캐스케이드 MR J-T 사이클의 혼합냉매 조성 변화에 따른 성능특성

Abstract

Recently, with the activation of the domestic semiconductor market, the demand for cryogenic chillers is also increasing. The target temperature of the cryogenic chiller is to supply low temperature fluid of -100 ℃, which is used in the etching and deposition process of semiconductors. This process is very sensitive to heat as a chemical process, and is cooled by the cryogenic chiller. Typical cycles for low temperature fluid production at –100 ° C include auto cascade cycles, plural refrigeration systems, and Joule-Thomson cycles using mixed refrigerants. The performance characteristics of the flammable and non-combustible mixed refrigerants were analyzed using the original MR JT cycle. The purpose of this study is to provide experimental results as basic design data of cryogenic freezer using mixed refrigerant. First, when the mass ratio of the high boiling point refrigerant R290 increases, it affects the suction temperature and the discharge side temperature of the compressor. When the composition ratio increases, the compressor suction temperature drops to -48.2 ~ -67.8 ℃, and the compressor discharge temperature is 118.6 ~ It was confirmed that the drop to 106.2 ℃. As for the cooling capacity, the cooling capacity increases from 1.69kW to 2.36kW when the composition ratio of the high boiling point refrigerant R290 is increased. However, as the high boiling point refrigerant increases, the mass ratio of the low boiling point refrigerant increases, which increases the operating pressure of the apparatus. When the high boiling point refrigerant is changed to R600a, the compressor discharge temperature drops with increasing composition ratio. The cooling capacity is similar to that of the mixed refrigerant with R290, but the brine supply temperature reaches the target temperature about 10 minutes later on average. This is considered to be a phenomenon in which the high boiling point refrigerants R600a and the middle boiling point refrigerants R116 and R23 do not overlap with each other in a temperature zone having a large enthalpy difference. In order to reduce the cooling time of the mixed refrigerant using R600a, it is necessary to apply the boiling point refrigerant between the high boiling point refrigerant and the middle boiling point refrigerant. R134a was selected as an alternative refrigerant for the combustible mixed refrigerant and the experiment was conducted. However, immediately after the evaporator inlet temperature reaches -106 ° C, the high pressure rises, the low pressure of the device falls below the vacuum pressure, and the device stops. This seems to occur when R134a freezes in the mixed refrigerant at the evaporation temperature below -103.3 ℃. As the above phenomenon, the performance experiment was performed according to the composition change using the high boiling point refrigerant R218. The ratio of R218, a high boiling point refrigerant, increases at the same mass charge rate, and the compressor discharge temperature can drop from 118 ° C to 98.2 ° C. However, when the mass of R218 is more than 40% in MR19, liquid compression occurs, resulting in unstable operation. In addition, the evaporation temperature of the device seems to be determined by the opening of the expansion valve regardless of the composition change of the high boiling point refrigerant. In the case of cooling capacity, the maximum cooling capacity in the composition ratio used is 1.82kW, compared to the maximum cooling capacity of the flammable mixed refrigerant. About 77.1% of performance can be obtained. As a result, the cooling capacity of the mixed refrigerant chiller at -100 ° C is higher when using the hydrocarbon-based refrigerants R600a and R290, and R218 is present as an alternative refrigerant. In order to reduce the cooling time, it is necessary to create a refrigerant composition in which a section having a large enthalpy difference according to the operating pressure overlaps in the operating temperature range. The experimental data is also used as the basic design data to select the working fluid for Cascade MR J-T refrigeration.