Turbo compressor and refrigeration device

Abstract

A turbo compressor (10) includes: an intermediate flow path (30) allowing a refrigerant to flow between a first impeller (11) and a second impeller (21); a diffuser flow path (40) through which a refrigerant having flowed out of the second impeller (21) flows; and a volute flow path (50) through which a refrigerant having passed through the diffuser flow path (40) flows. The diffuser flow path (40) includes: a flat flow path (43) extending in a radial direction; and a curved flow path (44) curved to a side opposite to a side on which a refrigerant flows in with respect to the flat flow path (43) in the axial direction. The volute flow path (50) is connected to the curved flow path (44) extending in the circumferential direction, and the maximum value (Rv) of the outer diameter of the volute flow path (50) is smaller than or equal to the maximum value (Rr) of the outer diameter of the intermediate flow path (30).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a turbo compressor and a refrigeration apparatus.BACKGROUND ART

[0002] Patent Document 1 discloses a multistage turbo compressor having two impellers. The turbo compressor includes a diffuser flow path through which a refrigerant having flowed out of the impeller of the latter stage flows, and a volute flow path through which a refrigerant having passed through the diffuser flow path flows. The diffuser flow path extends straight outward in the radial direction from an outflow port of the impeller of the latter stage. The volute flow path is connected to the outer end portion of the diffuser flow path in the radial direction.CITATION LISTPATENT DOCUMENT

[0003] Patent Document 1: U.S. Patent Publication No. 2023 / 013972SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0004] In recent years, a turbo compressor has been required to have a larger capacity. In order to improve the fluid efficiency of a turbo compressor having a large capacity, it is required to sufficiently reduce the flow velocity of a large amount of refrigerant in a diffuser flow path. In order to reduce the flow velocity of the refrigerant in the diffuser flow path, it is necessary to increase the length of the diffuser flow path.

[0005] If the diffuser flow path is made longer in order to increase the capacity of the turbo compressor disclosed of Patent Document 1, a connection position between the diffuser flow path and the volute flow path expands outward in the radial direction. The volute flow path expands further outward in the radial direction from the connection position. Thus, if the fluid efficiency of a conventional turbo compressor is increased, the size of the turbo compressor is increased. Conventional turbo compressors have room for improvement from the viewpoint of achieving both fluid efficiency and downsizing of a turbo compressor.

[0006] An object of the present disclosure is to downsize a turbo compressor while maintaining the fluid efficiency.SOLUTION TO THE PROBLEM

[0007] A first aspect of the technique disclosed herein is directed to a turbo compressor. The turbo compressor includes: a motor (100) having a stator (101) and a rotor (102); a shaft (201) extending in an axial direction and rotated by the rotor (102); a first impeller (11) attached to the shaft (201); a second impeller (21) attached to the shaft (201) and disposed adjacent to the first impeller (11) in the axial direction; an intermediate flow path (30) allowing a refrigerant to flow between an outflow port (14) of the first impeller (11) and an inflow port (22a) of the second impeller (21); a diffuser flow path (40) through which a refrigerant having flowed out of the second impeller (21) flows; and a volute flow path (50) through which a refrigerant having passed through the diffuser flow path (40) flows, wherein the intermediate flow path (30) includes a first flow path (31) extending in a radial direction, which is a direction extending radially from a center of the shaft (201), and communicating with the outflow port (14) of the first impeller (11), a second flow path (32) extending in the radial direction and communicating with the inflow port (22a) of the second impeller (21), and a connection flow path (33) connecting an outer portion of the first flow path (31) in the radial direction and an outer portion of the second flow path (32) in the radial direction, the diffuser flow path (40) includes a flat flow path (43) extending outward in the radial direction from an outflow port (24) of the second impeller (21), and a curved flow path (44) curved to a side opposite to a side on which a refrigerant flows in with respect to the flat flow path (43) in the axial direction, the volute flow path (50) extends in a circumferential direction about a center axis (X) of the shaft (201) so as to surround the casing housing the shaft (201) from an outside in the radial direction, and is connected to the curved flow path (44), and a maximum value (Rv) of an outer diameter of the volute flow path (50) with respect to the center axis (X) is smaller than or equal to a maximum value (Rr) of an outer diameter of the connection flow path (33) with respect to the center axis (X).

[0008] According to the first aspect, the volute flow path (50) is connected to the curved flow path (44), and thus is disposed on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40). Further, the maximum value of the outer diameter of the volute flow path (50) is smaller than or equal to the maximum value of the outer diameter of the connection flow path (30). Accordingly, the turbo compressor can be downsized in both the radial direction and the axial direction. Further, the diffuser flow path (40) has a long flow path length due to the curved flow path, and the flow velocity of the refrigerant can be reduced in the diffuser flow path (40), and thus the fluid efficiency can be maintained. Thus, the turbo compressor can be downsized while the fluid efficiency is maintained.

[0009] A second aspect of the technique disclosed herein is an embodiment of the first aspect. In the second aspect, the motor (100) is located on a side opposite to the first impeller (11) with respect to the second impeller (21) in the axial direction, and the casing is a motor casing (110) housing the motor (100).

[0010] According to the second aspect, the turbo compressor can be downsized in the radial direction and the axial direction by effectively utilizing the space around the motor casing (110).

[0011] A third aspect of the technique disclosed herein is an embodiment of the first or second aspect. In the third aspect, the volute flow path (50) has a shape so that a cross section taken along the radial direction increases while expanding inward in the radial direction, and a maximum length of the volute flow path (50) in the radial direction in a cross section taken along the radial direction is a first length (r), and a maximum length of the volute flow path (50) in the axial direction in the cross section taken along the radial direction is a second length (L), where in part of the volute flow path (50) where the radial cross sectional area is larger, a ratio of the second length (L) to the first length (r) is larger.

[0012] According to the third aspect, the volute flow path (50) can be prevented from expanding to the outer side in the radial direction, and the turbo compressor can be downsized. Further, the radial cross sectional area of the volute flow path (50) is increased, whereby the flow velocity of the refrigerant can be reduced; and thus the fluid efficiency can be improved. Thus, the turbo compressor can be downsized while the fluid efficiency is improved.

[0013] A fourth aspect of the technique disclosed herein is an embodiment of the third aspect. In the fourth aspect, in part of the volute flow path (50) where the radial cross sectional area is smallest, the first length (r) is larger than the second length (L), and in part of the volute flow path (50) where the radial cross sectional area is largest, the second length (L) is larger than the first length (r).

[0014] According to the fourth aspect, in the part of the volute flow path (50) where the radial cross sectional area is small, by making the length in the radial direction longer and the length in the axial direction shorter, flow separation can be reduced at the inlet portion of the volute flow path (50), and thus the fluid efficiency can be improved.

[0015] A fifth aspect of the technique disclosed herein is an embodiment of any one of the first to fourth aspects. In the fifth aspect, in a cross section of the diffuser flow path (40) taken along the radial direction, a ratio of a length (Dc) of the curved flow path (44) to a length (Dp) of the flat flow path (43) is 0.5 or more in an intermediate span of the diffuser flow path (40).

[0016] According to the fifth aspect, while the length of the diffuser flow path (40) in the radial direction can be shortened, the flow path itself can be made longer by the curved flow path (44). The flow velocity of the refrigerant can be reduced in the diffuser flow path (40), and thus the fluid efficiency of the turbo compressor can be improved.

[0017] A sixth aspect of the technique disclosed herein is an embodiment of the second aspect. In the sixth aspect, the motor casing (110) houses a bearing (121, 122, 123) supporting the shaft (201).

[0018] According to the sixth aspect, the bearings (121, 122, 123) are disposed in the motor casing (110), whereby the turbo compressor can be downsized in the radial direction and the axial direction by effectively utilizing the space around the motor casing (110).

[0019] A seventh aspect of the technique disclosed herein is an embodiment of any one of the first to sixth aspects. In the seventh aspect, the multistage turbo compressor further includes a two-stage inline structure in which a suction side of the first impeller (11) and a suction side of the second impeller (21) face in the same direction.

[0020] According to the seventh aspect, the inline structure is employed, and thus the turbo compressor can be downsized.

[0021] An eighth aspect of the technique disclosed herein is an embodiment of any one of the first to seventh aspects. In the eighth aspect, an inlet guide vane (23) is disposed on the suction side of the second impeller (21).

[0022] According to the eighth aspect, even when the inlet guide vane (23) is disposed on the suction side of the second impeller (21), the size of the turbo compressor can be held small in the axial direction.

[0023] A ninth aspect of the technique disclosed herein is an embodiment of any one of the first to eighth aspects. In the ninth aspect, an injection pipe (150) of an economizer (400) is disposed between the first impeller (11) and the second impeller (21).

[0024] According to the ninth aspect, even when the injection pipe (150) is disposed between the first impeller (11) and the second impeller (21), the size of the turbo compressor can be held small in the axial direction.

[0025] A tenth aspect of the technique disclosed herein is directed to a refrigeration apparatus including the multistage turbo compressor (10) of any one of the first to ninth aspects.

[0026] According to an eleventh aspect of the technique disclosed herein, the refrigerant is a low-pressure refrigerant.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] [FIG. 1] FIG. 1 is a block diagram of the configuration of a refrigeration apparatus including a turbo compressor according to an exemplary embodiment. [FIG. 2] FIG. 2 is a perspective view of the turbo compressor. [FIG. 3] FIG. 3 is a sectional view taken along line III-III shown in FIG. 2. [FIG. 4] FIG. 4 is a sectional view taken along line IV-IV shown in FIG. 3. [FIG. 5] FIG. 5 is an enlarged view of a region V in FIG. 3. [FIG. 6] FIG. 6 is a front view of the turbo compressor. [FIG. 7] FIG. 7 is an enlarged view of a diffuser flow path. [FIG. 8] FIG. 8 is a back view of the volute flow path. [FIG. 9] FIG. 9 is a sectional view of part of the volute flow path where the radial cross sectional area is smallest. [FIG. 10] FIG. 10 is a sectional view of part of the volute flow path where the radial cross sectional area is largest. DESCRIPTION OF EMBODIMENTS

[0028] Embodiments of the present disclosure will be described in detail below with reference to the drawings. The present disclosure is not limited to the embodiments shown below, and various changes can be made within the scope without departing from the technical concept of the present disclosure. Since each of the drawings is intended to illustrate the present disclosure conceptually, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for the sake of ease of understanding.(1) Refrigeration Apparatus

[0029] FIG. 1 shows a refrigeration apparatus (1) including a turbo compressor (10) according to this embodiment. The refrigeration apparatus (1) includes the turbo compressor (10), a condenser (300), an economizer (400), an evaporator (500), and a first pipe (610) to a fourth pipe (640).

[0030] The turbo compressor (10) is a centrifugal two-stage turbo compressor having a first impeller (11) and a second impeller (21). The turbo compressor (10) includes a motor (100) and a compression unit (200) having the first impeller (11) and the second impeller (21) rotated by the motor (100). The first impeller (11) and the second impeller (21) are attached to a shaft (201). Rotation of the motor (100) is transmitted to the first impeller (11) and the second impeller (21) via the shaft (201). A detailed configuration of the turbo compressor (10) will be described later.

[0031] The turbo compressor (10) compresses a refrigerant having exchanged heat in the condenser (300). The refrigerant is a low-pressure refrigerant. The refrigerant is, for example, hydrofluorocarbon such as 1233ZD, R123, DR-2, or 1336MZZ, which is a CFC substitute; or R718 (water).

[0032] The first pipe (610) is connected to the compression unit (200) and the condenser (300), and sends the refrigerant compressed by the compression unit (200) to the condenser (300). The condenser (300) condenses the refrigerant. The condenser (300) cools the refrigerant by heat exchange with coolant or the like to turn the refrigerant into a liquid state. The condenser (300) is, for example, a shell-and-tube heat exchanger.

[0033] The second pipe (620) is connected to the condenser (300) and the economizer (400), and sends the refrigerant condensed by the condenser (300) to the economizer (400). The economizer (400) separates the refrigerant into a gas phase and a liquid phase.

[0034] The economizer (400) includes an injection pipe (150). A nozzle (150a) of the injection pipe (150) is disposed in the compression unit (200). The injection pipe (150) sends the gas-phase refrigerant separated by the economizer (400) into the compression unit (200).

[0035] The third pipe (630) is connected to the economizer (400) and the evaporator (500), and sends the liquid-phase refrigerant separated by the economizer (400) to the evaporator (500). The evaporator (500) evaporates the refrigerant by heat exchange with water to turn the refrigerant into a saturated vapor state.

[0036] The fourth pipe (640) is connected to the evaporator (500) and the compression unit (200), and sends the refrigerant having exchanged heat in the evaporator (500) to the compression unit (200).(2) Turbo Compressor

[0037] The structure of the turbo compressor (10) will be described in detail with reference to FIGS. 2 to 10. In the following description, the "axial direction" indicates the direction in which the shaft (201) extends, the "radial direction" indicates the direction which extends radially from the center axis (X) of the shaft (201), and the "circumferential direction" indicates the direction which extends around the center axis (X) of the shaft (201). In the axial direction, the side on which the compression unit (200) is disposed is referred to as the front side, and the side on which the motor (100) is disposed is referred to as the rear side.

[0038] The turbo compressor (10) employs a two-stage inline structure in which the suction side of the first impeller (11) and the suction side of the second impeller (21) face in the same direction. As shown in FIG. 2, the turbo compressor (10) includes a motor casing (110) housing the motor (100), and a unit casing (210) housing the compression unit (200). The motor casing (110) is attached to the rear side of the unit casing (210). The motor casing (110) and the unit casing (210) also house the shaft (201).(2-1) Motor

[0039] As shown in FIG. 3, the motor (100) has a stator (101) and a rotor (102). The stator (101) is attached to an inner peripheral wall of the motor casing (110). The rotor (102) is attached to the shaft (201). The diameter of the motor (100) is equal to or slightly larger than the maximum value of the diameters of the first impeller (11) and the second impeller (21).

[0040] The motor casing (110) houses a first radial bearing (121), a second radial bearing (122), and a thrust bearing (123) as bearings that support the shaft (201).

[0041] The first radial bearing (121) and the second radial bearing (122) are, for example, magnetic bearings, and contactlessly support the shaft (201) by the electromagnetic force. The first radial bearing (121) is disposed closer to the compression unit (200) (the front side) than the rotor (102) is. The second radial bearing (122) is disposed on the side opposite to the compression unit (200) (the rear side) with respect to the rotor (102). The first radial bearing (121) is larger than the second radial bearing (122). The first radial bearing (121) and the second radial bearing (122) may be rolling bearings, sliding bearings, gas bearings, or the like.

[0042] The thrust bearing (123) is, for example, a magnetic bearing, and contactlessly supports a disc portion (201a) by the electromagnetic force disposed at a rear end portion of the shaft (201). The thrust bearing (123) is disposed at a rear end portion of the motor casing (110). The thrust bearing (123) may be a rolling bearing, a sliding bearing, a gas bearing, or the like.

[0043] The motor casing (110) further houses a first touchdown bearing and a second touchdown bearing. The first touchdown bearing and the second touchdown bearing support the shaft (201) by contacting the shaft (201) when the first radial bearing (121) and the second radial bearing (122) do not support the shaft (201). The first touchdown bearing is disposed in front of the first radial bearing (121). The second touchdown bearing is disposed between the second radial bearing (122) and the thrust bearing (123) in the axial direction.(2-2) Compression Unit

[0044] The compression unit (200) includes the first impeller (11), the second impeller (21), a front chamber (211), and a flow path through which the refrigerant flows.(2-2-1) First Impeller and Second Impeller

[0045] As shown in FIG. 3, the unit casing (210) houses the first impeller (11) and the second impeller (21). The first impeller (11) and the second impeller (21) are disposed adjacent to each other with a space therebetween in the axial direction. The first impeller (11) is attached to a front end portion of the shaft (201). The second impeller (21) is attached to the shaft (201) on the rear side of the first impeller (11).(2-2-2) Front Chamber

[0046] The front chamber (211) is disposed in part of the unit casing (210) that is between the first impeller (11) and the second impeller (21) in the axial direction. More specifically, the front chamber (211) is disposed between an intermediate flow path (30) described later and the second impeller (21) in the axial direction. As shown in FIG. 4, the front chamber (211) communicates with the nozzle (150a) of the injection pipe (150). A front wall portion (212) located on the front side of the front chamber (211) has a plurality of through holes (213). The plurality of through holes (213) are disposed at equal intervals in the circumferential direction.

[0047] The refrigerant from the economizer (400) is supplied to the front chamber (211) through the injection pipe (150). The refrigerant supplied to the front chamber (211) passes through the through holes (213), and flows into a second flow path (32) of the intermediate flow path (30) described later.(2-2-3) Flow Path

[0048] As shown in FIG. 3, in the unit casing (210), a first inflow path (12), the intermediate flow path (30), a second inflow path (22), a diffuser flow path (40), a volute flow path (50), and a final outflow path (60) (see FIG. 2) are disposed as flow paths through which the refrigerant flows.

[0049] The first inflow path (12) has a first inflow port (12a). The first inflow port (12a) is connected to the fourth pipe (640). The first inflow port (12a) corresponds to the inflow port of the first impeller (11).

[0050] A first inlet guide vane (13) (hereinafter referred to as the first IGV (13)) is disposed in the first inflow path (12). The first IGV (13) adjusts the flow rate of the refrigerant flowing toward the first impeller (11). A first adjustment mechanism (13a) that adjusts the opening degree of the first IGV (13) is attached to the unit casing (210). Part of the first adjustment mechanism (13a) is disposed around the first inflow path (12) in the unit casing (210).

[0051] A first outflow port (14) is located outside the first impeller (11) in the radial direction. The refrigerant compressed by the first impeller (11) flows out of the first outflow port (14).

[0052] As shown in FIG. 5, the intermediate flow path (30) allows the refrigerant to flow between the first outflow port (14) and a second inflow port (22a) which is the inlet of the second inflow path (22). The intermediate flow path (30) is formed over the entire part in the circumferential direction. As shown in FIG. 5, the intermediate flow path (30) has a first flow path (31), the second flow path (32), and a connection flow path (33) connecting the first flow path (31) and the second flow path (32). The second inflow port (22a) corresponds to the inflow port of the second impeller (21).

[0053] The first flow path (31) communicates with the first outflow port (14). The first flow path (31) extends in the radial direction from the first outflow port (14).

[0054] The second flow path (32) communicates with the second inflow port (22a). The second flow path (32) extends in the radial direction from the second inflow port (22a).

[0055] In the axial direction, the connection flow path (33) connects the outer end portion of the first flow path (31) in the radial direction and the outer end portion of the second flow path (32) in the radial direction. The connection flow path (33) has a U-shaped cross section taken along the radial direction, which is a cutting cross section taken along the plane along the center axis (X). The maximum value of the outer diameter of the connection flow path (33) with respect to the center axis (X) (hereinafter referred to as the maximum outer diameter (Rr)) is uniform in the circumferential direction. As shown in FIG. 6, part of the unit casing (210) in which the intermediate flow path (30) is located has a circular shape when viewed in the axial direction.

[0056] As shown in FIG. 5, the second inflow path (22) is curved in the axial direction from the second inflow port (22a) to the second impeller (21).

[0057] A second inlet guide vane (23) (hereinafter referred to as the second IGV (23)) is disposed on the suction side of the second impeller (21). The second IGV (23) is disposed in the second flow path (32) of the intermediate flow path (30) and the second inflow path (22). The second IGV (23) adjusts the flow rate of the refrigerant flowing toward the second impeller (21). A second adjustment mechanism (23a) that adjusts the opening degree of the second IGV (23) is attached to the unit casing (210). Part of the second adjustment mechanism (23a) is disposed in the front chamber (211).

[0058] As shown in FIG. 7, the diffuser flow path (40) extends from a second outflow port (24) which is the outflow port of the second impeller (21). The refrigerant compressed by the second impeller (21) and having flowed out of the second outflow port (24) flows through the diffuser flow path (40). The diffuser flow path (40) extends over the entire part in the circumferential direction. The diffuser flow path (40) is formed by a front surface portion (41) extending over the entire part in the circumferential direction and located relatively on the front side, and a rear surface portion (42) facing the front surface portion (41) in the axial direction. The diffuser flow path (40) has a flat flow path (43) and a curved flow path (44).

[0059] The flat flow path (43) extends in the radial direction from the second outflow port (24). The curved flow path (44) is curved to the side opposite to the side on which the refrigerant flows in with respect to the flat flow path (43) (to the rear side in the axial direction). In the cross section of the diffuser flow path (40) taken along the radial direction, the ratio of the length (Dc) of the curved flow path (44) to the length (Dp) of the flat flow path (43) is 0.5 or more in an intermediate span which is an intermediate position between the front surface portion (41) and rear surface portion (42) of the diffuser flow path (40). The maximum value of the outer diameter of the diffuser flow path (40) is equal to the maximum value of the outer diameter of the volute flow path (50) (hereinafter referred to as the maximum outer diameter (Rv)).

[0060] The refrigerant having passed through the diffuser flow path (40) flows through the volute flow path (50). The volute flow path (50) is located on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40). That is, the volute flow path (50) is located closer to the motor (100) in the axial direction with respect to the diffuser flow path (40). The volute flow path (50) is connected to the rear side of the curved flow path (44). The volute flow path (50) extends inward in the radial direction and rearward from a portion connected to the curved flow path (44). The position of the inlet portion of the volute flow path (50) in the radial direction is the same as the position of the outlet portion of the curved flow path (44) in the radial direction.

[0061] As shown in FIG. 8, the volute flow path (50) extends in the circumferential direction so as to surround the motor casing (110) from the outside in the radial direction. The maximum outer diameter (Rv) of the volute flow path (50) with respect to the center axis (X) is uniform in the circumferential direction. The maximum outer diameter (Rv) of the volute flow path (50) is smaller than or equal to the maximum outer diameter (Rr) of the connection flow path (33) over the entire part in the circumferential direction. In this embodiment, the ratio of the maximum outer diameter (Rv) of the volute flow path (50) to the maximum outer diameter (Rr) of the connection flow path (33) is about 0.96. Thus, when the turbo compressor (10) is viewed from the front side in the axial direction, the volute flow path (50) overlaps with the intermediate flow path (30) and is not visible.

[0062] The volute flow path (50) has a shape so that the cross section taken along the radial direction increases while expanding inward in the radial direction and rearward with the maximum outer diameter (Rv) held uniform. At the position of the volute flow path (50) in the axial direction, the outer diameter (Rm) of the motor casing (110) with respect to the center axis (X) is smaller than the minimum value of the inner diameter (Rvi) of the unit casing (210) with respect to the center axis (X). There is always a space between part of the unit casing (210) that forms the volute flow path (50) and the motor casing (110). At the position of the volute flow path (50), the ratio of the outer diameter (Rm) of the motor casing (110) to the inner diameter (Rvi) of the unit casing (210) is 0.95 or less in a part in which the unit casing (210) and the motor casing (110) are closest to each other in the radial direction.

[0063] As shown in FIGS. 9 and 10, the maximum length of the volute flow path (50) in the radial direction in the cross section taken along the radial direction is defined as a first length (r), and the maximum length of the volute flow path (50) in the axial direction in the cross section taken along the radial direction is defined as a second length (L). When the radial cross sectional area increases, the amount of change in the second length (L) is larger than or equal to the amount of change in the first length (r). In part of the volute flow path (50) where the radial cross sectional area is larger, the ratio of the second length (L) to the first length (r) is larger. As shown in FIG. 9, in part of the volute flow path (50) where the radial cross sectional area is smallest, the first length (r) is larger than the second length (L). In this part, the ratio of the second length (L) to the first length (r) is less than 1. In contrast, as shown in FIG. 10, in part of the volute flow path (50) where the radial cross sectional area is largest, the second length (L) is larger than the first length (r). In this part, the ratio of the second length (L) to the first length (r) is greater than 1.

[0064] As shown in FIG. 8, the final outflow path (60) is connected to part of the volute flow path (50) where the radial cross sectional area is largest. The final outflow path (60) allows the refrigerant of which the flow velocity has been reduced by the diffuser flow path (40) and the volute flow path (50) to flow out. The final outflow path (60) is connected to the first pipe (610).

[0065] The refrigerant flows in from the first inflow path (12), and the flow rate is adjusted by the first IGV (13). The refrigerant of which the flow rate has been adjusted is compressed by the first impeller (11), and flows out to the first flow path (31). After passing through the connection flow path (33), the refrigerant joins the refrigerant flowing from the economizer (400) in the second flow path (32). At this time, the flow rate of the refrigerant is adjusted by the second IGV (23). The flow velocity of the refrigerant decreases when passing through the first flow path (31), the connection flow path (33), and the second flow path (32). The refrigerant having passed through the second IGV (23) flows into the second impeller (21) via the second inflow path (22), and is compressed by the second impeller (21). The refrigerant compressed by the second impeller (21) flows out to the flat flow path (43). The refrigerant passes through the flat flow path (43) and the curved flow path (44) and flows into the volute flow path (50) while the flow velocity is reduced. After the flow velocity is reduced in the volute flow path (50), the refrigerant flows out of the final outflow path (60).(3) Advantages of Embodiment

[0066] In this embodiment, the intermediate flow path (30) includes the first flow path (31) extending in the radial direction and communicating with the outflow port (14) of the first impeller (11), the second flow path (32) extending in the radial direction and communicating with the inflow port (22a) of the second impeller (21), and the connection flow path (33) connecting the outer portion of the first flow path (31) in the radial direction and the outer portion of the second flow path (32) in the radial direction; the diffuser flow path (40) has the flat flow path (43) extending outward in the radial direction from the outflow port (24) of the second impeller (21), and the curved flow path (44) curved to the side opposite to the side on which the refrigerant flows in with respect to the flat flow path (43) in the axial direction; the volute flow path (50) is connected to the curved flow path (44) and extends in the circumferential direction about the center axis (X) of the shaft (201) so as to surround the casing housing the shaft (201) from the outside in the radial direction; and the maximum outer diameter (Rv) of the volute flow path (50) is smaller than or equal to the maximum outer diameter (Rr) of the connection flow path (33). In this embodiment, the curved flow path (44) is curved to the side opposite to the side on which the refrigerant flows in with respect to the flat flow path (43) in the axial direction, and thus the volute flow path (50) connected to the curved flow path (44) is disposed on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40). If the volute flow path (50) is disposed on the same side as the intermediate flow path (30) with respect to the diffuser flow path (40) in the axial direction, it is necessary to increase the distance between the first impeller (11) and the second impeller (21) in the axial direction in order to secure a space in which the volute flow path (50) is disposed. In this embodiment, the volute flow path (50) is disposed on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40), and thus the first impeller (11) and the second impeller (21) can be disposed adjacent to and close to each other in the axial direction. Accordingly, the turbo compressor (10) can be downsized in the axial direction. Further, the maximum outer diameter (Rv) of the volute flow path (50) is smaller than or equal to the maximum outer diameter (Rr) of the connection flow path (33), and thus the downsize can be achieved in the radial direction. Further, the diffuser flow path (40) has a long flow path length due to the curved flow path (44), and the flow velocity of the refrigerant can be reduced, and thus the fluid efficiency can be maintained. Thus, the turbo compressor (10) of this embodiment can be downsized while the fluid efficiency is maintained.

[0067] In this embodiment, the first impeller (11) and the second impeller (21) can be disposed adjacent to and close to each other in the axial direction, and thus the reliability of the turbo compressor (10) can be improved when being operated at a high number of rotations.

[0068] In this embodiment, the volute flow path (50) is disposed on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40), and thus the degree of freedom to route the intermediate flow path (30) can be increased.

[0069] In this embodiment, the maximum outer diameter of the connection flow path (33) is uniform in the circumferential direction, and the maximum outer diameter (Rv) of the volute flow path (50) is uniform in the circumferential direction. Accordingly, the maximum outer diameter (Rv) of the volute flow path (50) can be maximized in a range that is less than or equal to the maximum outer diameter (Rr) of the connection flow path (33). The radial cross sectional area of the volute flow path (50) can be increased, and thus the turbo compressor (10) of this embodiment can be downsized while the fluid efficiency is maintained.

[0070] In this embodiment, the motor (100) is located on the side opposite to the first impeller (11) with respect to the second impeller (21) in the axial direction, and the volute flow path (50) surrounds the motor casing (110) housing the motor (100) from the outside in the radial direction. The motor (100) is a downsized motor, and thus the periphery of the motor casing (110) tends to be a dead space. The turbo compressor (10) of this embodiment can be downsized in the radial direction and the axial direction by effectively utilizing the space around the motor casing (110).

[0071] In this embodiment, the volute flow path (50) has a shape so that the cross section taken along the radial direction increases while expanding inward in the radial direction; and in the cross section of the volute flow path (50) taken along the radial direction, in part of the volute flow path (50) where the radial cross sectional area is larger, the ratio of the second length (L) to the first length (r) is larger. Accordingly, the volute flow path (50) can be prevented from expanding to the outer side in the radial direction, and the turbo compressor (10) can be downsized in the radial direction. Further, the cross section of the volute flow path (50) taken along the radial direction is increased in the axial direction, whereby the radial cross sectional area can be efficiently increased. The radial cross sectional area of the volute flow path (50) is increased, whereby the flow velocity of the refrigerant can be reduced; and thus the fluid efficiency can be improved. Thus, the turbo compressor (10) of this embodiment can be downsized while the fluid efficiency is improved.

[0072] In this embodiment, in part of the volute flow path (50) where the radial cross sectional area is smallest, the first length (r) is larger than the second length (L); and in part of the volute flow path (50) where the radial cross sectional area is largest, the second length (L) is larger than the first length (r). In the part where the radial cross sectional area is small, by making the length in the radial direction longer and the length in the axial direction shorter, the refrigerant can flow along the wall surface of the volute flow path (50) at the inlet of the volute flow path (50). Accordingly, flow separation can be reduced at the inlet of the volute flow path (50), and thus the fluid efficiency of the turbo compressor (10) of this embodiment can be improved.

[0073] In this embodiment, at the position of the volute flow path (50), the ratio of the outer diameter (Rm) of the motor casing (110) to the inner diameter (Rvi) of the unit casing (210) is 0.95 or less in a part in which the unit casing (210) and the motor casing (110) are closest to each other in the radial direction. The space is secured between the unit casing (210) and the motor casing (110), and thus the insertability of tools can be enhanced. The maintainability of the turbo compressor (10) of this embodiment can be improved.

[0074] In this embodiment, in the cross section of the diffuser flow path (40) taken along the plane along the center axis (X), the ratio of the length (Dc) of the curved flow path (44) to the length (Dp) of the flat flow path (43) is 0.5 or more in the intermediate span of the diffuser flow path (40). While the distance of the diffuser flow path (40) in the radial direction can be shortened, the flow path length of the entire part of the diffuser flow path (40) can be made longer. Accordingly, the flow velocity of the refrigerant can be reduced in the diffuser flow path (40), and thus the fluid efficiency of the turbo compressor (10) of this embodiment can be improved.

[0075] In this embodiment, the motor casing (110) houses the bearings (121, 122, 123) supporting the shaft (201). The bearings (121, 122, 123) are disposed in the motor casing (110), whereby the turbo compressor (10) of this embodiment can be downsized in the radial direction and the axial direction by effectively utilizing the space around the motor casing (110).

[0076] In this embodiment, the turbo compressor (10) has the two-stage inline structure in which the suction side of the first impeller (11) and the suction side of the second impeller (21) face in the same direction. The intermediate flow path (30) can be easily routed as compared with when the inline structure is not employed, and thus the turbo compressor (10) of this embodiment can be downsized.

[0077] In this embodiment, the second IGV (23) is disposed on the suction side of the second impeller (21). The volute flow path (50) is located on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40), and thus the front chamber (211) can be formed between the second impeller (21) and the intermediate flow path (30) in the axial direction. The second adjustment mechanism (23a) can be disposed in the front chamber (211), and thus the second IGV (23) can be disposed while the size of the turbo compressor (10) of this embodiment is held small in the axial direction.

[0078] In this embodiment, the injection pipe (150) of the economizer (400) is disposed between the first impeller (11) and the second impeller (21). The front chamber (211) can be formed between the second impeller (21) and the intermediate flow path (30). The injection pipe (150) can be disposed in the front chamber (211), and thus the injection pipe (150) can be disposed while the size of the turbo compressor (10) of this embodiment is held small in the axial direction.(4) Other Embodiments

[0079] The maximum outer diameter (Rv) of the volute flow path (50) is not necessarily uniform in the circumferential direction. For example, the maximum outer diameter (Rv) of the volute flow path (50) may be smaller in part of the volute flow path (50) where the radial cross sectional area is smaller.

[0080] The volute flow path (50) may be expanded in only one of the radial direction or the axial direction in order to expand the cross section taken along the radial direction.

[0081] The motor (100) may be separate from the compression unit (200). In this case, the rotation of the motor (100) may be transmitted to the shaft (201) via a gear. The volute flow path (50) surrounds not the motor casing (110) but the casing housing the shaft (201).

[0082] The turbo compressor (10) may be a multistage turbo compressor including three or more impellers. In this case, an impeller is added upstream of the first impeller (11).

[0083] The first IGV (13), the second IGV (23), and the injection pipe (150) are not essential and may be omitted.

[0084] While the embodiments and variations thereof have been described above, it will be understood that various changes in form and details may be made without departing from the spirit and scope of the claims. The embodiment, the variation thereof, and the other embodiments may be combined and replaced with each other without deteriorating intended functions of the present disclosure.

[0085] The expressions of "first", "second", and "third" described above are used to distinguish the terms to which these expressions are given, and do not limit the number and order of the terms.INDUSTRIAL APPLICABILITY

[0086] As described above, the present disclosure is useful for a turbo compressor.DESCRIPTION OF REFERENCE CHARACTERS

[0087] 1Refrigeration Apparatus 11First Impeller 21Second Impeller 23Second Inlet Guide Vane 30Intermediate Flow Path 31First Flow Path 32Second Flow Path 33Connection Flow Path 40Diffuser Flow Path 43Flat Flow Path 44Curved Flow Path 50Volute Flow Path 100Motor 101Stator 102Rotor 110Motor Casing 121First Radial Bearing 122Second Radial Bearing 123Thrust Bearing 150Injection Pipe 201Shaft 400Economizer DcLength of Curved Flow Path DpLength of Flat Flow Path LSecond Length rFirst Length RrMaximum Value of Outer Diameter of Connection Flow Path RvMaximum Value of Outer Diameter of Volute Flow Path XCenter Axis

Examples

Embodiment Construction

[0028]Embodiments of the present disclosure will be described in detail below with reference to the drawings. The present disclosure is not limited to the embodiments shown below, and various changes can be made within the scope without departing from the technical concept of the present disclosure. Since each of the drawings is intended to illustrate the present disclosure conceptually, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for the sake of ease of understanding.

(1) Refrigeration Apparatus

[0029]FIG. 1 shows a refrigeration apparatus (1) including a turbo compressor (10) according to this embodiment. The refrigeration apparatus (1) includes the turbo compressor (10), a condenser (300), an economizer (400), an evaporator (500), and a first pipe (610) to a fourth pipe (640).

[0030]The turbo compressor (10) is a centrifugal two-stage turbo compressor having a first impeller (11) and a second impeller (21). The turbo compressor (10) includes a motor ...

TECHNICAL FIELD

[0001] The present disclosure relates to a turbo compressor and a refrigeration apparatus.BACKGROUND ART

[0002] Patent Document 1 discloses a multistage turbo compressor having two impellers. The turbo compressor includes a diffuser flow path through which a refrigerant having flowed out of the impeller of the latter stage flows, and a volute flow path through which a refrigerant having passed through the diffuser flow path flows. The diffuser flow path extends straight outward in the radial direction from an outflow port of the impeller of the latter stage. The volute flow path is connected to the outer end portion of the diffuser flow path in the radial direction.CITATION LISTPATENT DOCUMENT

[0003] Patent Document 1: U.S. Patent Publication No. 2023 / 013972SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0004] In recent years, a turbo compressor has been required to have a larger capacity. In order to improve the fluid efficiency of a turbo compressor having a large capacity, it is required to sufficiently reduce the flow velocity of a large amount of refrigerant in a diffuser flow path. In order to reduce the flow velocity of the refrigerant in the diffuser flow path, it is necessary to increase the length of the diffuser flow path.

[0005] If the diffuser flow path is made longer in order to increase the capacity of the turbo compressor disclosed of Patent Document 1, a connection position between the diffuser flow path and the volute flow path expands outward in the radial direction. The volute flow path expands further outward in the radial direction from the connection position. Thus, if the fluid efficiency of a conventional turbo compressor is increased, the size of the turbo compressor is increased. Conventional turbo compressors have room for improvement from the viewpoint of achieving both fluid efficiency and downsizing of a turbo compressor.

[0006] An object of the present disclosure is to downsize a turbo compressor while maintaining the fluid efficiency.SOLUTION TO THE PROBLEM

[0007] A first aspect of the technique disclosed herein is directed to a turbo compressor. The turbo compressor includes: a motor (100) having a stator (101) and a rotor (102); a shaft (201) extending in an axial direction and rotated by the rotor (102); a first impeller (11) attached to the shaft (201); a second impeller (21) attached to the shaft (201) and disposed adjacent to the first impeller (11) in the axial direction; an intermediate flow path (30) allowing a refrigerant to flow between an outflow port (14) of the first impeller (11) and an inflow port (22a) of the second impeller (21); a diffuser flow path (40) through which a refrigerant having flowed out of the second impeller (21) flows; and a volute flow path (50) through which a refrigerant having passed through the diffuser flow path (40) flows, wherein the intermediate flow path (30) includes a first flow path (31) extending in a radial direction, which is a direction extending radially from a center of the shaft (201), and communicating with the outflow port (14) of the first impeller (11), a second flow path (32) extending in the radial direction and communicating with the inflow port (22a) of the second impeller (21), and a connection flow path (33) connecting an outer portion of the first flow path (31) in the radial direction and an outer portion of the second flow path (32) in the radial direction, the diffuser flow path (40) includes a flat flow path (43) extending outward in the radial direction from an outflow port (24) of the second impeller (21), and a curved flow path (44) curved to a side opposite to a side on which a refrigerant flows in with respect to the flat flow path (43) in the axial direction, the volute flow path (50) extends in a circumferential direction about a center axis (X) of the shaft (201) so as to surround the casing housing the shaft (201) from an outside in the radial direction, and is connected to the curved flow path (44), and a maximum value (Rv) of an outer diameter of the volute flow path (50) with respect to the center axis (X) is smaller than or equal to a maximum value (Rr) of an outer diameter of the connection flow path (33) with respect to the center axis (X).

[0008] According to the first aspect, the volute flow path (50) is connected to the curved flow path (44), and thus is disposed on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40). Further, the maximum value of the outer diameter of the volute flow path (50) is smaller than or equal to the maximum value of the outer diameter of the connection flow path (30). Accordingly, the turbo compressor can be downsized in both the radial direction and the axial direction. Further, the diffuser flow path (40) has a long flow path length due to the curved flow path, and the flow velocity of the refrigerant can be reduced in the diffuser flow path (40), and thus the fluid efficiency can be maintained. Thus, the turbo compressor can be downsized while the fluid efficiency is maintained.

[0009] A second aspect of the technique disclosed herein is an embodiment of the first aspect. In the second aspect, the motor (100) is located on a side opposite to the first impeller (11) with respect to the second impeller (21) in the axial direction, and the casing is a motor casing (110) housing the motor (100).

[0010] According to the second aspect, the turbo compressor can be downsized in the radial direction and the axial direction by effectively utilizing the space around the motor casing (110).

[0011] A third aspect of the technique disclosed herein is an embodiment of the first or second aspect. In the third aspect, the volute flow path (50) has a shape so that a cross section taken along the radial direction increases while expanding inward in the radial direction, and a maximum length of the volute flow path (50) in the radial direction in a cross section taken along the radial direction is a first length (r), and a maximum length of the volute flow path (50) in the axial direction in the cross section taken along the radial direction is a second length (L), where in part of the volute flow path (50) where the radial cross sectional area is larger, a ratio of the second length (L) to the first length (r) is larger.

[0012] According to the third aspect, the volute flow path (50) can be prevented from expanding to the outer side in the radial direction, and the turbo compressor can be downsized. Further, the radial cross sectional area of the volute flow path (50) is increased, whereby the flow velocity of the refrigerant can be reduced; and thus the fluid efficiency can be improved. Thus, the turbo compressor can be downsized while the fluid efficiency is improved.

[0013] A fourth aspect of the technique disclosed herein is an embodiment of the third aspect. In the fourth aspect, in part of the volute flow path (50) where the radial cross sectional area is smallest, the first length (r) is larger than the second length (L), and in part of the volute flow path (50) where the radial cross sectional area is largest, the second length (L) is larger than the first length (r).

[0014] According to the fourth aspect, in the part of the volute flow path (50) where the radial cross sectional area is small, by making the length in the radial direction longer and the length in the axial direction shorter, flow separation can be reduced at the inlet portion of the volute flow path (50), and thus the fluid efficiency can be improved.

[0015] A fifth aspect of the technique disclosed herein is an embodiment of any one of the first to fourth aspects. In the fifth aspect, in a cross section of the diffuser flow path (40) taken along the radial direction, a ratio of a length (Dc) of the curved flow path (44) to a length (Dp) of the flat flow path (43) is 0.5 or more in an intermediate span of the diffuser flow path (40).

[0016] According to the fifth aspect, while the length of the diffuser flow path (40) in the radial direction can be shortened, the flow path itself can be made longer by the curved flow path (44). The flow velocity of the refrigerant can be reduced in the diffuser flow path (40), and thus the fluid efficiency of the turbo compressor can be improved.

[0017] A sixth aspect of the technique disclosed herein is an embodiment of the second aspect. In the sixth aspect, the motor casing (110) houses a bearing (121, 122, 123) supporting the shaft (201).

[0018] According to the sixth aspect, the bearings (121, 122, 123) are disposed in the motor casing (110), whereby the turbo compressor can be downsized in the radial direction and the axial direction by effectively utilizing the space around the motor casing (110).

[0019] A seventh aspect of the technique disclosed herein is an embodiment of any one of the first to sixth aspects. In the seventh aspect, the multistage turbo compressor further includes a two-stage inline structure in which a suction side of the first impeller (11) and a suction side of the second impeller (21) face in the same direction.

[0020] According to the seventh aspect, the inline structure is employed, and thus the turbo compressor can be downsized.

[0021] An eighth aspect of the technique disclosed herein is an embodiment of any one of the first to seventh aspects. In the eighth aspect, an inlet guide vane (23) is disposed on the suction side of the second impeller (21).

[0022] According to the eighth aspect, even when the inlet guide vane (23) is disposed on the suction side of the second impeller (21), the size of the turbo compressor can be held small in the axial direction.

[0023] A ninth aspect of the technique disclosed herein is an embodiment of any one of the first to eighth aspects. In the ninth aspect, an injection pipe (150) of an economizer (400) is disposed between the first impeller (11) and the second impeller (21).

[0024] According to the ninth aspect, even when the injection pipe (150) is disposed between the first impeller (11) and the second impeller (21), the size of the turbo compressor can be held small in the axial direction.

[0025] A tenth aspect of the technique disclosed herein is directed to a refrigeration apparatus including the multistage turbo compressor (10) of any one of the first to ninth aspects.

[0026] According to an eleventh aspect of the technique disclosed herein, the refrigerant is a low-pressure refrigerant.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] [FIG. 1] FIG. 1 is a block diagram of the configuration of a refrigeration apparatus including a turbo compressor according to an exemplary embodiment. [FIG. 2] FIG. 2 is a perspective view of the turbo compressor. [FIG. 3] FIG. 3 is a sectional view taken along line III-III shown in FIG. 2. [FIG. 4] FIG. 4 is a sectional view taken along line IV-IV shown in FIG. 3. [FIG. 5] FIG. 5 is an enlarged view of a region V in FIG. 3. [FIG. 6] FIG. 6 is a front view of the turbo compressor. [FIG. 7] FIG. 7 is an enlarged view of a diffuser flow path. [FIG. 8] FIG. 8 is a back view of the volute flow path. [FIG. 9] FIG. 9 is a sectional view of part of the volute flow path where the radial cross sectional area is smallest. [FIG. 10] FIG. 10 is a sectional view of part of the volute flow path where the radial cross sectional area is largest. DESCRIPTION OF EMBODIMENTS

[0028] Embodiments of the present disclosure will be described in detail below with reference to the drawings. The present disclosure is not limited to the embodiments shown below, and various changes can be made within the scope without departing from the technical concept of the present disclosure. Since each of the drawings is intended to illustrate the present disclosure conceptually, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for the sake of ease of understanding.(1) Refrigeration Apparatus

[0029] FIG. 1 shows a refrigeration apparatus (1) including a turbo compressor (10) according to this embodiment. The refrigeration apparatus (1) includes the turbo compressor (10), a condenser (300), an economizer (400), an evaporator (500), and a first pipe (610) to a fourth pipe (640).

[0030] The turbo compressor (10) is a centrifugal two-stage turbo compressor having a first impeller (11) and a second impeller (21). The turbo compressor (10) includes a motor (100) and a compression unit (200) having the first impeller (11) and the second impeller (21) rotated by the motor (100). The first impeller (11) and the second impeller (21) are attached to a shaft (201). Rotation of the motor (100) is transmitted to the first impeller (11) and the second impeller (21) via the shaft (201). A detailed configuration of the turbo compressor (10) will be described later.

[0031] The turbo compressor (10) compresses a refrigerant having exchanged heat in the condenser (300). The refrigerant is a low-pressure refrigerant. The refrigerant is, for example, hydrofluorocarbon such as 1233ZD, R123, DR-2, or 1336MZZ, which is a CFC substitute; or R718 (water).

[0032] The first pipe (610) is connected to the compression unit (200) and the condenser (300), and sends the refrigerant compressed by the compression unit (200) to the condenser (300). The condenser (300) condenses the refrigerant. The condenser (300) cools the refrigerant by heat exchange with coolant or the like to turn the refrigerant into a liquid state. The condenser (300) is, for example, a shell-and-tube heat exchanger.

[0033] The second pipe (620) is connected to the condenser (300) and the economizer (400), and sends the refrigerant condensed by the condenser (300) to the economizer (400). The economizer (400) separates the refrigerant into a gas phase and a liquid phase.

[0034] The economizer (400) includes an injection pipe (150). A nozzle (150a) of the injection pipe (150) is disposed in the compression unit (200). The injection pipe (150) sends the gas-phase refrigerant separated by the economizer (400) into the compression unit (200).

[0035] The third pipe (630) is connected to the economizer (400) and the evaporator (500), and sends the liquid-phase refrigerant separated by the economizer (400) to the evaporator (500). The evaporator (500) evaporates the refrigerant by heat exchange with water to turn the refrigerant into a saturated vapor state.

[0036] The fourth pipe (640) is connected to the evaporator (500) and the compression unit (200), and sends the refrigerant having exchanged heat in the evaporator (500) to the compression unit (200).(2) Turbo Compressor

[0037] The structure of the turbo compressor (10) will be described in detail with reference to FIGS. 2 to 10. In the following description, the "axial direction" indicates the direction in which the shaft (201) extends, the "radial direction" indicates the direction which extends radially from the center axis (X) of the shaft (201), and the "circumferential direction" indicates the direction which extends around the center axis (X) of the shaft (201). In the axial direction, the side on which the compression unit (200) is disposed is referred to as the front side, and the side on which the motor (100) is disposed is referred to as the rear side.

[0038] The turbo compressor (10) employs a two-stage inline structure in which the suction side of the first impeller (11) and the suction side of the second impeller (21) face in the same direction. As shown in FIG. 2, the turbo compressor (10) includes a motor casing (110) housing the motor (100), and a unit casing (210) housing the compression unit (200). The motor casing (110) is attached to the rear side of the unit casing (210). The motor casing (110) and the unit casing (210) also house the shaft (201).(2-1) Motor

[0039] As shown in FIG. 3, the motor (100) has a stator (101) and a rotor (102). The stator (101) is attached to an inner peripheral wall of the motor casing (110). The rotor (102) is attached to the shaft (201). The diameter of the motor (100) is equal to or slightly larger than the maximum value of the diameters of the first impeller (11) and the second impeller (21).

[0040] The motor casing (110) houses a first radial bearing (121), a second radial bearing (122), and a thrust bearing (123) as bearings that support the shaft (201).

[0041] The first radial bearing (121) and the second radial bearing (122) are, for example, magnetic bearings, and contactlessly support the shaft (201) by the electromagnetic force. The first radial bearing (121) is disposed closer to the compression unit (200) (the front side) than the rotor (102) is. The second radial bearing (122) is disposed on the side opposite to the compression unit (200) (the rear side) with respect to the rotor (102). The first radial bearing (121) is larger than the second radial bearing (122). The first radial bearing (121) and the second radial bearing (122) may be rolling bearings, sliding bearings, gas bearings, or the like.

[0042] The thrust bearing (123) is, for example, a magnetic bearing, and contactlessly supports a disc portion (201a) by the electromagnetic force disposed at a rear end portion of the shaft (201). The thrust bearing (123) is disposed at a rear end portion of the motor casing (110). The thrust bearing (123) may be a rolling bearing, a sliding bearing, a gas bearing, or the like.

[0043] The motor casing (110) further houses a first touchdown bearing and a second touchdown bearing. The first touchdown bearing and the second touchdown bearing support the shaft (201) by contacting the shaft (201) when the first radial bearing (121) and the second radial bearing (122) do not support the shaft (201). The first touchdown bearing is disposed in front of the first radial bearing (121). The second touchdown bearing is disposed between the second radial bearing (122) and the thrust bearing (123) in the axial direction.(2-2) Compression Unit

[0044] The compression unit (200) includes the first impeller (11), the second impeller (21), a front chamber (211), and a flow path through which the refrigerant flows.(2-2-1) First Impeller and Second Impeller

[0045] As shown in FIG. 3, the unit casing (210) houses the first impeller (11) and the second impeller (21). The first impeller (11) and the second impeller (21) are disposed adjacent to each other with a space therebetween in the axial direction. The first impeller (11) is attached to a front end portion of the shaft (201). The second impeller (21) is attached to the shaft (201) on the rear side of the first impeller (11).(2-2-2) Front Chamber

[0046] The front chamber (211) is disposed in part of the unit casing (210) that is between the first impeller (11) and the second impeller (21) in the axial direction. More specifically, the front chamber (211) is disposed between an intermediate flow path (30) described later and the second impeller (21) in the axial direction. As shown in FIG. 4, the front chamber (211) communicates with the nozzle (150a) of the injection pipe (150). A front wall portion (212) located on the front side of the front chamber (211) has a plurality of through holes (213). The plurality of through holes (213) are disposed at equal intervals in the circumferential direction.

[0047] The refrigerant from the economizer (400) is supplied to the front chamber (211) through the injection pipe (150). The refrigerant supplied to the front chamber (211) passes through the through holes (213), and flows into a second flow path (32) of the intermediate flow path (30) described later.(2-2-3) Flow Path

[0048] As shown in FIG. 3, in the unit casing (210), a first inflow path (12), the intermediate flow path (30), a second inflow path (22), a diffuser flow path (40), a volute flow path (50), and a final outflow path (60) (see FIG. 2) are disposed as flow paths through which the refrigerant flows.

[0049] The first inflow path (12) has a first inflow port (12a). The first inflow port (12a) is connected to the fourth pipe (640). The first inflow port (12a) corresponds to the inflow port of the first impeller (11).

[0050] A first inlet guide vane (13) (hereinafter referred to as the first IGV (13)) is disposed in the first inflow path (12). The first IGV (13) adjusts the flow rate of the refrigerant flowing toward the first impeller (11). A first adjustment mechanism (13a) that adjusts the opening degree of the first IGV (13) is attached to the unit casing (210). Part of the first adjustment mechanism (13a) is disposed around the first inflow path (12) in the unit casing (210).

[0051] A first outflow port (14) is located outside the first impeller (11) in the radial direction. The refrigerant compressed by the first impeller (11) flows out of the first outflow port (14).

[0052] As shown in FIG. 5, the intermediate flow path (30) allows the refrigerant to flow between the first outflow port (14) and a second inflow port (22a) which is the inlet of the second inflow path (22). The intermediate flow path (30) is formed over the entire part in the circumferential direction. As shown in FIG. 5, the intermediate flow path (30) has a first flow path (31), the second flow path (32), and a connection flow path (33) connecting the first flow path (31) and the second flow path (32). The second inflow port (22a) corresponds to the inflow port of the second impeller (21).

[0053] The first flow path (31) communicates with the first outflow port (14). The first flow path (31) extends in the radial direction from the first outflow port (14).

[0054] The second flow path (32) communicates with the second inflow port (22a). The second flow path (32) extends in the radial direction from the second inflow port (22a).

[0055] In the axial direction, the connection flow path (33) connects the outer end portion of the first flow path (31) in the radial direction and the outer end portion of the second flow path (32) in the radial direction. The connection flow path (33) has a U-shaped cross section taken along the radial direction, which is a cutting cross section taken along the plane along the center axis (X). The maximum value of the outer diameter of the connection flow path (33) with respect to the center axis (X) (hereinafter referred to as the maximum outer diameter (Rr)) is uniform in the circumferential direction. As shown in FIG. 6, part of the unit casing (210) in which the intermediate flow path (30) is located has a circular shape when viewed in the axial direction.

[0056] As shown in FIG. 5, the second inflow path (22) is curved in the axial direction from the second inflow port (22a) to the second impeller (21).

[0057] A second inlet guide vane (23) (hereinafter referred to as the second IGV (23)) is disposed on the suction side of the second impeller (21). The second IGV (23) is disposed in the second flow path (32) of the intermediate flow path (30) and the second inflow path (22). The second IGV (23) adjusts the flow rate of the refrigerant flowing toward the second impeller (21). A second adjustment mechanism (23a) that adjusts the opening degree of the second IGV (23) is attached to the unit casing (210). Part of the second adjustment mechanism (23a) is disposed in the front chamber (211).

[0058] As shown in FIG. 7, the diffuser flow path (40) extends from a second outflow port (24) which is the outflow port of the second impeller (21). The refrigerant compressed by the second impeller (21) and having flowed out of the second outflow port (24) flows through the diffuser flow path (40). The diffuser flow path (40) extends over the entire part in the circumferential direction. The diffuser flow path (40) is formed by a front surface portion (41) extending over the entire part in the circumferential direction and located relatively on the front side, and a rear surface portion (42) facing the front surface portion (41) in the axial direction. The diffuser flow path (40) has a flat flow path (43) and a curved flow path (44).

[0059] The flat flow path (43) extends in the radial direction from the second outflow port (24). The curved flow path (44) is curved to the side opposite to the side on which the refrigerant flows in with respect to the flat flow path (43) (to the rear side in the axial direction). In the cross section of the diffuser flow path (40) taken along the radial direction, the ratio of the length (Dc) of the curved flow path (44) to the length (Dp) of the flat flow path (43) is 0.5 or more in an intermediate span which is an intermediate position between the front surface portion (41) and rear surface portion (42) of the diffuser flow path (40). The maximum value of the outer diameter of the diffuser flow path (40) is equal to the maximum value of the outer diameter of the volute flow path (50) (hereinafter referred to as the maximum outer diameter (Rv)).

[0060] The refrigerant having passed through the diffuser flow path (40) flows through the volute flow path (50). The volute flow path (50) is located on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40). That is, the volute flow path (50) is located closer to the motor (100) in the axial direction with respect to the diffuser flow path (40). The volute flow path (50) is connected to the rear side of the curved flow path (44). The volute flow path (50) extends inward in the radial direction and rearward from a portion connected to the curved flow path (44). The position of the inlet portion of the volute flow path (50) in the radial direction is the same as the position of the outlet portion of the curved flow path (44) in the radial direction.

[0061] As shown in FIG. 8, the volute flow path (50) extends in the circumferential direction so as to surround the motor casing (110) from the outside in the radial direction. The maximum outer diameter (Rv) of the volute flow path (50) with respect to the center axis (X) is uniform in the circumferential direction. The maximum outer diameter (Rv) of the volute flow path (50) is smaller than or equal to the maximum outer diameter (Rr) of the connection flow path (33) over the entire part in the circumferential direction. In this embodiment, the ratio of the maximum outer diameter (Rv) of the volute flow path (50) to the maximum outer diameter (Rr) of the connection flow path (33) is about 0.96. Thus, when the turbo compressor (10) is viewed from the front side in the axial direction, the volute flow path (50) overlaps with the intermediate flow path (30) and is not visible.

[0062] The volute flow path (50) has a shape so that the cross section taken along the radial direction increases while expanding inward in the radial direction and rearward with the maximum outer diameter (Rv) held uniform. At the position of the volute flow path (50) in the axial direction, the outer diameter (Rm) of the motor casing (110) with respect to the center axis (X) is smaller than the minimum value of the inner diameter (Rvi) of the unit casing (210) with respect to the center axis (X). There is always a space between part of the unit casing (210) that forms the volute flow path (50) and the motor casing (110). At the position of the volute flow path (50), the ratio of the outer diameter (Rm) of the motor casing (110) to the inner diameter (Rvi) of the unit casing (210) is 0.95 or less in a part in which the unit casing (210) and the motor casing (110) are closest to each other in the radial direction.

[0063] As shown in FIGS. 9 and 10, the maximum length of the volute flow path (50) in the radial direction in the cross section taken along the radial direction is defined as a first length (r), and the maximum length of the volute flow path (50) in the axial direction in the cross section taken along the radial direction is defined as a second length (L). When the radial cross sectional area increases, the amount of change in the second length (L) is larger than or equal to the amount of change in the first length (r). In part of the volute flow path (50) where the radial cross sectional area is larger, the ratio of the second length (L) to the first length (r) is larger. As shown in FIG. 9, in part of the volute flow path (50) where the radial cross sectional area is smallest, the first length (r) is larger than the second length (L). In this part, the ratio of the second length (L) to the first length (r) is less than 1. In contrast, as shown in FIG. 10, in part of the volute flow path (50) where the radial cross sectional area is largest, the second length (L) is larger than the first length (r). In this part, the ratio of the second length (L) to the first length (r) is greater than 1.

[0064] As shown in FIG. 8, the final outflow path (60) is connected to part of the volute flow path (50) where the radial cross sectional area is largest. The final outflow path (60) allows the refrigerant of which the flow velocity has been reduced by the diffuser flow path (40) and the volute flow path (50) to flow out. The final outflow path (60) is connected to the first pipe (610).

[0065] The refrigerant flows in from the first inflow path (12), and the flow rate is adjusted by the first IGV (13). The refrigerant of which the flow rate has been adjusted is compressed by the first impeller (11), and flows out to the first flow path (31). After passing through the connection flow path (33), the refrigerant joins the refrigerant flowing from the economizer (400) in the second flow path (32). At this time, the flow rate of the refrigerant is adjusted by the second IGV (23). The flow velocity of the refrigerant decreases when passing through the first flow path (31), the connection flow path (33), and the second flow path (32). The refrigerant having passed through the second IGV (23) flows into the second impeller (21) via the second inflow path (22), and is compressed by the second impeller (21). The refrigerant compressed by the second impeller (21) flows out to the flat flow path (43). The refrigerant passes through the flat flow path (43) and the curved flow path (44) and flows into the volute flow path (50) while the flow velocity is reduced. After the flow velocity is reduced in the volute flow path (50), the refrigerant flows out of the final outflow path (60).(3) Advantages of Embodiment

[0066] In this embodiment, the intermediate flow path (30) includes the first flow path (31) extending in the radial direction and communicating with the outflow port (14) of the first impeller (11), the second flow path (32) extending in the radial direction and communicating with the inflow port (22a) of the second impeller (21), and the connection flow path (33) connecting the outer portion of the first flow path (31) in the radial direction and the outer portion of the second flow path (32) in the radial direction; the diffuser flow path (40) has the flat flow path (43) extending outward in the radial direction from the outflow port (24) of the second impeller (21), and the curved flow path (44) curved to the side opposite to the side on which the refrigerant flows in with respect to the flat flow path (43) in the axial direction; the volute flow path (50) is connected to the curved flow path (44) and extends in the circumferential direction about the center axis (X) of the shaft (201) so as to surround the casing housing the shaft (201) from the outside in the radial direction; and the maximum outer diameter (Rv) of the volute flow path (50) is smaller than or equal to the maximum outer diameter (Rr) of the connection flow path (33). In this embodiment, the curved flow path (44) is curved to the side opposite to the side on which the refrigerant flows in with respect to the flat flow path (43) in the axial direction, and thus the volute flow path (50) connected to the curved flow path (44) is disposed on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40). If the volute flow path (50) is disposed on the same side as the intermediate flow path (30) with respect to the diffuser flow path (40) in the axial direction, it is necessary to increase the distance between the first impeller (11) and the second impeller (21) in the axial direction in order to secure a space in which the volute flow path (50) is disposed. In this embodiment, the volute flow path (50) is disposed on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40), and thus the first impeller (11) and the second impeller (21) can be disposed adjacent to and close to each other in the axial direction. Accordingly, the turbo compressor (10) can be downsized in the axial direction. Further, the maximum outer diameter (Rv) of the volute flow path (50) is smaller than or equal to the maximum outer diameter (Rr) of the connection flow path (33), and thus the downsize can be achieved in the radial direction. Further, the diffuser flow path (40) has a long flow path length due to the curved flow path (44), and the flow velocity of the refrigerant can be reduced, and thus the fluid efficiency can be maintained. Thus, the turbo compressor (10) of this embodiment can be downsized while the fluid efficiency is maintained.

[0067] In this embodiment, the first impeller (11) and the second impeller (21) can be disposed adjacent to and close to each other in the axial direction, and thus the reliability of the turbo compressor (10) can be improved when being operated at a high number of rotations.

[0068] In this embodiment, the volute flow path (50) is disposed on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40), and thus the degree of freedom to route the intermediate flow path (30) can be increased.

[0069] In this embodiment, the maximum outer diameter of the connection flow path (33) is uniform in the circumferential direction, and the maximum outer diameter (Rv) of the volute flow path (50) is uniform in the circumferential direction. Accordingly, the maximum outer diameter (Rv) of the volute flow path (50) can be maximized in a range that is less than or equal to the maximum outer diameter (Rr) of the connection flow path (33). The radial cross sectional area of the volute flow path (50) can be increased, and thus the turbo compressor (10) of this embodiment can be downsized while the fluid efficiency is maintained.

[0070] In this embodiment, the motor (100) is located on the side opposite to the first impeller (11) with respect to the second impeller (21) in the axial direction, and the volute flow path (50) surrounds the motor casing (110) housing the motor (100) from the outside in the radial direction. The motor (100) is a downsized motor, and thus the periphery of the motor casing (110) tends to be a dead space. The turbo compressor (10) of this embodiment can be downsized in the radial direction and the axial direction by effectively utilizing the space around the motor casing (110).

[0071] In this embodiment, the volute flow path (50) has a shape so that the cross section taken along the radial direction increases while expanding inward in the radial direction; and in the cross section of the volute flow path (50) taken along the radial direction, in part of the volute flow path (50) where the radial cross sectional area is larger, the ratio of the second length (L) to the first length (r) is larger. Accordingly, the volute flow path (50) can be prevented from expanding to the outer side in the radial direction, and the turbo compressor (10) can be downsized in the radial direction. Further, the cross section of the volute flow path (50) taken along the radial direction is increased in the axial direction, whereby the radial cross sectional area can be efficiently increased. The radial cross sectional area of the volute flow path (50) is increased, whereby the flow velocity of the refrigerant can be reduced; and thus the fluid efficiency can be improved. Thus, the turbo compressor (10) of this embodiment can be downsized while the fluid efficiency is improved.

[0072] In this embodiment, in part of the volute flow path (50) where the radial cross sectional area is smallest, the first length (r) is larger than the second length (L); and in part of the volute flow path (50) where the radial cross sectional area is largest, the second length (L) is larger than the first length (r). In the part where the radial cross sectional area is small, by making the length in the radial direction longer and the length in the axial direction shorter, the refrigerant can flow along the wall surface of the volute flow path (50) at the inlet of the volute flow path (50). Accordingly, flow separation can be reduced at the inlet of the volute flow path (50), and thus the fluid efficiency of the turbo compressor (10) of this embodiment can be improved.

[0073] In this embodiment, at the position of the volute flow path (50), the ratio of the outer diameter (Rm) of the motor casing (110) to the inner diameter (Rvi) of the unit casing (210) is 0.95 or less in a part in which the unit casing (210) and the motor casing (110) are closest to each other in the radial direction. The space is secured between the unit casing (210) and the motor casing (110), and thus the insertability of tools can be enhanced. The maintainability of the turbo compressor (10) of this embodiment can be improved.

[0074] In this embodiment, in the cross section of the diffuser flow path (40) taken along the plane along the center axis (X), the ratio of the length (Dc) of the curved flow path (44) to the length (Dp) of the flat flow path (43) is 0.5 or more in the intermediate span of the diffuser flow path (40). While the distance of the diffuser flow path (40) in the radial direction can be shortened, the flow path length of the entire part of the diffuser flow path (40) can be made longer. Accordingly, the flow velocity of the refrigerant can be reduced in the diffuser flow path (40), and thus the fluid efficiency of the turbo compressor (10) of this embodiment can be improved.

[0075] In this embodiment, the motor casing (110) houses the bearings (121, 122, 123) supporting the shaft (201). The bearings (121, 122, 123) are disposed in the motor casing (110), whereby the turbo compressor (10) of this embodiment can be downsized in the radial direction and the axial direction by effectively utilizing the space around the motor casing (110).

[0076] In this embodiment, the turbo compressor (10) has the two-stage inline structure in which the suction side of the first impeller (11) and the suction side of the second impeller (21) face in the same direction. The intermediate flow path (30) can be easily routed as compared with when the inline structure is not employed, and thus the turbo compressor (10) of this embodiment can be downsized.

[0077] In this embodiment, the second IGV (23) is disposed on the suction side of the second impeller (21). The volute flow path (50) is located on the side opposite to the intermediate flow path (30) in the axial direction with respect to the diffuser flow path (40), and thus the front chamber (211) can be formed between the second impeller (21) and the intermediate flow path (30) in the axial direction. The second adjustment mechanism (23a) can be disposed in the front chamber (211), and thus the second IGV (23) can be disposed while the size of the turbo compressor (10) of this embodiment is held small in the axial direction.

[0078] In this embodiment, the injection pipe (150) of the economizer (400) is disposed between the first impeller (11) and the second impeller (21). The front chamber (211) can be formed between the second impeller (21) and the intermediate flow path (30). The injection pipe (150) can be disposed in the front chamber (211), and thus the injection pipe (150) can be disposed while the size of the turbo compressor (10) of this embodiment is held small in the axial direction.(4) Other Embodiments

[0079] The maximum outer diameter (Rv) of the volute flow path (50) is not necessarily uniform in the circumferential direction. For example, the maximum outer diameter (Rv) of the volute flow path (50) may be smaller in part of the volute flow path (50) where the radial cross sectional area is smaller.

[0080] The volute flow path (50) may be expanded in only one of the radial direction or the axial direction in order to expand the cross section taken along the radial direction.

[0081] The motor (100) may be separate from the compression unit (200). In this case, the rotation of the motor (100) may be transmitted to the shaft (201) via a gear. The volute flow path (50) surrounds not the motor casing (110) but the casing housing the shaft (201).

[0082] The turbo compressor (10) may be a multistage turbo compressor including three or more impellers. In this case, an impeller is added upstream of the first impeller (11).

[0083] The first IGV (13), the second IGV (23), and the injection pipe (150) are not essential and may be omitted.

[0084] While the embodiments and variations thereof have been described above, it will be understood that various changes in form and details may be made without departing from the spirit and scope of the claims. The embodiment, the variation thereof, and the other embodiments may be combined and replaced with each other without deteriorating intended functions of the present disclosure.

[0085] The expressions of "first", "second", and "third" described above are used to distinguish the terms to which these expressions are given, and do not limit the number and order of the terms.INDUSTRIAL APPLICABILITY

[0086] As described above, the present disclosure is useful for a turbo compressor.DESCRIPTION OF REFERENCE CHARACTERS

[0087] 1Refrigeration Apparatus 11First Impeller 21Second Impeller 23Second Inlet Guide Vane 30Intermediate Flow Path 31First Flow Path 32Second Flow Path 33Connection Flow Path 40Diffuser Flow Path 43Flat Flow Path 44Curved Flow Path 50Volute Flow Path 100Motor 101Stator 102Rotor 110Motor Casing 121First Radial Bearing 122Second Radial Bearing 123Thrust Bearing 150Injection Pipe 201Shaft 400Economizer DcLength of Curved Flow Path DpLength of Flat Flow Path LSecond Length rFirst Length RrMaximum Value of Outer Diameter of Connection Flow Path RvMaximum Value of Outer Diameter of Volute Flow Path XCenter Axis

Examples

Embodiment Construction

[0028]Embodiments of the present disclosure will be described in detail below with reference to the drawings. The present disclosure is not limited to the embodiments shown below, and various changes can be made within the scope without departing from the technical concept of the present disclosure. Since each of the drawings is intended to illustrate the present disclosure conceptually, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for the sake of ease of understanding.

(1) Refrigeration Apparatus

[0029]FIG. 1 shows a refrigeration apparatus (1) including a turbo compressor (10) according to this embodiment. The refrigeration apparatus (1) includes the turbo compressor (10), a condenser (300), an economizer (400), an evaporator (500), and a first pipe (610) to a fourth pipe (640).

[0030]The turbo compressor (10) is a centrifugal two-stage turbo compressor having a first impeller (11) and a second impeller (21). The turbo compressor (10) includes a motor ...

Claims

1. A multistage turbo compressor comprising: a motor (100) having a stator (101) and a rotor (102); a shaft (201) extending in an axial direction and rotated by the rotor (102); a first impeller (11) attached to the shaft (201); a second impeller (21) attached to the shaft (201) and disposed adjacent to the first impeller (11) in the axial direction; an intermediate flow path (30) allowing a refrigerant to flow between an outflow port (14) of the first impeller (11) and an inflow port (22a) of the second impeller (21); a diffuser flow path (40) through which a refrigerant having flowed out of the second impeller (21) flows; and a volute flow path (50) through which a refrigerant having passed through the diffuser flow path (40) flows, wherein the intermediate flow path (30) includes a first flow path (31) extending in a radial direction, which is a direction extending radially from a center of the shaft (201), and communicating with the outflow port (14) of the first impeller (11), a second flow path (32) extending in the radial direction and communicating with the inflow port (22a) of the second impeller (21), and a connection flow path (33) connecting an outer portion of the first flow path (31) in the radial direction and an outer portion of the second flow path (32) in the radial direction, the diffuser flow path (40) includes a flat flow path (43) extending outward in the radial direction from an outflow port (24) of the second impeller (21), and a curved flow path (44) curved to a side opposite to a side on which a refrigerant flows in with respect to the flat flow path (43) in the axial direction, the volute flow path (50) extends in a circumferential direction about a center axis (X) of the shaft (201) so as to surround the casing housing the shaft (201) from an outside in the radial direction, and is connected to the curved flow path (44), and a maximum value (Rv) of an outer diameter of the volute flow path (50) with respect to the center axis (X) is smaller than or equal to a maximum value (Rr) of an outer diameter of the connection flow path (33) with respect to the center axis (X).

2. The multistage turbo compressor of claim 1, wherein the motor (100) is located on a side opposite to the first impeller (11) with respect to the second impeller (21) in the axial direction, and the casing is a motor casing (110) housing the motor (100).

3. The multistage turbo compressor of claim 1 or 2, wherein the volute flow path (50) has a shape so that a cross section taken along the radial direction increases while expanding inward in the radial direction, and a maximum length of the volute flow path (50) in the radial direction in a cross section taken along the radial direction is a first length (r), and a maximum length of the volute flow path (50) in the axial direction in the cross section taken along the radial direction is a second length (L), where in part of the volute flow path (50) where the radial cross sectional area is larger, a ratio of the second length (L) to the first length (r) is larger.

4. The multistage turbo compressor of claim 3, wherein in part of the volute flow path (50) where the radial cross sectional area is smallest, the first length (r) is larger than the second length (L), and in part of the volute flow path (50) where the radial cross sectional area is largest, the second length (L) is larger than the first length (r).

5. The multistage turbo compressor of any one of claims 1 to 4, wherein in a cross section of the diffuser flow path (40) taken along the radial direction, a ratio of a length (Dc) of the curved flow path (44) to a length (Dp) of the flat flow path (43) is 0.5 or more in an intermediate span of the diffuser flow path (40).

6. The multistage turbo compressor of claim 2, wherein the motor casing (110) houses a bearing (121, 122, 123) supporting the shaft (201).

7. The multistage turbo compressor of any one of claims 1 to 6, further comprising: a two-stage inline structure in which a suction side of the first impeller (11) and a suction side of the second impeller (21) face in the same direction.

8. The multistage turbo compressor of any one of claims 1 to 7, wherein an inlet guide vane is disposed on the suction side of the second impeller (21).

9. The multistage turbo compressor of any one of claims 1 to 8, wherein an injection pipe (150) of an economizer (400) is disposed between the first impeller (11) and the second impeller (21).

10. A refrigeration apparatus comprising: the multistage turbo compressor (10) of any one of claims 1 to 9.

11. The refrigeration apparatus of claim 10, wherein the refrigerant is a low-pressure refrigerant.

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