Turbo compressors and refrigerators

Abstract

To provide a turbo compressor that can improve the accuracy of detecting the gap between the impeller and the casing. [Solution] The turbo compressor 100 comprises impellers 10A and 10B having a hub 11 and blades 12 provided on the outer circumferential surface of the hub 11, a rotating shaft 20 connected to the impellers 10A and 10B, bearings 33 and 34 supporting the rotating shaft 20, a casing 50 housing the impellers 10A and 10B, the rotating shaft 20, and the bearings 31 and 32 and having a first surface 51A facing the blades 12, a gap sensor 71 provided in the casing 50 for detecting the size of the gap between the impellers 10A and 10B and the first surface 51A, and a control unit 210 that controls the size of the gap based on the size of the gap detected by the gap sensor 71.

Description

Technical Field

[0001] The present disclosure relates to a turbo compressor and a refrigerator.

Background Art

[0002] For example, a turbo compressor in which a rotating shaft is supported by a radial magnetic bearing and a thrust magnetic bearing is known (see Patent Document 1). The control unit of this turbo compressor includes a load calculation means for calculating an axial thrust load generated by the pressure distribution of the compressor, and an axial support position control means for varying the axial support position of the rotating shaft by the thrust magnetic bearing based on the axial thrust load and controlling the gap between the impeller and the shroud to a target gap. The turbo compressor includes a plurality of gap sensors for detecting the axial support position of the rotating shaft. The plurality of gap sensors includes a gap sensor for detecting the axial position from the back side of the impeller.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In this embodiment of the turbo compressor, a gap sensor can detect the size of the gap between the impeller and the first surface. In a turbo compressor, the size of the gap on the front of the impeller changes. Factors causing this change in gap size include the effect of axial expansion of the rotating shaft due to heat and deformation due to the high-speed rotation of the impeller. In this embodiment of the turbo compressor, since the gap on the front of the impeller can be measured directly, the accuracy of gap detection 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 controls the thrust magnetic bearing based on the size of the gap detected by a gap sensor to control the axial position of the impeller.

[0009] A turbo compressor according to one aspect of the present disclosure has a casing drive mechanism for moving a first surface, and a control unit may control the casing drive mechanism to control the axial position of the first surface.

[0010] A turbo compressor according to one aspect of this disclosure has a casing cooling mechanism for cooling the casing. This turbo compressor can suppress thermal expansion of the casing.

[0011] In a turbo compressor according to one aspect of the present disclosure, the control unit calculates a control target value for the gap size and controls the gap size so that the detection result from the gap sensor becomes the control target value.

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

[0013] A turbo compressor according to one aspect of the present disclosure is a variable-speed turbo compressor, wherein the control unit may calculate the control target value based on the rotational speed of the impeller.

[0014] A turbo compressor according to one aspect of the present disclosure has an inlet guide vane that can adjust the flow rate of gas flowing into the impeller, and the control unit may calculate a control target value based on the opening degree of the inlet guide vane.

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

[0016] A chiller according to one aspect of this disclosure includes the turbo compressor described above. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram showing a refrigerator equipped with a turbo compressor according to the first embodiment. [Figure 2] This is a cross-sectional view showing a turbo compressor according to the first embodiment. [Figure 3] This is a diagram showing a magnified view of the impeller. [Figure 4] This diagram shows the arrangement of the gap sensors. [Figure 5] This is a block diagram showing the hardware configuration of a refrigerator according to the first embodiment. [Figure 6]FIG. 6(a) is a graph showing the relationship between the flow rate and the pressure ratio when the rotational speed is constant, FIG. 6(b) is a graph showing the relationship between the flow rate and the adiabatic efficiency when the rotational speed is constant, FIG. 6(c) is a graph showing the relationship between the flow rate and the pressure ratio when the opening degree of the inlet guide vane is constant, and FIG. 6(d) is a graph showing the relationship between the flow rate and the adiabatic efficiency when the opening degree of the inlet guide vane is constant. [Figure 7] FIG. 7(a) is a diagram showing the flow of the refrigerant flowing from the impeller into the diffuser when the gap size is small, and FIG. 7(b) is a diagram showing the flow of the refrigerant flowing from the impeller into the diffuser when the gap size is large. [Figure 8] It is a diagram showing the flow of the refrigerant flowing from the impeller into the diffuser. [Figure 9] It is a cross-sectional view showing the turbo compressor according to the second embodiment.

Embodiments for Carrying Out the Invention

[0018] While referring to the accompanying drawings, non-limiting examples of the present disclosure will be described. In the accompanying drawings, the same or corresponding members or components are given the same or corresponding reference numerals. Also, the overlapping descriptions of the same or corresponding members or components will be omitted below. Also, the members or components are not necessarily drawn to scale in the drawings. Therefore, those skilled in the art can arbitrarily determine the specific dimensions by referring to the following non-limiting examples. Also, the following examples are illustrative rather than limiting the invention. Also, the features described in the examples and their combinations are not necessarily essential to the invention.

[0019] [Overview of Refrigerator 110 According to the First Embodiment] Referring to Figures 1 to 8, a refrigerator 110 equipped with a turbo compressor 100 according to the first embodiment will be described. Figure 1 is a schematic diagram showing a refrigerator 110 equipped with a turbo compressor 100 according to the first embodiment. The refrigerator 110 shown in Figure 1 is used, for example, in air conditioning systems, refrigeration equipment, and refrigerator equipment. The refrigerator 110 may be used in other equipment. The refrigerator 110 performs a refrigeration cycle. The refrigeration cycle of the refrigerator 110 is a vapor compression refrigeration cycle. The refrigerator 110 comprises a turbo compressor 100, a condenser 120, an expansion valve 130, and an evaporator 140.

[0020] The refrigerant, which is the working fluid of the refrigeration unit 110, is not particularly 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 evaporates the refrigerant expanded by the expansion valve 130. The refrigerant gas evaporated in the evaporator 140 is drawn into the turbo compressor 100.

[0021] The turbo compressor 100 reversibly adiabatically compresses 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, causing a portion of the refrigerant to evaporate. The refrigerant absorbs heat at a constant pressure in the evaporator 140.

[0022] The refrigeration unit 110 is equipped with piping L11 to L14 through which the refrigerant flows. Piping L11 is an intake pipe connecting the evaporator 140 and the turbo compressor 100. Piping L12 connects the turbo compressor 100 and the condenser 120. Piping L13 connects the condenser 120 and the expansion valve 130. Piping L14 connects the expansion valve 130 and the evaporator 140.

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

[0024] [Turbo Compressor 100] Next, the turbo compressor 100 will be described. Figure 2 is a cross-sectional view showing the turbo compressor 100 according to the first embodiment. Figure 3 is an enlarged view showing the impellers 10A and 10B. The turbo compressor 100 is, for example, a two-stage compressor. The turbo compressor 100 may also be a single-stage compressor. As shown in Figure 2, the turbo compressor 100 comprises impellers 10A and 10B, a rotating shaft 20, bearings 31 to 34, a motor 40, and a casing 50. The turbo compressor 100 may be of the mixed-flow type or the centrifugal type.

[0025] The casing 50 houses the impellers 10A and 10B, the rotating 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 the same direction. The turbo compressor 100 may also have a back-to-back structure in which the backs of the impellers 10A and 10B face each other.

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

[0027] The casing 50 has an inlet 52 into which the compressed refrigerant flows. The inlet 52 extends in the axial direction of the rotating shaft 20. The refrigerant that flows through the inlet 52 is supplied to the impeller 10A. Inside the casing 50, a flow path 53 is formed that connects the diffuser 61 and the impeller 10B. The casing 50 also has an inlet 54 into which the refrigerant that has flowed through the flow path 53 flows. The inlet 54 is formed in the axial direction between the impeller 10A and the impeller 10B. The refrigerant that has flowed through the flow path 53 passes through the inlet 54 and is supplied to the impeller 10B.

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

[0029] [Impeller 10A, 10B] Impeller 10A is the low-pressure side impeller, and impeller 10B is the high-pressure side impeller. Impeller 10A is positioned closer to the intake port 52 in the axial direction of the rotating shaft 20, and impeller 10B is positioned closer to the motor 40. Impeller 10A has a hub 11 and blades 12 provided on the outer circumferential surface of the hub 11. Impeller 10B also has a hub 11 and blades 12 provided on the outer circumferential surface of the hub 11. Multiple blades 12 are provided at regular intervals on the outer circumferential surface of the hub 11.

[0030] The hub 11 has a roughly conical shape that widens in diameter from its front to its rear. In the axial direction of the rotating shaft 20, the side closer to the intake port 52 is considered the "front," and the side further from the intake port 52 is considered the "rear." The hub 11 rotates integrally with the rotating shaft 20. From the viewpoint of weight reduction, the inside of the hub 11 may be hollow except for the parts around the shaft and the outer edge.

[0031] The wings 12 extend radially outward from the outer circumferential surface 11a of the hub 11. The wings 12 are arranged in a helical pattern along the outer circumferential surface 11a of the hub 11.

[0032] [First surfaces 51A, 51B of casing 50] The casing 50 has a first surface 51A facing the blades 12 of the impeller 10A, and a first surface 51B facing the blades 12 of the impeller 10B. The first surfaces 51A and 51B form the walls of the flow path through which the refrigerant flows. The first surface 51A connects the inner surface of the intake 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.

[0033] [Rotation axis 20] The rotating shaft 20 has two ends 20a and 20b in the axial direction, as shown in Figure 2. End 20a is the end closer to the impellers 10A and 10B, and end 20b is the end further away from the impellers 10A and 10B. The impellers 10A and 10B are mounted on end 20a. The rotating shaft 20 includes the rotating shaft of the motor 40. The rotating shaft of the motor 40 includes the central portion between end 20a and end 20b in the axial direction of the rotating shaft 20.

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

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

[0036] Bearings 31-34 are, for example, oil-less bearings. Bearings 31 and 32 may be sliding bearings or rolling bearings. Bearings 31-34 may also be hydrostatic bearings. Oil-less bearings are bearings that do not require the supply of lubricating oil. Examples of oil-less bearings include gas bearings, air bearings, foil bearings, and magnetic bearings.

[0037] Bearings 31-34 may be air bearings. Air bearings are a type of hydrostatic bearing, in which compressed air is blown between the rotating shaft 20 and the bearing surface, allowing the rotating shaft 20 to float and support the load using air pressure. Bearings 31 and 32 may also be gas bearings, in which compressed gas is blown between the rotating shaft 20 and the bearing surface to float the rotating shaft 20. Gas bearings may also use refrigerant gas as the compressed gas to float the rotating shaft 20.

[0038] The bearings 31-34 may be foil bearings, which are a type of pneumatic bearing. A foil bearing has a thin film (foil) as the bearing surface. The thin film has low rigidity against bending and is flexible. The foil bearing supports the load by allowing the deflection of the foil. When the rotating shaft 20 rotates, a fluid film (air film) is formed between the rotating shaft 20 and the bearing surface, which is the foil. The foil bearing supports the rotating shaft 20 using the foil and the fluid film. Due to the flexibility of the foil, the foil bearing can form a bearing clearance that corresponds to the rotational speed of the rotating shaft 20, the load on the rotating shaft 20, the ambient temperature around the rotating shaft 20, and other operating conditions.

[0039] The types, positions, and quantities of bearings 31-34 are not limited to those described above. The turbo compressor 100 may also be equipped with touchdown bearings. Touchdown bearings are also called auxiliary bearings or backup bearings. Touchdown bearings limit the range of motion of the rotating shaft 20. Touchdown bearings can limit the range of motion of the rotating shaft 20 in the radial direction. Touchdown bearings can limit the range of motion of the rotating shaft 20 in the axial direction. Touchdown bearings can prevent contact between the stator and the rotor. Touchdown bearings can support the rotating shaft 20 when the magnetic bearings are not energized.

[0040] The turbo compressor 100 includes a control unit 210 (see Figure 5) capable of controlling the range of motion of the rotating shaft 20. The control unit 210 can control the current supplied to the coils of bearings 31-34, which are controlled magnetic bearings. By controlling the current supplied to the coils, the control unit 210 can control the range of motion of the rotating shaft 20 in the radial direction and in the axial direction.

[0041] [Motor 40] The motor 40 is the power source for the turbo compressor 100. The motor 40 has a rotor 41 and a stator 42. The rotor 41 is fixed to the rotating shaft 20 and rotates with the rotating shaft 20. The stator 42 is fixed to the casing 50 and is positioned around the rotor 41.

[0042] The refrigerator 110 is equipped with an inverter 80. The inverter 80 controls the rotational speed of the motor 40. The inverter 80 is a controller that controls the operating frequency of the motor 40. By controlling the operating frequency of the motor 40, the inverter 80 can change the rotational speed of the impellers 10A, 10B and the rotating shaft 20.

[0043] [Inlet guide vane 90] As shown in Figure 2, the turbo compressor 100 is equipped with an inlet guide vane 90 provided at the intake port 52. The control unit 210 can control the opening degree of the inlet guide vane 90. By changing the opening degree of the inlet guide vane 90, the control unit 210 can control the flow rate of refrigerant flowing into the impeller 10A.

[0044] [Gap Sensor 71] The turbo compressor 100 is equipped with a gap sensor 71. The gap sensor 71 is installed in the casing 50 and detects the size of the gap G10 between the impeller 10A and the first surface 51A. The gap sensor 71 also detects the size of the gap G10 between the blades 12 of the impeller 10A and the first surface 51A. The gap sensor 71 may also detect the 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 the 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. The gap sensor 71 may also detect the gap G1 between the impeller 10B and the first surface 51B in the axial direction of the rotating shaft 20. The size of the gap G1 may be the shortest distance of the gap G1, or the distance along the axial direction of the rotating shaft 20. The turbo compressor 100 may be equipped with multiple gap sensors 71.

[0046] The gap sensor 17 is positioned radially on the impeller 10A, outside the central position P11 of the impeller 10A's radius R10. The radius R10 of the impeller 10A is the length from the center C1 of the rotation axis 20 to the outer edge of the impeller 10A. The radius R11 from the center C1 of the rotation axis 20 to the central position P11 is half the length of the radius R10.

[0047] The turbo compressor 100 may also be equipped with other gap sensors. These other gap sensors can detect the axial position of the rotating shaft 20.

[0048] [Control Unit 210] Figure 5 is a block diagram showing the hardware configuration of the refrigerator 110 according to the first embodiment. As shown in Figure 5, the control unit 210 includes a CPU 211 and a memory unit 212. The CPU (Center Processing Unit) 211 is responsible for the overall processing in the refrigerator 110. The CPU 211 can control the rotational speed 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 memory unit 212 includes a ROM (Read Only Memory) 213 and a RAM (Random Access Memory) 214. The ROM 213 stores various programs for the CPU 211 to execute control processing, as well as various data necessary for the operation of the refrigerator 110. The RAM 214 can temporarily store data 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 bearings (thrust magnetic bearings) 33, 34 to control the axial position of the rotating shaft 20. The control unit 210 may also control the size of the gap G10 by controlling other actuators. The control unit 210 may also 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 for the size of the gap G10. The control unit 210 may also control the size of the gap G10 so that the detection result from 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 rotational speed 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 on the inlet side and the outlet side of the impeller 10A. The turbo compressor 100 can detect the temperature and pressure of the refrigerant on the inlet side and the outlet side of the impeller 10B.

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

[0054] The control unit 210 may calculate a control target value based on the rotational speeds of the impellers 10A and 10B. The turbo compressor 100 is a variable-speed machine in which the rotational speeds of the impellers 10A and 10B can be changed. The turbo compressor 100 may also be a constant-speed machine in which the rotational speeds of the impellers 10A and 10B are constant.

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

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

[0057] Figure 6(a) is a graph showing the relationship between flow rate and pressure ratio when the rotational speed is constant, Figure 6(b) is a graph showing the relationship between flow rate and adiabatic efficiency when the rotational speed is constant, Figure 6(c) is a graph showing the relationship between flow rate and pressure ratio when the opening of the inlet guide vane is constant, and Figure 6(d) is a graph showing the relationship between flow rate and adiabatic efficiency when the opening of the inlet guide vane is constant.

[0058] In Fig. 6(a), the corrected flow rate of the turbo compressor 100 is shown on the horizontal axis, and the pressure ratio is shown on the vertical axis. The corrected rotational speed is constant. The corrected rotational speeds N1, N2, and N3 are in descending order of magnitude (N1 < N2 < N3). In Fig. 6(a), the surge line SL is shown. In the region where the flow rate is less than that of the surge line SL, the turbo compressor 100 cannot be operated. In Fig. 6(b), the corrected flow rate of the turbo compressor 100 is shown on the horizontal axis, and the adiabatic efficiency is shown on the vertical axis.

[0059] The "corrected flow rate" and "corrected rotational speed" can be calculated using the following calculation formulas. The "corrected flow rate" and "corrected rotational speed" are values obtained by converting the obtained flow rate and rotational speed to the flow rate and rotational speed under standard conditions when the temperature during operation is different from the temperature under standard conditions.

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

[0061] The corrected rotational speed Nc can be calculated using the following formulas (1) and (2). Nc = N / θ 1 / 2 ···(1) θ = t / t0 ···(2) Here, "t0" is the temperature under standard conditions. "N" is the actual rotational speed. "t" is the actual temperature.

[0062] The corrected (mass) flow rate mc can be calculated using the following formulas (3) and (4). mc = mθ 1 / 2 / δ ···(3) δ = p / p0 ···(4) Here, "p0" is the pressure under standard conditions. "m" is the actual flow rate. "p" is the actual pressure.

[0063] In FIG. 6(c), the corrected flow rate of the turbo compressor 100 is shown on the horizontal axis, and the pressure ratio is shown on the vertical axis. The opening degree of the inlet guide vane 90 (IGV opening degree) is constant. The IGV opening degrees M1, M2, and M3 are in descending order of magnitude (M1 < M2 < M3). In FIG. 6(c), the surge line SL is shown. In FIG. 6(d), the corrected flow rate of the turbo compressor 100 is shown on the horizontal axis, and the adiabatic efficiency is shown on the vertical axis.

[0064] In the turbo compressor 100, maps as shown in FIGS. 6(a) to 6(d) are created by performing tests. Data regarding these maps are stored in the storage unit 212. In the turbo compressor 100, an optimal control target value (gap G10) is set for each point of these maps. For example, in the turbo compressor 100, in the operating region near the surge line SL, the positions of the impellers 10A and 10B in the axial direction may be controlled so as to widen the gap G10. Thereby, the flow of the refrigerant can be stabilized, and the operable range in the turbo compressor 100 can be widened.

[0065] Generally, in a turbo compressor, the performance of the impellers 10A and 10B and the diffusers 61 and 62 varies greatly 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. By reducing the size of the gap G10 at the rated point of the turbo compressor 100, the leakage amount can be suppressed. Thereby, the performance of the turbo compressor 100 can be improved. The rated point is, in design, an operating condition with good efficiency. The leakage amount is the flow rate of the refrigerant that passes through the gap G10 and flows from the high-pressure side to the low-pressure side, and is the flow rate of the refrigerant that is not compressed by the impellers 10A and 10B.

[0066] In the turbo compressor 100, for example, when the first flow rate Q12 is less than the first reference flow rate Q11, the size of the gap G10 can be controlled so as to increase the gap G10. Thereby, the area of the flow path through which the refrigerant communicating with the diffusers 61 and 62 flows can be widened, and the refrigerant can be efficiently introduced into the diffusers 61 and 62. As a result, the performance of the turbo compressor 100 can be improved.

[0067] [Changes in the size of gap G10] In the turbo compressor 100, changes in the size of the gap G10 can be detected based on the detection results from the gap sensor 71. In the turbo compressor 100, the gap G10 changes due to a difference between the amount of deformation due to thermal expansion of the casing 50 and the amount of deformation due to thermal expansion of the rotor portion. The rotor portion includes the rotating shaft 20 and the impellers 10A and 10B.

[0068] In the turbo compressor 100, the high rotational speed generates a large centrifugal force, which deforms the impellers 10A and 10B, changing the size of the gap G10. For example, the high rotational speed deforms the blades 12 of the impellers 10A and 10B so that they extend radially outward, reducing the size of the gap G10.

[0069] [Refrigerant flow from impeller 10A to diffuser 61] Next, the flow of refrigerant from the impeller 10A to the diffuser 61 will be described with reference to Figures 7 and 8. Figure 7(a) shows the flow of refrigerant from the impeller 10A to the diffuser 61 when the size of the gap G11 is small, and Figure 7(b) shows the flow of refrigerant from the impeller 10A to the diffuser 61 when the size of the gap G12 is large. Figures 7(a) and 7(b) show the impeller 10A as viewed from a direction perpendicular to the rotation axis 20. Figure 8 shows the flow of refrigerant from the impeller 10A to the diffuser 61. Figure 8 shows the impeller 10A as viewed from the axial direction of the rotation axis 20. In Figure 8, one of the multiple blades is shown. As described above, multiple blades 12 are provided on the outer circumferential surface of the hub 11.

[0070] The gaps G11 and G12 are gaps along the axial direction of the rotation axis 20. Gap G11 is smaller than gap G12. The sizes of gaps G11 and G12 follow the size of gap G10. When gap G11 is formed, the size of gap G10 is smaller than the size of gap G10 when gap G12 is formed. The gap sensor 71 may detect gaps G11 and G12.

[0071] The refrigerant flow velocity V11 when gap G11 is formed is slower than the refrigerant flow velocity V12 when gap G12 is formed. Flow velocities V11 and V12 are the speeds at which the refrigerant compressed by the impeller 10A flows into the diffuser 61.

[0072] As shown in Figure 7(b), when a gap G12 is formed, the effective outlet area of ​​the impeller 10A is reduced due to the blockage. As a result of this reduction in the effective outlet area of ​​the impeller 10A, the radial velocity component of the flow velocity V12 is larger than the radial velocity component of the flow velocity V11.

[0073] "Blocking reduces the effective outlet area" means that the effective outlet area decreases as the blocking coefficient increases. The "blocking coefficient" can also be a coefficient used to indicate the ratio of the main flow to the slower boundary layer within a passage cross-section when a fluid passes through a passage cross-section. If the average velocity within the passage cross-section is "u0" and the maximum velocity of the main flow is "U1", then the effective area ratio E = u / U and the blocking coefficient B = 1 - E are defined.

[0074] As shown in Figure 8, the flow velocity V11 is at an angle closer to the tangent to the circle representing the outer diameter OD10 of the impeller 10A, compared to the flow velocity V12. The flow velocity V12 is at an angle closer to the normal perpendicular to the tangent to the circle representing the outer diameter OD10, compared to the flow velocity V11.

[0075] A smaller gap G11 results in a flow velocity V11 where the refrigerant is more likely to backflow, leading to greater fluid loss at the inlet side of the diffuser 61. In other words, a smaller gap G12 results in a flow velocity V12 where the refrigerant is less likely to backflow, leading to less fluid loss at the inlet side of the diffuser 61. In the turbo compressor 100, in the low flow rate operating range and in the operating range close to the surge line SL, fluid loss can be reduced by controlling the gap G10 to increase its size. The turbo compressor 100 can stabilize operation near the surge line SL. In other words, the turbo compressor 100 can expand the range of conditions under which it can operate near the surge line SL.

[0076] [Surging] Next, we will explain surging. Compressors such as axial flow compressors and centrifugal compressors used in various applications may experience surging during operation. For example, in a centrifugal compressor, if the pressure is increased while the flow rate is reduced during operation, swirling stall or surging will occur. Generally, as the flow rate decreases, swirling stall occurs, and eventually surging occurs.

[0077] For example, when operating a centrifugal compressor, if the flow rate drops further beyond a certain threshold, a reverse flow region will occur circumferentially inside the centrifugal compressor (turbomachinery). This occurrence of a reverse flow region is called swirling stall. The phenomenon of reverse flow occurring is a localized phenomenon within the compressor that fluctuates circumferentially.

[0078] When surging occurs inside a compressor, large fluctuations in flow velocity and pressure due to backflow and pulsation occur throughout the entire piping system connected to the compressor. This places a heavy load on the equipment, including the piping system, making it impossible to continue operating the compressor.

[0079] For example, it is preferable to perform operational tests to predict the occurrence of surging and to take a safety factor so that the compressor's operating point does not fall within the region where surging occurs. By operating the compressor in a flow rate region higher than the operating point considering the safety factor, the occurrence of surging can be suppressed.

[0080] For example, in variable drive operation where the compressor's rotational speed is varied using an inverter, the flow rate at which surging occurs is determined for each rotational speed. By connecting the operating points at which surging occurs for each rotational speed, the surge line (operating limit line) SL, defined by the volumetric flow rate and the adiabatic head, is determined.

[0081] [Effects of the turbo compressor 100 according to the first embodiment] The turbo compressor 100 according to the first embodiment includes impellers 10A and 10B having a hub 11 and blades 12 provided on the outer circumferential surface 11a of the hub 11, a rotating shaft 20 connected to the impellers 10A and 10B, bearings 31 to 34 supporting the rotating shaft 20, a casing 50 housing the impellers 10A and 10B, the rotating shaft 20 and the bearings 31 to 34 and having a first surface 51A facing the blades 12, a 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 a 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.

[0082] With such a turbo compressor 100, the gap sensor 71 can detect the gap G10 between the impeller 10 and the first surface 51A, and the size of this gap G10 can be controlled based on its size. 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.

[0083] Furthermore, in the turbo compressor 100, the size of the gap G10 between the impellers 10A, 10B and the first surfaces 51A, 51B can be controlled to be smaller in the operating region away from the surge line SL. This reduces leakage flow between the impellers 10A, 10B and the casing 50, thereby improving operating efficiency.

[0084] Furthermore, in the turbo compressor 100, fluid loss can be reduced by controlling the gap G10 to increase its size in the operating region close to the surge line SL. In the turbo compressor 100, operation can be stabilized by increasing the flow rate by increasing the flow velocity on the outlet side of the impellers 10A and 10B near the surge line SL. The turbo compressor 100 can expand the range of operating conditions.

[0085] Furthermore, in the turbo compressor 100, the gap sensor 71 is positioned outside the center of the radius of the impeller 10A in the radial direction of the impeller 10A. In a turbo compressor 100 with this configuration, even if the blades 12 of the impellers 10A and 10B deform outward in the radial direction due to high-speed rotation, the gap sensor 71 can accurately detect changes in the size of the gap G10.

[0086] Furthermore, the turbo compressor 100 is equipped with sensors (pressure sensor and temperature sensor) for measuring the state of the refrigerant. The turbo compressor 100 only needs to have a temperature and pressure sensor at the inlet of the first stage and a temperature and pressure sensor at the outlet of the final stage, and does not need temperature and pressure sensors between stages. The space between stages could be, for example, between the first stage impeller 10A and the second stage impeller 10B. For example, in the turbo compressor 100, even if the number of stages is increased to achieve a high head, the increase in the installation cost of temperature and pressure sensors can be kept to a minimum.

[0087] Furthermore, with the turbo compressor 100, the size of the gap G10 between the impeller 10A and the casing 50 can be measured, eliminating the need for indirect calculation of the gap G10 size, including correction for thermal expansion. The turbo compressor 100 allows for direct measurement of the gap G10 size, enabling accurate measurement of the gap G10 size.

[0088] Furthermore, in the turbo compressor 100, the size of the gap G10 can be controlled based on the value of the gap G10 measured using the gap sensor 71, so it is not necessary to calculate the thrust load acting on the rotating shaft 20. For example, in conventional turbo compressors, the thrust load was calculated to control the axial position of the impeller, but in the turbo compressor 100, the size of the gap G10 can be controlled without calculating the thrust load.

[0089] [Turbo compressor 100B according to the second embodiment] Next, with reference to Figure 9, the turbo compressor 100B according to the second embodiment will be described. Figure 9 is a cross-sectional view showing the turbo compressor 100B according to the second embodiment. The difference between the turbo compressor 100B according to the second embodiment shown in Figure 9 and the turbo compressor 100 according to the first embodiment is that it is equipped with a cooling mechanism 150. Note that in the description of the second embodiment, explanations similar to those given in the description of the first embodiment above may be omitted.

[0090] [Cooling mechanism 150] The turbo compressor 100B is equipped with a cooling mechanism 150. The cooling mechanism 150 includes a first cooling passage 151 and a second cooling passage 152. In the turbo compressor 100B, the rotating shaft 20, bearings 31-34, motor 40, and casing 50 are cooled by flowing a refrigerant (cooling liquid) through the first cooling passage 151 and the second cooling passage 152. The refrigerant may be, for example, the refrigerant discharged from the condenser 120. Piping branched from piping L13 communicates with the first cooling passage 151 and the second cooling passage 152.

[0091] [First cooling channel 151] The first cooling channel 151 includes a channel formed inside the rotating shaft 20. The first cooling channel 151 has an inlet 151a and an outlet 151b. The casing 50 has a cylindrical body 50c and an end plate 50d. The rotating shaft 20, bearings 31-34, and motor 40 are housed inside the cylindrical body 50c. The end plate 50d is formed to close the rear of the cylindrical body 50c. "Rear" is the side furthest from the impellers 10A and 10B in the axial direction of the rotating shaft 20.

[0092] A boss portion 50e is provided at the radial center of the end plate 50d. The boss portion 50e is formed to penetrate the end plate 50d in the axial direction. The end portion 20b of the rotating shaft 20 is connected to the boss portion 50e. The first cooling channel 151 extends axially within the boss portion 50e and the rotating shaft 20. The first cooling channel 151 extends axially from the boss portion 50e to a position, for example, between the motor 40 and the bearing 31. The first cooling channel 151 includes a portion that extends radially. The inlet 151a of the first cooling channel 151 is formed in the boss portion 50e, and the outlet 151b is formed on the outer circumferential surface of the rotating shaft 20.

[0093] The refrigerant that has flowed through the first cooling channel 151 flows through the outlet 151b and enters the motor chamber 50b. The interior of the motor chamber 50b includes the space inside the cylindrical body 50c. The cylindrical body 50c has an outlet 151c formed therein for discharging the refrigerant to the outside of the cylindrical body 50c. The outlet 151c is formed in the axial direction, for example, near the bearings 33 and 34. The refrigerant that has entered the motor chamber 50b from the outlet 151b flows inside the motor chamber 50b, flows through the outlet 151c and is discharged to the outside of the turbo compressor 100. The refrigerant flowing inside the motor chamber 50b cools the rotating shaft 20, the bearings 31-34, the motor 40, and the casing 50.

[0094] [Second cooling channel 152] The second cooling channel 152 includes a channel formed inside the wall of the cylindrical body 50c. The second cooling channel 152 has an inlet 152a and an outlet 152b. The second cooling channel 152 is formed in the axial direction of the rotating shaft 20, for example, at a position corresponding to the motor 40. The inlet 152a is located in the axial direction, close to the bearing 31, and the outlet 152b is formed close to the bearing 32. The second cooling channel 152 is formed in a spiral shape along the circumferential direction of the cylindrical body 50c.

[0095] The refrigerant flowing in from the inlet 152a flows through the second cooling channel 152 and is discharged from the outlet 152b. The refrigerant flowing through the second cooling channel 152 cools the casing 50 and the motor 40.

[0096] The refrigerant discharged from the turbo compressor 100B after flowing through the first cooling channel 151 and the second cooling channel 152 may be returned, for example, to the piping L14 that communicates with the evaporator 140.

[0097] [Impeller 10A, 10B] Impellers 10A and 10B may be closed impellers, for example.

[0098] [Gap Sensor 71] The gap sensor 71 can detect, for example, the gap G10 between the outer circumferential surfaces of the impellers 10A and 10B and the first surfaces 51A and 51B of the casing 50. The outer circumferential surfaces of the impellers 10A and 10B may also be the outer surfaces of the shroud formed to cover the blades 12.

[0099] The turbo compressor 100B according to this second embodiment also provides the same effects as the turbo compressor 100 according to the first embodiment described above. The turbo compressor 100B is equipped with a cooling mechanism 150 that can cool the casing 50 and the rotating shaft 20. This suppresses the amount of change in the gap G10. The amount of change in the gap G10 in the axial direction is, for example, the difference between the amount of thermal expansion of the stator in the axial direction and the amount of thermal expansion of the rotor in the axial direction. The stator includes the casing 50, and the rotor includes the impellers 10A, 10B and the rotating shaft 20.

[0100] [Turbo compressor 100 with modified example] The modified turbo compressor 100 may have a casing drive mechanism for moving the first surfaces 51A and 51B. The casing drive mechanism can move the portion including the first surface 51A and the portion including the first surface 51B. The casing drive mechanism can move the portion including the first surface 51A and the portion including the first surface 51B, for example, in the axial direction. The casing drive mechanism may move the portion of the casing 50 using, for example, a hydraulic cylinder or a motor.

[0101] In the modified turbo compressor 100 described above, the size of the gap G10 may be controlled by moving the first surfaces 51A and 51B.

[0102] Preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the embodiments described above. Various modifications, substitutions, etc., can be applied to the embodiments described above without departing from the scope of the present invention. Furthermore, features described separately can be combined as long as no technical inconsistencies arise.

[0103] In the above embodiment, a refrigerator 110 equipped with a turbo compressor 100 is illustrated, but the turbo compressor 100 can be applied to applications other than refrigerators 110. The internal fluid of the turbo compressor 100 is not limited to a refrigerant.

[0104] One aspect of the present invention may be as follows:

[0105] <1> An impeller having a hub and wings provided on the outer surface of the hub, The rotating shaft connected to the impeller, A bearing that supports the aforementioned rotating shaft, A casing housing the impeller, the rotating shaft, and the bearing, and having a first surface facing the blade, A gap sensor is provided in the casing to detect the size of the gap between the impeller and the first surface, A turbo compressor comprising: a control unit that controls the size of the gap based on the size of the gap detected by the gap sensor. <2> The bearing includes a thrust magnetic bearing, The control unit controls the thrust magnetic bearing based on the size of the gap detected by the gap sensor to control the axial position of the impeller. <1> The turbo compressor described above. <3> It has a casing drive mechanism for moving the first surface, The control unit controls the casing drive mechanism to control the axial position of the first surface. <1> or <2> The turbo compressor described above. <4> The above-mentioned casing cooling mechanism has a casing cooling mechanism for cooling the casing. <1> ~ <3> A turbo compressor as described in one of the following documents. <5> The control unit, The control target value for the size of the aforementioned gap is calculated, The size of the gap is controlled so that the detection result from the gap sensor becomes the control target value. <1> ~ <3> A turbo compressor as described in one of the following documents. <6> The control unit, The control target value is calculated based on the pressure ratio, which is the ratio of the inlet pressure to the outlet pressure of the impeller, or the flow rate of the gas flowing into the impeller. <5> The turbo compressor described above. <7> A turbo compressor that is a variable-speed machine, The control unit, The above method calculates the control target value based on the rotational speed of the impeller. <5> or <6> The turbo compressor described above. <8> The impeller has an inlet guide vane that can change the flow rate of gas flowing into it, The control unit, The above method calculates the control target value based on the opening degree of the inlet guide vane. <5> or <6> The turbo compressor described above. <9> The aforementioned gap sensor is In the radial direction of the impeller, the above is located outside the central position of the radius of the impeller. <1> ~ <8> A turbo compressor as described in one of the following documents. <10> The above <1> ~ <9> A refrigerator equipped with a turbo compressor as described in one of the following documents. [Explanation of Symbols]

[0106] 100, 100B Turbo Compressor 110 Refrigeration unit 10A, 10B Impeller 11 Hubs 12 wings 20 Rotation axis 31,32 Bearings (Radial Magnetic Bearings) 33,34 Bearings (thrust magnetic bearings) 50 casing 51A,51B 1st page 71 Gap Sensor 90 Inlet Guide Vanes 210 Control Unit G10 Gap

Claims

1. An impeller having a hub and wings provided on the outer surface of the hub, The rotating shaft connected to the impeller, A bearing that supports the aforementioned rotating shaft, A casing housing the impeller, the rotating shaft, and the bearing, and having a first surface facing the blade, A gap sensor is provided in the casing to detect the size of the gap between the impeller and the first surface, A turbo compressor comprising: a control unit that controls the size of the gap based on the size of the gap detected by the gap sensor.

2. The bearing includes a thrust magnetic bearing, The turbo compressor according to claim 1, wherein the control unit controls the thrust magnetic bearing based on the size of the gap detected by the gap sensor to control the axial position of the impeller.

3. The casing has a drive mechanism for moving the first surface, The turbo compressor according to claim 1 or 2, wherein the control unit controls the casing drive mechanism to control the axial position of the first surface.

4. The casing has a casing cooling mechanism for cooling the casing. A turbo compressor according to claim 1 or 2.

5. The control unit, The control target value for the size of the aforementioned gap is calculated, The turbo compressor according to claim 1 or 2, wherein the size of the gap is controlled so that the detection result by the gap sensor becomes the control target value.

6. The control unit, The turbo compressor according to claim 5, wherein the control target value is calculated based on the pressure ratio, which is the ratio of the inlet pressure to the outlet pressure of the impeller, or the flow rate of the gas flowing into the impeller.

7. A turbo compressor that is a variable-speed machine, The control unit, The turbo compressor according to claim 5, which calculates the control target value based on the rotational speed of the impeller.

8. The impeller has an inlet guide vane that can change the flow rate of gas flowing into it, The control unit, The turbo compressor according to claim 5, which calculates the control target value based on the opening degree of the inlet guide vane.

9. The aforementioned gap sensor is The turbo compressor according to claim 1 or 2, wherein the impeller is positioned outside the central position of the radius of the impeller in the radial direction.

10. A refrigerator comprising a turbo compressor according to claim 1 or 2.

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