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Dynamic compressors

Dynamic compressors transfer of energy of the gas, speed and centrifugal force, and then translate into pressure energy. The most common type is a centrifugal compressor. Suction gas enters the axial direction in the eyes of the rotor, which has curved blades, and thrown on a tangent from the blade of a circle.

Energy gave the gas passing through such a machine depends on the speed and density of the gas. Since the density of the already established working conditions, design productivity of the centrifugal compressor will decide the speed of the rotor. Due to the low density gases used by the Council at a speed of 300 m/s are common. The motor speed 2900rev/min, single-stage machines require impeller 2 m in diameter. Reduced to a more manageable size, disks focus from standard high-speed motors or change frequency of supply network, to get higher engine speeds. The drive motor is an integral compressor Assembly and may be open or hermetic type. In single-stage centrifugal compressors for air-conditioning debt, rotor speed, typically about 10,000 rpm

Gas can be compressed in two or more stages.

Impellers on the same shaft, giving compact tandem arrangement with gas from one stage, passing directly to the next. Steps compression is not very large, and if the two stages gas can pass from the first to the second without any inter-cooling.

Centrifugal machines can be built for industrial use with ammonia and other refrigerants, and this can have up to seven degrees of compression. With high peripheral speeds in use, it is not practical to build a small car, and the lowest available centrifugal compressors for refrigeration debt of about 260kW. - Semi-hermetic compressors are made to 7000 kW and open the disc machines to 21 000 kW of power. No components that require lubrication, with the exception of bearings. As a result, the machine can work almost without oil.

System of this size requires a large diameter of the refrigerant pressure and suction to connect the components of the entire system. As a result, in addition to the large industrial enterprises, they almost always constructed as a liquid cooling system with water-cooled packages with the condenser and the evaporator as part of a complete factory manufacturing packaging. The main refrigerant for packaged water chillers centrifugal type R134a.

Pump characteristics of the centrifugal machine is different from the piston compressor with excessively high discharge pressure of the gas may grow around the rotor. This characteristic makes the centrifugal compressor sensitive to condensation of the state, giving higher fees and best performance factor, if the pressure drops, while punish the performance, if the head of the pressure rises. It also depends on the angle reduction capacity blades. Excessive pressure will lead to a reverse flow condition which followed a split second later, thanks to the flow as the head pressure falls. A couple of jumps with alternative direct and reverse the flow of gas, throwing additional loads on the impeller and drive motor. Such working conditions, which should be avoided as far as possible by the development of a fairly low pressure and good service condenser system. Rating curves indicate cabin or flutter.

With centrifugal machines are too big to manage the frequent stops and rebooting, some form of capacity reduction should be integrated. A General method to limit or reject the flow impeller suction gas. Most of the models can be reduced pumping capacity down to 10-15% of the full flow. The availability of cheap converters led to the use of a variable speed drive, that allows to improve the efficiency of the centrifugal compressor. However, it cannot completely replace the variable inlet guide vanes due to an early (low head surge arising from the low consumption of system head requirements (Brasz, 2007). An example of a centrifugal compressor with variable geometry shown in Fig. 4.28 . The recent entry in the field of compressors is a variable speed centrifugal compressor driven DC motor and magnetic bearings Fig. 4.29. This opens up the possibility oil free systems.

The jet compressor is a dynamic compressor on the other side of the scales. Currently the subject of scientific research and industrial implementation did not happen. Its use as a way of enhancing the absorption cycle has been successfully tested (IMZ, 2005).....

 
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