Patent Publication Number: US-9890973-B2

Title: Turbo refrigerator

Description:
TECHNICAL FIELD 
     The present invention relates to a turbo refrigerator configured to compress a gas-phase refrigerant by a turbo compressor, condenses the refrigerant by a condenser, evaporates the obtained liquid-phase refrigerant by an evaporator, and cools a cooling target by evaporation heat of the liquid-phase refrigerant. 
     BACKGROUND ART 
     In recent years, one type of such a turbo refrigerator has been proposed that is configured to use water as a refrigerant instead of a greenhouse effect gas, such as chlorofluorocarbon, as an environmental measure. In such a turbo refrigerator, the water having a higher boiling point than the chlorofluorocarbon is evaporated under low pressure, so that the refrigerant decreases in density and increases in volume flow rate. Therefore, the turbo compressor tends to increase in size. In contrast, heat exchangers, such as a condenser and an evaporator, do not increase in size as much as the turbo compressor does since the water has better thermal conductivity than the chlorofluorocarbon. 
     To be specific, although the devices increase in size, the turbo compressor, the condenser, and the evaporator do not increase in size at an equal rate, but only the turbo compressor increases in size as compared to the other components. Therefore, in a case where a typical structure of a chlorofluorocarbon turbo refrigerator in which a turbo compressor and a heat exchanger are formed as separate components and are connected to each other via a pipe is applied to a water refrigerant turbo refrigerator, only the turbo compressor increases in size, and a large dead space remains around a centrifugal impeller. 
     In a case where the pipe and the like are reduced in size as much as possible in order to suppress increases in sizes of the devices as much as possible, the flow velocity of the refrigerant tends to increase, and this increases the pressure loss. Thus, the performance of the turbo refrigerator deteriorates. 
     To solve these problems, proposed is a turbo refrigerator in which impellers of a two-stage centrifugal turbo compressor are arranged back-to-back (Japanese Patent No. 4191477). Instead of collecting by a scroll a refrigerant radially flowing out and then introducing the refrigerant to a pipe extending to a condenser, in the turbo refrigerator, a plurality of diffuser ducts are provided for each of the first-stage and second-stage impellers, and the first-stage diffuser ducts and the second-stage diffuser ducts are arranged alternately in a circumferential direction. 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the turbo compressor of the above conventional example is extremely complex in structure. In addition, a large dead space remains around the centrifugal impeller after all. 
     Here, an object of the present invention is to provide a turbo refrigerator including a centrifugal turbo compressor capable of: suppressing a decrease in efficiency by reducing the pressure loss of a vapor refrigerant due to a connecting pipe; being reduced in size by space saving; and smoothly introducing an evaporated refrigerant to a condenser with a simple configuration. 
     Solution to Problem 
     To achieve the above object, a turbo refrigerator according to one aspect of the present invention includes: a turbo compressor configured to compress a gas-phase refrigerant; a condenser configured to condense the gas-phase refrigerant compressed by the turbo compressor; and an evaporator configured to evaporate a liquid-phase refrigerant obtained by the condenser to cool down a cooling target by evaporation heat of the liquid-phase refrigerant. Then, the turbo compressor is a centrifugal type configured to cause the gas-phase refrigerant to flow in a radially outward direction, and the condenser is provided outside the turbo compressor so as to overlap the turbo compressor when viewed from each of an axial direction and radial direction of the turbo compressor. Here, “overlap” denotes a case where at least a part of the condenser overlaps the turbo compressor. 
     According to the turbo refrigerator, the condenser is provided outside the turbo compressor and at a position around and in the vicinity of the turbo compressor so as to overlap the turbo compressor when viewed from each of the axial direction and radial direction of the turbo compressor. Therefore, the vapor refrigerant radially flowing out from a centrifugal impeller of the turbo compressor can be directly, smoothly supplied to the condenser without flowing through a scroll and a long connecting pipe. 
     Therefore, the scroll for collecting the evaporated refrigerant and the connecting pipe for introducing the collected vapor refrigerant to the condenser become unnecessary, the scroll and the connecting pipe being provided in the existing turbo compressor. Therefore, there is no pressure loss generated by the scroll and the connecting pipe, so that the deterioration in efficiency of the turbo refrigerator can be suppressed. The condenser is provided by utilizing a space around the turbo compressor, the space being conventionally a large dead space. Therefore, the entire refrigerator can be reduced in size by space saving. 
     In the present invention, the turbo compressor may be a two-stage centrifugal type in which a compressor front stage and a compressor rear stage are arranged back-to-back so as to be lined up in the axial direction of the turbo compressor, and the condenser may be provided so as to overlap the compressor rear stage when viewed from each of the axial direction and radial direction of the turbo compressor. According to this configuration, the vapor refrigerant radially flowing out from the centrifugal impeller of the compressor rear stage of the two-stage centrifugal turbo compressor can be supplied to the condenser without flowing through the scroll and the long connecting pipe. 
     In the present invention, in a case where the compressor front stage and the compressor rear stage are lined up from one side in the axial direction toward the other side in the axial direction, and the turbo refrigerator further includes an intermediate passage through which the refrigerant discharged from a radially outer side of the compressor front stage is introduced to a suction port of the compressor rear stage, the suction portion being located at the other side in the axial direction, the condenser may be provided at a space between the intermediate passage and the compressor rear stage. According to this configuration, the vapor refrigerant flowing out from the compressor rear stage can be supplied to the condenser without flowing across the intermediate passage. 
     In the present invention, an intermediate cooler configured to cool down the refrigerant introduced from the compressor front stage to the compressor rear stage may be provided at the other side of the condenser in the axial direction of the turbo compressor. According to this configuration, the vapor refrigerant compressed by the compressor front stage and increased in temperature is cooled down by the intermediate cooler to be supplied to the compressor rear stage. With this, the compression efficiency of the compressor improves. In addition, the intermediate cooler can be compactly disposed concentrically with the turbo compressor. 
     Moreover, in the present invention, the turbo compressor may be a multiple-stage centrifugal type including two or more compressor stages lined up in the axial direction, and the condenser may be provided so as to overlap a rearmost one of the compressor stages when viewed from each of the axial direction and radial direction of the turbo compressor. According to this configuration, the vapor refrigerant radially flowing out from the centrifugal impeller of the compressor rearmost stage of the multiple-stage centrifugal turbo compressor can be supplied to the condenser without flowing through the scroll and the long connecting pipe. 
     Further, in the present invention, even in a case where the turbo compressor is a single-stage centrifugal type, the scroll for collecting the evaporated refrigerant and the connecting pipe for introducing the collected vapor refrigerant to the condenser become unnecessary. As a result, the deterioration in efficiency of the refrigerator can be suppressed, and the entire refrigerator can be reduced in size by space saving. 
     In the present invention, the turbo refrigerator may include a driving machine configured to drive the compressor, wherein the evaporator may be provided around the driving machine. According to this configuration, one advantage is that the driving machine can be cooled down by the evaporator. 
     In the present invention, the evaporator may be provided at one side or the other side of the turbo compressor in the axial direction, and the driving machine configured to drive the turbo compressor may be provided at its opposite side. According to this configuration, it is possible to prevent an adverse effect in which the evaporator is heated by heat generated by the driving machine. 
     In the present invention, at least the evaporator, the turbo compressor, and the condenser may be housed in the housing. In the present invention, the condenser is provided at a position around and in the vicinity of the turbo compressor. Therefore, the connecting pipe through which the vapor refrigerant flowing out from the turbo compressor and collected by the scroll is introduced to the condenser becomes unnecessary, and the evaporator, the compressor, and the condenser can be housed in the housing. On this account, the turbo refrigerator obtains a compact structure. 
     In the configuration in which the evaporator, the turbo compressor, and the condenser are housed in the housing, a return passage through which the liquid-phase refrigerant returns from the condenser to the evaporator may be provided in the housing. The return passage through which the liquid-phase refrigerant having a low volume flow rate flows may have a small diameter. Therefore, by providing the return passage in the housing, the turbo refrigerator can obtain a further compact structure. 
     Advantageous Effects of Invention 
     According to the turbo refrigerator of the present invention, the condenser is provided outside the turbo compressor so as to overlap the turbo compressor when viewed from each of the axial direction and radial direction of the turbo compressor. Therefore, the vapor refrigerant radially flowing out from the impeller can be directly supplied to the condenser without flowing through the scroll and the connecting pipe. The scroll and connecting pipe between the turbo compressor and the condenser become unnecessary, so that the deterioration in efficiency of the refrigerator can be suppressed. Further, the condenser is provided by effectively utilizing the space around the turbo compressor, so that the entire refrigerator can be reduced in size by space saving. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram showing an operation principle of a turbo refrigerator according to Embodiment 1 of the present invention. 
         FIG. 2  is a vertical sectional view showing the above turbo refrigerator. 
         FIG. 3  is a cross-sectional view taken along line III-III of  FIG. 2 . 
         FIG. 4  is a cross-sectional view showing a modification example of the turbo refrigerator of  FIG. 3 . 
         FIG. 5  is a cross-sectional view showing another modification example of the turbo refrigerator of  FIG. 3 . 
         FIG. 6  is a vertical sectional view showing the turbo refrigerator according to Embodiment 2 of the present invention. 
         FIG. 7  is a vertical sectional view showing the turbo refrigerator according to Embodiment 3 of the present invention. 
         FIG. 8  is a vertical sectional view showing the turbo refrigerator according to Embodiment 4 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be explained in detail in reference to the drawings. 
       FIG. 1  is a schematic configuration diagram showing a turbo refrigerator according to Embodiment 1 of the present invention. In Embodiment 1, water is used as a refrigerant. In this turbo refrigerator, a liquid refrigerant (liquid-phase refrigerant) R 3  is sprayed onto a heat exchanger tube  5  from above in an evaporator  1  to be evaporated, and by evaporation heat of the refrigerant, heat is extracted from a cooling target (cold water, for example) W 1  flowing in the heat exchanger tube  5 . Then, a low-pressure vapor refrigerant R 1  (gas-phase refrigerant) is suctioned and compressed by a turbo compressor  2  driven rotationally by a driving machine  3 , such as an electric motor. With this, a high-pressure vapor refrigerant R 2  is obtained and supplied to a condenser  4 . The vapor refrigerant R 2  dissipates the heat with respect to a heat removing object (cooling water, for example) W 2  flowing in a cooling tube  6  in the condenser  4 . Thus, the vapor refrigerant R 2  becomes the liquid refrigerant R 3 , and the liquid refrigerant R 3  is supplied to the evaporator  1 . 
     In the turbo refrigerator, water having a higher boiling point than, for example, chlorofluorocarbon that is a conventionally typical refrigerant is used as a refrigerant. Therefore, the compressor  2  operates under negative pressure, for example, 1/100 atmosphere at an inflow side thereof and 1/10 atmosphere at an outflow side thereof. Therefore, the refrigerant decreases in density and increases in volume flow rate, so that the turbo refrigerator increases in size as compared to a refrigerator using, for example, the chlorofluorocarbon as the refrigerant. The vapor refrigerant R 2  is supplied from the compressor  2  to the condenser  4 . The cold water W 1  in the heat exchanger tube  5  is cooled down in the evaporator  1 , for example, from 12° C. to 7° C. and then flows out to be used for, for example, indoor cooling of a building. The cooling water W 2  in the cooling tube  6  removes the heat from the vapor refrigerant R 2  in the condenser  4 , increases in temperature, for example, from 32° C. to 37° C., and is then supplied to a cooling tower. 
     In  FIG. 2  showing a vertical sectional view of the turbo refrigerator, a housing  8  that is an exterior body is configured such that an upper opening portion of a bottomed cylindrical housing main body  9  is sealed by a housing lid body  10 . The housing  8  houses major components, such as the evaporator  1 , the compressor  2 , and the condenser  4 , of the turbo refrigerator. The compressor  2  is arranged concentrically with the housing  8  such that a rotation axis of the compressor  2  substantially coincides with a center line of the housing  8  having a substantially cylindrical shape. 
     An electric motor  3  configured to drive the compressor  2  is provided at a bottom portion  9   a  of the housing main body  9  and is directly coupled to a rotating shaft  11  of the compressor  2 . The rotating shaft  11  extends in an upper-lower direction. An upper end portion of the rotating shaft  11  is rotatably supported by an inner wall portion  17  of the housing lid body  10  via a bearing  12 , and a lower portion thereof is rotatably supported by the housing main body  9  via a bearing  13  and the electric motor  3 . 
     A ring-shaped attachment plate  18  is externally fitted to and fixed to a case of the electric motor  3  at the bottom portion  9   a  of the housing main body  9 , and the attachment plate  18  is fixed to a peripheral wall of the bottom portion  9   a  of the housing main body  9  by a plurality of radial stays  19 . To be specific, the electric motor  3  is supported by the housing main body  9  via the attachment plate  18  and the plurality of stays  19 . The evaporator  1  having a circular shape is arranged under the plurality of radial stays  19  so as to surround the electric motor  3 . 
     A front-stage defining wall  15 A is provided above the attachment plate  18  and the plurality of stays  19  so as to be spaced apart from the attachment plate  18  and the plurality of stays  19 . An opening at the center of the front-stage defining wall  15 A communicates with a front-stage inlet portion  14   a  (suction port at one side in an axial direction of a compressor front stage) that opens at a lower portion of a casing  14  of the compressor  2 . In other words, the front-stage defining wall  15 A spreads from the front-stage inlet portion of the casing  14  of the compressor  2  toward an outer periphery, and an outer peripheral edge of the front-stage defining wall  15 A is joined to an inner surface of a peripheral wall of the housing main body  9 . The vapor refrigerant R 1  from the evaporator  1  receives a suction force, generated by the compressor  2 , to flow upward through spaces among the stays  19 . Then, the vapor refrigerant R 1  flows through a passage between the attachment plate  18  and the front-stage defining wall  15 A to be suctioned by the compressor  2 . 
     As with the front-stage defining wall  15 A, a rear-stage defining wall  15 B is provided between an outer periphery of a rear-stage inlet portion  14   b  (suction port at the other side in the axial direction of a compressor rear stage) that opens at an upper portion of the casing  14  of the compressor  2  and a peripheral wall of the housing main body  9  surrounding the outer periphery of the rear-stage inlet portion  14   b . The rear-stage defining wall  15 B is arranged under the inner wall portion  17  of the housing lid body  10  so as to be spaced apart from the inner wall portion  17 . As described below, a portion between the rear-stage defining wall  15 B and the inner wall portion  17  serves as a part of an intermediate passage  24  through which the refrigerant is introduced from a compressor front stage  2 F to a compressor rear stage  2 R. 
     The compressor  2  is a two-stage centrifugal type in which the compressor front stage  2 F on a lower side and the compressor rear stage  2 R on an upper side are arranged back-to-back. The compressor front stage  2 F is constituted by a front-stage impeller  20  and a front-stage diffuser  21  located on an outer side of the front-stage impeller  20  in a radial direction. The compressor rear stage  2 R is constituted by a rear-stage impeller  22  and a rear-stage diffuser  23  arranged concentrically with the rear-stage impeller  22  so as to be located on an outer side of the rear-stage impeller  22  in a radial direction R. 
     The front-stage impeller  20  suctions the vapor refrigerant R 1  from the evaporator  1  through the inlet portion  14   a  upward along an axial direction S of the rotating shaft  11 , causes the vapor refrigerant R 1  to flow outward in the radial direction R, and causes the vapor refrigerant R 1  to flow outward in the radial direction R through an outlet of an outer periphery of the front-stage impeller  20 . A vapor refrigerant R 21  having flowed out from the front-stage impeller  20  flows through the front-stage diffuser  21  to further flow outward in the radial direction R, that is, toward the peripheral wall of the housing main body  9 . 
     The vapor refrigerant R 21  discharged from the front-stage diffuser  21  as described above flows upward through a space between the peripheral wall of the housing main body  9  and a cylindrical passage inner wall  16  provided at an inner side of the peripheral wall of the housing main body  9  in the radial direction R so as to be spaced apart from the peripheral wall of the housing main body  9 . Then, the vapor refrigerant R 21  reaches a space above the rear-stage defining wall  15 B and flows toward the inner side in the radial direction R through a space between the rear-stage defining wall  15 B and the inner wall portion  17  located above the rear-stage defining wall  15 B. Then, the vapor refrigerant R 21  is suctioned through the rear-stage inlet portion  14   b  to the compressor rear stage  2 R. 
     To be specific, the intermediate passage  24  is formed, which extends from the outer peripheral edge of the front-stage diffuser  21  through the space between the peripheral wall of the housing main body  9  and the passage inner wall  16  and the space between the rear-stage defining wall  15 B and the inner wall portion  17  located above the rear-stage defining wall  15 B to the rear-stage inlet portion  14   b  to introduce the refrigerant from the compressor front stage  2 F to the compressor rear stage  2 R. An intermediate cooler  28  constituted by a heat exchanger is disposed on the intermediate passage  24  so as to be located between the rear-stage defining wall  15 B and the inner wall portion  17 . The vapor refrigerant R 21  is cooled down by the intermediate cooler  28  when flowing through the intermediate passage  24 . For example, water is used as a coolant of the intermediate cooler  28 . 
     The vapor refrigerant R 22  having flowed out from the intermediate cooler  28  is suctioned through the rear-stage inlet portion  14   b  downward along the axial direction S of the rotating shaft  11  and flows outward in the radial direction R through an outlet of the outer periphery of the rear-stage impeller  22 . The vapor refrigerant R 2  having flowed out from the rear-stage impeller  22  as described above flows through the rear-stage diffuser  23  outward in the radial direction R, that is, toward the peripheral wall of the housing main body  9  to flow out from a circular outlet  29 . 
     A circular space  30  whose outer side in the radial direction R is surrounded by the passage inner wall  16  is formed between the rear-stage diffuser  23  and the rear-stage defining wall  15 B located above the rear-stage diffuser  23 , and the circular outlet  29  opens to face the space  30 . The condenser  4  is provided in the circular space  30 , and the vapor refrigerant R 2  having flowed out through the outlet  29  directly, smoothly flows into the condenser  4 . The vapor refrigerant R 2  is condensed in the condenser  4  to become the liquid refrigerant R 3 , and the refrigerant R 3  flows through a return passage  31  to return to the evaporator  1 , the return passage  31  being constituted by a pipe shown by a virtual line in  FIG. 2  and having a small diameter. The return passage  31  is provided in the housing  8  and penetrates the front-stage diffuser  21  and the rear-stage diffuser  23  in the axial direction S. The return passage  31  may be provided so as to extend outside the housing  8 . 
     As described above, in the turbo refrigerator according to the present embodiment, the condenser  4  is provided outside the compressor rear stage  2 R so as to overlap the compressor rear stage  2 R when viewed from each of the axial direction S and the radial direction R, that is, the condenser  4  is provided at a position in the vicinity of the rear-stage impeller  22  of the compressor rear stage  2 R and at an outer side of the rear-stage impeller  22  in the radial direction R. Then, the vapor refrigerant R 2  having flowed out from the rear-stage impeller  22  of the compressor  2  is directly, smoothly introduced through the rear-stage diffuser  23  to the condenser  4 . Therefore, both a conventionally typical scroll in a centrifugal turbo compressor and a long connecting pipe through which a refrigerant collected by the scroll is introduced to a condenser are unnecessary. Since there is no pressure loss generated by the scroll and the connecting pipe, the deterioration in efficiency of the refrigerator can be suppressed. 
     The position in the vicinity of the rear-stage impeller  22  of the compressor rear stage  2 R and at the outer side of the rear-stage impeller  22  in the radial direction R is a large dead space in the conventional turbo refrigerator. Therefore, by utilizing this place as an installation location of the condenser  4 , the entire refrigerator can be reduced in size by space saving. Especially in the present embodiment, water which has a high boiling point is used as the refrigerant. Therefore, the operation pressure is low, and the refrigerant decreases in density. On this account, it is necessary to use the compressor  2  including the impellers  20  and  22  each having a comparatively large diameter. Thus, the large circular space  30  exists at an outer side of and in the vicinity of the compressor rear stage  2 R, constituted by the rear-stage impeller  22  and the rear-stage diffuser  23 , so as to overlap the compressor rear stage  2 R when viewed from each of the axial direction S and the radial direction R, and the condenser  4  can be easily provided at this space  30 . 
     As clearly shown in  FIG. 2 , in the present embodiment, the condenser  4  is provided so as to entirely overlap the compressor rear stage  2 R constituted by the rear-stage impeller  22  and the rear-stage diffuser  23 . However, the condenser  4  may be provided such that a part thereof overlaps the compressor rear stage  2 R. For example, the condenser  4  may be provided such that a portion thereof except for a portion (upper portion in  FIG. 2 ) located at one side in the axial direction overlaps the compressor rear stage  2 R. In addition, a circular space  32  exists so as to overlap the compressor front stage  2 F, constituted by the front-stage impeller  20  and front-stage diffuser  21 , when viewed from each of the axial direction S and the radial direction R. Therefore, for example, by providing a part of the evaporator  1  or the entire evaporator  1  at the space  32 , the space can be effectively utilized. 
     Further, in the present embodiment, the circular space  30  in which the condenser  4  is provided as described above is formed between the rear-stage diffuser  23  and the rear-stage defining wall  15 B, located above the rear-stage diffuser  23 , so as to be surrounded by the passage inner wall  16  from the outer side in the radial direction R. Therefore, the vapor refrigerant R 2  from the compressor rear stage  2 R can be supplied to the condenser  4  in the space  30  without flowing across the intermediate passage  24  extending from the outside of the passage inner wall  16  to the space above the rear-stage defining wall  15 B. On this account, the refrigerant passage between the compressor rear stage  2 R and the condenser  4  becomes short and simple in shape. 
     The vapor refrigerant R 21  that has been compressed by the compressor front stage  2 F and increased in temperature is cooled down by the intermediate cooler  28  and then supplied to the compressor rear stage  2 R. Therefore, the compression efficiency of the compressor  2  improves. In addition, since the scroll and connecting pipe located downstream of the compressor rear stage  2 R are unnecessary as described above, the major components, such as the evaporator  1 , the compressor  2 , and the condenser  4 , can be housed in the housing  8 , so that a compact structure is realized. Further, as the return passage  31  through which the liquid refrigerant R 3  having a low volume flow rate returns to the evaporator  1  from the condenser  4 , the pipe having the small diameter can be provided in the housing  8 , so that the further compact structure is realized. 
     Furthermore, since the evaporator  1  is provided so as to surround the driving machine  3 , configured to drive the compressor  2 , from the outer side in the radial direction R, radiant heat from the driving machine  3  can be absorbed by the evaporator  1  that is comparatively low in temperature, so that the driving machine  3  can be cooled down. 
     The condenser  4  is not limited to the circular condenser shown in  FIG. 3 . As shown in  FIG. 4 , two rectangular-solid or circular-arc condensers  4  may be provided so as to be opposed to each other in the radial direction R of the rear-stage impeller  22 . In addition, as shown in  FIG. 5 , four cubic condensers  4  may be provided outside the rear-stage impeller  22  so as to be located concentrically with the rear-stage impeller  22  at angular intervals of 90°. 
       FIG. 6  shows the turbo refrigerator according to Embodiment 2 of the present invention. The turbo refrigerator of Embodiment 2 is different from the turbo refrigerator of Embodiment 1 in that the electric motor  3  configured to drive the compressor  2  is provided above the compressor  2  (at one side or the other side in the axial direction of the compressor  2 ) and spaced apart from the evaporator  1  provided on its opposite side. The present embodiment has an advantage in which it is possible to prevent an adverse effect in which the evaporator  1  is heated by the heat generated by the electric motor  3 . 
       FIG. 7  shows the turbo refrigerator according to Embodiment 3 of the present invention. This turbo refrigerator includes a two-stage centrifugal compressor  33  in which the impeller  20  of the compressor front stage  2 F and the impeller  22  of the compressor rear stage  2 R are arranged in series and have the same orientation. The circular evaporator  1  is provided above the compressor  33 , and the electric motor  3  is provided at an inner side of the evaporator  1  in the radial direction R. The vapor refrigerant R 21  having flowed from the front-stage impeller  20  through the front-stage diffuser  21  is introduced to an inlet of the rear-stage impeller  22  through a crossover-shaped intermediate passage  34  (return channel) that turns down at an angle of 180°. The condenser  4  is provided at a position in the vicinity of the rear-stage impeller  22  of the compressor rear stage  2 R and at the outer side of the rear-stage impeller  22  in the radial direction R so as to overlap the compressor rear stage  2 R when viewed from each of the axial direction S and the radial direction R. 
     With this, unlike this type of conventional turbo refrigerator, the vapor refrigerant R 2  having flowed out from the rear-stage impeller  22  can be directly, smoothly supplied to the condenser  4  without flowing through the scroll and the long connecting pipe. Therefore, there is no pressure loss generated by the scroll and the connecting pipe, so that the deterioration in efficiency of the refrigerator can be suppressed. In addition, the condenser  4  is provided by effectively utilizing the space around the rear-stage impeller  22 , so that the dead space can be reduced, and the space can be saved. Thus, the entire refrigerator can be reduced in size. 
     In the compressor  33  of the serial arrangement, both the compressor front stage  2 F and the compressor rear stage  2 R face upward in  FIG. 7 . Therefore, the compressor  33  does not basically have a possible problem of the back-to-back type two-stage centrifugal compressor, that is, a problem that the intermediate passage  34  connecting the compressor front stage  2 F and the compressor rear stage  2 R intersects with the passage connecting the compressor rear stage  2 R and the condenser  4 . 
       FIG. 8  shows the turbo refrigerator according to Embodiment 4 of the present invention. This turbo refrigerator includes a single-stage centrifugal compressor  38  including a single impeller  39  and a single diffuser  40 . The condenser  4  is provided at an outer side of the impeller  39  of the compressor  38  in the radial direction R so as to overlap the compressor  38  when viewed from each of the axial direction S and the radial direction R. Therefore, in the turbo refrigerator, the vapor refrigerant R 2  can be directly, smoothly supplied to the condenser  4  without flowing through the scroll and the connecting pipe. On this account, there is no pressure loss generated by the scroll and the connecting pipe, so that the deterioration in efficiency of the refrigerator can be suppressed. In addition, since the condenser  4  is provided by utilizing the space around the impeller  39 , the dead space can be eliminated, and the space can be saved. Thus, the entire refrigerator can be reduced in size. 
     Each of the above-described embodiments has explained a vertical type in which the rotating shaft  11  of the compressor  2 ,  33 , or  38  extends in the upper-lower direction. However, the present invention is also applicable to a horizontal type in which the rotating shaft  11  of the compressor  2 ,  33 , or  38  extends in a horizontal direction. The structure shown in  FIG. 6  in which the evaporator  1  and the electric motor  3  are respectively arranged at opposite sides so as to sandwich the compressor  2  is also applicable to Embodiment 3 shown in  FIG. 7  and Embodiment 4 shown in  FIG. 8 . Further, the electric motor  3  configured to drive the compressor  2 ,  33 , or  38  may be provided outside the housing  8 . A speed-increasing gear may be provided between the electric motor  3  and the compressor  2 ,  33 , or  38 . 
     The present invention is not limited to the contents described in the above embodiments. Various additions, modifications, and deletions may be made within the spirit of the present invention, and such modifications and the like are also included in the scope of the present invention.