Centrifugal compressor and refrigeration apparatus

Abstract

A casing of a centrifugal compressor has a first wall facing a back surface of an impeller. A back gap is formed between the back surface of the impeller and the first wall. A specific speed of the impeller is set to be less than 0.1. A ratio of an axial width s of the back gap to an impeller radius r satisfies a relationship of 0.008≤s/r≤0.5, where the axial width s is a width of the back gap in an axial direction of the shaft, and the impeller radius r is a radius of the impeller.

1 . A centrifugal compressor comprising:
 a casing;   an impeller housed in the casing; and   a shaft coupled to the impeller,   the casing having a wall facing a back surface of the impeller,   the shaft being inserted into an insertion hole formed in the wall,   a back gap being formed between the back surface of the impeller and the wall, wherein   a specific speed of the impeller is set to be less than 0.1, and   a ratio of an axial width s of the back gap to an impeller radius r satisfies a relationship of 0.008≤s/r≤0.5, where the axial width s is a width of the back gap in an axial direction of the shaft, and the impeller radius r is a radius of the impeller.   
     
     
         2 . The centrifugal compressor of  claim 1 , wherein
 the back gap includes a first gap corresponding to an inner peripheral side of the back surface of the impeller, the first gap forming a seal that seals between the back surface ( 91 ) of the impeller and the wall, and   the back gap includes a second gap corresponding to an outer peripheral side of the back surface of the impeller, and the axial width s of the second gap is greater than the axial width s of the first gap and satisfies the relationship of the ratio (s/r) to the impeller radius r.   
     
     
         3 . The centrifugal compressor of  claim 2 , wherein
 the first gap extends in a direction perpendicular to an axis (X) of the shaft so as to be flat.   
     
     
         4 . The centrifugal compressor of  claim 1 , further comprising:
 a radial bearing supporting the shaft at an outer periphery of the shaft, wherein   the radial bearing is a foil bearing or a magnetic bearing.   
     
     
         5 . The centrifugal compressor of  claim 1 , wherein
 a maximum number of rotations of the shaft is 30000 rpm or more.   
     
     
         6 . The centrifugal compressor of  claim 1 , wherein
 the impeller pumps a refrigerant, and   the refrigerant is an HFC refrigerant, an HFO refrigerant, a natural refrigerant, or a refrigerant mixture thereof.   
     
     
         7 . A refrigeration apparatus comprising: a refrigerant circuit configured to perform a refrigeration cycle,
 the refrigerant circuit including the centrifugal compressor of  claim 1 .   
     
     
         8 . The centrifugal compressor of  claim 2 , further comprising:
 a radial bearing supporting the shaft at an outer periphery of the shaft, wherein   the radial bearing is a foil bearing or a magnetic bearing.   
     
     
         9 . The centrifugal compressor of  claim 3 , further comprising:
 a radial bearing supporting the shaft at an outer periphery of the shaft, wherein   the radial bearing is a foil bearing or a magnetic bearing.   
     
     
         10 . The centrifugal compressor of  claim 2 , wherein
 a maximum number of rotations of the shaft is 30000 rpm or more.   
     
     
         11 . The centrifugal compressor of  claim 3 , wherein
 a maximum number of rotations of the shaft is 30000 rpm or more.   
     
     
         12 . The centrifugal compressor of  claim 4 , wherein
 a maximum number of rotations of the shaft is 30000 rpm or more.   
     
     
         13 . The centrifugal compressor of  claim 8 , wherein
 a maximum number of rotations of the shaft is 30000 rpm or more.   
     
     
         14 . The centrifugal compressor of  claim 9 , wherein
 a maximum number of rotations of the shaft is 30000 rpm or more.   
     
     
         15 . The centrifugal compressor of  claim 2 , wherein
 the impeller pumps a refrigerant, and   the refrigerant is an HFC refrigerant, an HFO refrigerant, a natural refrigerant, or a refrigerant mixture thereof.   
     
     
         16 . The centrifugal compressor of  claim 3 , wherein
 the impeller pumps a refrigerant, and   the refrigerant is an HFC refrigerant, an HFO refrigerant, a natural refrigerant, or a refrigerant mixture thereof.   
     
     
         17 . The centrifugal compressor of  claim 4 , wherein
 the impeller pumps a refrigerant, and   the refrigerant is an HFC refrigerant, an HFO refrigerant, a natural refrigerant, or a refrigerant mixture thereof.   
     
     
         18 . The centrifugal compressor of  claim 5 , wherein
 the impeller pumps a refrigerant, and   the refrigerant is an HFC refrigerant, an HFO refrigerant, a natural refrigerant, or a refrigerant mixture thereof.   
     
     
         19 . The centrifugal compressor of  claim 8 , wherein
 the impeller pumps a refrigerant, and   the refrigerant is an HFC refrigerant, an HFO refrigerant, a natural refrigerant, or a refrigerant mixture thereof.   
     
     
         20 . The centrifugal compressor of  claim 9 , wherein
 the impeller pumps a refrigerant, and   the refrigerant is an HFC refrigerant, an HFO refrigerant, a natural refrigerant, or a refrigerant mixture thereof.