Analysis of performance factors of screw chiller assembly accessories

Analysis of performance factors of screw chiller assembly accessories

Screw chillers are widely used in industrial refrigeration in various industries such as plastics, electroplating, pharmaceuticals, chemicals, non-woven fabrics, shoemaking, and lasers. The performance of several major accessories that make up the screw chiller: compressor, evaporator, condenser, and throttling device directly affects the performance of the whole machine. To significantly improve the level of the screw chiller, not only must the performance of each component be improved , It is necessary to optimize their combination.

The compressor is the core of the chiller. The performance provided by the compressor directly affects the performance of the entire chiller, and the performance index of the compressor directly determines and limits the performance of the chiller. The evaporator and condenser inside the industrial chiller will directly affect the performance of the compressor, such as changes in the evaporating temperature, condensing temperature, superheat and subcooling.　

　 　　Screw type water chiller adopts shell and tube evaporator and condenser, which affect the performance of evaporator and condenser. There are roughly the following factors: 　

　 　　1. Homogenizer and inner end cap profile: The reasonable structure of the homogenizer can maximize the uniform distribution of the refrigerant at the inlet of the evaporator among the heat exchange tubes and alleviate the phenomenon of gas-liquid separation. The inner end cap profile converted in different processes should be as smooth as possible to reduce resistance, avoid gas-liquid separation, and make the refrigerant evenly distributed among the heat exchange tubes in the next process.

　　2. Heat exchange tubes: Whether the number of heat exchange tubes in different processes is reasonably allocated or not, the structure and length of the heat exchange tubes have a greater impact on their performance. The distribution ratio of the number of heat exchange tubes between different processes can be optimized to obtain a ratio with better heat exchange effect. You can also choose a corrugated inner fin tube with higher performance, which not only enhances the heat transfer on the fluorine side, but also on the water side.

3. Water running between the baffle and the shell: Although the heat transfer coefficient on the water side is larger than the heat transfer on the fluorine side, if the water running between the baffle and the shell occurs, it will seriously affect the water Heat transfer on the side. In order to reduce the adverse effects of water stringing, in addition to taking measures on the baffle structure, the water velocity on the shell side can also be optimized to obtain a more reasonable water velocity, such as 1.2 to 2.0 m/s.

　 　　4. The mass flow rate in the tube: From the relationship between the evaporation and heat exchange in the tube, it can be found that the evaporation in the tube is obviously affected by the mass flow rate of the refrigerant in the tube; and along the length of the evaporative heat exchange tube, the mass flow rate of the refrigerant gradually decreases. As a result, the refrigerant evaporation heat release coefficient gradually decreases along the length of the heat exchange tube, and the heat release coefficient of the latter process is much lower than that of the previous process. Therefore, calculation and optimization are carried out for different ranges of refrigerant flow to obtain the evaporation Reasonable range of refrigerant flow with higher heat transfer coefficient.　

5. Subcooler: The use of a subcooler in the condenser can effectively increase the subcooling degree of the refrigerant, and the subcooling degree can be as high as 7-8℃, which can effectively reduce the liquid supply temperature of the evaporator, thereby improving the cooling of the chiller the amount.