Abstract:
A turbo compressor including:
       multiple stages of compression devices arranged in series with respect to a gas passage, each of the compression devices including an impeller that rotates about an axis;   an oil tank capable of supplying lubricating oil to a sliding portion of the compression devices;   partitioned intermediate space formed so as to communicate with the passage in an upstream side of the compression devices via the gaps therebetween; and a pressure equalizer provided so as to continuously connect the intermediate space and the oil tank,   wherein a compression process is sequentially conducted by suctioning the gas in the passage.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a turbo compressor capable of compressing fluids using a plurality of impellers, and a refrigerator equipped with the turbo compressor. 
         [0003]    Priority is claimed on Japanese Patent Application No. 2008-027069, filed Feb. 6, 2008, the content of which is incorporated herein by reference. 
         [0004]    2. Description of the Related Art 
         [0005]    As a refrigerator that cools or refrigerates an object to be cooled such as water, a turbo refrigerator or the like is known which is equipped with a turbo compressor that compresses and discharges a refrigerant by a compression device provided with an impeller or the like. 
         [0006]    In the compressor, a higher compression ratio leads to a higher discharge temperature and a lower volumetric efficiency of the compressor. Accordingly, in the turbo compressor as mentioned above which is installed in the turbo refrigerator or the like, it is necessary, in some cases, to conduct the refrigerant compression through multiple stages. For example, in Japanese Unexamined Patent Application, First Publication No. 2007-177695, a turbo compressor is disclosed which has two compression stages, each of which is equipped with an impeller and a diffuser, and compresses a refrigerant sequentially through these compression stages. 
         [0007]    In addition, in such a turbo compressor, an oil tank is provided which stores a lubricating oil to be supplied to the sliding portion in the compression device. In this oil tank, in order to recover the lubricating oil supplied to the sliding portion, it is necessary to create a pressure gradient so that the internal pressure is lower than that of the space where the sliding portion is located. 
         [0008]    Accordingly, in the conventional turbo compressors, the pressure inside the oil tank has been made negative to recover the lubricating oil by directly connecting the oil tank and a suction port of the compression device via a piping (a pressure equalizer) so that the pressure inside the oil tank equals to that of the suction port, which has the lowest pressure in the compression device. 
         [0009]    Meanwhile, the conventional turbo compressors as described above have been associated with the following problems. 
         [0010]    That is, when operating a compressor, the pressure inside the oil tank reduces rapidly as the gas in the compressor is suctioned, since the oil tank and the suction port of the compression device are directly connected via a pressure equalizer. As a result, the gases which have been dissolved in the lubricating oil such as a refrigerant gas vaporize, resulting in what is known as oil foaming. Due to this oil foaming, the mist of oil filling inside the oil tank flows into the suction port through the pressure equalizer. For this reason, the amount of lubricating oil reduces which results in an insufficient supply of the lubricating oil to the sliding portion, and also the mist of oil mixes with the gas suctioned in by the compressor which results in the deterioration of compression properties. 
         [0011]    The present invention is made in view of the above circumstances and its object is to provide a turbo compressor and a refrigerator which enable the recovery of lubricating oil by making the pressure inside the oil tank negative, while preventing the reduction of lubricating oil and the deterioration of compression properties. 
       SUMMARY OF THE INVENTION 
       [0012]    In order to solve the aforementioned problems, the following configurations have been proposed in the present invention. 
         [0013]    That is, a turbo compressor according to the present invention is characterized by conducting a compression process sequentially by suctioning the gas in the passage, and having multiple stages of compression devices arranged in series with respect to a gas passage, each of the compression devices includes an impeller that rotates about the axis; an oil tank capable of supplying lubricating oil to a sliding portion of the compression devices; partitioned intermediate space formed so as to communicate with the passage in the upstream side of the compression devices via the gaps therebetween; and a pressure equalizer provided so as to continuously connect the intermediate space and the oil tank. 
         [0014]    According to the turbo compressor characterized by such features, the passage in the upstream side of the compression devices, that is, the space with the lower pressure communicates with the inside of the oil tank through the gaps therebetween, the intermediate space, and the pressure equalizer. By making the pressure inside the oil tank negative due to the above configurations, lubricating oil can be recovered. 
         [0015]    Moreover, when the mist of oil reaches the intermediate space via the pressure equalizer, since the intermediate space and the passages on both sides of the compression devices are connected only through the slight gaps therebetween, the oil mist can be retained in the intermediate space, as a result of which the contamination of the compression devices by the oil mist can be prevented. 
         [0016]    In addition, the turbo compressor according to the present invention is characterized in that the intermediate space has an annular shape having the axis as its center, and an open end of the pressure equalizer in the intermediate space is directed towards the tangential direction of the annular intermediate space. 
         [0017]    Due to the above configuration, the oil mist reaching the intermediate space via the pressure equalizer is discharged towards the tangential direction of the annular intermediate space, and the swirling flow in line with the annular shape can be generated inside the intermediate space. Therefore, the oil mist can be retained in the outer periphery of the intermediate space due to the centrifugal force caused by this swirling flow, and thus it will be possible to reliably prevent the oil mist to leak out from the gaps to the passage. 
         [0018]    Moreover, the turbo compressor according to the present invention is characterized in that a barrier plate is provided between the aforementioned gaps and the open end of the pressure equalizer in the intermediate space. 
         [0019]    Due to the above configuration, it is possible to prevent the oil mist, which is discharged from the pressure equalizer to the intermediate space, to reach the gaps and to leak out to the compression device side, even more reliably. 
         [0020]    Furthermore, the turbo compressor according to the present invention is characterized in that a flow rate adjusting unit which adjusts the suction amount of the compression devices is provided in the passage in the upstream side of the compression devices, and a drive section of the flow rate adjusting unit is accommodated within the intermediate space. 
         [0021]    Due to the above configuration, the drive section of the flow rate adjusting unit is driven in an atmosphere where the oil mist is present, and thus the longevity of the drive section can be extended. 
         [0022]    A refrigerator according to the present invention is characterized by having a condenser which cools and liquefies a compressed refrigerant; an evaporator which vaporizes the liquefied refrigerant and cools an object to be cooled by extracting heat of vaporization from the object to be cooled; and a compressor which compresses the refrigerant vaporized by the evaporator and supplies the refrigerant to the condenser; the compressor being a turbo compressor with any one of the above configurations. 
         [0023]    According to the refrigerator having such features, the same results/effects as those achieved by the abovementioned turbo compressor can be attained. 
         [0024]    According to the turbo compressor and refrigerator of the present invention, by providing the intermediate space between the passage in the upstream side of the compression devices and the oil tank, the oil mist can be retained in the intermediate space. As a result, it will be possible to prevent the deterioration of compression properties due to the contamination of the compression devices by the oil mist, and to supply sufficient amount of lubricating oil to the sliding portion by suppressing the reduction of lubricating oil. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a block diagram showing a schematic configuration of a turbo refrigerator according to a first embodiment of the present invention. 
           [0026]      FIG. 2  is a vertical cross sectional view of a turbo compressor provided in the turbo refrigerator according to the first embodiment of the present invention. 
           [0027]      FIG. 3  is an enlarged view of  FIG. 2  showing an essential part therein. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    One embodiment of a turbo compressor and refrigerator according to the present invention will be described below with reference to the accompanying drawings. It should be noted that the scale of each component in the drawings has been suitably altered in order to make each component a recognizable size. 
         [0029]      FIG. 1  is a block diagram showing a schematic configuration of a turbo refrigerator S (a refrigerator) according to the present embodiment. 
         [0030]    The turbo refrigerator S in the present embodiment is one to be installed, for example, in places like buildings and factories to produce cooling water for air conditioning, and includes a condenser  1 , an economizer  2 , an evaporator  3 , and a turbo compressor  4 , as shown in  FIG. 1 . 
         [0031]    The condenser  1  is a device where a compressed refrigerant gas X 1 , which is a refrigerant (fluid) compressed in a gaseous state, is supplied, and a refrigerant liquid X 2  is produced by cooling and liquefying the compressed refrigerant gas X 1 . As shown in  FIG. 1 , the condenser  1  is connected with the turbo compressor  4  via a passage R 1  where the compressed refrigerant gas X 1  flows through, and is also connected with the economizer  2  via a passage R 2  where the refrigerant liquid X 2  flows through. In addition, an expansion valve  5  for decompressing the refrigerant liquid  2  is disposed in the passage R 2 . 
         [0032]    The economizer  2  temporarily stores the refrigerant liquid X 2  decompressed at the expansion valve  5 . The economizer  2  is connected with the evaporator  3  via a passage R 3  where the refrigerant liquid X 2  flows through, and is also connected with the turbo compressor  4  via a passage R 4  where a gas phase component X 3  of the refrigerant generated in the economizer  2  flows through. In addition, an expansion valve  6  for further decompressing the refrigerant liquid  2  is disposed in the passage R 3 . Moreover, the passage R 4  is connected with the turbo compressor  4  so as to supply the gas phase component X 3  to a second compression stage  22  described later, which is provided in the turbo compressor  4 . 
         [0033]    The evaporator  3  vaporizes the refrigerant liquid X 2  and cools an object to be cooled, such as water, by extracting heat of vaporization from the object to be cooled. The evaporator  3  is connected with the turbo compressor  4  via a passage R 5  where a refrigerant gas X 4  generated by the vaporization of the refrigerant liquid  2  flows through. Note that the passage R 5  is connected with a first compression stage  21  described later, which is provided in the turbo compressor  4 . 
         [0034]    The turbo compressor  4  compresses the refrigerant gas X 4  to produce the abovementioned compressed refrigerant gas X 1 . 
         [0035]    As described above, the turbo compressor  4  is connected with the condenser  1  via the passage R 1  where the compressed refrigerant gas X 1  flows through, and is also connected with the evaporator  3  via the passage R 5  where the refrigerant gas X 4  flows through. 
         [0036]    In the turbo refrigerator S configured as described so far, the compressed refrigerant gas X 1  supplied to the condenser  1  via the passage R 1  is cooled and liquefied by the condenser  1  to produce the refrigerant liquid A 2 . 
         [0037]    The refrigerant liquid X 2  is decompressed by the expansion valve  5  when supplied to the economizer  2  via the passage R 2 , stored temporarily in the economizer  2  in a decompressed state, and then filter decompressed by the expansion valve  6  when supplied to the evaporator  3  via the passage R 3 . 
         [0038]    Further, the refrigerant liquid X 2  supplied to the evaporator  3  is vaporized by the evaporator  3  to produce the refrigerant gas X 4 , and the refrigerant gas X 4  is then supplied to the turbo compressor  4  via the passage R 5 . 
         [0039]    The refrigerant gas X 4  supplied to the turbo compressor  4  is compressed by the turbo compressor  4  to produce the compressed refrigerant gas X 1 , and the compressed refrigerant gas X 1  is again supplied to the condenser  1  via the passage R 1 . 
         [0040]    Note that the gas phase component X 3  of the refrigerant, which is generated when the refrigerant liquid X 2  is stored in the economizer  2 , is supplied to the turbo compressor  4  via the passage R 4 , and is then compressed together with the refrigerant gas X 4 . The compressed refrigerant gas X 1  produced as a result of the compression is then supplied to the condenser  1  via the passage R 1 . 
         [0041]    Additionally, in the turbo refrigerator S as described above, when vaporizing the refrigerant liquid X 2  at the evaporator  3 , an object to be cooled is cooled or refrigerated by extracting heat of vaporization from the object to be cooled, Next, the abovementioned turbo compressor  4  that most characterizes the present embodiment will be described in more detail.  FIG. 2  is a vertical cross sectional view of the turbo compressor  4 , and  FIG. 3  is an enlarged vertical cross sectional view of a compressor unit  20  provided in the turbo compressor  4 . 
         [0042]    As shown in these drawings, the turbo compressor  4  in the present embodiment has a motor unit  10 , a compressor unit  20 , and a gear unit  30 . 
         [0043]    The motor unit  10  is provided with a motor  12  having an output shaft  11  that rotates about an axis O and acting as a driving source for driving the compressor unit  20 ; and a motor housing  13  which surrounds the motor  12  to support the motor  12 . 
         [0044]    It should be noted that the output shaft  11  of the motor  12  is rotatably supported by a first bearing  14  and second bearing  15  fixed to the motor housing  13 . 
         [0045]    In addition, the motor housing  13  includes a leg portion  13   a  supporting the turbo compressor  4 . 
         [0046]    The leg portion  13   a  is formed so that the inside thereof is hollow, and is used as an oil tank  40 , where the recovered lubricating oil which has been supplied to the sliding portion of the turbo compressor  4  is stored. 
         [0047]    The compressor unit  20  has, as shown in detail in  FIG. 3 , a first compression stage  21  (compression device) that suctions and compresses the refrigerant gas X 4  (refer to  FIG. 1 ); and a second compression stage  22  (compression device) that further compresses the refrigerant gas X 4 , which has already been compressed by the first compression stage  21 , and discharges the resultant as the compressed refrigerant gas X 1  (refer to  FIG. 1 ). 
         [0048]    The first compression stage  21  includes: a first impeller  21   a  (impeller) that imparts velocity energy to the refrigerant gas X 4  supplied from the thrust direction and discharges the gas to the radial direction; a first diffuse  21   b  (diffuser) that compresses the refrigerant gas X 4  by converting the velocity energy imparted to the refrigerant gas X 4  by the first impeller  21   a  to pressure energy; a first scroll chamber  21   c  that guides the refrigerant gas X 4  compressed by the first diffuser  21   b  to the outside of the first compression stage  21 ; and a suction port  21   d  that suctions the refrigerant gas X 4  and then supplies the gas to the first impeller  21   a.    
         [0049]    Note that some parts of the first diffuser  21   b , first scroll chamber  21   c  and suction port  21   d  are formed by a first housing  21   e  that surrounds the first impeller  21   a.    
         [0050]    The first impeller  21   a  is fixed to a rotating shaft  23  and is rotated about the axis O due to the rotation of the rotating shaft  23 , which is imparted with the rotational power from the output shaft  11  of the motor  12 . 
         [0051]    The first diffuser  21   b  is disposed annularly in the periphery of the first impeller  21   a . Additionally, in the turbo compressor  4  of the present embodiment, the first diffuser  21   b  is a diffuser attached with a plurality of diffuser vanes  21   f  which reduce the tangential velocity of the refrigerant gas  4  in the first diffuser  21   b  and efficiently convert velocity energy to pressure energy. 
         [0052]    Further, in the suction port  21   d  of the first compression stage  21 , a plurality of inlet guide vanes  21   g  for regulating the suction amount of the first compression stage  21  are disposed. 
         [0053]    Each of the inlet guide vanes  21   g  is rotatably disposed so that the apparent area thereof as viewed from the flow direction of the refrigerant gas X 4  is changeable by a drive mechanism  21   i.    
         [0054]    Additionally, in the outer periphery of the first impeller  21   a  and the suction port  21   d  located more upstream of the first impeller  21   a , a partitioned annular intermediate space having the axis O as its center is formed by the first housing  21   e . Inside the intermediate space  21   h , the drive mechanism  21   i  for the inlet guide vanes  21   g  described above is installed. 
         [0055]    In addition, the intermediate space  21   h  communicates with the suction port  21   d  via slight gaps  21   j , as a result of which the pressure in the intermediate space  21   h  and that of the suction port  21   d  are always equal. 
         [0056]    Moreover, as shown in  FIGS. 2 and 3 , the intermediate space  21   h  is connected with the abovementioned oil tank  40  through a pressure equalizer  90 . The pressure equalizer  90  continuously connects the inside of the oil tank  40  with the intermediate space  21   h . Due to the above configuration, the pressure inside the oil tank  40  always remains equal to that of the intermediate space  21   h.    
         [0057]    Also, an open end  90   a  of the pressure equalizer  90  in the intermediate space  21   h  is disposed so as to be directed towards the tangential direction of the annular intermediate space. 
         [0058]    Furthermore, within the intermediate space  21   h , a barrier plate  21   k  is provided extending from near the gaps  21   j  and projected to the outer radial direction of the axis O. Due to the above configuration, the gaps  21   j  and the open end of the pressure equalizer  90  are separated so as not to face each other directly. 
         [0059]    The second compression stage  22  includes: a second impeller  22   a  (impeller) that imparts velocity energy to the refrigerant gas X 4 , which is compressed by the first compression stage  21  and supplied from the thrust direction, and discharges the gas to the radial direction; a second diffuser  22   b  (diffuser) that compresses the refrigerant gas X 4  by converting the velocity energy imparted to the refrigerant gas X 4  by the second impeller  22   a  to pressure energy, so as to discharge the resulting gas as the compressed refrigerant gas X 1 ; a second scroll chamber  22   c  that guides the compressed refrigerant gas X 1  discharged from the second diffuser  22   b  to the outside of the second compression stage  22 ; and an introduction scroll chamber  22   d  that guides the refrigerant gas X 4  compressed by the first compression stage  21  to the second impeller  22   a.    
         [0060]    Note that some parts of the second diffuser  22   b , second scroll chamber  22   c  and introduction scroll chamber  22   d  are formed by a second housing  22   e  that surrounds the second impeller  22   a.    
         [0061]    The second impeller  22   a  is fixed to the abovementioned rotating shaft  23  so as to be back to back with the first impeller  21   a , and is rotated due to the rotation of the rotating shaft  23 , which is imparted with the rotational power from the output shaft  11  of the motor  12  to rotate about the axis O. 
         [0062]    The second diffuser  22   b  is disposed annularly in the periphery of the second impeller  22   a . Additionally, in the turbo compressor  4  of the present embodiment, the second diffuser  22   b  is a vaneless diffuser with no diffuser vanes to reduce the tangential velocity of the refrigerant gas  4  in the second diffuser  22   b  and efficiently convert velocity energy to pressure energy. 
         [0063]    The second scroll chamber  22   c  is connected with the passage R 1  that is provided for supplying the compressed refrigerant gas X 1  to the condenser  1 , and supplies the compressed refrigerant gas X 1  emitted from the second compression stage  22  to the passage R 1 . 
         [0064]    It should be noted that the first scroll chamber  21   c  of the first compression stage  21  and the introduction scroll chamber  22   d  of the second compression stage  22  are connected through an external piping (not illustrated) provided independently from the first compression stage  21  and second compression stage  22 , and the refrigerant gas X 4  compressed by the first compression stage  21  is supplied to the second compression stage  22  via the external piping. The external piping is connected with the abovementioned passage R 4  (refer to  FIG. 1 ) so that a gas phase component X 3  of the refrigerant which is generated in the economizer  2  is supplied to the second compression stage  22  via the external piping. 
         [0065]    Also, the rotating shaft  23  is rotatably supported by a third bearing  24  and a fourth bearing  25 , the third bearing  24  being fixed to the second housing  22   e  of the second compression stage  22  in a space  50  between the first compression stage  21  and second compression stage  22 , and the fourth bearing  25  being fixed to the second housing  22   e  in the motor unit  10  side. 
         [0066]    A gear unit  30  is provided for transmitting the rotational power of the output shaft  11  in the motor  12  to the rotating shaft  23 , and is installed in a space  60  formed by a motor housing  13  of the motor unit  10  and the second housing  22   e  of the compressor unit  20 . 
         [0067]    The gear unit  30  is configured from a large diameter gear  31  fixed to the output shaft  11  in the motor  12  and a small diameter gear  32  fixed to the rotating shaft  23  while engaging with the large diameter gear  31 , and transmits the rotational power of the output shaft  11  in the motor  12  to the rotating shaft  23  so that the number of revolutions of the rotating shaft  23  increase with respect to the number of revolutions of the output shaft  11 . 
         [0068]    Further, the turbo compressor  4  includes a lubricating oil supply equipment  70  which supplies the lubricating oil stored in the oil tank  40  to sliding portions, such as bearings (first bearing  14 , second bearing  15 , third bearing  24 , and fourth bearing  25 ), the portions between the impellers (first impeller  21   a  and second impeller  22   a ) and housings (first housing  21   e  and second housing  22   e ), and the gear unit  30 . It should be noted that only a portion of the lubricating oil supply equipment  70  is illustrated in the drawings. 
         [0069]    In addition, the space  50  where the third bearing  24  is disposed and the space  60  where the gear unit  30  is installed are connected by a through hole  80  formed in the second housing  22   e , and the space  60  is also connected with the oil tank  40 . As a result, the lubricating oil supplied to the spaces  50  and  60  and then flown out from the sliding portions is recovered by the oil tank  40 . 
         [0070]    Next, the operation of the turbo compressor  4  according to the present embodiment configured in such a manner will be described. 
         [0071]    First, lubricating oil is supplied from the oil tank  40  to the sliding portions of the turbo compressor  4  by the lubricating oil supply equipment  70 , and then the motor  12  is driven. Then the rotational power of the output shaft  11  in the motor  12  is transmitted to the rotating shaft  23  via the gear unit  30 , thereby rotating the first impeller  21   a  and second impeller  22   a  in the compressor unit  20 . 
         [0072]    When the first impeller  21   a  is rotated, the pressure at the suction port  21   d  of the first compression stage  21  becomes negative, as a result of which the refrigerant gas X 4  from the passage R 5  flows into the compression stage  21  via the suction port  21   d.    
         [0073]    The refrigerant gas X 4  flown inside the first compression stage  21  is flown into the first impeller  21   a  from the thrust direction and then discharged to the radial direction due to the velocity energy imparted by the first impeller  21   a.    
         [0074]    The refrigerant gas X 4  discharged from the first impeller  21   a  is compressed due to the conversion of the velocity energy thereof to the pressure energy by the first diffuser  21   b . It should be noted here that in the turbo compressor  4  in the present embodiment, since the first diffuser  21   b  is a diffuser attached with the diffuser vanes  21   f , the tangential velocity of the refrigerant gas  4  rapidly reduces by hitting the diffuser vanes  21 , as a result of which the velocity energy is efficiently converted to the pressure energy. 
         [0075]    The refrigerant gas X 4  discharged from the first diffuser  21   b  is guided to the outside of the first compression stage  21  via the first scroll chamber  21   c.    
         [0076]    The refrigerant gas X 4  guided to the outside of the first compression stage  21  is supplied to the second compression stage  22  via the external piping. 
         [0077]    The refrigerant gas X 4  supplied to the second compression stage  22  is flown into the second impeller  22   a  from the thrust direction via the introduction scroll chamber  22   d  and then discharged to the radial direction due to the velocity energy imparted by the second impeller  22   a.    
         [0078]    The refrigerant gas X 4  discharged from the second impeller  22   a  is further compressed due to the conversion of the velocity energy thereof to the pressure energy by the second diffuser  22   b , resulting in the production of compressed refrigerant gas X 1 . 
         [0079]    The compressed refrigerant gas X 1  discharged from the second diffuser  22   b  is guided to the outside of the second compression stage  22  via the second scroll chamber  22   c.    
         [0080]    The compressed refrigerant gas X 1  guided to the outside of the second compression stage  22  is supplied to the condenser  1  via the passage R 1 . 
         [0081]    According to the turbo compressor  4  in the present embodiment as described above, the suction port  21   d  located in the upstream side of the first impeller  21   a  communicates with the inside of the oil tank  40  via the gaps  21   j , the intermediate space  21   h , and the pressure equalizer  90 , and thus the pressure at the suction port  21   d  and that of the inside of the oil tank  40  become equal. Therefore, when the first impeller  21   a  is rotated to make the pressure at the suction port  21   d  negative, the pressure inside the oil tank  40  also becomes negative. 
         [0082]    For this reason, the lubricating oil supplied to the spaces  50  and  60  and then flown out therefrom flows towards the oil tank  40  with a negative pressure, as a result of which the lubricating oil can be readily recovered to the oil tank  40 . 
         [0083]    On the other hand, in the oil tank  40  where the pressure is negative, the gases which have been dissolved in the lubricating oil vaporize as the pressure reduces rapidly, resulting in the generation of oil foaming. Although the oil mist filling inside the oil tank  40  flows into the intermediate space  21   h  via the pressure equalizer  90  due to the oil foaming, since the intermediate space  21   h  and the suction port  21   d  are connected only through the slight gaps  21   j  therebetween, the oil mist can be retained in the intermediate space  21   h.    
         [0084]    Therefore, the oil mist does not leak out to the suction port  21   d  to contaminate the first impeller  21   a , and thus the deterioration of compression properties due to the contamination by the oil mist in the first compression stage can be prevented. Furthermore, since the reduction of the amount of lubricating oil can be suppressed, it will be possible to continuously supply sufficient amount of lubricating oil to the sliding portions. 
         [0085]    In addition, in the present embodiment, the intermediate space  21   h  has an annular shape having the axis O as its center, and the open end  90   a  of the pressure equalizer  90  in the intermediate space  21   h  is directed towards the tangential direction of the annular intermediate space  21   h . As a result, the oil mist reaching the intermediate space  21   h  via the pressure equalizer  90  is discharged towards the tangential direction of the annular intermediate space  21   h.    
         [0086]    Accordingly, the swirling flow (as indicated by the arrows in  FIG. 3 ) in line with the annular shape can be generated inside the intermediate space  21   h . Therefore, the oil mist can be retained in the outer periphery of the intermediate space  21   h  due to the centrifugal force caused by the swirling flow, and thus it will be possible to reliably prevent the oil mist from leaking out to the suction port  21   d.    
         [0087]    Further, since the barrier plate  21   k  is provided within the intermediate space  21   h  between the gaps  21   j  and the open end  90   a  of the pressure equalizer  90 , the oil mist is blocked by this barrier plate  21   k  and does not reach the gaps  21   j , and thus the leakage of the oil mist to the suction port  21   d  can be prevented even more reliably. 
         [0088]    Moreover, the drive section  21   i  of the inlet guide vanes  21   g  is accommodated within the intermediate space  21   h , and the drive section  21   i  is driven in an atmosphere where the oil mist is present, and thus the longevity of the drive section  21   i  can be extended. 
         [0089]    Note that the lubricating oil recovered by the present configuration and retained within the intermediate space  21   h  is returned to the inside of the oil tank  40  using an unillustrated pump or an auxiliary device such as an ejector. 
         [0090]    Preferred embodiments of the turbo compressor and refrigerator according to the present invention have been described above with reference to the accompanying drawings. However, it goes without saying that the present invention is in no way limited to the abovementioned embodiments. Various shapes, combinations, and the like for the respective constituting elements described in the abovementioned embodiments are merely some examples thereof, and those skilled in the art will appreciate that various modifications, as based on the design requirements or the like, are possible without departing from the spirit and scope of the present invention. 
         [0091]    For example, although the configuration provided with two compression stages (first compression stage  21  and second compression stage  22 ) has been described in the abovementioned embodiments, the present invention is not limited to this configuration, and it is also possible to adopt a configuration having three or more compression stages. 
         [0092]    In addition, in the abovementioned embodiments, the turbo refrigerator has been described as one to be installed in buildings and factories to produce cooling water for air conditioning. 
         [0093]    However, the present invention is not limited to those installed in buildings and factories to produce cooling water for air conditioning, but can also be applied to household and commercial refrigerators or freezers, or to domestic air conditioners. 
         [0094]    Moreover, in the abovementioned first embodiment, a configuration has been described where the first impeller  21   a  provided to the first compression stage  21  and the second impeller  22   a  provided to the second compression stage  22  are disposed so as to be back to back. 
         [0095]    However, the present invention is not limited to the above configuration, and it may also be configured so that the back surface of the first impeller  21   a  provided to the first compression stage  21  and the back surface of the second impeller  22   a  provided to the second compression stage  22  are facing the same direction. 
         [0096]    Furthermore, in the abovementioned first embodiment, a turbo compressor has been described, which is provided with each of the motor unit  10 , the compressor unit  20 , and the gear unit  30 . 
         [0097]    However, the present invention is not limited to the turbo compressor with the above configuration, and it is also possible to adopt a configuration where a motor is disposed between the first compression stage and the second compression stage, for example. 
         [0098]    While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.