**5. Conclusions**

Four different types of working fluids were selected for low-temperature production of below −100°C, which is required in the semiconductor manufacturing process, and experiments were carried out for R290 and R600a, which are HC refrigerants that show the largest enthalpy differences per unit mass among the high boiling point refrigerants of R290, R600a, R218, and R134a. The effects of changing the composition of the high boiling point refrigerant when the total charging amount is the same in both refrigerant groups was analyzed, and the results show that there is an advantage: as the mass ratio of the high boiling point refrigerant increases, the time for reaching the target temperature decreases, and the average pressure in the device is low. However, as the mass ratio of the high boiling point refrigerant decreases, the cooling capacity increases. The MR shows that the time for reaching the target temperature is short, and the cooling capacity is high when R290 is used as the high boiling point refrigerant among R290 and R600a.
