In recent years two-sage centrifugal refrigeration compressors with a built-in electric drive revolving in bearings without lubricant have been widely applied to water-cooled machines of conditioning system of low refrigeration output, lower than 100 kWt (1, 2, 3, 4). The realization of such conventional designs concerning compressors has become possible owing to the achievement in allied industries, first of all in the field of high-performance regulated electric drivers and bearings without lubricant including gas bearings). Low mass and dimensions indices, the lack of lubricant system, step-up gear and revolving seals, high vibroacoustic characteristics and high effectiveness of regulation during the operation on off-design conditions are the advantages of applying centrifugal refrigeration compressors with built-in electric drive running on gas bearings in cold producing machines in comparison with compressors of other types. The main problem of centrifugal refrigeration compressors engineering is providing of energy efficiency what determines the field of centrifugal refrigeration compressors ration exploitation. It is connected with the fact that at low capacity and because of small geometric dimensions, the negative influence of scale factor and high conventional Mach numbers on gas-dynamic characteristics of centrifugal stages has revealed in a greater extent. Moreover, friction losses (ventilation losses) of built-in electric drive have considerably increased in refrigerant medium on account of high rotor speed (40 000 - 50 000 revolution per minute, RPM) which is required. Current information about combined influence of scale factor and Mach numbers do not allow to predict with a high degree of accuracy the characteristics of centrifugal stages and it is limited by the experience of applying high-speed built-in electric drive running on gas bearings for air compressors where operating conditions essentially differ from the operating conditions of a refrigeration compressor (4). In this work the results of comprehensive calculation, theoretical and experimental researches of low consumption two-stage centrifugal refrigeration compressors with built-in electric drive running on gas bearings have been presented. This type of compressor has been designed for the operating on Refrigerant RC318 in the structure of water-cooled machine having the refrigeration output equal to 32 kWt for conditioning systems.
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