Pump diffusor having improved diffusor blades

Abstract: The present invention provides a novel diffusor for a diffusor pump. The diffusor comprises a body (12) having a side portion and a plurality of blades (16) placed on the side portion of the body (12) so as to be along a flow direction of a treating liquid, each of the plural blades (16) including at least one aperture (22) so as to be divided into a plurality of parts (18, 20). The body (12) has a cylindrical shape. The blade (16) is divided into first and second parts (18, 20) by a single aperture (22). The first part (18) of the blade (16) has a solidity in the range from 0.75 to 1.25 when the treating liquid flows from the first part (18) to the second part (20).

Description: This invention relates to a diffusor pump, and more particularly to a diffusor blade for a diffusor pump. A normal diffusor pump includes diffusors with a plurality of blades forcing a handling liquid to exhibit a flow straightening. A liquefied natural gas submerged pump (a LNG submerged pump) is one of typical diffusor pumps. The liquefied natural gas submerged pump also includes the diffusors, each of which has a side face placed with a plurality of blades. The structure of a normal LNG submerged diffusor pump will be described with reference to FIG. 1. The LNG submerged diffusor pump comprises a motor section and a pump section. The pump section of the LNG submerged diffusor pump comprises multiple stages, each of which includes on impeller 10 and a diffusor 12. The diffusor 12 is provided at its side portion with a plurality of vane 14. A handling liquid flows through the impeller 10 by which a rise of pressure of the handling liquid appears. After that, the handling liquid flows on the side portion of the diffusor 12 with the vane 14 and then transmitted to a next stage. The structure of the conventional diffusor 12 with the vane 14 involved in the LNG submerged diffusor pump will subsequently be described with reference to FIG. 2. The diffusor 12 comprises a cylindrical-shaped body. The cylindrical-shaped diffusor 12 has a side portion which is placed with a plurality of the diffusor vane 14. The plural diffusor vane 14 are so arranged as to be in parallel to each other at a predetermined interval. Each of the diffusor vane 14 is further so arranged as to have a longitudinal direction along a desired flow direction of the handling liquid, because the longitudinal direction of each of the diffusor vane 14 defines a flow direction of the handling liquid. The arrangement of the diffusor vane 14 is thus symmetrical in the axial direction. The diffusor vane 14 define the flow direction of the handling liquid on the side of the diffusor 12. The existence of the diffusor vane 14 forces the handling liquid flowing on the side of the diffusor 12 to exhibit a flow straightening. As a result, the flow rate of the handling liquid is reduced. Concurrently, a rise of pressure of the handling liquid appears. Namely, the diffusor vane 14 make the flow rate of the handling liquid reduced and cause the pressure rising of the handling liquid. The conventional diffusor pumps, and particularly the LNG submerged diffusor pumps are, however, engaged with the following disadvantages in the flow of the handling liquid on the side portion of the diffusor 12. Under a normal condition, such axial symmetrical diffusor vane 14 accomplish the above mentioned effects of both the pressure rising of handling liquid and the forced flow straightening. Thus, when a discharge flow rate of the handling liquid is within a reference discharge flow rate range, such axial symmetrical diffusor vane 14 are able to exhibit excellent functions of the pressure rising and the flow straightening of the handling liquid. Under the normal state in the reference discharge flow rate range, there exists no problem in the flow of the handling liquid. However, if the handling liquid has a discharge flow rate below in the reference discharge flow rate range, the flow of the handling liquid but in the vicinity of the diffusor vane 14 exhibits a revolution and a stall. The undesirable phenomenon of the revolution and the stall of the flow of the handling liquid causes an axial vibration of the diffusor 12. This makes the life-time of bearings of the diffusor 12 shortened. This also makes the Q-H property inferior thereby lowering the pump efficiency. In addition, when the revolution and the stall of the flow of the handling liquid appear, the hunting of the flow of the handling liquid also appears. The above mentioned undesirable phenomenon are considerable in the LNG submerged diffusor pump. To prevent the above undesirable phenomenon in the flow of the handling liquid, it is required that the discharge flow rate of the handling liquid is so controlled as to be within the reference discharge flow rate range. In the prior art, the operation of such LNG submerged diffusor pump is placed on a restriction, if the discharge flow rate of the handling liquid is lower than a discharge flow rate at which the revolution and the stall of the handling liquid flow appear. Under such lower discharge flow rate, the diffusor pump is not operative. It is desirable to make lowering as much as possible a critical discharge flow rate at which the revolution and the stall occur so that the operative range of the discharge flow rate becomes wide. It is, therefore, required to develop novel diffusor blades of the diffusor pump, which are able to make the diffusor pump operative in a wide range of the discharge flow rate of the handling liquid. From GB-A-181 525 a multiple stage centrifugal pump or compressor is known which comprises a body with blades arranged on the body. No means to increase the life-time of the bearings of this pump are described. Also, FR-A-2 185 222 comprises a pump or turbine pump to provide an opening in wings adjacent to blades of the pump. Consequently, also from this document no means to increase the life-time of bearings of the pump are known. Accordingly, it is a primary object of the present invention to provide a novel diffusor blade of a diffusor pump. It is a further object of the present invention to provide a novel diffusor blade of a diffusor pump, which permits the diffusor pump to operate in a wide range of a discharge flow rate of a handling liquid. It is a still further object of the present invention to provide a novel diffusor blade of a diffusor pump, which is able to reduce a critical discharge flow rate at which a revolution and a stall of a handling liquid flow occur. The above and other objects, features and advantages of the present invention will be apparent from the following descriptions. The present invention provides a novel diffusor for a diffusor pump. The diffusor comprises a body having a side portion and a plurality of blades placed on the side portion of the body so as to be along a flow direction of a handling liquid, each of which includes at least one aperture so as to be divided into a plurality of parts. The body has a cylindrical shape. The blade is divided into first and second parts by a single aperture. The first part of the blade has a solidity in the range from 0.75 to 1.25 when the handling liquid flows from the first part to the second part. Preferred embodiments of the present invention will hereinafter fully be described in detail with reference to the accompanying drawings. FIG. 1 is an elevation view illustrative of the conventional LNG submerged diffusor pump. FIG. 2 is a perspective view illustrative of the conventional diffusor with diffusor blades. FIG. 3 is a perspective view illustrative of a diffusor with improved blades of a preferred embodiment according to the present invention. FIG. 4 is a view illustrative of an improved diffusor blade of a preferred embodiment according to the present invention. A preferred embodiment of the present invention will be described with reference to FIGS. 3 and 4. The present invention provides an improved diffusor blade of a diffusor pump. A diffusor 12 comprises a cylindrical-shaped body. The cylindrical-shaped diffusor 12 has a side portion which is placed with a plurality of diffusor blades 16. The plural diffusor blades 16 are so arranged as to be in parallel to each other at a predetermined interval. Each of the diffusor blades 16 is further so arranged as to have a longitudinal direction along a desired flow direction of the handling liquid, because the longitudinal direction of each of the diffusor blades 16 defines a flow direction of the handling liquid. The arrangement of the diffusor blades 16 is thus symmetrical in the axial direction. Each of the diffusor blades 16 comprises a dual diffusor blade and thus a first blade portion 18, a second blade portion 20 and an aperture 22. The aperture 22 are placed between the first and second blade portions 18 and 20 so that the diffusor blade 16 is divided into two portions and thus the first and second blade portions 18 and 20. Namely, the first and second blade portions 18 and 20 are spaced from each other through the aperture 22. Preferably, the first blade portion 18 of the diffusor blade 16 has a solidity in the range from 0.75 to 1.25. The handling liquid flows along the longitudinal direction of the diffusor blade 16 from the first blade portion 18 to the second blade portion 20. In FIGS. 3 and 4, the flow direction of the handling liquid is represented by labeled arrow marks. The flow direction of the handling liquid is defined by the diffusor blades 16 placed on the side portion of the diffusor 12. Namely, the flow of the handling liquid is subjected to a flow straightening. This results in that the handling liquid exhibits a reduction of a flow rate. Further, the handling liquid is subjected to pressure rising. If the discharge flow rate of the handling liquid is relatively slow, the handling liquid flowing in the vicinity of the diffusor blade 16 is subject to a revolution and a stall. This is why the handling liquid is subjected to a flow straightening by the diffusor blade 16. This results in that the handling liquid flowing at a relatively slow along the first blade portion 18 of the diffusor blade 16 is also likely to exhibit a revolution and a stall of the flow due to the flow straightening forced by the diffusor blade 16. However, when the flow of the handling liquid approaches or reaches the aperture 22 of the diffusor blade 16, the existence of the aperture 22 makes the handling liquid become free from the forced flow straightening by the first blade portion 18 of the diffusor blade 16. As a result, the indication likely to cause the rotating stall of the handling liquid disappears. Thus, the existence of the aperture 22 allows the flow of the handling liquid to be free from the revolution and the stall. After that, the handling liquid flows along the second blade portion 20 of the diffusor blade 16. Although the handling liquid is again subjected to the forced flow straightening by the second blade portion 20 of the diffusor blade 16, the revolution and the stall of the flow of the handling liquid do not appear. This is why the indication likely to cause the revolution and the stall of the flow of the handling liquid is sufficiently dissolved by the aperture 22 of the diffusor blade 16. Preferably, the second blade portion 20 is so positicned that both longitudinal center lines of the first and second blade portions 18 and 20 are slightly deflected from each other so as to prevent the handling liquid to flow across the diffusor blade 16 through the aperture 22. This is represented in FIG. 4. From the following descriptions, it is understood that the novel diffusor blade 16 having the aperture 22 provides the following advantages. The novel diffusor blade 16 having the aperture 22 is able to keep the handling liquid exhibiting a relatively slow flow from the revolution and the stall. This allows lowering considerably a critical discharge flow rate point where the handling liquid flow exhibits the revolution and the stall. This permits the diffusor pump including the improved diffusor blades 16 to be operative in the wide range of the discharge flow rate of the handling liquid. Namely, the novel diffusor pump is operative even if the handling liquid has a relatively low flow rate. Physically, when the second blade portion 20 of the diffusor blade 16 has a solidity of 1.0, the novel diffusor blade 16 makes the inoperative flow rate range, in which the revolution and the stall occur, reduced up to 57 %. Further, the reduction of the critical discharge flow rate point by the novel diffusor blade 16 is able to suppress the handling liquid such as LNG to exhibit a hunting. Since the flow of the handling liquid is free from the revolution and the stall, an axial vibration of the diffusor pump does not appear thereby making the life-time of the bearing become long. The novel diffusor blade 16 is further able to improve the pump efficiency of the diffusor pump. It is also an advantage that the novel diffusor blade may readily be formed. Although in the preferred embodiment the novel diffusor blade 16 is divided by the sole aperture 22 into the dual parts and thus the first and second blade portions 18 and 20, it is available as a modification that the diffusor blade is divided by two or more apertures into triple parts or more parts so as to match variable conditions. Whereas modifications of the present invention will no doubt be apparent to a person having ordinary skill in the art, to which the invention pertains, it is to be understood that the embodiments shown and described by way of illustration are by no means intended to be considered in a limiting sense.

Claims: A diffusor of a submerged motor pump for liquified gas comprising: a body (12) having a side portion and a cylindrical shape; and a plurality of blades (16) placed on said side portion of said body (12) so as to be along a flow direction of a treating liquid, each of said plural blades including at least one aperture (22) so as to be divided into a plurality of parts (18, 20), and projecting outwardly from the envelope surface of the cylindrically shaped body. The diffusor of a submerged motor pump for liquified gas as claimed in claim 1, wherein said blade (16) is divided into first and second parts (18, 20) by a single aperture (22). The diffusor of a submerged motor pump for liquified gas as claimed in claim 2, wherein said first part (18) of said blade (16) has a solidity in the range from 0.75 to 1.25 when said treating liquid flows from said first part (18) to said second part (20). A diffusor blade for the diffusor of a submerged motor pump for liquified gas according to any of claims 1-3, comprising: at least one aperture (22); and a plurality of blade portions (18, 20) being spaced through said aperture (22), said plural blade portions (18, 20) being arranged along a flow direction of a treating liquid. The diffusor blade as claimed in claim 4, wherein said diffusor blade (16) comprises first and second blade portions (18, 20) and a single aperture (22) for separating said first and second blade portions (18, 20) from each other. The diffusor blade as claimed in claim 5, wherein said first blade portion (18) has a solidity in the range from 0.75 to 1.25 when said treating liquid flows from said first blade portion (18) to said second blade portion (20).

Inventors: NAKAGAWA YUZO, OGAWA MOTOYASU, NAKAGAWA, YUZO, OGAWA, MOTOYASU
Applicants: NIKKISO CO LTD, NIKKISO CO., LTD.
Application year: 1993
Main classification: F04D29
IPC codes: F04D29