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
15、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 compressor port, at the top of the opposite end of the casing, is compressed within it and expelled from the high pressure discharg
16、e port at the bottom of the casing, near the centre. Ideally, there is no internal transfer of fluid within the machine between the expansion and compression sections which each take place in separate chambers.If the same machine presented in Fig. 5.25 is used as a two stage compressor, only the por
17、ts of the second stage will exchange their places. The low pressure port of the second stage will be located on the top of the machine and the high pressure discharge will be at the machine bottom. This offers a compact two stage machine which may be used either in the oil flooded or dry operation m
18、ode. A similar arrangement is valid for a two stage expander.5.5 Multifunctional Screw Machines 109Fig. 5.25. View of the multifunctional rotors acting simultaneously as compressorand expander5.5.2 Design Characteristics of Multifunctional Screw RotorsSince compression and expansion are carried out
19、separately in multifunctional rotors the compressor and expander profiles could be different. However, this would make manufacture extremely difficult, due to the small clearance space between the two rotor functions. Hence to make it possible for the proposed multifunctional rotors to be utilized,
20、the rotors must form a full sealing line on both contacting surfaces so that the same profile may be used both for the expander and the compressor sections.An example of how the rotor profile will then appear is given in Fig. 5.26.Additionally the expansion section can contain a capacity control suc
21、h as a slide or lifting valve at suction to alter the volume passing through it at part load, in a manner identical to capacity controls normally used in screw compressors.If the rotors are used for multistage compression, they can retain their profile shape common for screw compressors with a small
22、 blow hole on one side and a relatively large one on the opposite side.110 5 Examples of Modern Screw Compressor DesignsFig. 5.26. Compressor-Expander Rotors5.5.3 Balancing Forces on Compressor-Expander RotorsAn important novelty of the compressor expander arrangement on one pair of rotors is in the
23、 positioning of the ports. Because the high pressure ports of such machine are in the centre of the unit and arranged so that they are on opposite sides of the casing, the high pressure forces due to compression and expansion are opposed to each other and, more significantly, only displaced axially
24、from each other by a relatively short distance. The radial forces on the bearings are thereby significantly reduced. In addition, since both ends of the rotors are at more or less equal pressure, the axial forces virtually balance out The following example of a combined compressor and expander in th
25、e high pressure application indicates the extent of the advantages, which are possible from this arrangement.A refrigerator uses 2.75m3/min CO2 as a working fluid which leaves the evaporator and enters the compressor as dry saturated vapour at a suction pressure of 35 bar to leave the compressor and
26、 enter the condenser at a discharge pressure of 100 bar. The compressor rotor required would be 102mm in diameter with a length/diameter ratio of 1.5. The expander required to replace a throttle valve in this system would have a main rotor of the same diameter but with a length/diameter ratio of onl
27、y 1.1. Force calculations showed what bearing loads must be resisted if the refrigeration system is designed with a conventional screw compressor drive. On the main rotor alone, there is an axial force of 92 kN and radial bearing forces of 132.9 kN at the high pressure end and 45,5 kN at the suction
28、 end. A similar calculation was performed for the expander rotors and their corresponding bearing forces. Here, the axial bearing load on the main rotor is 91,9 kN while the corresponding radial loads中文译文104 5现代螺杆压缩机设计实例图 5.20。螺杆压缩机转子为轻型制冷和空调优化责任（左）和转子为重型制冷责任（右）。电机的冷却过程中，抽真空通过补气端口。隔开从必然导致在工厂的生产能力降低，
29、压缩机效率将保持不变。这样的冷却概念的压缩机如图5.23所示。5.4.5 多转子螺杆式空压机在一个螺杆式压缩机的主要的“或”门的多个转子的使用，以增加容量几乎在提出这些机器的引进。如图5.24所示。5.4设计的制冷压缩机105图5.21 。原转子压缩机制冷和优化空调责任表5.1 。压缩机性能实验比较改造和标准转子标准转子蒸发/冷凝温度 -15/30 -35/35轴转速（rpm） 2920 2920制冷容量千瓦 626 216电动机功率kW 178 156COP 3.523 1.383优化的转子蒸发/冷凝温度 -15/30 -35/35 0 / 35轴速度rpm 2920 2920 2920制冷
30、容量千瓦 669 243 1187电动机功率kW 182 168 245COP 3.671 1.486 4.98COP改进新/旧的 104.2 107.5 - 显示两个门转子 multirotor 螺杆压缩机，作为在给定Sakun，1960年。这个想法已不尚未被全面商业化。然而，几个最近一直在专利，如肖，1999年和钟，2002发表在这一领域。很明显，multirotor 压缩机的能力将多个相应的普通丝杠的能力压缩机。尽管如此，虽然它是相当自我的显而易见的它不是尚未充分感谢 multirotor 的机器的效率会比不好那数个单转子双压缩机。Multirotor 安排的另一个特点是平衡径向主要转子
31、上的部队。不幸的是，主要的转子轴向力106现代螺杆压缩机设计实例图5.22 。优化的转子压缩机和改造一般制冷税相比原转子（光线路）5.4设计的制冷压缩机107图5.23 。半封闭压缩机的电机冷却通过补气端口在电机外壳，最右边图5.24 。布局的多转子螺杆压缩机108 5现代螺杆压缩机设计实例同时成倍增加。一般来说，它是轴向配合比转子径向力，通过使用，例如，平衡活塞。因此，这功能可被视为优点。闸转子部队几乎不受这种安排。5.5多功能螺丝机阳性比其他类型的螺杆机的潜在优势位移机是他们有能力执行压缩扩展等功能，同时，只使用一对转子。进一步特点，这是利用两个接触表面上，这样的密封转子相同的配置文件，可
32、以使用扩展器和压缩机部分。这意味着可进行机械加工的压缩机和膨胀机的转子或分离地在一个单一的切割操作，然后通过机械加工在他们临别槽完成后叶形成。此外，通过机端口的位置，如图所示，在图。 5.25，压力负载可以部分的平衡，从而，机械摩擦损失将小于如果两个函数是在单独的机器上进行。5.5.1同时压缩和扩展一对转子此类机器的应用领域是节气阀的更换在制冷和空调系统，高压力应用，燃料细胞，多级压缩或膨胀，真的，任何其他应用程序同时压缩和扩张是必需的。一个例子的这样一个不寻常的，但方便的应用是压缩机容量控制被压缩的气体的部分扩大。如示5.25所示。高压气体进入级联端口在壳体的顶部上，中心附近，从低压排出在所
33、述壳体的底部，在其一端的端口。扩展过程会导致温度下降。然而，在这里是用来恢复的压力降功率和使转子转动。气体进入低压压气机口，在所述壳体的另一端的顶部，内被压缩和上面的底部从高压排出口排出壳体上，中心附近。在理想的情况下，没有内部内的流体输送机之间的膨胀和压缩部分，每次取放置在单独的腔。如果在同一台机器示于图5.25作为一个两阶段的压缩机，只有端口的第二阶段，将交换他们的地方。低压力口的第二阶段，将设在机器顶部和将在机器底部的高压放。这提供了一个紧凑的两阶段机器可被使用，也可以在油淹没或干燥运行模式。类似的安排是有效的两个阶段扩展。5.5多功能螺丝机109图5.25 。同时作用的多功能转子压缩机
34、和扩展5.5.2多功能螺杆转子设计特点由于压缩和膨胀分别进行多功能转子的压缩机和膨胀机配置文件也可能不同。然而，这制造非常困难的，由于小的间隙空间之间的两个转子的功能。因此，建议有可能使利用多功能转子，转子必须形成一个完整的密封线两个接触表面上，这样，可以使用相同的配置文件，无论是对膨胀机和压缩机部分。转子齿形如何然后会出现图中给出的一个例子。图5.26 。此外，扩展部分可以包含一个容量控制，如吸幻灯片或升降阀，通过它在改变音量部分负荷，容量相同的方式控制中通常使用的螺钉压缩机。如果转子是用于多级压缩，可以保留他们的常见的廓形在一个小的打击孔螺杆压缩机侧的相对侧上的一个比较大的一个。110 5
35、现代螺杆压缩机设计实例图5.26 。压缩膨胀转子5.5.3在压缩机，膨胀机转子上的制衡力量在一对压缩机的膨胀器的安排的一个重要的新颖性转子是在定位的端口。因为高压端口这样的机器是在单元的中心，并布置成使得它们在壳体的相对侧，高压迫使由于压缩扩张，彼此相对，并且更重要的是，只位移彼此沿轴向由一个相对短的距离。上的径向力轴承，而显着降低。此外，由于两端的转子是或多或少平等的压力，无形中平衡轴向力下面的例子在高的压缩机和膨胀压力的应用程序表示的范围内的优点，这是可能的从这样的安排。冰箱使用2.75m3/min CO2作为工作流体离开蒸发器和干饱和蒸汽进入压缩机的吸入为35巴的压力离开压缩机，并进入冷凝器的放电100巴的压力。所需要的压缩机转子。将102毫米的中直径与长度/直径比为1.5 。需要替换的膨胀在本系统中，将有相同的直径上的主转子的节气门但只有1.1的长度/直径比。力的计算表明什么如果制冷系统的设计有一个轴承负荷必须抵制传统的螺杆压缩机驱动。仅在主转子，有一个轴向力92 kN和132.9千牛的径向轴承部队在高压力结束在吸气端和45.5千牛。类似的计算进行膨胀机转子和其相应的支承力。在这里，轴向上的主转子的轴承负荷91,9 kN的，而相应的径向载荷
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