  extend to line EE, which is about 5-7 inches (e.g., 6 inches) from the center of the hub  16  (i.e., the rotational axis of the rotor  10 ). In the depicted embodiment the primary and secondary blades  68 ,  70  are approximately evenly spaced apart on the hub  16 . It should be appreciated that alternative embodiments may include more or less blades. For example, one alternative embodiment could include ten blades and another alternative embodiment could include fifteen blades. 
         [0029]    In the depicted embodiment, line AA passing through a tip  95  and a tail  82  of a primary blade  68  is disposed at an angle t between about 10-20 degrees from a dashed line shown passing through the tail  82  of the blade  68  and the center of the hub  16 . The tip  95  is located on the proximal end of the blade  68  and the tail  82  is located on the distal end of the blade  68 . More particularly, the angle α is as shown between about 14-16 degrees. Generally, this configuration may be referred to as an example of a backward inclined configuration. In the depicted embodiment, the line AA passes primarily outside of the primary blade  68  because the primary blade is curved. The angle α describes the orientation of the blade as a whole and not necessarily the orientation of any particular part of the blade  68 . Line CC passes through the center of the proximal fourth of the blade and is disposed at an angle β between about 120 degrees to about 140 degrees relative to the line passing through the tip  95  of the blade  68  and the center of the hub  16 . More particularly, the angle β is between about 125 degrees to about 135 degrees. 
         [0030]    The line BB passing through the tip  84  and tail  86  of a secondary blade  70  is disposed at an angle γ between about 5 degrees to about 10 degrees from a line passing though the center of the hub  16  to the tail  86  of the secondary blade  70 . More preferably, the angle γ is between about 6 degrees to 8 degrees. In the depicted embodiment the angle α is greater than the angle γ. In other words, the primary blades  68  are more inclined than the secondary blades  70 . Also, angle β+α is less than 180 degrees, in other words, the first portion of the primary blade  68  is more inclined than the blade as a whole. It should be appreciated that in alternative embodiments of the invention the above angles can vary outside of the above example ranges. 
         [0031]    In the depicted embodiment the profile of one of the primary blades  68  can be described by a line connecting the following Cartesian coordinates of the referenced points, provided first in inches: 90 (9.36, 0.143); 91 (7.450, 1.058); 92 (6.54, 1.555); 93 (6.093, 1.834); 94 (5.875, 1.990); 95 (5.699, 2.302). The polar coordinates of the referenced points in degrees and inches are as follows: 90 (9.36, 2.55°);  91  (7.525, 8.08°); 92 (6.722, 13.37°); 93 (6.363, 16.75°); 94 (6.203, 18.72°); 95 (6.146, 22.00°). The polar coordinates above expressed in terms of R are as follows: 90 (R9.36/13.5, 2.55°); 91 (R7.525/13.5, 8.08°); 92 (R6.722/13.5, 13.37°); 93 (R6.363/13.5, 16.75°); 94 (R6.203/13.5, 18.72°); 95 (R6.146/13.5, 22.00°). In the depicted embodiment the radius R of the rotor is about 13.5 inches. Though the geometry and layout of a primary and secondary blade  68 ,  70  are described in particular detail herein, it should be appreciated that many other blade configurations and arrangements are also possible. For example, in an alternative embodiment the R coordinates at the various angles might vary by +/−0.04 or more. More preferably, the R coordinates might vary by +/−0.02 or less. The numerical value for R itself may also vary. For example, in some embodiments the R value is between about 11-15 inches, and in other embodiments the R value is between about 12-14 inches. 
         [0032]    Referring to  FIG. 10 , the geometry of a primary blade  68  is shown in greater detail. The blade geometry is described herein with reference to an upper curve (line  80 - b ) and a lower curve (line  80 - c ). Generally, the blade geometry may be referred to as an example of a blade that bears similarity to an airfoil. In  FIG. 10 , the tip  80  of the primary blade  68  has been oriented over point (0.0,0.0) on a Cartesian coordinate system, and the midpoint of the tail end of the blade  68  (i.e., the point between points b and c) has been oriented on the X axis. The chart below provides the approximate coordinates for the referenced points. The coordinates are provided in inches and dimensionless as a function of L, wherein L is the distance between the tip  80  and tail end of the primary blade  68 . 
         [0000]                                                                          X       Y       Reference   X (L)   (inches)   Y (L)   (inches)                                80   0   0   0L         0       b   L   8.081   0.00965L   0.078 +/− 30%       c   L   8.081   −0.00965L    −0.078 +/− 30%        d   L/2   4.040   0.10345L   0.836 +/− 30%       e   L/2   4.040   0.04925L   0.398 +/− 30%       f   L/4   2.020   0.09045L   0.731 +/− 30%       g   L/4   2.020   0.02710L   0.219 +/− 30%       h   3L/4   6.061   0.06694L   0.541 +/− 30%       i   3L/4   6.061   0.03068L   0.248 +/− 30%       j   L/8   1.010   0.06138L   0.496 +/− 30%       k   L/8   1.010   0.00371L   0.030 +/− 30%       l   L/16   0.505   0.04282L   0.346 +/− 30%       m   L/16   0.505   −0.008786L   −0.071 +/− 30%        n   L/32   0.253   0.03143L   0.254 +/− 30%       o   L/32   0.253   −0.009405L   −0.076 +/− 30%        p   L/4   2.020   0.05878L   0.475 +/− 30%       q   3L/4   6.061   0.04889L   0.395 +/− 30%       r   0.4102L   3.315   0.10642L   0.860 +/− 30%       s   0.4981L   4.025   0.00493L   .0399 +/− 30%                    
With the exception of points p and q, all the above points are along the upper and lower curves that define the geometry of the depicted primary blade  68 . Points p and q are used to define the lines bisecting the end portions of the primary blade  68 . It should be appreciated that the above coordinates describe a particular geometry that can vary in alternative embodiments of the invention. For example, in an alternative embodiment of the invention one or more of the Y coordinates might vary by as much as 30 percent or even more. For example, the Y coordinates at reference b can be between about 0.0546-0.1014 (i.e., 0.078−0.3*0.078 and 0.078+0.3*0.078), more preferably, the Y coordinates vary 10 percent or less. The L value can also vary. For example, in some embodiments the L value is between 6-10 inches. In other example embodiments the L value is between 7-9 inches. It should be appreciated that in alternative embodiments of the invention, the above coordinates and L values can vary even outside of the above example ranges.
 
         [0033]    In the depicted embodiment the angle δ is the angle defined between the line that bisects the front and rear portions of the primary blade  68 . The line that bisects the front of the blade passes through point  80  and point p, and the line that bisects the rear portions of the blade passes through the end of the primary blade between points b and c and through point q. The point q is ¾ the length of the blade and approximately midway between points h and i (vertically). Similarly, point p is ¼ the length of the blade and approximately midway between points f and g (vertically). As included in the chart below, the angle δ in the depicted embodiment is about 155.72°. It should be appreciated that in alternative embodiments the angle δ may be greater than or less than 155.72°. For example, the angle δ may in some embodiments range from 145-165 degrees. 
         [0000]                                            References   Measures                           δ_the angle defined between the line   155.72°           that bisects the front and rear ends of           the primary blade           Distance along line 80-b   8.3792 inches (1.037L)           Distance along line 80-c   8.1754 inches (1.012L)           Distance along line 80-r (where r is   3.5183 inches (0.435L)           the point of inflection on line 80-b)           Distance along line 80-s (where s is   4.1100 inches (0.509L)           the point of inflection on line 80-c)                        
The above chart compares the length of the upper curve (line  80 - b ) and the lower curve (line  80 - c ). The upper curve is longer than the lower curve. In the depicted embodiment, the length of the upper curve (line  80 - b ) is about 102 percent longer than the length of the lower curve (line  80 - c ). The above chart also describes the relative lengths of the curves in terms of L, which, as discussed above, is the distance between the tip  80  and tail end of the primary blade  68 . The chart above also provides data describing how and where blades  68  bend. In the depicted embodiment the inflection point (i.e., the point where the slope changes) of the upper curve is forward (towards the tip) in comparison to the inflection point of the lower curve. The location of the inflection point of the upper curve is about 3.5183/8.3792 (0.42) towards the front end of the upper curve, whereas the location of the inflection point of the lower curve is about midway at about 4.1100/8.1754 (0.50) of the length of the lower curve. It should be appreciated that in alternative embodiments of the invention the data can vary even outside of the above example ranges.
 
         [0034]    Referring to  FIG. 11 , the geometry of a secondary blade  70  is shown in greater detail. The blade geometry is described by an upper curve (line  84 -B) and a lower curve (line  84 -C). Generally, the geometry may be referred to as an example of an airfoil geometry. In  FIG. 11 , the tip  84  of the secondary blade  68  has been positioned over point (0.0,0.0) on a Cartesian coordinate system, and the midpoint of the tail end of the blade  70  (i.e., the point between points B and C) has been positioned on the X axis. The chart below provides the approximate coordinates for the referenced points. The coordinates are provided in inches and dimensionless as a function of LL, wherein LL is the distance between the tip  84  and tail end of the primary blade  70 . It should be appreciated that in alternative embodiments of the invention the above coordinates and LL values can vary. For example, in an alternative embodiment of the invention one or more of the Y coordinates might vary by as much as 30 percent or even more. 
         [0000]                                                                          X       Y       Reference   X (LL)   (inches)   Y (LL)   (inches)                                84   0   0   0LL   0       B   LL   3.869   0.0189LL +/− 30%   0.073       C   .998LL   3.861   −0.0189LL +/− 30%    −0.073       D   LL/2   1.935   0.0050LL +/− 30%   0.0195       E   LL/2   1.935   −0.0180LL +/− 30%    −0.070       F   LL/4   0.967   0.0535LL +/− 30%   0.207       G   LL/4   0.967   −0.0264LL +/− 30%    −0.102       H   3LL/4   2.902   0.0383LL +/− 30%   0.148       I   3LL/4   2.902   −0.0178LL +/− 30%    −0.069       J   LL/8   0.484   0.0051LL +/− 30%   0.198       K   LL/8   0.484   −0.0036LL +/− 30%    −0.141       L   LL/16   0.242   0.0406LL +/− 30%   0.157       M   LL/16   0.242   −0.0341LL +/− 30%    −0.132       N   LL/32   0.121   0.0292LL +/− 30%   0.113       O   LL/32   0.121   −0.0276LL +/− 30%    −0.107       P   LL/4   0.967   0.0137LL +/− 30%   0.053       Q   3LL/4   2.902   0.0101LL +/− 30%   0.039                    
With the exception of points P and Q, all the above points are along the upper and lower curves that define the geometry of the secondary blade  70 . Points P and Q are to define the lines bisecting the end portions of the secondary blade  70 . In the depicted embodiment the angle θ is the angle defined between the line that bisects the front and rear portions of the secondary blade  70 . The line that bisects the front of the blade passes through point  84  and point P, and the line that bisects the rear portions of the blade passes through the end of the secondary blade between points B and C and through point Q. The point Q is ¾ the length of the blade and approximately midway between points H and I (vertically). Similarly, point P is ¼ the length of the blade and approximately midway between points F and G (vertically). As included in the chart below, the angle θ in the depicted embodiment is about 174.56°, which indicates that the blade is almost straight (straight would be 180°). It should be appreciated that in alternative embodiments of the invention the angle θ, the angle defined between the line that bisects the front and rear ends of the secondary blade values, can vary. In the depicted embodiment the secondary blades  70  are straighter than the primary blades  68 . The secondary blade  70  is about 48% percent ( 3.896/8.081) the length of the primary blade  68 . As discussed above, though precise numerical values and ratios have been referenced in the description of the blades, it should be appreciated that the values and ratios are not meant to be absolute and limiting. Alternative embodiments of the invention may include numerous modifications to the above provided blade geometries.
 
         [0035]    The rotor  10  in one embodiment is molded from a synthetic resin. In one embodiment the resin used is commonly referred to as a Neat Resin. The Neat Resin can be, for example, RTM VE441 OFG which has a tensile strength of 13,000 psi, flexural strength of 24,000 psi, flexural modulus of 510,000 psi, and heat distortion temperature at 264 psi of 245 degrees F. For high temperature environments the Neat Resin can be, for example, RTM EP8606 OFG which has a tensile strength of 9,300 psi, flexural strength of 15,000 psi, flexural modulus of 390,000 psi, and Glass Transition Temperature of 344 degrees F. The rotor  10  can be molded as one piece by using a wax core molding process. The process involves using a first mold to form a wax core in the shape of the empty space inside the rotor  10 . Fibers are then placed into a second mold around the wax core, wherein the second mold is in the shape of the outer surfaces of the rotor  10 . Subsequently, resin is injected into the second mold to impregnate the fibers therein. After the resin is cured, the wax core is melted out from within the rotor  10 . 
         [0036]    The above specification, examples, and data provide a complete description of the manufacture and design of a rotor embodying the principles of the present disclosure. Since many alternative embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.