First, the characteristics of centrifugal refrigeration compressor. Centrifugal refrigeration compressor as a speed compressor, has the following advantages: 1. In the case of the same amount of cooling, especially in large capacity, compared with the screw compressor group, The huge oil separator is omitted, the weight and size of the unit are small, and the floor space is small. 2. The centrifugal compressor has simple and compact structure, less moving parts, reliable work, durability and low operating cost. Stage compression and a variety of evaporation temperatures, easy to achieve intermediate cooling, resulting in lower power consumption; 4. There is very little lubricating oil mixed in the centrifugal unit, which has less effect on the heat transfer effect of the heat exchanger, and the unit has higher efficiency. Has the following disadvantages: 1. The rotor speed is high, in order to ensure a certain width of the impeller, it must be used for large and medium flow occasions, not suitable for small flow occasions; 2. Single stage pressure ratio is low, in order to obtain higher pressure ratio, multiple stages are required. Impeller, generally use speed increasing gear; 3. Surge is the inherent shortcoming of centrifugal compressor, the unit must be added anti-surge system; 4. The same unit operating conditions can not have large changes, the scope of application is narrow. Second, centrifugal refrigeration compression Application status and trends. At present, most of the domestic centrifugal chillers are mainly occupied by some refrigeration companies in Europe, Japan and the United States. More famous companies such as Trane, Carrier, York, McQuay, AXIMA (formerly Sulzer) , Liaoyuan, Mitsubishi, etc. rely on advanced technology and good technology to dominate the centrifugal chiller market. Domestic enterprises are mainly Chongqing GM, the early introduction of NREC technology to develop centrifugal chillers. With the development of society, users need more cooling capacity The higher the price, the higher the market for centrifugal units due to the demand for energy saving. Some domestic air conditioner manufacturers such as Haier, Aikema, Gree and Midea (merger with Chongqing GM) have launched their own centrifugal chillers. Cooperated with AXIMA to develop centrifugal heat pump units for centrifugal chillers and district heating. Most of these centrifugal units use environmentally friendly working medium R134a. With the increasing intensity of energy, energy saving is a major trend in product development. The level of development continues to increase, and building energy consumption continues to increase. Centrifugal chillers with zui high performance coefficients will undoubtedly become In recent years, the sales volume of centrifugal chillers has been increasing. Most domestic companies that develop centrifugal chillers only buy imported compressors, which basically have no profit. Foreign centrifuge manufacturers will not easily sell their core technologies. Centrifugal refrigeration compressors only take the road of independent development. With the continuous maturity of design and manufacturing technology, the development of domestic centrifugal refrigeration compressors has become possible. Third, the difficulties, key points and countermeasures for the development of centrifugal compressors. The development of a centrifugal compressor includes many aspects: pneumatic thermal calculation, strength and vibration calculation, structural design, selection of various materials, processing and manufacturing process design, automatic control and adjustment design, and drive type selection. The main points are as follows: 1. The design of the impeller is the moving part of the centrifugal compressor. The core part is the impeller. At present, all the centrifuges at home and abroad use the ternary flow method to design the impeller. The ternary flow method Require designers to have numerical simulations, computational fluid dynamics, and fluid mechanical interiors Flow field theory and other very professional knowledge. Most of the domestic company technicians do not have this professional knowledge, and must design efficient three-dimensional impellers. Only cooperate with university research institutions. Experts in centrifugal compressors in universities mainly have Shanghai Jiaotong University. Professor Gu Chuangang and Professor Wang Shangjin of Xi'an Jiaotong University. Professor Gu has been engaged in the research of centrifuges for a long time. He has presided over 6 National Natural Science Foundation projects, designed in centrifuge ternary flow, compressor group test, monitoring and control, system anti-surge. He has in-depth research in other aspects. The project “Aerodynamic Design Technology and Application of Multi-stage Centrifugal Compressorâ€, which he presided over, won the second prize of National Science and Technology Progress Award in 2004. Xi’an Jiaotong University’s Saier Pump Research Group led by Professor Wang The characteristic design theory of controllable vortex impeller has excellent application in unit reform in petrochemical and other fields. 2. Impeller processing The impeller blade shape designed by ternary flow theory is generally space curved surface, blade and impeller. Machining and forming is the key point of manufacturing, and it is also difficult. For the three-element impeller, there are two main processing methods: 1) Three-body welding Form: that is to say, the wheel, the blade and the wheel cover are separately processed. This processing method requires relatively simple equipment. The wheel and the wheel cover only need the shape of the car. The blade processing is troublesome. First, the three coordinates are used. The machine tool mills out the blade mold, then heats the lower material blade to obtain the desired blade shape. After welding the blade to the wheel, the wheel cover is welded. Coordinate milling machines, heat treatment furnaces, hydraulic presses and other conventional equipment required, the investment required is relatively low, it is more suitable to start. 2) Overall milling: that is, the wheel and the blade are integrated together using multi-coordinate equipment for overall milling In order to avoid interference, the international processing of such impellers is mostly carried out by using a five-axis machining center. A five-coordinate device is probably from several million to tens of millions, and the cost is very high. Taking the 600mm impeller as an example, the domestic five-axis bed is about 3.5 million yuan, and the imported five-axis bed is about 4.8 million yuan. The ternary leaf is realized by the tilt of the four-axis machine tool rotating table. The four-coordinate overall milling, if the blade consistency is relatively large, the interference problem is inevitable in the four coordinates. The four-coordinate device is relatively cheap, about 1 million RMB. 3. The critical speed of the rotor is calculated. An important factor to consider when rotating the speed, the rotor speed should avoid the critical speed. The calculation of the critical speed is generally based on the Proll method. There is software for calculating the critical speed on the market, and you can also develop the calculation software yourself. 4. Anti-surge The design of the system is known from the working mechanism of the centrifugal compressor. Surge is the inherent property of the centrifuge and cannot be eliminated, but it can be avoided by effective means. The cause of surge in the centrifugal refrigeration compressor: low flow and condensation The pressure is too high. The surge is quite harmful to the unit. The anti-surge system must be carefully designed. 5. The design of the sliding bearing The centrifugal refrigeration compressor generally adopts the speed increasing gear. The rotor speed is generally above 5000RPM, and the sliding bearing is used. The design of the sliding bearing is also a key point in the development of the centrifuge. IV. The general steps of developing a centrifugal compressor: 1. Collecting and learning Relevant standards for compressors and centrifugal chillers. 2. Organize relevant personnel to learn the basic knowledge of centrifugal compressors and achieve the level of compressor design by one-way flow theory. 3. Organize relevant personnel to relevant research institutes and professional production. Manufacturers learn to visit. 4. Cooperate with scientific research institutes to design the three-element impeller. 5. Develop and develop the whole machine. 6. Prototype test improvement. V. A little thought In the 1950s, Chinese scientist Wu Zhonghua proposed the impeller mechanical ternary flow. Theory has laid the theoretical foundation for the design of ternary flow. Some large foreign companies such as NRC have developed the design and processing software of centrifugal impeller machinery according to this theory. Scientists and scientists in China have also carried out a lot of fruitful research. The design and processing of centrifugal compressors have been deeply studied, and a series of research results have been formed. Compared with foreign countries, it is not inferior. It is recommended that domestic refrigeration enterprises hold high the banner of national industry and develop a true meaning. Localized centrifugal refrigeration compressors. 5. Design of sliding bearings Centrifugal refrigeration compressors generally use speed-increasing gears. The sub-rotation speed is generally above 5000RPM, all of which use sliding bearings. The design of the sliding bearing is also a key point in the development of the centrifuge. IV. The general steps of developing a centrifugal compressor: 1. Collecting and learning centrifugal compressors and centrifugal cold water Relevant standards of the unit. 2. Organize the relevant personnel to learn the basic knowledge of the centrifugal compressor, and reach the level of designing the compressor with the one-way flow theory. 3. Organize the relevant personnel to study and visit the relevant research institutes and professional manufacturers. The research institute cooperated with the design of the ternary impeller. 5. Developed the whole machine. 6. The prototype test improved. V. A little thought In the 1950s, Chinese scientist Wu Zhonghua proposed the theory of ternary flow of impeller machinery and laid the ternary flow. The theoretical basis of the design. Some large foreign companies such as NREC developed the design and processing software of centrifugal impeller machinery according to this theory. Chinese scientists and scientists have also carried out a lot of fruitful research on the design of centrifugal compressors. And processing has carried out in-depth research, and formed a series of research results, compared with foreign countries, no less. Yee domestic refrigeration enterprises hold high the banner of national industry, developed the localization of centrifugal refrigeration compressor boutique in the true sense Source: mechanical total net
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