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1、英文原文104 5 Examples of Modern Screw Compressor DesignsFig. 5.20. Screw compressor rotors optimized for air conditioning and light refrigerationduty, left and rotors designed for heavy refrigeration duty, rightthe motor cooling process is evacuated through the superfeed port. Apart from the inevitable
2、 resulting decrease in the plant capacity, the compressor efficiency will be unchanged. A compressor with such a cooling concept is shown in Fig. 5.23.5.4.5 Multirotor Screw CompressorsThe use of multiple main or gate rotors in one screw compressor to increase capacity was proposed almost at the int
3、roduction of these machines. In Fig. 5.245.4 Design of Refrigeration Compressors 105Fig. 5.21. Original rotors and compressor optimized for general refrigeration andair conditioning dutyTable 5.1. Experimental Comparison of Compressor Performance with Retrofit andStandard RotorsStandard Rotors Evapo
4、ration/Condensation Temp 15/30 35/35 Shaft Speed rpm 2920 2920 Refrig Capacity kW 626 216 Motor Power kW 178 156 COP 3.523 1.383 Optimized Rotors Evaporation/Condensation Temp 15/30 35/35 0/35 Shaft Speed rpm 2920 2920 2920 Refrig Capacity kW 669 243 1187 Motor Power kW 182 168 245 COP 3.671 1.486 4
5、.98 COP Improvement New/Old 104.2% 107.5% -a multirotor screw compressor with two gate rotors is shown, as given in Sakun, 1960. The idea has not yet been fully commercialised. However, several patents, such as those of Shaw, 1999 and Zhong, 2002 have been recently published in that area. It is obvi
6、ous that the capacity of multirotor compressor will be a multiple the capacity of the corresponding ordinary screw compressor Nonetheless, although it is fairly self evident, it is not yet fully appreciated that the efficiency of a multirotor machine will be no better than that of a number of single
7、 rotor pair compressors.Another feature of the multirotor arrangement is the balancing of radial forces on the main rotor. Unfortunately the axial forces on the main rotor106 5 Examples of Modern Screw Compressor DesignsFig. 5.22. Compressor and retrofit rotors optimized for general refrigeration du
8、tycompared with the original rotors (light line)5.4 Design of Refrigeration Compressors 107Fig. 5.23. Semihermetic compressor with motor cooling through superfeed port atthe motor housing, far rightFig. 5.24. Layout of the multirotor screw compressor108 5 Examples of Modern Screw Compressor Designsa
9、re simultaneously multiplied. Generally, it is easier to cope with axial than with radial rotor forces by using, for example balancing pistons. Hence this feature can be regarded as an advantage. The gate rotor forces are virtuallyunaffected by this arrangement.5.5 Multifunctional Screw MachinesOne
10、of the potential advantages of screw machines over other types of positivedisplacement machine is their ability to perform both the compression andexpansion functions simultaneously, using only one pair of rotors. A furtherfeature of this is the use of the rotors which seal on both contacting surfac
11、es sothat the same profile may be used both for the expander and the compressor sections. This means the compressor and expander rotors can be machined or ground in a single cutting operation and then separated by machining a parting slot in them on completion of the lobe formation. Moreover, by loc
12、ation of the machine ports, as shown, in Fig. 5.25, the pressure loads can be partially balanced and thereby, mechanical friction losses will be less than if the two functions are performed in separate machines.5.5.1 Simultaneous Compression and Expansionon One Pair of RotorsFields of application of
13、 such machines are replacement of the throttle valve in refrigeration and air conditioning plants, high pressure applications, fuel cells, multistage compression or expansion and, really, any other application where simultaneous compression and expansion are required. One example of such an unusual,
14、 but convenient application is compressor capacity control by partial expansion of the compressed gas.As is shown in Fig. 5.25 high pressure gas enters the expander port at the top of the casing, near the centre, and is expelled from the low pressure port at the bottom of the casing at one end. The expansion process causes the temperature to drop. However, here the fall in pressure is used to recover power and causes the rotors to turn. Gas enters the low pressure compresso
