With the need for deep emission reduction in the industrial field, the refrigeration and refrigeration industry chain also needs to transform to low carbon. The production process and technological innovation of refrigeration compressors for refrigeration and refrigeration must move towards the direction of green environmental protection, and continue to carry out technological innovation to achieve both low cost. With the characteristics of high energy efficiency, it enhances market competitiveness and meets the high requirements of the market for product quality.
1. Research status of scroll compressors for refrigeration and refrigeration
Scroll compressors have the characteristics of precise structure, small size, high reliability and stable operation, and their products and markets are mainly air conditioners.
According to whether it supports operation with economizer, scroll compressors can be divided into two types: liquid injection type and air supply type. The air supply type is generally slightly larger than the liquid injection type, and the operation efficiency is also higher.
With its excellent performance, the share of scroll compressors in the field of refrigeration and refrigeration has gradually increased in recent years, and most of them are used in cold storage and retail industries. In the field of refrigeration and refrigeration, due to the need to add components such as economizers to achieve lower temperatures and high manufacturing costs, the main direction of scroll compressors in the field of refrigeration and refrigeration is the medium and high temperature market, and the market share is relatively low. few.
One of the key factors affecting the scroll compressor is the leakage loss inside the compressor, which mainly includes radial leakage and tangential leakage. There are few studies on the leakage of scroll compressors for refrigeration and refrigeration in the existing literature. Compared with the scroll compressor for air conditioning, the pressure ratio of the scroll compressor for refrigeration is larger, which leads to larger leakage loss inside the compressor, so more in-depth theoretical and experimental research is required.
At present, common leakage models include nozzle model, Fanno model and two-phase flow leakage model. These models can be applied to scroll compressors for refrigeration and refrigeration, and can also provide reference for leakage research in refrigeration and refrigeration scroll compressors. .
The air supply technology can be applied to the scroll compressors for refrigeration and refrigeration, and the air supply volume, air supply pressure and the setting of the air supply ports have a great influence on the performance of the compressor; the liquid injection technology can also be applied to the scroll compressors for refrigeration and refrigeration. The amount of liquid injection and the setting of the liquid injection port also have a great influence on the performance of the compressor. The air supply technology and liquid injection technology of the scroll compressor for refrigeration and refrigeration still need more in-depth theoretical research. On the other hand, the dynamic characteristics of various components in the scroll compressor directly affect the thermal performance, reliability and life of the compressor. The existing research results can better describe the dynamic characteristics of the dry-type and oil-lubricated scroll compressors. . In addition, the dynamic characteristics of the individual bearings in the scroll compressor will also affect the shaft power of the compressor.
Compared with the air-conditioning condition, the condensing pressure and the evaporating pressure are quite different in the freezing and refrigerating condition. The higher pressure ratio causes the wear between the moving parts in the compressor to increase, which in turn affects the reliability of the compressor. There are certain restrictions on the scope of application. The development of a new line is a direct means to solve the low operating efficiency of scroll compressors in refrigeration and refrigeration conditions. In terms of profile optimization, it is necessary to make full use of multi-disciplinary methods such as structural mechanics and aerodynamics to improve the friction and leakage characteristics of the compressor and improve the thermal performance of the compressor. At the same time, it is necessary to take into account the processing and manufacturing costs.
As a competitor of screw compressors, multi-unit units of scroll compressors for refrigeration and refrigeration need to simplify control, reduce failure rates, and develop in the direction of large cooling capacity, striving to launch stand-alone competing products. The method of combining big data and artificial intelligence can train a customized model for each compressor, so as to achieve the optimal control of the system when multiple machines are connected in parallel. In addition, the selection of working fluid of the scroll compressor for refrigeration has an important influence on the performance of the compressor.
2. Research status of rotor compressors for refrigeration and refrigeration
The rotor compressor has simple structure, few parts, small vibration and stable operation. It is the main model used in air conditioners.
Figure 2 shows a schematic diagram of a fully enclosed airless valve swing rotor compressor, which mainly includes a motor, a compressor and an oil pool. In recent years, the development speed of the real estate industry has slowed down, the household air-conditioning industry is saturated, and the rolling rotor compressor has opened up markets in the fields of refrigeration and refrigeration. The formulation of QB/T 5203-2017 "liquid-injection rotary compressors for refrigeration and refrigeration" has further accelerated the speed of rotary compressors in seizing the market, and even replaced some fully enclosed piston compressors and scroll compressors.
The power of the rotary compressor can currently reach a maximum of 8.8 kW. Due to the power limit, it is difficult for the rotary compressor to match the large-scale refrigeration system. At present, the main application occasions are display cabinets and small cold storages. In order to match the high pressure ratio brought by the lower evaporating temperature and solve the cooling capacity attenuation caused by the high pressure ratio, the rotary compressor is gradually developing towards two-cylinder two-stage compression, and even some companies are developing three-cylinder rotary compressors.
Through the multi-cylinder design technology, the application scope of the rotary compressor can be further expanded, thereby seizing the market share. In addition, similar to household air conditioner compressors, with the continuous investment of manufacturers in research and development, the cost of rotary compressors for refrigeration and refrigeration will be significantly reduced. The cost advantage will make the rotary compressor more competitive in the field of light commercial refrigeration.
The technical development trend of rotary compressors generally depends on the development needs of the application in which they are located.
In the field of vapor-compression refrigeration systems, rotor compressors are usually updated with new technologies in order to adapt to new operating conditions or the application of new refrigerants, or to achieve higher energy efficiency, lower noise and lower costs. The field of refrigeration and refrigeration is the direction that rotary compressors are entering. At present, there is a lack of in-depth theoretical research. The technology of rotary compressors for household air conditioners is relatively mature, and related technologies can be used as a reference.
The thermal performance and dynamic characteristics of the rotary compressor are the key factors affecting the efficiency of the compressor, and scholars at home and abroad have studied the two in detail.
(1) Thermal performance
The leakage characteristics are mainly considered. There are many models for calculating the leakage in the compressor, including the one-dimensional isentropic nozzle model, the Fanno model and the two-phase flow model. Considering that the rotor compressor for refrigeration and refrigeration generally needs to use lubricating oil for cooling, The two-phase flow model can more accurately describe the flow process in the compressor gap. In terms of dynamic characteristics, the motion, force and friction characteristics of rotor, eccentric shaft and vane are mainly considered. Considering that each clearance of the compressor is filled with lubricating oil, the fluid lubrication model between large plates, the boundary lubrication model and the bearing lubrication theory can be selected for the analysis and calculation of the friction characteristics between different moving parts.
(2) Vibration and noise
The noise generated by the rotary compressor mainly includes mechanical noise and hydrodynamic noise. Mechanical noise is mainly produced by solid vibration, including collision, friction and vibration between moving parts. The hydrodynamic noise is mainly generated by the fluid vibration in the compressor, mainly including the hydrodynamic noise generated by the suction and exhaust of the compressor, and the hydrodynamic noise induced by the pulsation of the high-pressure gas flow on the exhaust side is more significant. Manufacturers generally use a muffler on the exhaust valve to eliminate this part of the noise, and the related technology of the muffler is relatively mature. However, how to reduce or even eliminate part of the fluid noise at the root has become a major development trend in the field of vibration and noise reduction.
(3) Refrigeration medium
Compared with R134a and R600a, R22 and R404A can make compressors with smaller displacement have higher cooling capacity. However, for R22, the compressor discharge temperature is higher, even exceeding 150 °C; for R404A, the compressor discharge temperature also exceeds 120 °C, the higher discharge temperature will affect the performance of the compressor, and may even Causes lubricating oil to carbonize.
In order to solve this problem, relevant manufacturing companies consider using the intermediate liquid injection technology to reduce the temperature of the refrigerant in the compression chamber of the compressor by using the liquid refrigerant after a throttling. However, it is still necessary to further study the liquid injection pressure, the setting of the liquid injection port and the liquid injection amount. How to avoid the liquid hammer phenomenon in the compressor is also the key point to be considered in the liquid injection technology. important direction for the development of the field.