JPS60132099A - centrifugal compressor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] (1) The present invention relates to a centrifugal compressor equipped with a vaned diffuser used in a turbo refrigerator, etc., and particularly to the structure of the vaned diffuser.

[Background of the invention]

As shown in FIGS. 1 and 2, a typical conventional centrifugal compressor has two compressors facing each other in order to efficiently convert the kinetic energy of a fluid flow 2 discharged from an impeller 1 into pressure energy. It has a structure in which a vaned diffuser 3 in which guide vanes 3 are arranged in a circular shape between the provided side walls is provided on the discharge side (downstream side) of the impeller 1, and on the outer peripheral side of the impeller 1. A diffuser flow path 5 is formed between the guide vanes 4, 4, and fluid flows in each of these flow paths 5 in the direction of the arrow 6. In such known compressors, surging occurs under low flow operating conditions, resulting in a significant reduction in performance, and in extreme cases, normal operation may become impossible.

Next, for convenience of explanation of the surging phenomenon, two adjacent guide vanes 4a and 4b of the guide vanes 4 of the diffuser as shown in FIG. 3 will be described (2).

Due to the discharge flow from an impeller (not shown) blowing onto the guide vanes 4a and 4b, the side 8 of the guide vane 4a facing the flow path 5a becomes a pressure surface, and the side 9 of the guide vane 4b facing the flow path 5a becomes a negative pressure surface. It becomes a pressure surface. The fluid phenomena that occur near the guide vanes 4a and 4b are as shown in FIGS. 4 and 5, and FIG.
The figures each show a state in which the diffuser stalls at a relatively small flow rate.

4 and 5, considering the line BC connecting the leading edges 7a and 7b of the guide vanes 4a and 4b, this line BC is approximately parallel to the tangent to the impeller (not shown) in the vicinity of the illustration. It can be considered that Arrows 11a and llb in the figure indicate the impeller discharge flows blown onto the guide vanes 4-a and 4b, respectively, and dash-dotted lines 12a and 12b indicate the guide vanes 4a, respectively.

4b is the warp line.

At the design point, as shown in FIG. 4, the angle δ between the discharge flow 11b and the approximate tangent line BC approaches the angle δ2 between the warp line 12b(3) and the approximate tangent line BC. These angles δ
Guide vane 4 is set so that the difference δ between 1 and δ2 is a small value.
If b is provided, the difference δ is a small value, so the discharged fluid flows filling the flow path 5a, the diffuser exhibits the specified performance, and the compressor can operate normally. is possible.

If the flow rate is reduced while maintaining the rotational speed of the impeller in this normal state, the tangential component of the impeller's discharge flow velocity will hardly change, and the radial component will decrease, so the flow 11. 'a, 11' b is in a direction close to the direction of the approximate tangent line BC, as shown in FIG. Therefore, the angle between the flows 11'a, 11'b and the approximate tangent line BC is:
Curved line 12a.

12b and the approximate tangent BC by δ8. If this value of 62 is larger than the limit value determined by the shape and arrangement of the guide vanes 4a, 4b, the flow 11' b
does not flow along the negative pressure surface 9 of the guide vane 4b, so a large-scale separated flow region 13 occurs.

(4) This separated flow region 13 occurs not only on the negative pressure surface of the guide vane 4b, but also on most or all of the guide vanes constituting the diffuser, and a sufficient pressure increase is not achieved and a surging phenomenon occurs. In order to prevent such a surging phenomenon, there is generally a means for rotating the guide vanes 4 in the direction of arrow D-E about a support shaft 15 parallel to the rotation axis 14 of the impeller 1, as shown in FIG. It has been implemented.

However, according to the above means, in order to drive all the guide vanes 4, the mechanism for driving the support shaft 15 becomes large, and the entire diffuser device also becomes large.
The weight increases, which increases the cost. In addition, since all the guide vanes 4 are rotated, a relatively large amount of fluid leaks from the gap between the side surface of the guide vane 4 and the casing surface facing it, so that the centrifugal compressor can operate normally. The disadvantage is that the performance at times deteriorates.

[Purpose of the invention]

In view of the above, it is an object of the present invention to prevent the occurrence of surging phenomenon during small flow (5) operation using a simple structure, and to improve the efficiency of the compressor.

[Summary of the invention]

In order to achieve the above object, the present invention provides a centrifugal compressor equipped with a known bladed diffuser, in which a closing member is embedded in one side wall of the diffuser so as to be movable in the axial direction, and the closing member is provided during low flow rate operation. This is characterized in that the flow path is partially blocked by advancing into the flow path between the guide vanes or in the circumferential direction on the inlet side or the circumferential direction on the outlet side of the guide vanes.

[Embodiments of the invention]

Examples of the present invention will be described below.

In FIGS. 7 and 8, 1 is an impeller attached to a rotating shaft 14, and 16 is inserted into a groove 19 provided in a diffuser side wall 18 on one side (the left side in the figure) through a support rod 17 in the axial direction. Closing members movably housed in, 20a to 20
n is an arbitrary number of guide vanes arranged in a circular shape on the outer peripheral side of the impeller 1 and between the opposing diffuser side walls 18, 18 (6).

Next, the operation of this embodiment configured as described above will be explained.

When the compressor is operated at a large flow rate, the closing member 16 is housed in a groove 19 provided in the diffuser side wall 18, as shown by the solid line in FIG. The flow 2 flows filling the flow path 21 between adjacent guide vanes of the guide vanes 20a to 2On. Conversely, when the compressor is operated at a small flow rate, the closing member 16 is connected to the support rod 17.
moves in the axial direction (to the right in the figure), and partially blocks the inlet part 21a of the flow path 21 between the guide vanes 20a and 20b (not shown), as shown by the one-point chain in Figure 7. do. That is, as shown in FIG. 8, narrow channels 22a and 22b are formed between the closing member 16 and the guide vanes 20a and 20b, so that the flow of fluid discharged from the impeller 1 is limited to the narrow channels 22a and 22b, respectively. The fluid flows through the flow paths 22a and 22b as shown by arrows.

The narrow flow passages 22a and 22b are shaped (7) to have the width necessary for the required small flow rate to flow, so that no backflow occurs and the compressor does not suffer from the surging phenomenon. There is no fear of it happening. Narrow passage 22
a and 22b are enlarged from the inlet side (impeller 1 side) to the outlet side (counter-impeller side). In other words, if the impeller is formed so that it expands as it moves away from the impeller 1, part of the kinetic energy of the fluid flow discharged from the impeller 1 can be converted into pressure, thereby increasing the efficiency of the compressor. There is an advantage that it can be further improved.

In the second embodiment shown in FIG. 9, the closing member 16 is provided in a part of a large number of channels 21 formed by guide vanes 20, that is, in an even-numbered channel or an odd-numbered channel.

With this configuration, although the flow rate control performance is inferior to that of the first embodiment (FIG. 8), it has the advantage of simplifying the structure.

In the third embodiment shown in FIG. 10, a long guide vane 2OL and a short guide vane 20M are arranged in combination, and a circumferentially long closing member 16A is arranged on the inlet side of the short guide vane 20M. . This configuration (8) has the advantage that the number of closing members can be reduced and the structure can be further simplified.

In the fourth embodiment shown in FIG. 11, the closing members 16 are arranged in the circumferential direction on the inlet side of the guide vanes 20, that is, on the inner circumferential side of the guide vanes 20, and the gap 23 between the adjacent closing members 16° 16 is reduced. There is a flow path and a chittle during flow rate operation. With this configuration, there is an advantage that the accuracy of the relative dimensions of the guide vane 20 and the closing member 16 does not have to be strict.

In the fifth embodiment shown in FIG. 12, the closing members 16 are arranged in the circumferential direction on the outlet side of the guide vanes 20, that is, on the outer circumferential side of the guide vanes 2O. With this configuration, there is an advantage that the accuracy of the relative dimensions of the guide vane 20 and the closing member 16 does not have to be strict, as in the fourth embodiment.

〔Effect of the invention〕

As described above, according to the present invention, the simple structure can prevent the surging phenomenon from occurring during low flow rate operation and improve the efficiency of the compressor.

(9)

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a centrifugal compressor, Figure 2 is a view taken along the line A-A in Figure 1, Figure 3 is a partially enlarged view of the guide vane in Figure 2, and Figure 4. 5 is an explanatory diagram of the operation, FIG. 6 is a schematic diagram of a conventional surging prevention means, FIG. 7 is a sectional view of a main part showing an embodiment of the centrifugal compressor of the present invention, and FIG. The BB arrow view and FIGS. 9 to 12 are diagrams showing essential parts of other embodiments of the present invention. 1... Impeller, 16.16A... Closing member, 18.
...Diffuser side wall, 19...Groove, 20.20a~
20n. 20L, 20M--Guide vane, 21--Flow path, 21
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Claims (1)

[Scope of Claims] 1. A centrifugal compressor in which a vaned diffuser having guide vanes arranged in a circular shape between opposing side walls is provided on the outer peripheral side of the impeller, and a closing member is provided on one side of the side wall. The closing member is buried so as to be movable in the axial direction, and when operating at a small flow rate, the closing member is advanced into the flow path between the guide vanes or in the circumferential direction on the inlet side of the guide vanes or in the direction toward the first side. A centrifugal compressor characterized by being partially blocked. 2. A patent characterized in that the flow paths formed between the closing member and the guide vane or between the closing members in the extended state of the closing member are formed so as to expand as they move away from the impeller. A centrifugal compressor according to claim 1.