CN1081757C - Centrifugal compressor and diffuser for centrifugal compressor - Google Patents

Abstract

The present invention relates to a multi-stage centrifugal compressor with multiple blade wheels installed on a rotating shaft or a single-stage centrifugal compressor with a blade diffuser which is provided with multiple guide blades and is installed on the down stream side of the blade wheel and a blade-free diffuser part formed in the down stream of the blade diffuser. The blade diffuser has a small wing chord pitch ratio, and each meridian plane of the two wall surfaces of the blade-free diffuser formed in the down stream of the blade diffuser presents a cross section shape that the flow passage height is gradually decreased in the direction of the down stream. The ratio of the flow passage height of the inlet to the flow passage height of the outlet of the blade-free diffuser is 0.3 to 0.6. A second blade diffuser with a small amount of guide blades can be used for replacing the blade-free diffuser. In one case, two wall surfaces forming the second blade diffuser can also be gradually contracted in the direction of the down stream. In another case, the flow passages are contracted in the position of the down stream of the blade diffuser to prevent the generation of obvious rotary separation in a low specific speed blade wheel, and therefore, the efficiency of the compressor is enhanced by the blade diffuser.

Description

Centrifugal compressor and diffuser for centrifugal compressor

The present invention relates to a centrifugal compressor and a diffuser for the centrifugal compressor, and more particularly to a centrifugal compressor and a centrifugal blower for handling a small amount of gas and a diffuser for them.

Diffusers used in centrifugal compressors are generally classified into vaneless diffusers and vaned diffusers, among these diffusers, vane diffusers change the flow direction by guide vanes, and the flow velocity is also reduced by guide vanes , so the efficiency near the design flow rate is usually higher compared to vaneless diffusers. However, the operating range is narrowed due to the vanes adding losses and the vanes separating the flow, resulting in inefficiency at high and low flow rates.

Therefore, in Japanese Patent Unexamined Publication No. 53-119411, a diffuser with a small chord pitch ratio (hereinafter referred to as a low-density vaned diffuser) is disclosed, wherein, even if a vaned diffuser is used, , the operating range is not narrow, and the efficiency can be increased.

In the example disclosed in Japanese Utility Model Unexamined Publication No. 56-97598, the height of the flow passage at the vaneless part located downstream of the low-density vane diffuser is sharply narrowed, and the flow passage length of the vaneless part is shortened, to reduce friction loss. Furthermore, in the example disclosed in Japanese Patent Unexamined Publication No. 1-125599, in a compressor stage having a lower specific rotational speed, the flow path height of the vaned portion of the vaned diffuser gradually decreases in the downstream direction, thereby Efficiency is enhanced due to reduced friction losses.

In the case of impellers for so-called low specific speed compressors, where the specific speed determined by the speed flow rate and the adiabatic head of the compressor is not greater than 250 (rpm, m ³ /min, m), the discharge of the impeller The flow angle, that is, the flow angle at the inlet of the diffuser is smaller, and the axial height of the flow channel is lower. Therefore, when a vaneless diffuser is used as a diffuser, there is a disadvantage of increasing friction loss. On the other hand, when a vaneless diffuser is used in a low specific speed compressor stage, in many cases the vaneless diffuser section is rotationally separated. Therefore, in a multi-stage compressor in which the pressure of the working medium is high, there is a disadvantage in that the operating range is limited due to the vibration of the fluid due to the rotational separation.

In order to prevent the narrowing of the operating range due to rotational separation, various methods of delaying the rotational separation are provided when using a vaneless diffuser. One of the methods is to reduce the height of the fluid flow channel at the inlet part of the diffuser (reducing the flow channel height at a certain stage will be referred to as "contraction" hereinafter), so that the flow rate at the separation start point is converted to a low flow rate . However, the efficiency of the diffuser of this structure is lower than that of the vaned diffuser, and in addition, the height of the fluid flow path including the diffuser, the stable flow path is low, so it has the disadvantage of increasing the wet area and thus increasing the friction loss. shortcoming. In addition, even if this diffuser is used, it is difficult to absolutely prevent the rotation separation, and the reliability is lowered.

On the other hand, the efficiency can be increased by using a high-density vaned diffuser (the vaned diffuser has a larger chord-to-pitch ratio). However, when this type of vaned diffuser is used, fluctuations are generated at small flow rates due to the separation of the vanes themselves, and furthermore, there is a narrowing of the operating range due to choking in the region of larger flow rates. Disadvantages and therefore impractical.

It is known that a low-density vaned diffuser with a smaller chord pitch ratio is more efficient than a vanedless diffuser, resulting in a wider operating range. However, in order to employ such a low-density vane diffuser, a vaneless diffuser must be provided downstream of the low-density vane diffuser in order to obtain greater pressure recovery. In the case of low-density vane diffusers, the flow path height of the vaneless portion downstream of the guide vanes has hitherto been made the same as the flow path height of the vane diffuser. The use of low-density vaned diffusers cannot divert the flow sufficiently. Thus, if the fluid inlet angle into the diffuser is small, even if the flow is deflected to the extent that it is in the vaneed part of the diffuser, rotational separation will occur in the vaneless part, in which case the operating range is limited.

In the above-mentioned example disclosed in Japanese Utility Model Unexamined Publication No. 56-97598, considering that the diffuser can be used in a compressor stage with a relatively high specific speed, the height of the flow path is sharply contracted downstream of the diffuser guide vane, so that The axial height of the runner is reduced. However, in this known example, any consideration of rotational separation is insufficient to extend the operating range of the compressor. That is, in this known example, the following two points that are important for preventing rotational separation are not considered. The first point is the flow path height ratio (contraction ratio) between the vane portion and the vaneless portion. In the example disclosed in the above-mentioned Japanese Utility Model Unexamined Publication No. 56-97598, the value is 0.6 to 0.9, however, it is insufficient from the viewpoint of preventing rotation separation.

The second point is that the flow is unstable due to the non-uniform flow downstream of the diffuser guide vane. The flow downstream of the diffuser vane is not uniform in the peripheral direction due to the wake of the vane, especially in the low specific speed compressor stage, the flow angle (the angle measured in the peripheral direction) even when the flow channel passes through the vane Portion post is also smaller. Since the flow in the vaneless part is a decelerating flow, this uneven flow distribution is difficult to be consistent. Furthermore, due to the large static pressure gradient in the radial direction, the flow becomes unstable. Therefore, if the diffuser shrinks sharply or discontinuously at the vaneless portion, the static pressure gradient in the radial direction becomes discontinuous, and the flow in the peripheral direction cannot be consistent and becomes unstable. From the viewpoint of preventing rotational separation Look, this has the opposite effect.

In the low specific speed compressor stage, the inlet angle into the diffuser is small, so when the diffuser vanes are insufficient to deflect the flow, or when the diffuser vanes are partially separated, in the diffuser The area downstream of the leafy portion can cause spin separation.

Japanese Patent Unexamined Publication No. 1-125599 discloses an example in which the guide vanes of the diffuser deflect the flow, and at the same time, the flow path is also contracted without applying a large load on the guide vanes. Parts can deflect the flow considerably. In this known example, the flow angle of the inlet of the vaneless part downstream of the vane part of the diffuser is relatively large, so that the advantage of reducing the length of the flow channel of the vaneless part can be obtained. However, the overall flow channel height of the vaneless section becomes lower and the wet area of the fluid becomes larger. Therefore, the two effects cancel each other out, so that the effect of reducing friction loss in the bladeless part cannot be fully revealed.

As mentioned above, especially in the low specific speed centrifugal compressor stage, it is important to prevent rotational separation in the diffuser, in addition to the performance indicated by efficiency and operating range, however, in the above-mentioned conventional techniques, sufficient consideration has not been given to meet these requirements at the same time.

An object of the present invention is to provide a centrifugal compressor with a low specific speed centrifugal compressor stage, specific speed 80-250, wherein the rotational separation generated in the diffuser is prevented, and has high efficiency, wide operating range and high reliability, and also provides a diffuser for centrifugal compressors.

Another object of the present invention is to provide a diffuser for a centrifugal compressor in which the structure for preventing rotational separation is simple and low in cost, and also to provide a centrifugal compressor having such a diffuser.

Still another object of the present invention is to provide a diffuser for a multi-stage centrifugal compressor that prevents rotational separation, and also to provide a centrifugal compressor having such a diffuser.

In order to achieve the above object, according to one aspect of the present invention, a single-stage or multi-stage centrifugal compressor is provided, comprising: a rotating shaft, one or more impellers mounted on the rotating shaft, and a first bladed diffuser A compressor which is located radially outside of at least one impeller and has two opposing wall surfaces and a plurality of first guide vanes spaced from each other in the circumferential direction arranged between the wall surfaces, wherein the vaneless diffuser Located on the downstream side of the first vane diffuser, the vaneless diffuser has two opposing wall surfaces between which the axial distance gradually decreases from the inlet to the outlet.

According to another aspect of the present invention, there is provided a single-stage or multi-stage centrifugal compressor comprising: a rotating shaft, one or more impellers mounted on the rotating shaft, and a vaned diffuser positioned at least Radially outer of an impeller and having two opposed wall surfaces and a plurality of first guide vanes spaced apart from each other in the circumferential direction arranged between the wall surfaces, wherein, on the downstream side of the first vaned diffuser A second vane diffuser is provided, the second vane diffuser has two opposite wall surfaces and a plurality of second guide vanes spaced apart from each other along the circumferential direction between the wall surfaces, the first The axial distance between the two wall surfaces of the two-vane diffuser gradually decreases from the inlet to the outlet.

Preferably, the meridional cross-sectional shape of each of the two wall surfaces forming the vaneless diffuser consists of a smooth line including a straight line or an arc.

Preferably, the inlet guide vane angle of the first guide vane of the first vaned diffuser is 4°-12° measured in the peripheral direction.

Preferably, the axial height of the outlet of the vaneless diffuser is 0.3-0.6 times greater than the axial height of the outlet of the first vaned diffuser.

One of the opposed wall surfaces forming the vaneless diffuser is arranged radially in a meridional plane section, and the other wall surface is gradually inclined in the downstream direction approaching said one wall surface.

The vane height at the outlet of the impeller is equal to the distance between two opposing wall surfaces of the first vaned diffuser.

Both opposing wall surfaces forming the vaneless diffuser are gradually inclined toward the side corresponding to the impeller core plate in the downstream direction.

Preferably, the specific speed of the impeller is 80-250, especially, the specific speed of the impeller is 100-200.

Preferably, the first vanes of the first vaned diffuser are of such dimensions that a line perpendicular to the first vane at the outlet does not intersect adjacent first vanes.

In order to achieve the above object of the present invention, according to the third aspect of the present invention, a single-stage or multi-stage centrifugal compressor is provided, comprising: a rotating shaft, one or more impellers mounted on the rotating shaft, and a first a vaned diffuser located radially outwardly of at least one of the impellers and having two opposed wall surfaces and a plurality of first vanes spaced circumferentially from one another disposed between the wall surfaces, wherein, A rotational separation protector that prevents rotational separation of fluid flowing out of the impeller surrounds the outer periphery of the first vaned diffuser.

In order to achieve the above objects, according to a fourth aspect of the present invention, there is provided a diffuser, comprising: a first vane diffuser portion on the outer periphery of the impeller, surrounding the first vane diffuser portion A vaneless diffuser portion on the outer periphery, the first vane diffuser portion has two opposing wall surfaces and a plurality of guide vanes spaced apart from each other in the circumferential direction between the wall surfaces, and has two opposing A vaneless diffuser with wall surfaces placed, wherein, in a meridian section, the distance between two wall surfaces forming the vaneless diffuser portion gradually decreases gradually from the inner side to the outer side.

Fig. 1 is a longitudinal sectional view of a multi-stage centrifugal compressor of the present invention.

Fig. 2 is a longitudinal sectional view of an intermediate stage of the centrifugal compressor of Fig. 1, mainly showing a diffuser part in an enlarged manner.

Fig. 3 is a sectional view along line A-A in Fig. 2 .

4-8 show longitudinal sections of another embodiment of the invention, each mainly showing an enlarged diffuser section.

Figure 9 is a front view of one embodiment of the vaned diffuser of the present invention.

10 and 11 are longitudinal sectional views of still another embodiment of the present invention, each mainly showing an enlarged diffuser portion.

Fig. 12 is a longitudinal sectional view of an embodiment of the single-stage centrifugal compressor of the present invention.

Several embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 1 shows a longitudinal sectional view of a multistage centrifugal compressor of the present invention. A compressor unit formed in a multi-stage manner by a plurality of impellers 1a-1e and a plurality of diffusers composed of vane diffusers 2a-2e and vaneless diffusers 3a-3e is stacked together in the axial direction to form Multi-stage centrifugal compressor 100. That is, a plurality of impellers 1a-1e are axially stacked on a rotating shaft 8, and both ends of the rotating shaft 8 are rotatably supported by bearings 10, respectively. The vane diffusers 2a-2e are respectively located radially outside the impellers 1a-1e (that is, the downstream side of the impellers 1a-1e), and there are also vaneless diffusers 3a-3e on the radially outside of these vane diffusers. . The vaneless diffusers 3a-3e in all stages except the last stage are respectively connected with the rotary pipe 4, and each rotary pipe supplies the working medium to the next stage, forming a radially inward diffuser on the downstream side of each rotary pipe 4 Circuit 5 for supplying the working medium. A scroll 6 (scroll) is formed on the downstream side of the last-stage vaneless diffuser 3e to collect the working medium flowing out of the last-stage impeller and discharge it into a discharge pipe (not shown in the figure). The vaned diffusers 2a-2e, the vaneless diffusers 3a-3e, the rotary tube 4, the circuit 5 and the scroll tube 6 are all fixed parts, which are fixed or formed on the compressor housing 7. An interstage seal portion 12 for preventing leakage is formed between any two adjacent stages of the compressor. Here, the vaneless diffuser of each stage except the last stage is a part extending from the outer radial position 60 of the guide vane of the vaned diffuser to the starting bending position 61 of the rotary pipe 4, and the part of the last stage The vaneless diffuser is the portion extending from the outer radial location of the vaned diffuser to the end of the wall surface protruding into the scroll casing 6 .

Next, the operation of the multistage centrifugal compressor constructed in this way will be described. The pressure of the working medium sucked in through the inlet 9 is increased by the first-stage impeller 1a, while passing through the vane diffuser part 2a and the vaneless diffuser part 3a, the pressure is further increased, and then, the working medium passes through the rotary pipe 4 The flow direction of the flow changes from radially outward to radially inward. Afterwards, the working medium is supplied to the second-stage impeller through the circuit 5. Then, such a flow is repeated at each stage, so that the working medium The pressure is gradually increased, and the working medium is fed into the discharge pipe through the discharge scroll 6 after passing through the last stage diffuser. In such a multi-stage centrifugal compressor, the specific speed gradually decreases from the first stage toward the last stage, and generally, the specific speed near the last stage is less than 200.

Figure 2 shows a detail view of a portion of a stage of the multi-stage compressor of Figure 1 extending from the outlet portion of the impeller towards the next stage. Fig. 3 is a view along line A-A of Fig. 2 . The height b of the axial channel of each vaneless diffuser part 3 is radially from the outlet 60 of the vaneless diffuser part 2 (the inlet of the vaneless diffuser part) to the outlet 61 of the vaneless diffuser The field decreases gradually or slowly. A wall surface 58 constituting the vane diffuser 2 and the vaneless diffuser 3 is integrally formed with its inner diameter end from the impeller outlet portion and its outer diameter end at the position where the swivel tube 4 starts to bend.

In this embodiment, see Fig. 2, the flow direction of the working medium flowing out from the impeller is changed by the guide vane 2z of the vane diffuser whose guide vane height is substantially equal to the height of the vane of the impeller, and the working The medium flows into the vaneless diffuser part 3 . In the low specific speed (specific speed does not exceed 200) compressor stages, the operating performance is enhanced by reducing the discharge angle of the impeller. Moreover, the traditional method of narrowing the width of the flow channel at the diffuser outlet increases the area where fluctuations occur, which is not desirable. It is ideal to reduce the installation angle α of the diffuser guide vanes to 4°-12°. If this mounting angle α is increased to some extent, the flow angle is increased by deflection of the flow direction by the guide vanes 2z, thereby suppressing the rotational separation. However, in this embodiment, when the installation angle α is less than 12°, the inlet angle of the working medium entering the vaneless portion 3 does not increase much even when the flow is deflected and decelerated by the guide vanes 2z. In the case where the vaneless portion 3 is formed of parallel walls, the flow state is as shown by the dotted line in FIG. 3 . As a result, the average flow angle of the working medium becomes smaller, and under the influence of the wake 14 of the diffuser guide vane 2z, the flow becomes unstable and rotation separation tends to occur.

In this embodiment, the wall 31 of the vaneless diffuser portion 3 corresponding to the impeller side plate is gradually inclined in the radially outward direction toward the side corresponding to the impeller core plate. In the embodiment shown in Fig. 2, the flow path height b of the vaneless diffuser part 3 decreases substantially linearly in the radial direction, and by gradually reducing the flow path height b of the vaneless diffuser part 3 in this way, the Flow 20 of Figure 3, and the flow angle is larger compared to flow 20a. Therefore, the formation of the wall surface boundary layer can be suppressed, the flow can be stabilized, and the spin separation can be suppressed. In this embodiment, the shrinkage ratio b ₂ /b ₁ is about 0.5. If the constriction ratio b ₂ /b ₁ is smaller, the average flow angle of the working medium in the vaneless diffuser part 3 becomes larger, which enhances the protection effect of the rotational separation and also enhances the reliability of overcoming the rotational separation . However, if the constriction ratio b ₂ /b ₁ is reduced, the flow channel height downstream of the vaneless diffuser sections 3a-3e is also reduced, the wetted perimeter area and thus the friction losses increase. Therefore, it is desirable that the shrinkage ratio b ₂ /b ₁ is 0.3-0.6, preferably about 0.5.

As mentioned above, it is necessary to provide the sealing portion 12 between any two adjacent stages of the multistage compressor, therefore, it is obvious that the width L of the inner wall of the rotary pipe 4 is larger than the predetermined length. Therefore, in the case of a low specific speed stage, the radius of curvature r of the rotary tube 4 increases unnecessarily, increasing the length of the circuit, thereby increasing the friction loss. In this embodiment, the diffuser wall 31 near the previous stage (that is, on the side corresponding to the side plate of the impeller) is inclined, and the loop height of the vaneless part gradually decreases in the downstream direction. With this structure, the radius of curvature r of the inner wall of the swivel tube 4 can be made small compared with when the wall 31 corresponding to the core plate of the impeller is inclined, so that the frictional loss in the swivel tube 4 can be reduced.

FIG. 4 is a longitudinal sectional view corresponding to FIG. 2 of another embodiment of the diffuser according to the invention. The difference between this embodiment and the embodiment of FIG. 2 is that the wall surface 34 of the vaneless diffuser 3 corresponding to the impeller core plate is inclined toward the side corresponding to the impeller side plate. In this embodiment, the two wall surfaces 33 and 34 of the vaneless diffuser portion are linearly formed in an inclined manner, and the height of the flow channel gradually decreases in the downstream direction, so that the degree of constriction of the flow channel is substantially the same as that of the opposite wall surfaces. The same, so the two wall surfaces form approximately the same boundary layer, which can make the flow distribution in the height direction of the flow channel more uniform, and can enhance the recovery of the static pressure in the vaneless diffuser part 3 .

Fig. 5 shows a modification of the embodiment shown in Fig. 4, the two walls 35, 36 of the vaneless diffuser part 3 adjacent to the vaned diffuser are each formed by a curved surface with a radius of curvature R1, while approaching the Parts of each of the two walls of the tube are formed by curved surfaces with a radius of curvature R2, the two walls have approximately the same profile, and the height of the flow channel tapers in the downstream direction. In this modified example, the flow channel shrinks slowly, so that the liquid flow in the diffuser is more gentle, so that the effect of reducing the flow loss in the vaneless diffuser can be further obtained.

Fig. 6 shows the modified example of Fig. 2 embodiment, and the wall surface 37 of vaneless diffuser 3 corresponding to impeller side plate is formed by the arc shape that radius of curvature is R1, and the flow channel of vaneless diffuser 3 is downstream The direction gradually shrinks. In this modification, compared with the embodiment shown in FIG. 2 , the disadvantages are that the processing is inconvenient and the wet area is increased. However, the constriction rate of the first half of the vaneless diffuser 3 flow path is increased, increasing the meridian plane speed (meridian plane speed) of the first half of the vaneless diffuser part 3, so that the early vaneless diffuser part 3 The flow angle can be increased, therefore, a surprising effect of preventing rotational separation is obtained. That is, this modification is applicable to give rotation separation protection superior to performance. In this modification, although the wall surface of the vaneless diffuser corresponding to the impeller side plate is formed as a smooth surface by one arc, the wall surface may also be formed as a curved surface by connecting plural arcs together, or A curved shape and a straight line can be combined to form a smooth curved surface. With this arrangement, a very smooth curved surface can be easily formed by an NC machining tool.

Fig. 7 is another modification of the embodiment in Fig. 2. By connecting two arcs R1 and R2 together, the wall 39 of the vaneless diffuser 3 adjacent to the vaned diffuser 2 forms a curved surface. In this modified example, the effect similar to that obtained by the embodiment in Fig. 2 can be obtained, and the processing of the diffuser is also slightly inconvenient compared with the embodiment in Fig. 2, but compared with the embodiment in Fig. Effect of flow loss in diffuser section 3.

FIG. 8 is a longitudinal sectional view of still another embodiment of the present invention, and FIG. 9 is a transverse sectional view thereof. The second vane diffuser 50 instead of the vaneless diffuser has three rotating guard guide plates 40, the second diffuser 50 is located downstream of the vane diffuser 2, and the second vane diffuser 50 has The runner height gradually shrinks in the downstream direction.

In a vaneless diffuser, when the reverse flow of the boundary layer occurs locally, it will cause a separation flow, and the separation flow will rotate in the diffuser, thereby creating a rotational separation. In this embodiment, even when a small reverse flow occurs in the second vane diffuser section instead of the conventional vaneless diffuser, the rotating guard guide stops the rotation, thereby preventing the generation of a wide range of separated flow. For this reason, it is preferable to provide several rotating guard plates 40, and in this embodiment, there are three guard plates. With this structure, rotation separation can be prevented more reliably, and a highly reliable compressor can be provided. When the rotating fender 40 is provided, the contraction ratio b ₂ /b ₁ of the second vaned diffuser portion 50 can be set to be larger than 0.3-0.6.

Figures 10 and 11 show, respectively, another embodiment of the diffuser of the present invention, the two wall surfaces 41 and 42 forming the vaneless diffuser part 3, and the two wall surfaces forming the second vane diffuser 50. 44 and 45 are inclined towards the side plates corresponding to the core plate of the impeller. In addition, the flow path height of each of the vaneless diffuser portion 3 and the second vane diffuser portion 50 gradually contracts in the downstream direction. While adopting this structure, determining the necessary axial length L for installing the intermediate seal 12 can reduce the radius of curvature r of the inner wall of the rotary pipe 4 .

The vane diffuser 2 and the vaneless diffuser 3 reduce the flow velocity, but the inlet radius of the swivel tube 4 is not different from its outlet radius. Therefore, in the low specific speed stage of the compressor whose peripheral member is large, the flow velocity does not decrease, and the greater the flow path length, the greater the friction loss. Therefore, by reducing the radius of curvature of the inner wall of the swivel pipe as in this embodiment, the effect of reducing friction loss in the swivel pipe portion can be obtained.

FIG. 12 shows a single-stage centrifugal compressor. The impeller 1 is installed on the rotating shaft 8a. The fluid passes through the impeller 1, the vane diffuser part 2 and the vane diffuser part 3, and is discharged from the scroll casing 6. Here, the vaneless diffuser section 3 is the section extending from the outer radial position of the guide vanes of the vaned diffuser section 2 to the end of the wall surface 46 protruding into the scroll casing 6 . In this embodiment, the wall surface 46 corresponding to the impeller side plate (one of the two wall surfaces forming the vaneless diffuser portion 3 ) is inclined radially outward, while the wall surface 47 corresponding to the impeller core plate is The wall surface 46 is inclined. With this structure, the fluid gradually contracts in the downstream direction. A scroll 6 is formed downstream of the diffuser portion, collects the working medium discharged from the impeller 1, and supplies it to a discharge pipe (not shown in the figure). The vaneless diffuser is constricted and with this arrangement the outlet housing can be freely chosen without compromising fluid performance and the effect of inhibiting spin separation. In this embodiment, the effect of preventing the rotation separation is obtained regardless of the specific rotational speed of the impeller, but when the specific rotational speed is small and especially not more than 200, this effect is very surprising.

Furthermore, in any of the above-described embodiments, the vaned diffuser is not limited to a vaned shape, and any type of diffuser may be used. However, its effect is significant in low-density vaned diffusers. Herein, the term "low-density vaned diffuser" means a vane whose vanes are short such that a line perpendicular to the inlet angle of the diffuser vane does not pass through adjacent vanes and divides the diffuser vane inlet The value divided by the average pitch of the diffuser guide vane outlet and the chord length of the diffuser guide vane is not greater than 1.

As mentioned above, in this embodiment, in the low specific speed stage of the multi-stage centrifugal compressor (the specific speed is 80-250, preferably 100-200), a vaneless diffuser part is formed or a vane diffuser is formed. Both wall surfaces of the second vane diffuser portion downstream of the compressor are tapered gradually in the downstream direction, and with this structure, the effect of preventing rotational separation can be obtained. In the low specific speed stage of the single-stage centrifugal compressor (the specific speed is 80-250, preferably 100-200), the vaneless diffuser part located downstream of the vane diffuser gradually contracts in the downstream direction, using this With this structure, a compressor that prevents rotation separation and has a wide operating range can be obtained.

The described preferred embodiments of the invention have been described by way of example without limitation, the scope of the invention is shown in the appended claims and the invention embraces any modification which falls within the scope of the claims .

Claims (16)

1. multistage centrifugal compressor, comprise: a running shaft, a plurality of impellers that are installed on the described running shaft, with one first vaned diffuser, it the radially outer of the one-level at least of described impeller and have two opposed wall surfaces and a plurality of be arranged between the described wall surface, at first stator of circumferencial direction space; It is characterized in that, be provided with vaneless diffuser in the downstream side of described first vaned diffuser, described vaneless diffuser has two opposed wall surfaces, and the axial distance between the two reduces gradually from inlet to outlet.

2. according to the described centrifugal compressor of claim 1, it is characterized in that each the meridian plane sectional shape of described two wall surfaces that forms described vaneless diffuser is made of straight line.

3. according to the described centrifugal compressor of claim 1, it is characterized in that each the meridian plane sectional shape of described two wall surfaces that forms described vaneless diffuser comprises an arc.

4. according to the described centrifugal compressor of claim 1, it is characterized in that, is 4 °-12 ° at the inlet guide vane angle of first stator periphery orientation measurement, described first vaned diffuser of first stator of described first vaned diffuser.

5. according to claim 1 or 4 described centrifugal compressors, it is characterized in that the axial height of described vaneless diffuser outlet is that the 0.3-0.6 of axial height of described first vaned diffuser outlet is doubly big.

6. multistage centrifugal compressor, comprise: a running shaft, a plurality of impellers that are installed on the described running shaft, with one first vaned diffuser, it the radially outer of the one-level at least of described impeller and have two opposed wall surfaces and a plurality of be arranged between the described wall surface, at first stator of circumferencial direction space; It is characterized in that, be provided with one second vaned diffuser in the downstream side of described first vaned diffuser, described second vaned diffuser has second stator of two opposed wall surfaces and a plurality of space settings along the circumferential direction between described wall surface, and the axial distance between two wall surfaces of described second vaned diffuser reduces gradually from inlet to outlet.

7. according to claim 1 or 6 described centrifugal compressors, it is characterized in that one of described opposed wall surface that forms described vaneless diffuser radially is arranged to the cross section of meridian plane, and another wall surface moves closer to a described wall surface at downstream direction.

8. according to claim 1 or 6 described centrifugal compressors, it is characterized in that the distance between two opposed walls surfaces of the blade height at described impeller outlet place and described first vaned diffuser equates.

9. according to claim 1 or 6 described centrifugal compressors, it is characterized in that described two the opposed wall surfaces that form described vaneless diffuser all tilt along downstream direction gradually towards the sidepiece corresponding to described impeller central layer.

10. according to claim 1 or 6 described centrifugal compressors, it is characterized in that the specific speed of described impeller is 80-250.

11., it is characterized in that the specific speed of described impeller is 100-200 according to claim 1 or 6 described centrifugal compressors.

12., it is characterized in that first stator of described first vaned diffuser has such size according to claim 1 or 2 described centrifugal compressors, make perpendicular to the line of described first stator not crossing with the first adjacent stator.

13. centrifugal compressor, comprise: a running shaft, an impeller that is installed on the described running shaft, with a vaned diffuser, it the radially outer of described impeller and have two opposed wall surfaces and a plurality of be arranged between the described wall surface, at the stator of circumferencial direction space; It is characterized in that, in the downstream side of described vaned diffuser one vaneless diffuser is set, described vaneless diffuser has two opposed wall surfaces, and the axial distance between two wall surfaces reduces lentamente gradually from inlet to outlet.

14., it is characterized in that the scope of the specific speed of described impeller is 80-250 according to the described centrifugal compressor of claim 13.

15., it is characterized in that the stator of described vaned diffuser has such size according to the described centrifugal compressor of claim 13, feasible not crosscut of line adjacent guide vane perpendicular to described stator.

16. Diffuser, comprise: the vaned diffuser part that is located at the outer periphery of impeller, one is centered around the vaneless diffuser part of the outer periphery of described vaned diffuser, described vaned diffuser partly has the stator of two opposed wall surfaces and a plurality of space settings along the circumferential direction between described wall surface, and described vaneless diffuser has two opposed wall surfaces; It is characterized in that on the meridian cross section, the distance that forms between two wall surfaces of described vaneless diffuser reduces gradually from the inner to the outer end.

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