JPS6165099A - Return channel of centrifugal compressor - Google Patents

Abstract

PURPOSE:To relax a rapid increase and decrease in a speed of fluid, by providing slits in return vane so as to free an outflow and an inflow of the fluid in a belly surface side and a back surface of the vane in the return channel of a centrifugal compressor. CONSTITUTION:A centrifugal compressor has an impeller 1 and a seal device 3, and a return vane 9 in a return channel 10 in the centrifugal compressor provides slits 14 connecting a belly surface side of the return vane 9 with its back surface side and permitting fluid to freely circulate. Accordingly, the centrifugal compressor, allowing the fluid to flow in accordance with its flow amount from the belly surface side to the back surface side or reversely to that direction so as to relax a rapid increase and decrease in a speed of the fluid, enables the generation of exfoliation and surging to be prevented particularly in a low flow quantity range of air by suppressing an increase of loss in the whole flow quantity range of air.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has a configuration in which velocity energy given by an impeller is recovered by a diffuser, decelerated and pressurized, and unrecovered velocity energy is recovered by a return channel. The present invention relates to a return chamfer in a centrifugal compressor having a centrifugal compressor.

[Prior art]

Conventionally, in a multi-stage compressor having a return channel, as shown in FIG. and each blade m1. l' is accommodated in an impeller chamber partitioned by the compressor main body 2, suction cover 5, and middle body 6.6'6''.The outlet of the impeller 1 passes through a diffuser 7, It connects to the inlet of the impeller 1° of the next stage through a return channel 10 consisting of a U-turn part 8 formed by the middle body 6.6" and a flow path in which a return vane 9 is arranged, and the outlet of the impeller 1° is connected to the inlet of the impeller 1° of the next stage. The misfortune is connected to chamber 11 through the diffuser 7°.

In the figure, 12 is a suction pipe connected to the suction cover 5;
3. +3° is impeller 1. 1' Knoll apparatus is shown.

The action of such a multi-stage compression stage is that the impeller increases the suction T.
Fluid is sucked in from 'l' 12, pressurized, and given velocity energy, and then sent to the diffuser 7 to decelerate, pressurize, and recover velocity energy. However, diffuser 7
, the velocity energy of the fluid is not sufficiently recovered;
It still has considerable velocity energy, and this residual velocity energy is further recovered by reaching the return channel 10 consisting of the U-turn section 8 and the flow path with 1/9th of the return channel. 1', and further reaches the swirl chamber 11 via a diffuser 7'.

[Problem that the invention seeks to solve]

Here, a flow path with a return channel will be considered.

Returning now, if the fluid velocity at one point is C7, the air volume, flow path width, and flow angle (angle with respect to the circumferential direction) at the U-turn exit are Q, B, R-, α, respectively.

When C5-Q-, /2rt Rs Bs Sin α.

becomes. On the other hand, the throat of the return channel (the position where the return vanes start forming the channel) is indicated with t, and the diameter of the throat and the number of vanes are indicated as Dt and Z, respectively.
Then, the velocity C of the fluid at the throat becomes Ct-Qs/ZDt-Bs.

The relationship between C1 and Ct is as shown in Figure 3 (a) and (b), and there is almost no change from C2 to CL at the design air volume, but at air volumes other than the design point, in the low air volume region. It decelerates and increases the speed in the high air volume range, and if the deceleration rate becomes large in the low air volume range, it may cause surging.

That is, outside the design point, the radius R of the throat vane ventral surface side is
At the position, the speed is equal to C3, but the average speed at the throat is Ct, so a rapid deceleration or speed increase is required on the back side of the vane between the radius R1 position and the throat position. (See Figure 3 (b) IIq) Therefore, if the deceleration rate on the back side of the vane increases in a low air volume region, the fluid will separate on the back side of the vane before it reaches the throat, causing a large loss of force, and the air volume will further decrease. This develops into surging.

Therefore, the number of failures, tnn, which represents the performance of the return channel of a conventional centrifugal compressor (total pressure lost from the vane inlet to the vane outlet, divided by the dynamic pressure at the vane inlet to make it dimensionless), is shown in Figure 4. So, at the design point, the lapse coefficient ξ. is the minimum, but it increases dramatically as the air volume deviates from the design air volume.

Here, it is thought that the increase in air loss in the low wind region (■) is largely due to the deceleration from the vane inlet to the throat, while the increase in air loss in the large air volume area is largely due to the increase in speed after the throat. ' The present invention solves the above-mentioned conventional problems, alleviates the drastic increase and deceleration of the fluid on the back side of the return vane, suppresses the increase in li loss in the current wind m range, and is particularly effective for low air volume. The purpose is to prevent the occurrence of 'fiI 1TIIf and surging in the area.

(Means for Solving the Problems) As a means for solving the above-mentioned problems, the present invention recovers the velocity energy given by the impeller using a diffuser, decelerates and boosts the pressure, and further collects the unrecovered velocity energy. In a centrifugal compressor configured to collect fluid in a return channel, a slit is provided in the return vane in the return channel to allow fluid to freely flow in and out from the vent side and the back side of the vane.

With the above configuration, the fluid flows between the ventral side and the back side through the slit, alleviates drastic increase and deceleration, and suppresses the increase in dissipation in the entire air volume range, especially in the low air volume range. The occurrence of peeling and surging can be prevented.

〔Example〕

Embodiments of the present invention shown in FIGS. v and 5 will be described below.

As shown in FIG. 5, a sulin H4 is provided in the return channel 1O in the return channel 10 so as to communicate the vent side and the back side of the return vane 9 and not allow free flow of fluid.

Therefore, the compressor operates at a low wind composition, the deceleration rate on the back side of the vane between the vane inlet and the throat increases, and the flow rate on the back side of the vane decreases. It flows into the back side of the vane through the flow, mitigating the rapid deceleration of the flow and suppressing the development of a boundary layer in this region. Therefore, in operation in a low air volume region below the design point, it is possible to suppress flow separation on the back surface of the vane, and maintain operational performance near the design point.

Further, when the pressure 11 is operated in a large air volume region, the fluid flows through the slit 14 from the back side of the heel 79 to the vent side. This occurs because the pressure relationship after the throat reverses around the design point as shown in Figure 3 (a), and in a large air volume area, the return chancel 1
A flow bypassing the throat of the vane is generated to alleviate excessive speed increase between the vane inlet and the throat, thereby improving the performance of the return channel lO.

Therefore, as shown by the broken line in Fig. 4, the return line in this example is almost the same as the creation point, and the high performance area is expanded to the high air volume area and the low air volume area on both sides of the design point, and the area is wide. I1 can be operated as a highly efficient return channel over the operating range and can also contribute to improving the efficiency of the compressor.

In the embodiment shown in FIG. 5, two slits 14 are provided for each vane in the range from the vane entrance to the throat, but this number may be - or any suitable number of two or more. You can also.

〔Effect of the invention〕

As described above, the present invention provides a slit in the return vane in the return channel to allow fluid to freely flow in and out from the ventral side of the vane, so that the fluid flows from the ventral side to the back side or vice versa depending on the magnitude of the flow rate. This reduces the sudden increase and deceleration of the fluid, suppresses the increase in loss in the entire air volume range, prevents separation and surging in the low air volume range, and improves compressor efficiency in the entire air volume range. The efficiency value at the design point can be improved.

[Brief explanation of drawings]

Figure 1 is a vertical side view of a conventional multistage compressor, and Figure 2 is a vertical side view of a conventional multistage compressor.
The cross-sectional view showing the return vane in Figure 3 (a) is the suction Jl! II? A diagram showing the relationship between F, vane population, and fluid velocity at the throat, Figure 3 (b) is a diagram showing the A19 distribution of fluid at the throat of the channel, and Figure 4 shows changes in fluid flow rate and efficiency of the return channel. figure,
FIG. 5 is a diagram similar to FIG. 2 showing an embodiment of the present invention. 1. Bi impeller, 2- compressor main body, 3- bearing and sole device, 4- drive shaft, 5 suction cover, 6.
6°, 6' Nakatou-7, 7' Diffuser, 8-
U-turn, 9 - return vane, lO - return channel, IL vortex chamber, I2 suction pipe, 13.13'
- Sole device, 14 - Slit, 134 Passage width B at the outlet of the diffuser, - Passage width DL at the exit of the U-turn section Return channel throat diameter C3 Speed of the exit of the U-turn section C4 - Speed of the return chancel throat. Patent Applicant Ebara Corporation Agent Patent Attorney Masayuki Takagi Agent Patent Attorney Yori 1) Takashi Part 3 Figure 3

Claims (1)

[Claims] 1. In a centrifugal compressor having a configuration in which velocity energy given by an impeller is recovered by a diffuser to decelerate and increase pressure, and unrecovered velocity energy is recovered by a return channel, A return channel for a centrifugal compressor characterized by providing a slit in the return vane to allow fluid to freely flow in and out from the ventral and rear sides of the vane. 2. The return channel of a centrifugal compressor according to claim 1, wherein the slit of the return vane is provided in a range from the return vane inlet to the throat of the return vane.