Development Of An Automatic Charging Device For Refrigerant Mixtures

The auto—cascade refrigeration system is a kind of refrigeration system, in which refrigerant mixture is employed and only one single—stage compressor with oil lubrication is required. Since auto—cascade refrigeration system is simple, having no moving parts working at low temperature, and highly efficient in temperature range of—40℃～—160℃, it has been widely used in the fields of electronics, medicine, freeze drying and gas liquefaction.The optimization of the composition of refrigerant mixture is important for the auto—cascade refrigeration system. Appropriate composition will facilitate the matching of water equivalences of high and low pressure side and reduce the irreversible loss in heat transfer and throttling processes. Usually numerical simulation and experimental test are used to optimize the composition. Due to the lack of property data of multi-component refrigerant mixture, the results of numerical simulation are different to the performance of actual system. Therefore, experimental tests is the primary means to obtain the ideal composition. Due to the variation of system and application, and the number of adjustable variable, the debugging of the charging process is hard and time-consuming. In order to raise the efficiency of debugging of auto-cascade refrigeration system, in this paper, an automatic charging device was designed and tested on an existing auto-cascade system. The main work carried out are listed as follows:1. domestic and foreign work about refrigerant charging device and composition optimization of refrigerant mixture for auto-cascade refrigeration system were summarized.2. an automatic charging device was designed to charge refrigerants automatically and accurately for the composition optimization process, avoiding the disturbance and inaccuracy caused by the manual operation. 3. based on the automatic charging device, experiments that utilized ternary and quaternary refrigerant mixture were done to study the impacts of refrigerants with different boiling points on the system running.4. composition optimization experiment were conducted from several initial charging states for ternary refrigerant mixture R50/R23/R600a and quaternary refrigerant mixture R50/R23/R600a/R1150. It was found that similar charging quantities were achieved after optimization. Compared with the system efficiency for the case of ternary refrigerant mixture, the system efficiency for the case of quaternary refrigerant mixture was increased by 8-12%.