Speaker
Description
Mixed-refrigerant Joule-Thomson refrigeration (MJTR) is the primary cooling method for the temperature range from 80 to 230 K. It can be used in cryosurgery, high temperature superconductivity and sensor cooling. However, most of the studies are on nitrogen-hydrocarbon refrigerants, which are not allowed in applications where there is a special need for flammability. Therefore, non-flammable mixed refrigerants were investigated in this study.
The composition of the mixed refrigerant is a key factor in the system performance (refrigeration temperature, refrigeration capacity, etc). However, the purely mathematical optimization method lacks physical knowledge in optimization process, and may have disadvantages of time-consuming. In this study, the isothermal throttling effect of mixed refrigerants is optimized, and the optimization process is based on the partial molar enthalpy difference of each component. The method is based on thermodynamic properties and is time-saving.
Non-flammable mixed refrigerants with refrigeration temperatures from 100 K to 140 K were designed in this study. The results show that the designed mixed refrigerant has a higher COP compared to the reference. Argon has an advantage at refrigeration temperatures from 120 K to 140 K, while nitrogen has an advantage from 100 K to 120 K. In addition, systems with pre-cooling stage were studied and the results showed that the highest exergy efficiency is achieved at a pre-cooling temperature of 250 K. The exergy efficiencies with pre-cooling stage are nearly twice as high as that without pre-cooling. Therefore, a pre-cooling stage for nonflammable mixed refrigerants is necessary where there is no requirement for system size.
Acknowledgement: This work is financially supported by the Key Project of National Natural Science Foundation of China under the contract number of 52036010 and Youth Innovation Promotion Association CAS (2021028).
