Claims:We claim:
1. A 3D impeller of centrifugal compressor with low flow coefficient ranging from 0.035 to 0.029 for compressing fluid with high aerodynamic efficiency, the 3D impeller comprises:
a rotor; 5
a hub disc (1) connected to the rotor, wherein the hub disc is covered by a shroud disc (3);
a plurality of blades radially protruding from the hub disc (1) and spaced equidistantly on circumference of the hub disc (1), wherein the plurality of blades are disposed between the hub disc (1) and the shroud disc (3); and 10
wherein blade angle distribution at inlet and exit of impeller at the hub disc (1) is (-) 60o deg. and (-) 55o deg. respectively with maximum angle location is at 55% of meridional flow path length.
2. The 3D impeller of centrifugal compressor stage as claimed in claim 1, wherein impeller blade angle distribution at inlet and exit of impeller at the shroud 15 disc (3) is (-) 62.5o deg. and (-) 55o deg. respectively with maximum angle location is at 85% of the meridional flow path length.
3. The 3D impeller of centrifugal compressor stage as claimed in claim 1, wherein impeller wrap angle distribution at the shroud disc (3) decreases uniformly in range from 0.0o deg. to (-) 75o deg. and at the hub disc (1) is in range 20 from (-) 3.5o to (-) 57o deg.
4. The 3D impeller of centrifugal compressor stage as claimed in claim 1, wherein impeller shroud disc contours (4) slope varying uniformly in range from 7.0o deg. at inlet to 87o deg. at exit and the hub contours (2) slope varying uniformly in range from 17o deg. at inlet to 89o deg. at exit. 25
5. The 3D impeller of centrifugal compressor stage as claimed in claim 1, wherein the 3D impeller further comprises blade curvatures hub and shroud contours influences the blade loading, relative velocity distribution, pressure rise and there by efficiency. Variation in curvature that has resulted higher efficiency at hub and shroud surface 30
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6. The 3D impeller of centrifugal compressor stage as claimed in claim 1, wherein the 3D impeller further comprises impeller inlet hub radius with outer diameter in range of 315 mm to 630 mm as 37% - 39% of impeller outer diameter and inlet shroud radius as 60% - 62% of impeller outer diameter.
7. The 3D impeller of centrifugal compressor stage as claimed in claim 1, 5 wherein the 3D impeller further comprises impeller blade lean angle which is 10o deg at inlet and 25o deg at exit, wherein maximum of the impeller blade lean angle is at 25% and minimum is at 75% of the impeller meridional flow path length which has variation like sleeping "S" shape.
8. The 3D impeller of centrifugal compressor stage as claimed in claim 1, 10 wherein the 3D impeller further comprises impeller exit blade width “B2” which has outer diameter in range 315 mm to 630 mm as in range 3.5% to 3.85% of impeller exit diameter. , Description:SHROUDED 3D IMPELLER FOR MULTI-STAGE CENTRIFUGAL COMPRESSOR WITH LOW FLOW COEFFICIENT
FIELD OF INVENTION:
[001] The present subject matter described herein, relates to a 3D impeller of multi-stage centrifugal compressor with low flow coefficient and, in particular, to 5 impeller geometrical parameters along meridional flow path from impeller inlet to impeller exit. The present subject matter is more particularly relates to shrouded 3D impeller with low flow coefficient ranging from 0.035 to 0.029 of multi-stage centrifugal compressor.
BACKGROUND AND PRIOR ART: 10
[002] In general, 3D impeller of centrifugal compressors comprises two rotary discs, i.e., a disk and a shroud, and a plurality of vanes. The plurality of vanes is disposed between the disk and the shroud and substantially equidistantly in a circumferential direction to define the flow passage by means of the disk and the shroud and the vanes. The geometric configuration of rotor blading significantly 15 affects aerodynamic efficiency of the compressor, due to the fact that the geometric characteristics of the blade determine the distribution of the relative velocities of the fluid flow along the rotor, diffusion of fluid within the impeller, blade to blade loading at hub, shroud and intermediate planes, and flow passage area distribution that affect the flow behavior in the flow path and various internal 20 and the external losses.
[003] US patent no. US 6715991B2, dated 06/04/2004 titled “Rotor blade for centrifugal compressor with a medium flow coefficient” describes a cylindrical blade for a rotor of the purely radial type of impeller that is 2D in nature and typical coordinates with varying radius. Fig. 1 illustrates the design of impeller of 25 the present US patent. The suction and pressure surface of the vane referred a convex and concave surface respectively. The impeller blade geometry coordinates are fixed and are given in Cartesian co-ordinates in terms of impeller exit radius which is 200 mm.
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[004] US patent no. US 7563074 B2, dated 21/07/2009 titled “Impeller for a centrifugal compressor” describes impeller rotatable in a direction of rotation in a centrifugal compressor having an intake ring. Fig. 2 illustrates the impeller of present US patent. In the present US patent, the impeller is of open impeller without shroud disc generally of single stage of very high operating tip speed 5 generally suitable for turbo chargers. The impeller includes a back plate having a hub portion and a plurality of blades that extend from the back plate. Each blade includes a leading edge that extends radially outward along a non-linear path from adjacent the hub portion. Further it relates to centrifugal compressor impeller of open type without shroud surface for very high speed applications like turbo 10 charging.
[005] US patent no. US 5,158,435 dated 13/11/2012 titled “Impeller stress improvement through over-speed” describes a method for improving the capability of a body to withstand stress experienced during rotation by inducing at a selected location in the body a residual compressive stress which opposes the 15 steady tensile stress experienced at the selected location during rotation of the body. Fig. 3 illustrates cross section of the impeller. The present US patent is purely related to improving the impeller mechanical strength by inducing localized residual stresses in the impeller.
[006] US patent no. US 8,308,420 B2, dated 13/11/2012, titled “Centrifugal 20 compressor, impeller and operating method of the same” describes a centrifugal compressor is equipped with an impeller having a blade angle distribution that makes it possible to achieve a relatively wide operating range. The blade angle of a shroud side facing a circular plate of a blade is termed a first angle and a blade angle of a hub side disposed at the circular plate is a second. The shroud side is 25 formed in a curved shape having an angle distribution from a front area in a shaft direction toward a centrifugal direction in which the first angle is the local maximum point before a substantially middle portion and the local minimum point after the substantially middle point. The geometry is not defined neither in terms of coordinates nor in terms of parameterized form. Also the blade angle 30
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distribution, wrap angle distribution at various sections of blade from hub to shroud is not mentioned. Fig. 4 illustrates the blade angle distribution of the impeller at the inlet and exit of the blade.
[007] One of the main demands from all the industries is the high aerodynamic efficiency that needs to be achieved in all the stages of multi stage compressor 5 where the 3D impellers are employed. None of the above mentioned prior arts discusses about the efficiency improvement of 3D impeller and current efficiency levels achieved are not mentioned. It is required to improve the efficiency of 3D impeller of multi-stage centrifugal compressor which is very close to the theoretical efficiency by adopting proper impeller geometry. Therefore, it is 10 necessary to provide proper impeller geometry which provides high aerodynamic efficiency of working at all stages of the low flow coefficient 3D impeller of multi-stage compressor.
OBJECTS OF THE INVENTION:
[008] The principal objective of the present invention is to provide a geometrical 15 parameter, i.e., blade angle distribution of low flow coefficient 3D impeller along the meridional flow path from the impeller inlet to impeller exit to achieve high aerodynamic efficiency in multi-stage centrifugal compressor.
[009] Another object of the present invention is to provide geometrical parameter, i.e., blade wrap angle of low flow coefficient 3D impeller along the 20 meridional flow path from the impeller inlet to impeller exit to achieve high aerodynamic efficiency in multi-stage centrifugal compressor.
[0010] Another object of the present invention is to provide geometrical parameter, i.e., blade curvature at hub and shroud of low flow coefficient 3D impeller along the meridional flow path from the impeller inlet to impeller exit to 25 achieve high aerodynamic efficiency in multi-stage centrifugal compressor.
[0011] Another object of the present invention is to provide geometrical parameter, i.e., passage area distribution of low flow coefficient 3D impeller along
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the meridional flow path from the impeller inlet to impeller exit to achieve high aerodynamic efficiency in multi-stage centrifugal compressor.
[0012] Another object of the present invention is to provide geometrical parameter, i.e., an inlet hub radius of low flow coefficient 3D impeller along the meridional flow path from the impeller inlet to impeller exit to achieve high 5 aerodynamic efficiency in multi-stage centrifugal compressor.
[0013] Another object of the present invention is to provide geometrical parameter, i.e., an inlet shroud radius of low flow coefficient 3D impeller along the meridional flow path from the impeller inlet to impeller exit to achieve high aerodynamic efficiency in multi-stage centrifugal compressor. 10
[0014] Yet another object of the present invention is to provide geometrical parameter, i.e., blade lean angle of low flow coefficient 3D impeller along the meridional flow path from the impeller inlet to impeller exit to achieve high aerodynamic efficiency in multi-stage centrifugal compressor.
[0015] Yet another object of the present invention is to provide geometrical 15 parameter, i.e., blade width at exit of low flow coefficient 3D impeller along the meridional flow path from the impeller inlet to impeller exit to achieve high aerodynamic efficiency in multi-stage centrifugal compressor.
SUMMARY OF THE INVENTION:
[0016] The present subject matter relates to 3D impeller of centrifugal compressor 20 stage with low flow coefficient for compressing fluid with high aerodynamic efficiency. The 3D impeller comprises a rotor, a hub disc (1) and shroud disc (3). Further, the 3D impeller comprises a plurality of blades radially protruding from the hub disc (1) and spaced equidistantly on circumference of the hub disc (1). In the present 3D impeller, blade angle distribution with respect to meridional plane 25 at inlet and exit of impeller at the hub disc (1) is (-) 60o deg. and (-) 55o deg. respectively with maximum angle location is at 55% of meridional flow path length. Further, the present 3D impeller adopts appropriate Blade angle distribution, Wrap angle distribution, Passage area distribution, Slope &
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Curvatures at hub and shroud sections from inlet to exit of impeller to achieve high aerodynamic efficiency.
[0017] In order to further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative 5 only but not used to limit scope of the present subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally 10 effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods or structure in accordance with embodiments of the present 15 subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0019] Fig.1, Fig. 2, Fig. 3, and Fig. 4 illustrate the view of the impeller of centrifugal compressor as known in the prior art;
[0020] Fig. 5 illustrates a 3D view of impeller having twisted 3D impeller blade, 20 in accordance with an embodiment of the present subject matter;
[0021] Fig. 6 illustrates cross sectional view of the impeller with shroud disc, in accordance with an embodiment of the present subject matter;
[0022] Fig. 7 illustrates impeller blade angle distribution from inlet to exit at hub and shroud surfaces of the impeller, in accordance with an embodiment of the 25 present subject matter;
[0023] Fig. 8 illustrates impeller blade wrap angle distribution from inlet to exit at hub and shroud surfaces of the impeller, in accordance with an embodiment of the present subject matter;
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[0024] Fig. 9 illustrates impeller blade slop distribution from inlet to exit at hub and shroud surfaces of the impeller, in accordance with an embodiment of the present subject matter;
[0025] Fig. 10 illustrates impeller blade curvature distribution from inlet to exit at hub and shroud surfaces of the impeller, in accordance with an embodiment of the 5 present subject matter;
[0026] Fig. 11 illustrates impeller blade passage area distribution from inlet to exit of the impeller along impeller meridional flow path length, in accordance with an embodiment of the present subject matter;
[0027] Fig. 12 illustrates impeller blade lean angle distribution from inlet to exit 10 of the impeller along impeller meridional flow path length, in accordance with an embodiment of the present subject matter;
[0028] Fig. 13 illustrates impeller blade to blade loading distribution of the impeller, in accordance with an embodiment of the present subject matter;
[0029] Fig. 14 illustrates relative velocity distribution on the impeller blade at 15 both suction and pressure surfaces at hub and shroud sections of the impeller, in accordance with an embodiment of the present subject matter;
[0030] Fig. 15 (a) and (b) illustrate pressure recovery coefficient at pressure side and suction side at hub and shroud sections of the impeller, in accordance with an embodiment of the present subject matter; and 20
[0031] Fig. 16 (a) and (b) illustrate static pressure distribution on the blade suction and pressure surfaces at hub and shroud sections of the impeller, in accordance with an embodiment of the present subject matter.
[0032] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from 25 the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0033] The subject matter disclosed herein relates to shrouded 3D impeller of centrifugal compressor stage with low flow coefficient. In the centrifugal compressor, fluid enters axially at the first stage and gets compressed in the impeller and passes through a diffuser, “U” shaped bend and through a row of 5 plurality of vanes or blades in the return channel that reduces the tangential or swirl component of flow, and then enters the next stage impeller for further compression. The pressurized gas from the last stage impeller goes into a volute/collector chamber that concentrically arranged inside the inter-stage duct. In the present subject matter, 3D impeller geometrical parameters, such as Blade 10 angle, Wrap angle, Slope, Curvature, Passage area, Inlet hub radius, Inlet shroud radius, Impeller blade exit width, Impeller blade circumferential pitch are achieved along the meridional flow path for high aerodynamic efficiency. The 3D impellers are made according to achieved geometrical parameters which gave high aerodynamic efficiency which is very close to theoretical efficiency. The 15 present geometrical parameters make the low flow coefficient 3D impellers more efficient and increases the overall efficiency of the multi stage centrifugal compressors.
[0034] All impellers of the centrifugal compressors differ in the channel length and the geometry. With the change in geometry, noticeable differences in the 20 aerodynamic efficiency can be seen. The blade angles are different on the impeller at the inlet and at the exit edge. Thus there has to be a transition in the blade angle along the meridional flow path length of the blade. The blade angle distribution has a significant effect on impeller efficiency. Therefore, the geometry of the blade is often mechanically complicated and the accuracy of the flow prediction 25 varies with the geometry of the meridional flow path. Further, the blade angle distribution at hub along the meridional flow path has greater effect on the aerodynamic efficiency as compared to blade angle distribution at the shroud.
[0035] Further, centrifugal compressors with 3D impeller are basically meant for yielding higher aerodynamic efficiency. All the elements of compressor stage like 30
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Inducer, Impeller, Diffuser, U bend, Return channel and Exit element contributes to the higher efficiency. However, impeller of the compressors where in the energy is added to the working fluid plays main role in achieving higher efficiency. To achieve higher efficiency, compressor demands proper blade loading, Relative velocity distribution and Static pressure distribution of the 5 impeller blade that results in fluid flow without flow recirculation, flow separation, low momentum zone in the entire flow path of compressor stage. This is achieved by adopting appropriate Blade angle distribution, Wrap angle distribution, Passage area distribution, Slope & Curvatures at hub and shroud sections from inlet to exit of impeller. 10
[0036] As explained above in the problem in prior art section, the efficiency of the low flow coefficient multi-stage centrifugal compressor is low, and there are more frictional losses and less blade loading. Design and structure of the impeller is not capable to achieve the high efficiency. Geometrical parameters of the impeller, known in the prior art, provide less efficiency and more frictional losses. 15
[0037] According to an implementation of the present subject matter, an impeller blade angle “ß” distribution at impeller hub and shroud surfaces along the impeller inlet to impeller exit along the meridional flow path is defined. The blade angle “ß” distribution completely controls the flow physics within the impeller like diffusion, pressure recovery coefficient, pressure loss coefficient, relative 20 velocity distribution, impeller passage area distribution, flow pattern at impeller exit and along the downstream of the compressor stage. The blade angle ß distribution from the inlet to outlet of an impeller in a centrifugal compressor at each stage provides significant influence on its flow characteristics. Further, the blade angle distribution explains performance, loss generation, and operating 25 range of the impeller in the centrifugal compressor.
[0038] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the 30
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same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to 5 aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, 10 together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0039] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be 15 noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0040] Fig. 5 illustrates front view of 3D impeller blade, in accordance with the 20 present subject matter. Fig. 6 illustrates the meridional cross section of the 3D impeller, in accordance with the present subject matter. The 3D impeller has rotor shaft and a hub disc and shroud disc 1 connected to the rotor. Further, the hub disc has two parts hub disc 1 and hub contour 2. Similarly, the shroud disc has two parts shroud disc 3 and shroud disc 4. Further, the 3D impeller has a plurality of 25 blades/vanes 5 (in fig. 6 meridional cross section of one blade of the impeller is shown for clarity) supported by the hub disc 1 and radially protruding from the disc. The plurality of blades 6 is circumferentially and equidistantly spaced on the disc. Further, the plurality of blades, interchangeably can be referred as blade, 5 are covered by the shroud disc and contour 3, 4 which forms an outer surface or 30
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boundary to flow of liquid in a flow passage defining a flow direction. The plurality of blades 5 is disposed between the hub disc and the shroud disc and substantially equidistantly in a circumferential direction to define the flow passage by means of the disk and the shroud and the vanes. The width of the Impeller blade ?B
2” plays major role in achieving the overall efficiency of compression 5 stage. Impeller inlet hub radius “R1h” in centrifugal compressor stage affects the roto-dynamic behaviour of the compressor. In the centrifugal compressor, higher inlet hub radius “R1h” demands higher inlet shroud radius “R1s” which increases the inlet relative velocity at shroud.
[0041] Fig. 7 illustrates impeller blade angle distribution from inlet to exit at hub 10 and shroud surfaces of the impeller, in accordance with an embodiment of the present subject matter. The impeller blade angle distribution plays an important role in the functioning and efficiency of the multi-stage centrifugal compressor with low flow coefficient. The blade angle “ß” distribution completely controls the flow physics within the impeller like diffusion, pressure recovery coefficient, 15 pressure loss coefficient, relative velocity distribution, impeller passage area distribution, flow pattern at impeller exit and along the downstream of the compressor stage. The impeller blade angle variation at hub and shroud sections along the percentage length of meridional flow path “A” is governed by Equation.1 and Equation.2 respectively. 20
For Hub
ß= 0.777569 * A - 0.0158993 * A2+ 0.000281987 * A3 - 4.05454*10-6 * A4
+ 3.10251*10-8 * A5 - 52.8743 - 1.00629*10-10 * A6 - 59.9399 --- Eq.1
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For Shroud
ß = (-) 0.154357 * A + 0.00865261 * A2 - 0.000119929 * A3 + 9.88163*10-7 * A4
- 4.25188 * 10-9 * A5- 62.494 ---- Eq.2
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[0042] Further, 3D impeller of centrifugal compressor stage with blade angle distribution at inlet is (-) 60 deg. and at exit is (-) 55 deg. of impeller at hub disc (1). The maximum angle location of the blade angle distribution at hub disc (1) is
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at 55% of meridional flow path length. Furthermore, the impeller blade angle distribution at inlet is (-) 62.5 deg. and at exit is (-) 55 deg. of impeller at shroud disc. The maximum angle location of the blade angle distribution at the shroud disc (3) is at 85% of meridional flow path length.
[0043] Fig. 8 illustrates impeller blade wrap angle distribution from inlet to exit at 5 hub and shroud surfaces of the impeller, in accordance with an embodiment of the present subject matter. The Impeller wrap angle “?” distribution at impeller hub and shroud surfaces from impeller inlet to impeller exit influences blade loading / relative velocity distribution, the pressure recovery, flow behaviour and thereby efficiency. The present subject matter explains the wrap angle distribution which 10 decreases uniformly from impeller inlet to impeller exit for achieving higher efficiency as shown in Fig. 8. Numerically the wrap angle variation is in range of 0.00 deg. to (-) 750 deg. for shroud; and (-) 3.50 to (-) 77o deg. for the hub with respect to the meridional plane or meridional flow path. The impeller wrap angle variation at the hub and the shroud sections along the percentage length of 15 meridional flow path “A” is governed by Equation.3 and Equation.4 respectively.
For Hub
?= (-)1.71782*A + 0.025255*A2 - 0.000288591* A3 + 1.93339*10-6* A4
- 5.97986*10-9*A5 – 2.75711 ---- Eq.3
For Shroud 20
? = (-)1.11151 * A - 0.00348257*A2 + 0.000252706 * A3 - 3.45506 *10-6 * A4
+ 2.23017 *10-8 * A5 - 5.92562*10-11 * A6+0.00159656 ---- Eq.4
[0044] Fig. 9 illustrates impeller blade slop distribution from inlet to exit at hub and shroud surfaces of the impeller, in accordance with an embodiment of the present subject matter. The impeller hub and shroud disc contours slopes 25 influence the blade loading, relative velocity distribution, pressure rise and there by overall efficiency of the impeller. Variation in slope with respect to meridional plane at hub and shroud surface is shown in Fig. 9. The present subject matter explains the slope of 7.0o deg. at inlet and 87o deg. at exit at the shroud surface
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where as the slope is 17
o deg. and 89o deg. at hub surface of the impeller. The variation of the slope of impeller “S” at hub and shroud sections along the percentage length of meridional flow path “A” is governed by Equation. 5 and Equation. 6 respectively.
At Hub 5
S = 1.0812 * A + 0.015068 *A2 -0.000181107 * A3–5.38536 *10-6* A4
+ 9.13188 *10-8 * A5 - 3.80017*10-10 * A6 +17.4363 --- Eq.5
At Shroud
S = 2.10441* A -0.00403687 *A2 -000559293 * A3 + 8.03172 * A4 *10-6 -3.334 *10-8 * A5+ 6.82489 --- Eq.6 10
[0045] Fig. 10 illustrates impeller blade curvature distribution from inlet to exit at hub and shroud surfaces of the impeller, in accordance with an embodiment of the present subject matter. The curvatures of impeller blade at hub and shroud contours influences the blade loading, relative velocity distribution, pressure rise and there by overall efficiency of the impeller. Variation in curvature results in 15 higher efficiency in the present subject matter at hub and shroud surfaces are shown in Fig. 10. The impeller curvatures slope “C” variation at hub and shroud sections along the percentage length of meridional flow path “A” is governed by Equation. 7 and Equation. 8 respectively.
At Hub 20
C = 0.0127383+ 0.0000536735 *A - 0.0000810948 * A2- 1.1734*10-6* A3+
+ 2.20419 *10-8 *A4-1.72568 *10-10 *A5 +4.88763*10-13 * A6 --- Eq.7
At Shroud
C = 0.0287384 + 0.000179445 * A - 0.0000439008 * A2 + 9.95984 *10-7 * A3 - 8.57041*10-9* A4 + 2.54829 *10-11 * A5 --- Eq.8 25
[0046] Other embodiment of the present subject matter explains circumferential pitch of the impeller blades in terms of degree depends of the total number of
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blade in the impeller. The number of blades shows major impact on the peak blade loading and total frictional losses. It is observed that low flow stages requires lesser number of impeller blades whereas high flow stages demands more number of impeller blades to achieve proper blade loading which results in efficient flow behaviour in the entire compressor stage. For the present subject matter which is a 5 low flow impeller, the circumferential pitch is in range of 27
o deg. to 24o deg. for achieving better blade loading and lesser friction losses which has ultimately resulted higher efficiency.
[0047] Another embodiment of the present subject matter relates to impeller inlet hub radius ?R1h” in a centrifugal compressor stage. Where higher inlet hub radius 10 “R1h”demands higher inlet shroud radius which increases the inlet relative velocity at the shroud. The Inlet tip velocity reduces the impeller diffusion rate and accordingly pressure recovery and impeller efficiency. Inlet hub radius “R1h”also influences every stage of the centrifugal compressor shaft diameter in view of compressor rotodynamic behaviour. Therefore, considering above all 15 requirements, for the present subject matter which has 450 mm impeller diameter with flow range of 70% to 130% of design flow. Further, the inlet hub diameter is 37% to 39% of impeller exit hub diameter. The impeller inlet hub radius with outer diameter is in range of 315 mm to 630 mm as 37% - 39% of impeller outer diameter and inlet shroud radius as 60% - 62% of impeller outer diameter. 20
[0048] Furthermore, the Impeller inlet shroud radius ?R1s” (as shown in fig. 6) is free to increase or decrease whereas the hub radius “R1h” is fixed by the rotodynamic requirement. This is basically controlled by operating range of compressor stage as reducing the inlet shroud radius “R1s” drastically will result in chocking at higher flow. The present subject matter has the inlet shroud radius 25 of 61% for the flow range of 70% to 130% of design flow.
[0049] Yet another embodiment of the present subject matter describes the impeller blade width at exit ?B2” (as shown in fig. 6) plays major role in achieving the overall efficiency of compressor stage. The impeller blade exit width “B2” influences diffusion, flow associated problems like re-circulation, 30
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separation & low momentum zones. The impeller exit blade width “B
2” is directly related to impeller exit blade angle ?ß2b” and flow coefficient of fluid. Increasing the impeller width demands higher pinching in the diffuser width in order to avoid flow associated problems like recirculation, separation, and low momentum zones in the diffuser and further downstream. The diffuser pinching in the width more 5 than 25% can cause flow disturbance at the diffuser inlet. For example, in the present subject matter, impeller blade exit diameter is 450 mm where the flow co-efficient is low with the impeller exit blade angle (-) 55o and the impeller exit blade width is 17 mm. The impeller exit blade width “B2” which has outer diameter in range 315 mm to 630 mm as in range 3.5% to 3.85% of impeller exit 10 diameter.
[0050] Fig. 11 illustrates impeller blade passage area distribution from inlet to exit of the impeller along impeller meridional path length, in accordance with an embodiment of the present subject matter. The impeller passage area distribution is mainly responsible for diffusion of the fluid within the impeller. The impeller 15 passage area distribution varies from high flow to low flow stages. Further, continuous increase in the impeller passage area from impeller inlet to impeller exit along the meridional flow path ensures conversion of kinetic energy in to pressure; and also eliminates recirculation zones within the impeller. The impeller passage area distribution for achieving the higher efficiency for present subject 20 matter which is of low flow coefficient is shown in Fig. 11. The impeller passage area “PA” distribution along the percentage length of meridional flow path “A” is governed by Equation.9.
PA = 0.000117705 *A -0.0000418384*A2 + 4.59313*10-6 *A3 -2.39599 *10-7* A4
+ 7.16947 *10-9* A5 -1.2938*10-10* A6 + 1.38933*10-12 *A7 - 8.16851 *10-15*A8 25
+ 2.02307 *10-17 * A9 + 0.0100192 --- Eq.9
[0051] Fig. 12 illustrates impeller blade lean angle distribution from inlet to exit of the impeller along impeller meridional flow path length, in accordance with an embodiment of the present subject matter. The impeller blade lean angle
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influences the induced centrifugal stresses in the impeller. However, blade lean angle also influences manufacturability of impeller particularly the shrouded impellers and also plays important role in flow behaviour within the impeller and at the downstream. The blade lean angle at inlet is 10
o deg. and at exit is 25o deg. with peak at 20% and minimum at 75% of the meridional flow path having 5 variation like sleeping "S" shape. The blade lean angle variation adopted for the present subject matter which has enabled to achieve the good flow behaviour while limiting the stresses within the allowable limit has been shown in Fig. 12.The impeller blade lean angle “L” distribution along the percentage length of meridional flow path “A” is governed by Equation.10. 10
L = 2.03765 * A - 0816475 * A2 + 0.00137891 * A3 - 0.0000123158* A4
+ 4.80532 *10-8* A5+10.0984 --- Eq.10
[0052] In the present subject matter, impeller geometrical parameters along the meridional flow path from impeller inlet to impeller exit like Blade angle, Wrap angle, Slope, Curvature, Passage area, Inlet hub radius, Inlet shroud radius, 15 Impeller blade exit width, Impeller blade circumferential pitch are finalized based on systematic design approach with the rich experience of compressor design and extensive computational fluid dynamics (CFD) analysis and performance testing of prototype where the efficiency achieved is very close to the theoretical efficiency. 20
[0053] Conventionally, no information is available regarding the blade angle distribution, wrap angle distribution, slope distribution, curvature distribution and passage area distribution from impeller inlet to impeller exit is also not defined. Further, no information and geometrical parameters are available regarding the impeller inlet hub radius and shroud radius. From the above explained geometrical 25 parameters, the impeller central blade loading and relative velocity distribution is known.
[0054] Fig. 13 illustrates impeller blade to blade loading distribution of the impeller, in accordance with an embodiment of the present subject matter.
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Further, Blade to blade loading is defined as the ratio of difference in relative velocities to the average velocity of the suction and pressure side of the impeller. Central loading which is mostly preferred has been achieved in the present aspect. Fig. 14 illustrates relative velocity distribution on the impeller blade at both suction and pressure surfaces at hub and shroud sections of the impeller, in 5 accordance with an embodiment of the present subject matter. These are the major factors influenced the relative velocity distribution, blade loading, diffusion, static pressure distribution, flow behaviour within the impeller and further downstream which ultimately results in higher efficiency of compressor stage. From the rigorous CFD studies, it has been revealed that scaling of impeller up to 40% 10 upward and 40% downward can the give the same performance while the ratios of other impeller geometrical parameter are maintained.
[0055] Diffusion is achieved in the impeller from impeller inlet to exit along the length of meridional flow path in terms of pressure recovery coefficient is presented in the Fig. 15 (a) and Fig.15 (b). Pressure recovery co-efficient is 15 defined as the ratio of gain in static pressure to inlet dynamic head. Average pressure recovery co-efficient gradually increasing from impeller inlet to middle portion and gradually decreasing towards impeller exit ensures smooth pressures recovery without any acceleration within the impeller. Further, pressure recovery coefficient is defined as the ratio of gain in static pressure to the inlet dynamic 20 head. Similarly, static pressure recovered on both the pressure side and suction of the impeller blade is presented in the Fig. 16 (a) and Fig.16 (b). Pressure recovery on both pressure and suction surface of the impeller blade along the meridional flow path length of the impeller without any chattering or jig jag pattern ensures smooth pressure recovery and flow behavior. 25
[0056] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the 30
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system/device/structure of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.