Turbo compressor and refrigerator

Abstract

A turbo compressor includes an impeller including a hub and a blade provided on an outer peripheral surface of the hub, a shaft connected to the impeller, a bearing supporting the shaft, a casing accommodating the impeller, the shaft, and the bearing, and including a first surface facing the blade, a gap sensor provided in the casing and configured to detect a size of a gap between the impeller and the first surface, and a control unit configured to control the size of the gap based on the size of the gap detected by the gap sensor.

Description

TECHNICAL FIELD

[0001] The disclosures herein relate to turbo compressors and refrigerators.BACKGROUND ART

[0002] For example, a turbo compressor in which a shaft is supported by a radial magnetic bearing and a thrust magnetic bearing is known (see Patent Literature (PTL) 1). A control unit of the turbo compressor includes a load calculator for calculating an axial thrust load generated by a pressure distribution of the compressor, and an axial support position controller for varying the axial support position of the shaft by the thrust magnetic bearing based on the axial thrust load, and controlling a gap between an impeller and a shroud to become a target gap. The turbo compressor includes a plurality of gap sensors for detecting the axial support position of the shaft. The plurality of gap sensors include a gap sensor for detecting the axial position from behind the impeller.CITATION LISTPATENT LITERATURE

[0003] PTL 1: Japanese Laid-Open Patent Publication No. 2014-231826SUMMARY OF THE INVENTIONPROBLEM TO BE SOLVED BY THE INVENTION

[0004] The turbo compressor of the related art has a gap sensor and detects the axial support position of the shaft. However, in a technology of the related art, detection accuracy of the gap between the impeller and the shroud is not sufficient.

[0005] The present disclosure provides a turbo compressor capable of improving the detection accuracy of a gap between an impeller and a casing.MEANS FOR SOLVING THE PROBLEM

[0006] A turbo compressor includes an impeller including a hub and a blade provided on an outer peripheral surface of the hub, a shaft connected to the impeller, a bearing supporting the shaft, a casing accommodating the impeller, the shaft, and the bearing, and including a first surface facing the blade, a gap sensor provided in the casing and configured to detect a size of a gap between the impeller and the first surface, and a control unit configured to control the size of the gap based on the size of the gap detected by the gap sensor.

[0007] In the turbo compressor of the present aspect, the size of the gap between the impeller and the first surface can be detected by the gap sensor. In the turbo compressor, the size of the gap in a front surface of the impeller changes. The factors for changing the size of the gap include the effect of axial elongation of the shaft due to heat and deformation of the impeller due to high-speed rotation. Since the turbo compressor of the present aspect can directly measure the gap in the front surface of the impeller, accuracy of detecting the gap can be improved.

[0008] In a turbo compressor according to one aspect of the present disclosure, the bearing includes a thrust magnetic bearing, and the control unit is configured to control an axial position of the impeller by controlling the thrust magnetic bearing based on the size of the gap detected by the gap sensor.

[0009] The turbo compressor according to one aspect of the present disclosure may include a casing driving mechanism configured to move the first surface, wherein the control unit may control an axial position of the first surface by controlling the casing driving mechanism.

[0010] The turbo compressor according to one aspect of the present disclosure includes a casing cooling mechanism configured to cool the casing.

[0011] In the turbo compressor according to one aspect of the present disclosure, the control unit may calculate a control target value of the size of the gap, and control the size of the gap such that a result detected by the gap sensor becomes the control target value.

[0012] In the turbo compressor according to one aspect of the present disclosure, the control unit may calculate the control target value based on a pressure ratio which is a ratio between an inlet pressure and an outlet pressure of the impeller, or a flow rate of gas flowing into the impeller.

[0013] In the turbo compressor according to one aspect of the present disclosure, the turbo compressor being a variable speed machine, the control unit may calculate the control target value based on a number of rotations of the impeller.

[0014] The turbo compressor according to one aspect of the present disclosure may include an inlet guide vane configured to change a flow rate of gas flowing into the impeller, wherein the control unit may calculate the control target value based on an opening degree of the inlet guide vane.

[0015] In the turbo compressor according to one aspect of the present disclosure, the gap sensor may be disposed farther out, in a radial direction of the impeller, than a midpoint of a radius of the impeller.

[0016] A refrigerator according to one aspect of the present disclosure includes the turbo compressor described above.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] [FIG. 1] FIG. 1 is a schematic diagram illustrating a refrigerator including a turbo compressor according to a first embodiment. [FIG. 2] FIG. 2 is a cross-sectional view illustrating the turbo compressor according to the first embodiment. [FIG. 3] FIG. 3 is an enlarged cross-sectional view illustrating impellers. [FIG. 4] FIG. 4 is an enlarged cross-sectional view illustrating a gap sensor arrangement. [FIG. 5] FIG. 5 is a block diagram illustrating a hardware configuration of the refrigerator according to the first embodiment. [FIG. 6] FIG. 6 (a) is a graph illustrating a relationship between a flow rate of an internal fluid and a pressure ratio when a number of rotations of the impeller is constant, FIG. 6 (b) is a graph illustrating a relationship between the flow rate of the internal fluid and adiabatic efficiency when the number of rotations of the impeller is constant, FIG. 6 (c) is a graph illustrating a relationship between the flow rate of the internal fluid and the pressure ratio when an opening degree of an inlet guide vane is constant, and FIG. 6 (d) is a graph illustrating a relationship between the flow rate of the internal fluid and the adiabatic efficiency when the opening degree of the inlet guide vane is constant. [FIG. 7] FIG. 7 (a) is a drawing illustrating a flow of a refrigerant flowing into a diffuser from the impeller when a gap size is small, and FIG. 7 (b) is a drawing illustrating a flow of the refrigerant flowing into the diffuser from the impeller when the gap size is large. [FIG. 8] FIG. 8 is a drawing illustrating the flow of the refrigerant flowing into the diffuser from the impeller. [FIG. 9] FIG. 9 is a cross-sectional view illustrating a turbo compressor according to a second embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the following, non-limited examples of the present invention will be described with reference to the accompanying drawings. In the drawings, the same or corresponding constituent elements are denoted with the same reference numerals, and redundant description thereabout may be omitted. In the drawings, members or parts are not necessarily drawn to scale. Therefore, a person skilled in the art can selectively determine specific dimensions by referring to the following non-limited examples. In addition, the following examples are illustrative rather than limiting the invention. In addition, the features and combinations described in the examples are not necessarily essential to the invention.[OUTLINE OF REFRIGERATOR 110 ACCORDING TO FIRST EMBODIMENT]

[0019] Referring to FIGS. 1 to 8, a refrigerator 110 including a turbo compressor 100 according to a first embodiment will be described. FIG. 1 is a schematic diagram illustrating the refrigerator 110 including the turbo compressor 100 according to the first embodiment. The refrigerator 110 shown in FIG. 1 is used, for example, for an air conditioner, a refrigeration apparatus, and a cold-storage apparatus. The refrigerator 110 may be used for other equipment. The refrigerator 110 executes a refrigeration cycle. The refrigeration cycle of the refrigerator 110 is a vapor compression refrigeration cycle. The refrigerator 110 includes the turbo compressor 100, a condenser 120, an expansion valve 130, and an evaporator 140.

[0020] The refrigerant which is a working fluid of the refrigerator 110 is not limited. The turbo compressor 100 compresses the refrigerant gas. The condenser 120 condenses the refrigerant gas compressed by the turbo compressor 100. The expansion valve 130 expands the refrigerant condensed by the condenser 120. The evaporator 140 vaporizes the refrigerant expanded by the expansion valve 130. The refrigerant gas evaporated by the evaporator 140 is sucked into the turbo compressor 100.

[0021] The turbo compressor 100 performs reversible adiabatic compression of the refrigerant gas. The refrigerant gas supplied to the condenser 120 releases heat at a constant pressure and liquefies. The liquefied refrigerant irreversibly expands at a constant enthalpy in the expansion valve 130, and part of the refrigerant evaporates. The refrigerant absorbs heat at a constant pressure in the evaporator 140.

[0022] The refrigerator 110 includes pipes L11 to L14 through which refrigerant flows. The pipe L11 is a suction pipe connecting the evaporator 140 and the turbo compressor 100. The pipe L12 connects the turbo compressor 100 and the condenser 120. The pipe L13 connects the condenser 120 and the expansion valve 130. The pipe L14 connects the expansion valve 130 and the evaporator 140.

[0023] The refrigerant gas flows through the pipe L11 and is sucked into the turbo compressor 100. The refrigerant gas compressed by the turbo compressor 100 flows through the pipe L12 and is supplied to the condenser 120. The refrigerant liquid liquefied by the condenser 120 flows through the pipe L13 and flows into the expansion valve 130. The refrigerant expanded by the expansion valve 130 flows through the pipe L14 and is supplied to the evaporator 140. The refrigerant gas that has absorbed heat at the evaporator 140 flows through the pipe L11 and is supplied to the turbo compressor 100.[TURBO COMPRESSOR 100]

[0024] Next, the turbo compressor 100 will be described. FIG. 2 is a cross-sectional view illustrating the turbo compressor 100 according to the first embodiment. FIG. 3 is an enlarged cross-sectional view illustrating impellers 10A and 10B. FIG. 4 is an enlarged cross-sectional view illustrating a gap sensor arrangement. The turbo compressor 100 is, for example, a two-stage compressor. The turbo compressor 100 may be a single-stage compressor. As shown in FIG. 2, the turbo compressor 100 includes the impellers 10A and 10B, a shaft 20, bearings 31 to 34, a motor 40, and a casing 50. The turbo compressor 100 may be an oblique flow type or a centrifugal type.

[0025] The casing 50 contains the impellers 10A and 10B, the shaft 20, the bearings 31 to 34, and the motor 40. The turbo compressor 100 has an in-line structure in which the impellers 10A and 10B are connected in a same direction. The turbo compressor 100 may have a back-to-back structure in which backs of the impellers 10A and 10B face each other.

[0026] The casing 50 has a compression chamber 50a containing the impellers 10A and 10B, and a motor chamber 50b containing the shaft 20, the bearings 31 to 34, and the motor 40. Diffusers 61 and 62 are formed in the compression chamber 50a. As shown in FIG. 3, the diffuser 61 is formed outside the impeller 10A in the radial direction of the impeller 10A. The diffuser 62 is formed outside the impeller 10B in the radial direction of the impeller 10B.

[0027] The casing 50 is formed with a suction port 52 into which compressed refrigerant flows. The suction port 52 extends in the axial direction of the shaft 20. The refrigerant flowing in the suction port 52 is supplied to the impeller 10A. A flow path 53 connecting the diffuser 61 and the impeller 10B is formed in the casing 50. In addition, an inlet 54 into which the refrigerant flowing in the flow path 53 flows is formed in the casing 50. The inlet 54 is formed between the impeller 10A and the impeller 10B in the axial direction. The refrigerant flowing in the flow path 53 is supplied to the impeller 10B through the inlet 54.

[0028] The refrigerant compressed by the impeller 10A flows in the diffuser 61, the flow path 53, and the inlet 54, and is supplied to the impeller 10B. The refrigerant compressed by the impeller 10B flows in the diffuser 62, and is exhausted from the turbo compressor 100.[IMPELLER 10A, 10B]

[0029] The impeller 10A is a low-pressure side impeller, and the impeller 10B is a high-pressure side impeller. The impeller 10A is arranged at a position closer to the suction port 52 in the axial direction of the shaft 20, and the impeller 10B is arranged at a position closer to the motor 40. The impeller 10A includes a hub 11 and blades 12 provided on the outer peripheral surface of the hub 11. The impeller 10B includes the hub 11 and the blades 12 provided on the outer peripheral surface of the hub 11. The plurality of blades 12 are provided on the outer peripheral surface of the hub 11 at constant intervals.

[0030] The hub 11 has a substantially conical shape whose diameter expands from the front to rear. In the axial direction of the shaft 20, the side closer to the suction port 52 is referred to as "front" and the side farther from the suction port 52 is referred to as "rear". The hub 11 rotates integrally with the shaft 20. In order to reduce weight, the hub 11 may be hollow on the inside except for a portion surrounding the shaft and an outer edge.

[0031] The blades 12 project radially outward from the outer peripheral surface 11a of the hub 11, as shown in FIG. 4. The blades 12 are arranged spirally along the outer peripheral surface 11a of the hub 11.[FIRST SURFACES 51A AND 51B OF THE CASING 50]

[0032] As shown in FIG. 3, the casing 50 has a first surface 51A facing the blade 12 of the impeller 10A, and a first surface 51B facing the blade 12 of the impeller 10B. The first surfaces 51A and 51B form a wall surface of the flow path through which the refrigerant flows. The first surface 51A connects the inner surface of the suction port 52 to the inner surface of the diffuser 61. The first surface 51B connects the inner surface of the inlet 54 to the inner surface of the diffuser 62.[SHAFT 20]

[0033] The shaft 20 has both ends 20a and 20b in the axial direction, as shown in FIG. 2. The end 20a is closer to the impellers 10A and 10B, and the end 20b is farther from the impellers 10A and 10B. The impellers 10A and 10B are provided at the end 20a. The shaft 20 includes the shaft of the motor 40. The shaft of the motor 40 includes a central portion between the ends 20a and 20b in the axial direction of the shaft 20.[BEARING]

[0034] The bearings 31 to 34 rotatably support the shaft 20. The bearings 31 to 34 are fixed to the casing 50. The bearings 31 and 32 are radial magnetic bearings, and the bearings 33 and 34 are thrust magnetic bearings.

[0035] The bearings 31 to 34 may be magnetic bearings that support the shaft by utilizing magnetic attraction or repulsion. The bearings 31 to 34 may also be active magnetic bearings (AMB). The radial magnetic bearing includes an electromagnet disposed around the shaft 20. The electromagnet has an iron core and a coil. The thrust magnetic bearing includes an axial disk 21 projecting radially outward from the shaft 20 and an electromagnet arranged so as to face the axial disk 21 in the axial direction.

[0036] The bearings 31 to 34 are, for example, oil-less bearings. The bearings 31 and 32 may also be sliding bearings or rolling bearings. The bearings 31 to 34 may also be hydrostatic bearings. The oil-less bearing is a bearing that does not require supply of lubricating oil. Examples of the oil-less bearing include a gas bearing, an air bearing, a foil bearing, and a magnetic bearing.

[0037] The bearings 31 to 34 may also be air bearings. The air bearing is a type of hydrostatic bearing, and can support the load by blowing compressed air between the shaft 20 and the bearing surface to float the shaft 20 by air pressure. The bearings 31 and 32 may also be gas bearings that float the shaft 20 by blowing compressed gas between the shaft 20 and the bearing surface. The gas bearing may float the shaft 20 by blowing refrigerant gas as compressed gas.

[0038] The bearings 31 to 34 may alternatively be foil bearings, which are a type of air dynamic pressure bearings. The foil bearing has a thin film (foil) as a bearing surface. The thin film has low rigidity against bending and also has flexibility. The foil bearing supports the load by allowing a deflection of the foil. When the shaft 20 rotates, a fluid film (air film) is formed between the shaft 20 and the bearing surface which is the foil. The foil bearing supports the shaft 20 by using the foil and the fluid film. The foil bearing can form a bearing gap according to the number of rotations of the shaft 20, the load of the shaft 20, an ambient temperature of the shaft 20, and other operating conditions due to the flexibility of the foil.

[0039] The type, position, and quantity of bearings 31 to 34 are not limited to those described above. The turbo compressor 100 may include a touchdown bearing. The touchdown bearing is also referred to as a guide bearing or a backup bearing. The touchdown bearing restricts a range of motion of the shaft 20. The touchdown bearing can restrict the range of motion of the shaft 20 in the radial direction. The touchdown bearing can restrict the range of motion of the shaft 20 in the axial direction. The touchdown bearing can prevent the stator from contacting with the rotor. The touchdown bearing can support the shaft 20 when the magnetic bearing is not energized.

[0040] The turbo compressor 100 includes a control unit 210 (see FIG. 5) capable of controlling a movable range of the shaft 20. The control unit 210 can control a current supplied to coils of the bearings 31 to 34 which are control type magnetic bearings. The control unit 210 can control the movable range in the radial direction and the movable range in the axial direction of the shaft 20 by controlling the current supplied to the coil.[MOTOR 40]

[0041] The motor 40 shown in FIG. 2 is a driving source of the turbo compressor 100. The motor 40 has a rotor 41 and a stator 42. The rotor 41 is fixed to the shaft 20 and rotates with the shaft 20. The stator 42 is fixed to the casing 50 and arranged around the rotor 41.

[0042] The refrigerator 110 includes an inverter 80 as shown in FIGS. 1 and 5. The inverter 80 controls the number of rotations of the motor 40. The inverter 80 is a controller that controls the operating frequency of the motor 40. The inverter 80 can change the number of rotations of the impellers 10A and 10B and the shaft 20 by controlling the operating frequency of the motor 40.[INLET GUIDE VANE 90]

[0043] As shown in FIG. 2, the turbo compressor 100 includes an inlet guide vane 90 provided in the suction port 52. The control unit 210 can control the opening degree of the inlet guide vane 90. The control unit 210 can control the flow rate of the refrigerant flowing into the impeller 10A by changing the opening degree of the inlet guide vane 90.[GAP SENSOR 71]

[0044] The turbo compressor 100 is provided with a gap sensor 71 as shown in FIGS. 2 to 5. The gap sensor 71 is provided in the casing 50 and detects the size of the gap G10 (see FIG. 4) between the impeller 10A and the first surface 51A. The gap sensor 71 detects the size of the gap G10 between the blade 12 of the impeller 10A and the first surface 51A. The gap sensor 71 may detect a distance between the outer peripheral surface 11a of the hub 11 of the impeller 10A and the first surface 51A. The control unit 210 may calculate the size of the gap G10 between the impeller 10A and the first surface 51A based on data acquired by the gap sensor 71. The gap sensor 71 may be, for example, an eddy current type gap sensor. The gap sensor 71 may be a gap sensor of other structure.

[0045] The gap sensor 71 may detect the gap G10 between the impeller 10B and the first surface 51B (see FIG. 3). The gap sensor 71 may detect a gap G1 between the impeller 10B and the first surface 51B in the axial direction of the shaft 20. The size of the gap G1 may be a shortest distance of the gap G1 or a distance along the axial direction of the shaft 20. The turbo compressor 100 may include a plurality of gap sensors 71.

[0046] The gap sensor 17 is disposed farther out, in the radial direction of the impeller 10A, than a midpoint P11 of the radius R10 of the impeller 10A, as shown in FIG. 4. The radius R10 of the impeller 10A is a length from a center C1 of the shaft 20 to the outer edge of the impeller 10A. The radius R11 from the center C1 of the shaft 20 to the midpoint P11 is half the length of the radius R10.

[0047] The turbo compressor 100 may include other gap sensors. The other gap sensors can detect the axial position of the shaft 20.[CONTROL UNIT 210]

[0048] FIG. 5 is a block diagram illustrating a hardware configuration of the refrigerator 110 according to the first embodiment. As shown in FIG. 5, the control unit 210 includes a CPU 211 and a storage unit 212. The CPU (Center Processing Unit) 211 controls overall processing in the refrigerator 110. The CPU 211 can control the number of rotations of the motor 40 via the inverter 80. The CPU 210 can control the opening and closing operation of the expansion valve 130. As described above, the control unit 210 can control the opening degree of the inlet guide vane 90.

[0049] The storage unit 212 includes a ROM (Read Only Memory) 213 and a RAM (Random Access Memory) 214. The ROM 213 stores various programs for causing the CPU 211 to execute control processing, and various data and the like necessary for operation of the refrigerator 110. The RAM 214 can temporarily store data and the like acquired from various sensors.

[0050] The control unit 210 controls the size of the gap G10 based on the size of the gap G10 detected by the gap sensor 71. The control unit 210 can control the size of the gap G10 by controlling the axial position of the shaft 20, by controlling the bearings (thrust magnetic bearings) 33 and 34. The control unit 210 may control the size of the gap G10 by controlling other actuators. The control unit 210 may control the gap G10 by moving a portion of the casing 50 including the first surface 51.

[0051] The control unit 210 can calculate a control target value related to the size of the gap G10. The control unit 210 may control the size of the gap G10 such that the result detected by the gap sensor 71 becomes the control target value.

[0052] The turbo compressor 100 may include a temperature sensor for detecting the temperature of the refrigerant, a pressure sensor for detecting the pressure of the refrigerant, a sensor for detecting the number of rotations of the impellers 10A and 10B, and a sensor for detecting the opening degree of the inlet guide vane 90. The turbo compressor 100 can detect the temperature and pressure of the refrigerant at both the inlet and outlet of the impeller 10A. The turbo compressor 100 can detect the temperature and pressure of the refrigerant at both the inlet and outlet of the impeller 10B.

[0053] The control unit 210 may calculate the control target value based on the pressure ratio which is a ratio between the inlet pressure and the outlet pressure of the impellers 10A and 10B. The pressure ratio may be a ratio between the pressure of the refrigerant flowing into the turbo compressor 100 and the pressure of the refrigerant discharged from the turbo compressor 100.

[0054] The control unit 210 may calculate the control target value based on the number of rotations of the impellers 10A and 10B. The turbo compressor 100 is a variable speed machine capable of changing the number of rotations of the impellers 10A and 10B. The turbo compressor 100 may be a constant speed machine in which the number of rotations of the impellers 10A and 10B are constant.

[0055] The control unit 210 may calculate the control target value based on the flow rate of the refrigerant flowing into the impeller 10A. The flow rate of the refrigerant flowing into the impeller 10A may be the flow rate of the refrigerant flowing into the suction port 52.

[0056] The control unit 210 may calculate the control target value based on the opening degree of the inlet guide vane 90.

[0057] FIG. 6 (a) is a graph illustrating a relationship between a flow rate of an internal fluid and a pressure ratio when the number of rotations of the impeller is constant, FIG. 6 (b) is a graph illustrating a relationship between the flow rate of the internal fluid and adiabatic efficiency when the number of rotations of the impeller is constant, FIG. 6 (c) is a graph illustrating a relationship between the flow rate of the internal fluid and the pressure ratio when the opening degree of the inlet guide vane is constant, and FIG. 6 (d) is a graph illustrating a relationship between the flow rate of the internal fluid and the adiabatic efficiency when the opening degree of the inlet guide vane is constant.

[0058] In FIG. 6 (a), a horizontal axis indicates a corrected flow rate of the turbo compressor 100, and a vertical axis indicates the pressure ratio. In the case shown in FIG. 6 (a), a corrected number of rotations of the impeller is constant. The corrected number of rotations N1, N2, and N3 increase in this order (N1 < N2 < N3). In FIG. 6 (a), a surge line SL is illustrated. In a region where the flow rate is lower than the surge line SL, the turbo compressor 100 cannot be operated. In FIG. 6 (b), the horizontal axis shows the corrected flow rate of the turbo compressor 100, and the vertical axis shows the adiabatic efficiency.

[0059] "The corrected flow rate" and "the corrected number of rotations" can be calculated using the following equations. "The corrected flow rate" and "the corrected number of rotations" are values obtained by converting the obtained flow rate and number of rotations into the flow rate and number of rotations under a standard condition when the temperature of the internal fluid (refrigerant) during the operation of the turbo compressor differs from the temperature under the standard condition.

[0060] Basically, the standard condition is calculated using a standard atmospheric pressure (101.325 kPa) and a standard atmospheric temperature (15°C).

[0061] The corrected number of rotations Nc of the impeller can be calculated using the following equations (1) and (2). Nc = N / θ 1 / 2 θ = t / t 0

[0062] Here "t0" is a temperature of the internal fluid in the standard condition. "N" is an actual number of rotations of the impeller. "t" is an actual temperature of the internal fluid.

[0063] A corrected (mass) flow rate mc can be calculated using the following equations (3) and (4). mc = mθ 1 / 2 / δ δ = p / p 0

[0064] Here "p0" is a pressure of the internal fluid in the standard state. "m" is an actual flow rate of the internal fluid. "p" is an actual pressure of the internal fluid.

[0065] In FIG. 6 (c), the horizontal axis shows the corrected flow rate of the turbo compressor 100, and the vertical axis shows the pressure ratio. The opening degree (IGV opening degree) of the inlet guide vane 90 is constant. The IGV opening degrees M1, M2, and M3 increase in this order (M1 < M2 < M3). In FIG. 6 (c), the surge line SL is illustrated. In FIG. 6 (d), the horizontal axis shows the corrected flow rate of the turbo compressor 100, and the vertical axis shows the adiabatic efficiency.

[0066] In the turbo compressor 100, a test is executed to create maps as shown in FIGS. 6 (a) to 6 (d). Data related to these maps are stored in the storage unit 212. In the turbo compressor 100, an optimum control target value (gap G10) is set for each point of these maps. For example, in the turbo compressor 100, the axial positions of the impellers 10A and 10B may be controlled so as to widen the gap G10 in the operating region near the surge line SL. Thus, the flow of the refrigerant can be stabilized, and the range capable of operating the turbo compressor 100 can be widened.

[0067] Generally, in the turbo compressor, performance of the impellers 10A and 10B and the diffusers 61 and 62 greatly differs depending on the size of the gap G10 between the impellers 10A and 10B and the first surfaces 51A and 51B of the casing 50. At a rated point of the turbo compressor 100, a leakage can be reduced by reducing the size of the gap G10. Thus, the performance of the turbo compressor 100 can be improved. The rated point refers to an operating condition that is designed to provide high efficiency. The leakage refers to a flow rate of the refrigerant that passes from a high-pressure side to a low-pressure side through the gap G10, and that is not compressed by the impellers 10A and 10B.

[0068] In the turbo compressor 100, the size of the gap G10 can be controlled so as to increase the gap G10 when, for example, the first flow rate Q12 is smaller than the first reference flow rate Q11. Thus, an area of the flow path through which the refrigerant communicates with the diffusers 61 and 62 can be expanded, and the refrigerant can efficiently flow into the diffusers 61 and 62. As a result, the performance of the turbo compressor 100 can be improved.[CHANGE IN SIZE OF GAP G10]

[0069] The turbo compressor 100 can detect a change in the size of the gap G10 based on the detection result by the gap sensor 71. In the turbo compressor 100, the gap G10 changes due to a difference between an amount of deformation due to thermal expansion of the casing 50 and an amount of deformation due to thermal expansion of the rotor portion. The rotor portion includes the shaft 20 and the impellers 10A and 10B.

[0070] In the turbo compressor 100, a large centrifugal force is applied to the impellers 10A and 10B at a high rotational speed, and the size of the gap G10 changes. For example, due to the high rotational speed, the blades 12 of the impellers 10A and 10B are deformed so as to extend radially outward, and the size of the gap G10 decreases.[FLOW OF REFRIGERANT FLOWING INTO DIFFUSER 61 FROM IMPELLER 10A]

[0071] Next, the flow of refrigerant flowing into the diffuser 61 from the impeller 10A will be described with reference to FIGS. 7 and 8. FIG. 7 (a) is a drawing illustrating a flow of a refrigerant flowing into the diffuser 61 from the impeller 10A when a size of a gap G11 is small, and FIG. 7 (b) is a drawing illustrating a flow of the refrigerant flowing into the diffuser 61 from the impeller 10A when a size of a gap G12 is large. FIGS. 7 (a) and 7 (b) are views of the impeller 10A viewed from a direction orthogonal to the shaft 20. FIG. 8 is a drawing illustrating the flow of the refrigerant flowing into the diffuser 61 from the impeller 10A. FIG. 8 is a view of the impeller 10A viewed from the axial direction of the shaft 20. FIG. 8 shows one of the plurality of blades. As described above, the plurality of blades 12 are provided on the outer peripheral surface of the hub 11.

[0072] The gaps G11 and G12 are gaps along the axial direction of the shaft 20. The gap G11 is smaller than the gap G12. The sizes of the gaps G11 and G12 follow the size of the gap G10. The size of the gap G10 when the gap G11 is formed is smaller than the size of the gap G10 when the gap G12 is formed. The gap sensor 71 may detect the gaps G11 and G12.

[0073] The flow velocity V11 of the refrigerant when the gap G11 is formed is slower than the flow velocity V12 of the refrigerant when the gap G12 is formed. The flow velocities V11 and V12 are the velocities at which the refrigerant compressed by the impeller 10A flows into the diffuser 61.

[0074] As shown in FIG. 7 (b), when the gap G12 is formed, an effective outlet area of the impeller 10A decreases in a blockage. Thus, due to the decrease in the effective outlet area of the impeller 10A, the velocity component of the flow velocity V12 in the radial direction of the impeller 10A is larger than the velocity component in the radial direction of the flow velocity V11.

[0075] "An effective outlet area decreases in a blockage" means that the effective outlet area decreases due to an increase in the blockage coefficient. The "blockage coefficient" may be a coefficient used to indicate a ratio between a main stream and a slow velocity boundary layer in a path section when the fluid passes through the path section. The effective area ratio E is defined as E = u / U and the blockage coefficient B is defined as B = 1 - E, where an average velocity in the path section is referred to as "u0", and a maximum velocity in the main stream is referred to as "U1".

[0076] As shown in FIG. 8, the flow velocity V11 shows an angle closer to a tangent to a circle representing an outer diameter OD10 of the impeller 10A than an angle of the flow velocity V12. The flow velocity V12 is closer to a normal line perpendicular to the tangent to the circle representing the outer diameter OD10 than the angle of the flow velocity V11.

[0077] The flow velocity V11 with the smaller gap G11 tends to cause refrigerant to flow back, and fluid loss at the inlet of the diffuser 61 is larger. In other words, the flow velocity V12 with the smaller gap G12 tends to not cause refrigerant to flow back, and fluid loss at the inlet of the diffuser 61 is smaller. In the turbo compressor 100, fluid loss can be reduced by controlling the gap G10 so as to increase the gap G10 in the operating region where the flow rate is small and near the surge line SL. In the turbo compressor 100, the operation can be stabilized near the surge line SL. In other words, the turbo compressor 100 can expand the operating condition range near the surge line SL.[SURGING]

[0078] Next, surging is described. In a compressor such as an axial compressor and a centrifugal compressor used in various applications, surging may occur during operation. For example, during an operation of the centrifugal compressor, when the pressure is increased while the flow rate is reduced, rotating stall or surging may occur. Generally, when the flow rate decreases, a rotating stall may occur, which may eventually cause surging.

[0079] For example, during an operation of the centrifugal compressor, when the flow rate drops further after a certain flow rate, a region of reverse flow occurs in a circumferential direction inside the centrifugal compressor (turbomachinery). The occurrence of such a region of reverse flow is called rotating stall. A phenomenon of the occurrence of the region of reverse flow is a local phenomenon inside the compressor of fluctuation in the circumferential direction.

[0080] When surging occurs inside the compressor, large fluctuations in flow velocity and pressure due to reverse flow and pulsation occur in the entirety of a pipeline system connected to the compressor. This causes a large load on equipment including the pipeline system, which disables continued operation of the compressor.

[0081] For example, it is preferable to conduct an operational test to assess a potential for surging to occur, and to apply a sufficient safety factor to ensure that an operating point of the compressor is not in a region where surging may occur.

[0082] For example, in a variable drive operation in which the number of rotations of the compressor is varied by an inverter, the flow rate at which surging occurs is determined for each number of rotations. By connecting the operating point at which surging occurs for each number of rotations, the surge line (operating limit line) SL defined from a volume flow rate and an adiabatic head is determined.[EFFECT OF TURBO COMPRESSOR 100 ACCORDING TO FIRST EMBODIMENT]

[0083] The turbo compressor 100 according to the first embodiment includes the impellers 10A and 10B including the hub 11 and the blades 12 provided on the outer peripheral surface 11a of the hub 11, the shaft 20 connected to the impellers 10A and 10B, the bearings 31 to 34 supporting the shaft 20, the casing 50 accommodating the impellers 10A and 10B, the shaft 20, and the bearings 31 to 34, and including the first surface 51A facing the blade 12, the gap sensor 71 provided in the casing 50, for detecting the size of the gap G10 between the impeller 10A and the first surface 51A, and the control unit 210 for controlling the size of the gap G10 based on the size of the gap G10 detected by the gap sensor 71.

[0084] In the turbo compressor 100, the gap sensor 71 can detect the gap G10 between the impeller 10 and the first surface 51A, and control the size of the gap G10 based on the size of the gap G10. The turbo compressor 100 can directly measure the size of the gap G10 to be controlled. The turbo compressor 100 can improve the detection accuracy of the gap G10 between the impeller 10A and the casing 50.

[0085] In addition, the turbo compressor 100 can be controlled so as to reduce the size of the gap G10 between the impellers 10A and 10B and the first surfaces 51A and 51B in the operating region away from the surge line SL. Thus, the leakage flow between the impellers 10A and 10B and the casing 50 can be reduced, and the operating efficiency can be improved.

[0086] In the turbo compressor 100, fluid loss can be reduced by controlling the gap G10 so as to increase the gap G10 in the operation region close to the surge line SL. In the turbo compressor 100, the operation can be stabilized by increasing the flow rate by increasing the flow velocity at the outlet side of the impellers 10A and 10B near the surge line SL. In the turbo compressor 100, the operating condition range can be expanded.

[0087] In the turbo compressor 100, the gap sensor 71 is disposed outside the midpoint of the radius of the impeller 10A in the radial direction of the impeller 10A. In the turbo compressor 100 having such a configuration, even when the blades 12 of the impellers 10A and 10B are deformed to extend radially outward due to high-speed rotation, the gap sensor 71 can accurately detect the change in the size of the gap G10.

[0088] In addition, the turbo compressor 100 is provided with sensors (pressure sensor and temperature sensor) for measuring a quantity of the state of the refrigerant. The turbo compressor 100 is provided with a temperature and pressure sensor at the inlet of a first stage of the turbo compressor 100 and a temperature and pressure sensor at the outlet of a last stage of the turbo compressor 100, and does not require any temperature and pressure sensors in a region between stages. The region between the stages may be, for example, a region between the first impeller 10A and the second impeller 10B. For example, in the turbo compressor 100, because of a high head, even when the number of stages is increased, it is possible to prevent an increase in installation cost of the temperature and pressure sensors.

[0089] In addition, since the turbo compressor 100 can measure the size of the gap G10 between the impeller 10A and the casing 50, it is not necessary to calculate the size of the gap G10 indirectly including correction by thermal expansion. In the turbo compressor 100, the size of the gap G10 can be directly measured, and the size of the gap G10 can be accurately measured.

[0090] In addition, since the turbo compressor 100 can control the size of the gap G10 based on a value of the gap G10 measured using the gap sensor 71, it is not necessary to calculate the thrust load acting on the shaft 20. For example, in the turbo compressor according to the related art, the axial position of the impeller is controlled by calculating the thrust load, but in the turbo compressor 100, the size of the gap G10 can be controlled without calculating the thrust load.[TURBO COMPRESSOR 100B ACCORDING TO SECOND EMBODIMENT]

[0091] Next, the turbo compressor 100B according to a second embodiment will be described with reference to FIG. 9. FIG. 9 is a cross-sectional view illustrating a turbo compressor 100B according to the second embodiment. The turbo compressor 100B according to the second embodiment shown in FIG. 9 differs from the turbo compressor 100 according to the first embodiment in that it includes a cooling mechanism 150. In the description of the second embodiment, the same description as that of the first embodiment described above may be omitted.[COOLING MECHANISM 150]

[0092] The turbo compressor 100B includes the cooling mechanism 150. The cooling mechanism 150 includes a first cooling flow path 151 and a second cooling flow path 152. In the turbo compressor 100B, refrigerant (coolant) flows through the first cooling flow path 151 and the second cooling flow path 152 to cool the shaft 20, the bearings 31 to 34, the motor 40, and the casing 50. The refrigerant may be, for example, a refrigerant discharged from the condenser 120. A pipe branched from the pipe L13 communicates with the first cooling flow path 151 and the second cooling flow path 152.[FIRST COOLING FLOW PATH 151]

[0093] The first cooling flow path 151 includes a channel formed inside the shaft 20. The first cooling flow path 151 includes an inlet 151a and an outlet 151b. The casing 50 includes a cylindrical body 50c and a mirror plate 50d. The cylindrical body 50c houses the shaft 20, the bearings 31 to 34, and the motor 40 inside. The mirror plate 50d is formed so as to close the rear of the cylindrical body 50c. The "rear" is farther from the impellers 10A and 10B in the axial direction of the shaft 20.

[0094] A boss 50e is provided at the center of the mirror plate 50d in the radial direction. The boss 50e is formed to penetrate the mirror plate 50d in the axial direction. The end 20b of the shaft 20 is connected to the boss 50e. The first cooling flow path 151 extends in the axial direction inside the boss 50e and the shaft 20. The first cooling flow path 151 extends in the axial direction from the boss 50e to a position between, for example, the motor 40 and the bearing 31. The first cooling flow path 151 includes a portion extending in the radial direction. The inlet 151a of the first cooling flow path 151 is formed in the boss 50e, and the outlet 151b is formed on the outer peripheral surface of the shaft 20.

[0095] The refrigerant flowing through the first cooling flow path 151 flows through the outlet 151b and flows into the motor chamber 50b. The inside of the motor chamber 50b includes a space inside the cylindrical body 50c. The cylindrical body 50c has an outlet 151c for discharging the refrigerant outside the cylindrical body 50c. The outlet 151c is formed close to the bearings 33 and 34 in the axial direction, for example. The refrigerant flowing into the motor chamber 50b from the outlet 151b flows through the motor chamber 50b, flows through the outlet 151c, and is discharged to the outside of the turbo compressor 100. The refrigerant flowing through the motor chamber 50b cools the shaft 20, the bearings 31 to 34, the motor 40, and the casing 50.[SECOND COOLING FLOW PATH 152]

[0096] The second cooling flow path 152 includes a flow path formed inside the wall of the cylindrical body 50c. The second cooling flow path 152 has an inlet 152a and an outlet 152b. The second cooling flow path 152 is formed at a position corresponding to, for example, the motor 40 in the axial direction of the shaft 20. The inlet 152a is arranged near the bearing 31 in the axial direction, and the outlet 152b is formed near the bearing 32. The second cooling flow path 152 is spirally formed along the circumferential direction of the cylindrical body 50c.

[0097] The refrigerant flowing in from the inlet 152a flows through the second cooling flow path 152 and is discharged from the outlet 152b. The refrigerant flowing through the second cooling flow path 152 cools the casing 50 and the motor 40.

[0098] The refrigerant flowing through the first cooling flow path 151 and the second cooling flow path 152 and discharged from the turbo compressor 100B may be returned, for example, to the pipe L14 communicating with the evaporator 140.[IMPELLERS 10A AND 10B]

[0099] The impellers 10A and 10B may be closed impellers, for example.[GAP SENSOR 71]

[0100] The gap sensor 71 can detect, for example, the gap G10 between the outer peripheral surfaces of the impellers 10A and 10B and the first surfaces 51A and 51B of the casing 50. The outer peripheral surfaces of the impellers 10A and 10B may be the outer surfaces of a shroud formed to cover the blades 12.

[0101] The turbo compressor 100B according to the second embodiment has the same operation and effect as the turbo compressor 100 according to the first embodiment. The turbo compressor 100B includes the cooling mechanism 150 and can cool the casing 50 and the shaft 20. Thus, the amount of change in the gap G10 can be suppressed. The amount of change in the axial direction of the gap G10 is, for example, a difference between the amount of thermal elongation in the axial direction of the stator and the amount of thermal elongation in the axial direction of the rotor. The stator includes the casing 50, and the rotor includes impellers 10A and 10B and the shaft 20.[TURBO COMPRESSOR 100 ACCORDING TO MODIFIED EXAMPLE]

[0102] The turbo compressor 100 according to a modified example may include a casing driving mechanism for moving the first surfaces 51A and 51B. The casing driving mechanism can move the portion including the first surface 51A and the portion including the first surface 51B. The casing driving mechanism can move the portion including the first surface 51A and the portion including the first surface 51B in the axial direction, for example. The casing driving mechanism may move the portion of the casing 50 using, for example, a hydraulic cylinder or a motor.

[0103] Thus, in the turbo compressor 100 according to the modified example, the size of the gap G10 may be controlled by moving the first surfaces 51A and 51B.

[0104] Further, the present invention is not limited to these embodiments, and various variations and modifications may be made without departing from the scope of the present invention. The features described separately can be combined as long as there is no technical contradiction.

[0105] In the above embodiments, the refrigerator 110 with the turbo compressor 100 is illustrated, but the turbo compressor 100 can be applied to applications other than the refrigerator 110. The internal fluid of the turbo compressor 100 is not limited to a refrigerant.

[0106] One aspect of the present invention may be as follows. <1> A turbo compressor including: an impeller including a hub and a blade provided on an outer peripheral surface of the hub; a shaft connected to the impeller; a bearing supporting the shaft; a casing accommodating the impeller, the shaft, and the bearing, and including a first surface facing the blade; a gap sensor provided in the casing and configured to detect a size of a gap between the impeller and the first surface; and a control unit configured to control the size of the gap based on the size of the gap detected by the gap sensor. <2> The turbo compressor according to <1>, wherein: the bearing includes a thrust magnetic bearing; and the control unit is configured to control an axial position of the impeller by controlling the thrust magnetic bearing based on the size of the gap detected by the gap sensor. <3> The turbo compressor according to <1> or <2>, including a casing driving mechanism configured to move the first surface, wherein the control unit is configured to control an axial position of the first surface by controlling the casing driving mechanism. <4> The turbo compressor according to any one of <1> to <3>, including a casing cooling mechanism configured to cool the casing. <5> The turbo compressor according to any one of <1> to <3>, wherein the control unit is configured to: calculate a control target value of the size of the gap; and control the size of the gap such that a result detected by the gap sensor becomes the control target value. <6> The turbo compressor according to <5>, wherein the control unit is configured to calculate the control target value based on: a pressure ratio which is a ratio between an inlet pressure and an outlet pressure of the impeller; or a flow rate of gas flowing into the impeller. <7> The turbo compressor according to <5> or <6>, the turbo compressor being a variable speed machine, wherein the control unit is configured to calculate the control target value based on a number of rotations of the impeller. <8> The turbo compressor according to <5> or <6>, including an inlet guide vane configured to change a flow rate of gas flowing into the impeller, wherein the control unit is configured to calculate the control target value based on an opening degree of the inlet guide vane. <9> The turbo compressor according to any one of <1> to <8>, wherein the gap sensor is disposed farther out, in a radial direction of the impeller, than a midpoint of a radius of the impeller. <10> A refrigerator including the turbo compressor of any one of <1> to <9>.

[0107] The present application is based on and claims priority to Japanese patent application No. 2024-170510 filed on September 30, 2024, with the Japan Patent Office, the entire contents of which are hereby incorporated by reference.DESCRIPTION OF REFERENCE NUMERALS

[0108] 100, 100Bturbo compressor 110refrigerator 10A,10Bimpeller 11hub 12blade 20shaft 31, 32bearing (radial magnetic bearing) 33, 34bearing (thrust magnetic bearing) 50casing 51A, 51Bfirst surface 71gap sensor 90inlet guide vane 210control unit G10gap

Claims

1. A turbo compressor comprising: an impeller including a hub and a blade provided on an outer peripheral surface of the hub; a shaft connected to the impeller; a bearing supporting the shaft; a casing accommodating the impeller, the shaft, and the bearing, and including a first surface facing the blade; a gap sensor provided in the casing and configured to detect a size of a gap between the impeller and the first surface; and a control unit configured to control the size of the gap based on the size of the gap detected by the gap sensor.

2. The turbo compressor according to claim 1, wherein: the bearing includes a thrust magnetic bearing; and the control unit is configured to control an axial position of the impeller by controlling the thrust magnetic bearing based on the size of the gap detected by the gap sensor.

3. The turbo compressor according to claim 1 or 2, comprising a casing driving mechanism configured to move the first surface, wherein the control unit is configured to control an axial position of the first surface by controlling the casing driving mechanism.

4. The turbo compressor according to any one of claims 1 to 3, comprising a casing cooling mechanism configured to cool the casing.

5. The turbo compressor according to any one of claims 1 to 4, wherein the control unit is configured to: calculate a control target value of the size of the gap; and control the size of the gap such that a result detected by the gap sensor becomes the control target value.

6. The turbo compressor according to claim 5, wherein the control unit is configured to calculate the control target value based on: a pressure ratio which is a ratio between an inlet pressure and an outlet pressure of the impeller; or a flow rate of gas flowing into the impeller.

7. The turbo compressor according to claims 5 or 6, the turbo compressor being a variable speed machine, wherein the control unit is configured to calculate the control target value based on a number of rotations of the impeller.

8. The turbo compressor according to claims 5 or 6, comprising an inlet guide vane configured to change a flow rate of gas flowing into the impeller, wherein the control unit is configured to calculate the control target value based on an opening degree of the inlet guide vane.

9. The turbo compressor according to any one of claims 1 to 8, wherein the gap sensor is disposed farther out, in a radial direction of the impeller, than a midpoint of a radius of the impeller.

10. A refrigerator comprising the turbo compressor of any one of claims 1 to 9.

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