JP2018159306A - Turbo compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a turbo compressor capable of highly accurately judging whether surging occurs.SOLUTION: A turbo compressor (1a) comprises a rotary shaft (11), an impeller (12), a casing (20), a discharge flow passage (25), a microphone (50) and a controller (55). The microphone (50) is disposed while being exposed on a volute (23) or the discharge flow passage (25) inside of the casing (20) or being disposed outside of the casing (20) around the casing (20). In a case where a sound pressure level of a frequency matched to a product of the number of blades (12a) in an outlet (15b) of a flow passage for a working fluid in the impeller (12) and a rotation frequency of the rotary shaft (11) is equal to or higher than a predetermined value in a signal that is outputted from the microphone (50), the controller (55) judges that surging occurs, and performs control for cancelling the surging.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a turbo compressor.

  Surging may occur in a turbo compressor depending on operating conditions. For this reason, a technique for detecting surging in a turbo compressor is known.

  For example, as shown in FIG. 7, Patent Document 1 describes a device that performs surging detection in a turbo compressor 300. This surging detection apparatus includes a pressure detector 308, a motor current detector 309, and a controller 310. The pressure detector 308 detects the inlet pressure of the diffuser 305 of the turbo compressor 300. The motor current detector 309 detects the current of the motor 304 that drives the impeller 303 of the turbo compressor 300. The controller 310 calculates the output signals of the pressure detector 308 and the motor current detector 309, and the reference value PS and the reference value that both the current change rate DA at a predetermined time and the pressure change rate DP at the same time are preset. When greater than AS, a surging signal is output. When the surging signal is output, the opening degree of the guide vane 307 is controlled.

JP-A-6-167299

  According to the technique described in Patent Document 1, occurrence of surging may not be properly detected depending on conditions. Therefore, the present disclosure provides a new technique that can determine whether or not surging has occurred in a turbo compressor with high accuracy.

This disclosure
A rotation axis;
An impeller fixed to the rotating shaft and having a plurality of blades for compressing the working fluid;
A casing having a volute surrounding the impeller radially outward of the impeller;
At least one discharge channel connected to the volute and extending toward the outside of the volute;
A microphone that is exposed to the volute or the discharge flow path inside the casing, or is exposed to the outside of the casing around the casing; and
In the signal output from the microphone, the sound pressure level at a frequency that matches the product of the number of blades at the outlet of the working fluid flow path of the impeller and the rotational frequency of the rotating shaft is a predetermined value or more. In this case, a turbo compressor is provided that includes a controller that determines that surging has occurred and performs control for eliminating the surging.

  The turbo compressor can determine whether surging has occurred or not with high accuracy.

FIG. 1 is a cross-sectional view illustrating an example of a turbo compressor according to the present disclosure. FIG. 2 is a cross-sectional view taken along the line II-II shown in FIG. FIG. 3A is a graph showing changes in pressure over time when surging occurs and when surging does not occur. FIG. 3B is a graph showing the relationship between the magnitude of the sound pressure level and the frequency when surging occurs and when surging does not occur. FIG. 4 is a flowchart showing a process for determining whether or not surging has occurred. FIG. 5A is a front view showing the bearing housing when surging does not occur. FIG. 5B is a front view showing the bearing housing when surging occurs. FIG. 6 is a cross-sectional view illustrating another example of the turbo compressor of the present disclosure. FIG. 7 is a schematic cross-sectional view showing a conventional turbo compressor.

<Knowledge based on studies by the present inventors>
It is conceivable to use a turbo compressor that increases the pressure of the working fluid by rotational kinetic energy in a large heat pump cycle and refrigeration cycle apparatus. In order to properly operate the turbo compressor, there is a predetermined restriction on the relationship between the flow rate of the working fluid and the pressure ratio in the turbo compressor.

  When the rotation speed of the impeller is constant in the turbo compressor, the pressure ratio increases when the flow rate of the working fluid is reduced by restricting the valve (discharge valve) for adjusting the flow rate of the working fluid in the discharge flow path. In this case, when the flow rate of the working fluid is less than a predetermined value, a periodic backflow phenomenon of the working fluid, that is, surging occurs. If surging occurs in the turbo compressor, the rotating shaft may vibrate abnormally and the bearing may be damaged. In addition, since a part of the hot gas in the discharge side space in the turbo compressor flows into the suction side space, the temperature of the working fluid sucked into the impeller rises.

  The critical value of the flow rate of the working fluid where surging occurs increases as the impeller speed increases. Therefore, the turbo compressor is typically operated such that the flow rate of the working fluid does not fall below the critical value of the flow rate of the working fluid where surging occurs. However, surging may occur unintentionally in actual operation of the turbo compressor. For this reason, as in the technique described in Patent Document 1, when a surging detection device is incorporated in a turbo compressor and the occurrence of surging is detected, the operating condition of the turbo compressor is changed so that surging is eliminated. Can be considered.

  However, depending on the conditions, the pressure fluctuation or temperature fluctuation of the working fluid when surging occurs may be small. For example, if the working fluid has a saturated vapor pressure that is lower than atmospheric pressure at normal temperature (20 ° C. ± 15 ° C .: Japanese Industrial Standard JIS Z 8703), or if mild surging occurs, surging has occurred. Sometimes the pressure fluctuation or temperature fluctuation of the working fluid tends to be small. In this case, it may be possible to set the working fluid pressure threshold low to determine whether surging has occurred, but it may exceed that threshold even in normal operation where surging has not occurred. Will be falsely detected. Further, if the threshold value of the working fluid pressure for determining whether surging has occurred or not is set high, surging may not be detected even if surging actually occurs. In this case, the operation of the turbo compressor is continued in a state where surging occurs, and the rotating shaft may vibrate abnormally and the bearing may be damaged.

  Therefore, the present inventors have attempted to develop a technology capable of determining the presence or absence of surging with high accuracy even when the pressure fluctuation of the working fluid when surging occurs is small in the turbo compressor. Specifically, the present inventors made a prototype of a turbo compressor using a working fluid having a saturated vapor pressure lower than the atmospheric pressure at an ordinary pressure at normal temperature. In addition, the present inventors have conducted day and night studies on a technology capable of operating the turbo compressor under conditions where surging occurs and determining the presence or absence of surging with high accuracy. As a result of the study, the present inventors have newly found that a unique sound is generated when surging occurs, and that the frequency of the sound is approximately equal to the product of the number of impeller blades and the rotational frequency of the rotating shaft. I found it. Based on such new knowledge, the present inventors have devised the turbo compressor of the present disclosure. In addition, said knowledge is knowledge based on examination of the present inventors, and does not admit as prior art.

The first aspect of the present disclosure is:
A rotation axis;
An impeller fixed to the rotating shaft and having a plurality of blades for compressing the working fluid;
A casing having a volute surrounding the impeller radially outward of the impeller;
At least one discharge channel connected to the volute and extending toward the outside of the volute;
A microphone that is exposed to the volute or the discharge flow path inside the casing, or is exposed to the outside of the casing around the casing; and
In the signal output from the microphone, the sound pressure level at a frequency that matches the product of the number of blades at the outlet of the working fluid flow path of the impeller and the rotational frequency of the rotating shaft is a predetermined value or more. In this case, a turbo compressor is provided that includes a controller that determines that surging has occurred and performs control for eliminating the surging.

  According to the first aspect, the presence or absence of surging is determined based on the sound pressure level of the specific frequency in the signal output from the microphone, not the pressure fluctuation of the working fluid of the turbo compressor. For this reason, the turbo compressor according to the first aspect can determine the presence or absence of surging with high accuracy even when the pressure fluctuation of the working fluid when surging occurs is small, for example. In addition, the turbo compressor which concerns on a 1st aspect can determine the presence or absence of surging with high precision, even when the pressure fluctuation of the working fluid when surging occurs is not small.

  The second aspect of the present disclosure provides, in addition to the first aspect, a turbo compressor in which the microphone is exposed to the volute or the discharge flow path inside the casing. In this case, sound generated around the turbo compressor is not easily received by the microphone. For this reason, even if the sound generated in the vicinity of the turbo compressor includes a sound of a specific frequency for determining whether or not surging occurs, erroneous detection of the occurrence of surging is unlikely to occur. As a result, the turbo compressor according to the second aspect can more accurately determine the presence or absence of surging.

  According to a third aspect of the present disclosure, in addition to the first aspect or the second aspect, the motor further rotates the rotating shaft, and the controller controls the motor in the control for eliminating the surging. And the turbo compressor which changes the rotation speed of the said rotating shaft is provided. According to the third aspect, when surging occurs, the rotational speed of the rotating shaft is changed, and as a result, surging is eliminated.

  In addition to any one of the first to third aspects, the fourth aspect of the present disclosure further includes a valve for adjusting the flow rate of the working fluid in the discharge flow path, and the controller includes: In the control for eliminating the surging, a turbo compressor is provided that controls the valve to increase an opening degree of the valve. According to the fourth aspect, when surging occurs, the opening of the valve for adjusting the flow rate of the working fluid in the discharge flow path increases, and as a result, surging is eliminated.

  According to a fifth aspect of the present disclosure, in addition to any one of the first to fourth aspects, the controller further includes a movable vane disposed upstream of the impeller in the flow direction of the working fluid. In the control for eliminating the surging, a turbo compressor is provided that controls the movable vane to increase the magnitude of a component in the rotation direction of the impeller of the flow velocity of the working fluid sucked into the impeller. To do. According to the fifth aspect, when the surging is occurring, the magnitude of the component in the rotation direction of the impeller of the flow velocity of the working fluid sucked into the impeller is increased, and as a result, the surging is eliminated.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The following embodiments are merely examples of the present invention, and the present invention is not limited to these. In the accompanying drawings, the X-axis indicates the same direction, the Y-axis indicates another same direction orthogonal to the X-axis, and the Z-axis indicates a direction orthogonal to the X-axis and the Y-axis. The XY plane is horizontal.

  As shown in FIGS. 1 and 2, the turbo compressor 1a includes a rotating shaft 11, an impeller 12 for compressing a working fluid, a casing 20, at least one discharge passage 25, a microphone 50, and a controller. 55. The impeller 12 is fixed to the rotating shaft 11 and has a plurality of blades 12a. The casing 20 has a volute 23 that surrounds the impeller 12 on the radially outer side of the impeller 12. The discharge flow path 25 is connected to the volute 23 and extends toward the outside of the volute 23. The microphone 50 is exposed to the volute 23 or the discharge passage 25 inside the casing 20, or is exposed to the outside of the casing 20 around the casing 20. In the signal output from the microphone 50, the controller 55 determines the number of blades 12 a (B) at the outlet 15 b of the working fluid flow path of the impeller 12 and the rotational frequency (N [Hz]) of the rotating shaft 11. When the sound pressure level of the frequency matching the product (B × N) is equal to or greater than a predetermined value (Lt), it is determined that surging has occurred. In addition, when it is determined that surging has occurred, the controller 55 performs control for eliminating surging.

  In FIG. 3A, the solid line graph shows an example of the change over time of the pressure of the working fluid discharged from the turbo compressor 1a when surging occurs in the turbo compressor 1a. Further, in FIG. 3A, a broken line graph shows an example of a temporal change in pressure of the working fluid discharged from the turbo compressor 1a when surging does not occur in the turbo compressor 1a. When surging occurs in the turbo compressor 1a, part of the working fluid flows backward in the discharge path 25, and the pressure of the working fluid discharged from the turbo compressor 1a temporarily decreases as shown by the solid line graph in FIG. 3A. To do. However, since the fluctuation of the pressure of the working fluid discharged from the turbo compressor 1a when surging occurs is small, if the presence or absence of surging is determined based on the pressure of the working fluid, false detection or non-detection of surging occurs. Probability is high.

  In FIG. 3B, the solid line graph shows the relationship between the sound pressure level of the sound generated at a predetermined position and the frequency when surging occurs in the turbo compressor 1a. In FIG. 3B, the broken line graph shows the relationship between the sound pressure level of the sound generated at a predetermined position and the frequency when surging has not occurred in the turbo compressor 1a. The sound pressure level at the rotation frequency N [Hz] of the rotating shaft 11 is relatively high regardless of whether surging occurs. On the other hand, a sound having a frequency that matches the product (B × N) of the number (B) of blades 12 a at the outlet 15 b of the working fluid flow path of the impeller 12 and the rotational frequency (N [Hz]) of the rotating shaft 11. The pressure level increases significantly when surging occurs. When surging occurs, the turbulence in the pressure of the working fluid generated in a part of the discharge passage 25 propagates upstream in the flow direction of the working fluid, and the tongue T, which is a connection portion between the volute 23 and the discharge passage 25. It is thought that the working fluid flows backward in the vicinity of. Furthermore, it is considered that a sound wave having a frequency of B × N is generated when the working fluid flowing backward at the outlet 15 b of the working fluid flow path of the impeller 12 interferes with the impeller 12. In the turbo compressor 1a, the presence or absence of surging is determined using a significant increase in the sound pressure level of the frequency that matches B × N when surging occurs. For this reason, the turbo compressor 1a can determine whether or not surging has occurred with high accuracy even when the pressure fluctuation of the working fluid when surging occurs is small, for example.

  The working fluid in the turbo compressor 1a has, for example, a saturated vapor pressure that is lower than atmospheric pressure in absolute pressure at normal temperature. Such a working fluid is, for example, water. In this case, the pressure fluctuation of the working fluid when surging occurs in the turbo compressor 1a is small, and in the conventional technique, there is a possibility that erroneous detection or non-detection of surging occurs. However, in the turbo compressor 1a, as described above, the presence or absence of surging can be determined with high accuracy based on the sound pressure level of the frequency that matches B × N.

  As shown in FIGS. 1 and 2, in the turbo compressor 1 a, the microphone 50 is disposed, for example, exposed outside the casing 20 around the casing 20. As a result, the influence of the working fluid on the microphone 50 can be prevented. In this case, the shortest distance between the microphone 50 and the outer surface of the casing 50 is, for example, within 5 m.

  The rotating shaft 11 is, for example, a columnar member that extends horizontally. The impeller 12 is fixed to the rotating shaft 11 inside the casing 20. The turbo compressor 1a further includes, for example, a first bearing 13a and a second bearing 13b, and a first bearing box 30a and a second bearing box 30b. Each of the first bearing 13a and the second bearing 13b is, for example, a cylindrical fluid bearing having a through hole, and supports a load in the radial direction of the rotating shaft 11 with the rotating shaft 11 inserted into the through hole. . As the lubricant used for the first bearing 13a and the second bearing 13b, the same type of fluid (for example, water) as the working fluid can be used.

  As shown in FIG. 1, the first bearing 13 a supports, for example, the end of the rotating shaft 11 positioned in front of the impeller 12. The 1st bearing 13a is accommodated in the inside of the 1st bearing box 30a, for example. The first bearing housing 30a is arranged in the circumferential direction of the rotary shaft 11 between the inner cylinder and the outer cylinder that are arranged in the radial direction of the rotary shaft 11, and the outer surface of the inner cylinder and the inner surface of the outer cylinder. And a plurality of connecting portions. The plurality of connecting portions connect the inner cylinder and the outer cylinder. The first bearing 13a is accommodated in the inner cylinder of the first bearing box 30a. Further, the outer cylinder of the first bearing box 30 a is attached to the inner peripheral surface of the casing 20 in front of the impeller 12.

  The second bearing 13 b supports the end of the rotating shaft 11 located behind the impeller 12. The second bearing 13b is accommodated, for example, inside the second bearing box 30b. The second bearing box 30b is a cylindrical member.

  The turbo compressor 1a is, for example, a centrifugal fluid machine. At the front end of the impeller 12, an inlet 15a of a flow path for the working fluid is defined by a plurality of blades 12a. A suction space 61 is defined in front of the inlet 15a of the working fluid flow path by, for example, the casing 20 and the first bearing box 30a.

  During the operation period of the turbo compressor 1a, the impeller 12 rotates together with the rotating shaft 11, and the working fluid in the suction space 61 flows toward the impeller 12. The working fluid sucked into the impeller 12 from the inlet 15a of the working fluid channel is discharged to the outside of the impeller 12 through the outlet 15b of the working fluid channel. Thereafter, the working fluid is discharged to the outside of the turbo compressor 1 a through the volute 23 and the discharge passage 25.

  During the operation period of the turbo compressor 1a, the controller 55 determines whether surging has occurred. The controller 55 is configured by, for example, a digital signal processor (DSP), and is connected to the microphone 50 so that an output signal from the microphone 50 can be received.

  For example, a series of processes shown in FIG. 4 are executed during the operation period of the turbo compressor 1a. First, in step S <b> 10, the controller 55 acquires the output signal Sm from the microphone 50. Next, in step S20, the controller 55 determines a sound pressure level L1 at a frequency of B × N [Hz] from the output signal Sm. In this case, the controller 55 receives a detection signal indicating the rotation frequency N of the rotation shaft 11 from a predetermined sensor, and determines the rotation frequency N of the rotation shaft 11 in advance. The controller 55 includes, for example, a filter that allows signals in the frequency bands near B × N [Hz] and B × N [Hz] to pass, and determines the sound pressure level L1 based on the signal that has passed through the filter. . Instead, the controller 55 may determine the sound pressure level L1 by, for example, performing a fast Fourier transform on the output signal Sm. Next, in step S30, the controller 55 determines whether or not the sound pressure level L1 is greater than or equal to a predetermined value Lt. The predetermined value Lt is experimentally determined based on, for example, a sound pressure level generated when surging occurs in the turbo compressor 1a. Lt is, for example, 80 to 90 dB.

  If the determination result in step S30 is negative, the controller 55 determines that surging has not occurred, and returns to step S10. If the determination result in step S30 is affirmative, the controller 55 proceeds to step S40 and determines that surging has occurred. Next, the controller 55 performs control for eliminating surging in step S50. As described above, according to the turbo compressor 1a, it is possible to determine whether surging has occurred or not using inexpensive electronic components such as the microphone 50 and the filter without using a high-precision pressure sensor.

  An example of control for eliminating surging will be described. As shown in FIG. 1, the turbo compressor 1 a further includes, for example, a motor 40 that rotates the rotating shaft 11. The motor 40 is connected to the controller 55 so that the control signal transmitted from the controller 55 can be received. For example, the controller 55 controls the motor 40 to change the rotational speed of the rotary shaft 11 in the control for eliminating the surging in step S50. Specifically, the controller 55 transmits a control signal for changing the rotational speed of the rotary shaft 11 to the motor 40.

  For example, when the opening degree of a discharge valve, which will be described later, is constant, the controller 55 controls the motor 40 to reduce the rotational speed of the rotary shaft 11 in the control for eliminating surging. On the other hand, under another condition, the controller 55 may increase the rotational speed of the rotating shaft 11 by controlling the motor 40 in the control for eliminating surging.

  As shown in FIG. 1, the motor 40 includes a rotor 41 and a stator 42. For example, the motor 40 is disposed inside the housing 43 between the impeller 12 and the second bearing 13 b in the axial direction of the rotary shaft 11. The housing 43 is fixed to the casing 20 in the axial direction of the rotating shaft 11. A second bearing box 30 b is also arranged inside the housing 43. The rotor 41 is a cylindrical member and, for example, is shrink-fitted on the rotating shaft 11. For example, the stator 42 is disposed with a predetermined gap from the outer surface of the rotor 41, and the outer surface of the stator 42 is fixed to the inner surface of the housing 43. For example, the stator 42 is electrically connected to the controller 55, and the rotation speed of the motor 40 is adjusted by the controller 55. For example, the controller 55 can control the motor 40 so that the frequency of the rotating magnetic field applied to the stator 42 is lowered, and can reduce the rotational speed of the rotating shaft 11.

  Another example of control for eliminating surging will be described. As shown in FIG. 2, the turbo compressor 1 a further includes, for example, a valve 70 (discharge valve) for adjusting the flow rate of the working fluid in the discharge flow path 25. The valve 70 is connected to the controller 55 so that the control signal transmitted from the controller 55 can be received. For example, the controller 55 controls the valve 70 to increase the opening degree of the valve 70 in the control for eliminating surging in step S50. Specifically, the controller 55 transmits a control signal for increasing the opening degree of the valve 70 to the valve 70. The valve 70 is, for example, a control valve that can continuously adjust the valve opening.

  Another example of control for eliminating surging will be described. As shown in FIG. 1, the turbo compressor 1 a further includes a movable vane 35. The movable vane 35 is arranged upstream of the impeller 12 in the flow direction of the working fluid. The movable vane 35 is connected to the controller 55 so as to receive a control signal transmitted from the controller 55. For example, in the control for eliminating surging in step S50, the controller 55 controls the movable vane 35 to increase the size of the component of the flow velocity of the working fluid sucked into the impeller 12 in the rotation direction of the impeller 12. . Specifically, the controller 55 transmits to the movable vane 35 a control signal for increasing the magnitude of the component of the flow velocity of the working fluid sucked into the impeller 12 in the rotation direction of the impeller 12. As a result, the working fluid flows in the suction space 61 while turning in the rotation direction of the impeller 12, and surging can be eliminated.

  The movable vane 35 has, for example, an actuator (not shown), and the actuator operates according to a control signal received from the controller 55. Thereby, the attitude | position of the movable vane 35 changes and the magnitude | size of the component in the rotation direction of the impeller 12 of the flow velocity of the working fluid suck | inhaled by the impeller 12 can be made to increase. For example, the actuator moves the front end of the movable vane 35 in the direction opposite to the rotation direction of the impeller 12 and moves the rear end of the movable vane 35 in the rotation direction of the impeller 12. The movable vane 35 also serves as a connection part of the first bearing box 30a, for example.

  Control for eliminating surging is not limited to the above example as long as surging can be eliminated, and control according to the above example may be performed alone or in combination.

  The turbo machine 1a can be changed from various viewpoints. For example, the turbo compressor may be changed to a multistage compressor including a plurality of impellers. In this case, the plurality of impellers desirably have different numbers of blades at the outlet of the working fluid flow path of the impeller. As a result, the frequency at which the sound pressure level significantly increases when surging occurs differs from stage to stage, so it is easy to identify the stage where surging occurs.

  The turbo compressor 1a may be changed, for example, like a turbo compressor 1b illustrated in FIG. The turbo compressor 1b is configured similarly to the turbo compressor 1a unless otherwise described. Components of the turbo compressor 1b that are the same as or correspond to components of the turbo compressor 1a are assigned the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 6, in the turbo compressor 1 b, the microphone 50 is exposed to the volute 23 or the discharge flow path 25 inside the casing 20. The microphone 50 can receive a sound having a frequency of B × N generated in the vicinity of the tongue T when surging occurs. According to the turbo compressor 1b, it is difficult for the microphone 50 to receive sound generated around the turbo compressor 1b. For this reason, even if the sound generated in the vicinity of the turbo compressor 1b includes a sound having a frequency of B × N for determining the presence or absence of surging, erroneous detection of the occurrence of surging is unlikely to occur.

  The turbo compressor of the present disclosure can be advantageously applied to a heat pump, a refrigerator, and an air conditioner.

DESCRIPTION OF SYMBOLS 1a, 1b Turbo compressor 11 Rotating shaft 12 Impeller 12a Blade 15b Outlet of flow path of working fluid 20 Casing 23 Volute 25 Discharge flow path 35 Movable vane 40 Motor 50 Microphone 55 Controller 70 Valve

Claims (5)

A rotation axis;
An impeller fixed to the rotating shaft and having a plurality of blades for compressing the working fluid;
A casing having a volute surrounding the impeller radially outward of the impeller;
At least one discharge channel connected to the volute and extending toward the outside of the volute;
A microphone that is exposed to the volute or the discharge flow path inside the casing, or is exposed to the outside of the casing around the casing; and
In the signal output from the microphone, the sound pressure level at a frequency that matches the product of the number of blades at the outlet of the working fluid flow path of the impeller and the rotational frequency of the rotating shaft is a predetermined value or more. A controller that determines that surging has occurred and performs control to eliminate the surging, and
Turbo compressor.   The turbo compressor according to claim 1, wherein the microphone is exposed to the volute or the discharge flow path inside the casing. A motor for rotating the rotating shaft;
3. The turbo compressor according to claim 1, wherein, in the control for eliminating the surging, the controller controls the motor to change the rotation speed of the rotating shaft. 4. A valve for adjusting the flow rate of the working fluid in the discharge flow path;
The turbo compressor according to any one of claims 1 to 3, wherein the controller controls the valve to increase an opening degree of the valve in the control for eliminating the surging. A movable vane disposed upstream of the impeller in the flow direction of the working fluid;
The controller, in the control for eliminating the surging, controls the movable vane to increase the magnitude of a component in the rotation direction of the impeller of the flow velocity of the working fluid sucked into the impeller. Item 5. The turbo compressor according to any one of Items 1 to 4.

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