PLACE THE SCREW COMPRESSOR MARKET
Because these two types of compressors practically the only types that are used in industrial refrigeration, the roles of the two compressors are interrelated. From time to time in the early 1970s, when the screw compressor appeared on the market of refrigeration screw compressor has captured a major share of industrial refrigeration practice, at least in terms of cooling power. Screw compressor has established itself as a reliable machine, as a rule, capable of 50,000 hours or more transactions between overhauls.
Limiting the pressure ratio of 8 or 9, facing the piston compressor does not apply to screw type, which is capable adequately to a pressure ratio of 20 or more. And the ability to work against high pressure ratio is available, the benefits of multi-stage compression, as a rule, lead to the choice of several compressors and multi-stage compression. Even in multi-stage of the plant, however, there may be periods of light cooling load, when it is advantageous to abandon savings multi-stage compression and operate one of the screw compressor in one stage in the mode of low evaporating pressure from the pressure of condensation.
Maximum pressure sustainable use of screw compressors is about 2400 kPa (350 psi)and the compressor can run against a pressure difference of about 1700 kPa (250 psi).
The minimum practical suction pressure is about 17 kPa (2.5 psi).
A typical first-comparison of costs between the screw and reciprocating compressors, is shown in Fig. 5.34. One piston compressors, as a rule, will cost less than one screw compressor. Maximum speed pumping piston compressors 0.33 to 0.47 m3/sec (700 to 1000 ft. / min)and higher cooling load two piston compressors are required. At this moment, and in more refrigerating capacity of the screw compressor below cost.
A controversial issue-tolerance screw compressors and hydraulic shock with liquid refrigerant. An enthusiastic promoter screw compressors may argue that the screw compressor does not affect the ingress of liquid refrigerant. It may be true that the screw compressor is less sensitive to slugging compared to the reciprocating type, but the bullet liquid refrigerant evaporates, and interrupt the flow of the injected oil resulting scored rotors. One engineer recommends inspection machine, following any known specimen tubes.
The size and power range screw compressor extends from the small mini-screw machines large aggregates of engines, 1000 kW and more. Mini-screw unit is available in the refrigerating capacity as low as about 100 kW (28 tons of cooling). Due to the small diameter rotors mini-screw, as a rule, are not as effective as larger units. Mini-screw one manufacturer operating with-6.7C (20F) boiling point and 35C (95F) condensing temperature develops performance factor 3.94. When appropriate evaporating temperature condensing temperature, large compressor exhibits COP-4.10, thus, about 4% improvement in efficiency...
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Industrial 