US2803396A - Compressor - Google Patents

Description

Aug. 20, 1957 K. A. DARROW COMPRESSOR 2 Sheets-Sheet 1 Filed Sept. 29, 1954' Fig.2.

inventor.- .Kenneh A parrow, by 4 United States Fatent @rfrce masses Patented Aug. 20, 1957 CGMPRESSOR Kenneth A. Darrow, Sprakers, N. Y., assignor to General Electric Company, a corporation of New York Application September 29, 1954, Seriai No. 459,042

4 Claims. (Cl. 236-114) This invention relates to compressors and more particularly to a method and apparatus for eliminating pulsation in such compressors.

Pulsation is an unstable, intermittent flow condition in which there is a cyclic reversal of flow caused by excess flow-throttling. This condition is a serious limitation in the operating range of a centrifugal or axial flow compressor because it greatly reduces compressor performance at low rates and limits the minimum flow rate possible. Such pulsation occurs when the flow rate in the compressor has been reduced to some value below the designed operating point of the machine either by throttling the inlet or outlet thereof. Flow in both the impeller and diffuser of the compressor becomes completely separated along the full length of the flow passages to produce pulsation. In large compressors, the efiect may become so violent that the machineis destroyed thereby.

Accordingly, it is an object of my invention to provide anovel apparatus to eliminate compressor pulsation.

It is another object of the invention to provide an improved difluser structure which will eliminate vpulstlf On in the compressor.

It is another object of the invention to provide animproved compressor with a stable non-pulsating flow from normal flow to zero flow conditions.

It is another object of the invention to provide an improved compressor in which higher efficiencies are maintained at the low flow range near or below the normal pulsation point.

It is a further object of the invention to provide a novel method of eliminating pulsation in a compressor.

In carrying out my invention in one form a flexible diffuser wall is provided in the compressor to give a correct variable area ratio for all compressor flows.

These and various other objects, features and advantages of the invention will be better understood from the following description taken in connection with the accom panying drawing in which:

Fig. 1 is a sectional view of a centrifugal compressor which embodies my invention;

Fig. 2 is a sectional view similar to Fig. l with the flexible wall in a closed position;

Fig. 3 is a sectional view of a centrifugal compressor in which the fluid has partially separated from the walls;

Fig. 4 is a sectional view similar to Fig. 3 in which the fluid has completely separated from the walls;

Fig. 5 is a sectional view similar to Fig. 4 in which a flexible member is provided to produce the correct difiuser area ratio;

Fig. 6 is a graph of compressor pressure rise plotted against fluid flow at variable speed; and

Fig. 7 is a graph of compressor pressure rise plotted against fluid flow at constant speed.

In Fig. 1 of the drawing, a centrifugal compressor is shown generally at 10 which comprises a casing 11 to define a chamber 12 therein. Casing 11 is provided with an upper wall 13 in which an air inlet or aperture 14 is centrally disposed. An electric motor 15 is secured at the marginal edge of opening 14 and vertically spaced there from by means of suitable spacing elements 16 and bolts 17. Motor 15 has a shaft 18 to project downwardly into chamber 12. A centrifugal blower impeller 19 with a plurality of curved blades 20 is mounted on shaft 18 to drive air from inlet 14 downwardly and outwardly toward the inner wall of casing 11.

A vaneless diffuser 21 surrounds impeller 19 to provide a back wall 22 and a forward wall 23. A flexible wall 24 is positioned on the inner surface of back wall 22 and secured thereto adjacent the difluser inlet by any suitable means, such as, for example, by screws 25. If it is desired, either wall 22 or 23 could be composed of flexible material to eliminate wall 24. The periphery of flexible wall 24 is provided with a plurality of spaced apertures for purposes to be explained hereinbelow.

An aperture 26 is provided in wall 13 in axial alignment with each of the apertures in flexible wall 24. A casing 27 is fitted over each aperture 26 and secured to wall 13 by means of screws 28. A vent 29 is located in casing 27 to communicate with the atmosphere. A flexible member 39 is positioned across aperture 26 to provide a diaphragm to which a rod 31 is secured by a nut 32. The opposite end of rod 31 is retained in the aperture in wall 24 by a pair of nuts 33. An adjustable screw 34 extends through casing 27 to provide a support for a spring 35 which is connected to the opposite side of diaphragm 30.

In Fig. 2 of the drawing, flexible member 24 is shown in contact with wall 23 to provide a closure for the outlet of diffuser 21. Such a closure is produced by an increase in pressure in chamber 12 which is exerted against diaphragm 30 to force spring 35 outwardly. A partial clo sure is attained when compressor 10 approaches the zero flow condition to provide only a small exit area which maintains the high velocity flow from the difluser outlet.

In Fig. 3, fluid, which is designated by arrows 40, is forced from the air inlet through impeller 19 and diffuser 21 toward the inner wall of the compressor casing. Initial separation of the fluid from the walls of the impeller and diffuser is shown by areas 41 and 42. Arrow 43 designates the fluid which has separated from the impeller wall and reversed its direction of flow.

In Fig. 4, pulsation conditions are shown in compressor 10 which is not provided with a flexible member 24 to break a continuous low kinetic path 44. Path 44 is produced by complete separation of fluid along the full length of the flow passage. Pulsation is caused by a feedback through path 44 of air which is designated by arrows 45.

In Fig. 5, flexible member 24 is positioned adjacent wall 23 of diffuser 21 to produce the correct diffuser area ratio for this flow condition. Such closure prevents separation and pulsation which would occur otherwise.

In the operation of compressor 11 in Figs. 1 and 2, centrifugal action of impeller blades 20 drives air which comes in inlet 14 downwardly and outwardly toward the inner wall of casing 11. While a constant flow rate is provided in compressor 10, flexible member 24 remains in juxtaposition with diffuser wall 22 to allow fluid flow to proceed through the outlet of diffuser 21. When flow is reduced, motor 15 is unloaded to increase the speed and pressure. Difierential pressure between chamber 12 and the atmosphere moves diaphragm 30 to operate flexible member 24 which provides the correct difl'fuser area ratio for any particular flow. The position of member 24 allows full flow through the diffuser outlet to prevent separation. When fluid flow returns to its normal Value, a decrease in pressure in chamber 12 allows diaphragm 30 to return to its original position. Thus, rod 31 is pushed downwardly by spring 35 to move flexible member 24 adjacent wall 22. The diffuser outlet remains open until a subsequent decrease of fluid flow occurs.

is reduced in a conventional compressor below the design point, separation begins at areas 41 and 42. In Fig. 4, complete separation has resulted in pulsation which is caused by feedback through the low kinetic energy path 44 of air which is designated by arrows 45.

In Fig. 5, flexible member 24 prevents complete separation and pulsation in compressor because a correct diffuser area ratio is maintained for any particular flow. Thus, there is no low kinetic energy path through which an air feedback occurs. If compressor 10 operates at a constand speed, a Pitot tube could be used to measure the change in velocity head with the change of fluid flow to operate diaphragm 30.

In Fig. 6, a graph of compressor pressure rise in head inches of Water (H2O) is plotted against fluid flow in cubic feet per minute at variable speed. The speed of the impeller increased as the loadrwas decreased with decreasing flow. .As the normal pulsation point was approached, difiuser area ratio was decreased enough to give the correct area ratio to prevent separation. This. area ratio was progressively decreased with decreasingfiow to the zero flow point. The primary reason that pressure increased with decreasing flow is the increased speed of the impeller. 1

In Fig. 7, a graph of compressor pressure rise in head inches of water (H2O) is plotted against fluid flow in cubic feet per'minute at a constant impeller speed of 15,000 revolutions per minute. This graph discloses the increase in, operating range below the normal pulsation point which results from the use of flexible member 24.

As will be apparent to those skilled in the art, the objects of my-invention are attained by the use of a flexible diffuser wall which provides a correct variable area ratio for all compressor flows.

While other modifications of this invention and variations of apparatus which may be employed within the scope of the invention have not been described, the invention is intended to include all such as may be embraced within the following claims.

What I claim as new and desire to secure by Letters tioned in said casing wall and connected to said rod, and biasing means to return said annular member to its unflexed position.

2. Pulsation control means for centrifugal compressors and the like comprising in combination, an annular diffuser surrounding and arranged to receive fluid from an impeller, said ditfuser having a spaced apart back and forward wall, an annular casing encircling said difiuser, an annular flexible member positioned adjacent one of said walls within said diflt'user, the inner circumference of said annular member being aflixed to its associated wall and the outer circumference being free for movement, and a pulsation sensitive device in said casing and attached to the free circumference of said annular member, whereby upon a pulse pressure rise in said casing, said pulsation sensitive device acts upon said annular memher to reduce the cross-sectional area between said diffuser walls to prevent the formation of pulsation conditions.

3. The invention as claimed in claim 2 wherein said pulsation sensitive device includes a diaphragm positioned in the wall of and sensitive to pressure variations within said casing, a rod connecting said diaphragm and the free end of said annular member, and spring means for biasing said rod to maintain said annular member in an unflexed condition.

4. The invention as claimed in claim 3 wherein said pressure sensitive device includes adjusting means for varying the force applied by said biasing means, and means associated with said rod and the free end of said annular member for adjustably positioning the annular member in said difiuser.

References Cited in the file of this patent UNITED STATES PATENTS 1,095,767 Adams May 5, 1914 1,188,995 Rice June 27, 1916 1,401,668 Brown et a1 Dec. 27, 1921 1,620,111 Lewis Mar. 8, 1927 2,285,976 Huitson June 9, 1942 2,648,195 Wilde'et al Aug. 11,1953 2,684,634 Schneider July 27, 1954 FOREIGN PATENTS 50,411 France Mar. 12, 1940 (Addition to 829,826)

285,815 Great Britain May 17, 1928 305,214 Great Britain Jan. 29, 1949 611,726 Great Britain Nov. 3, 1948 875,086 France June 8, 1942

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