Experimental study on the characteristics of R1150/R600 mixed refrigerant Joule-Thomson low-temperature freezer

In this paper, a low-temperature freezer based on Joule-Thomson system with a variable frequency fan was developed by using the natural binary mixture of R1150/R600. The experiment results demonstrated the feasibility of using this mixture to obtain the low freezing temperature below −70 °C. It could be found that when the concentration of R1150 was 27.5 %, it had the lowest daily energy consumption of 5.94 kWh/24 h. Furthermore, the influences of different fan speeds and active fan speed control on the cool-down characteristics of the system were also studied. The results indicated that lower fan speed in the early stage could effectively improve the cool-down performance. It was 51 min faster than that of the fixed operating fan speed under the optimal fan speed control at the target freezing temperature. Finally, the noise test of the freezer was carried out, and the influences of on–off temperature and fan speed on the system noise were also analyzed. The noise level of the system is between 46.71 dB and 51.62 dB, which is acceptable for the users. Moreover, the influence of fan speed on system noise was greater than that of different on–off temperatures. Therefore, improving the heat exchange efficiency of the condenser to reduce the fan speed is the possible direction of noise reduction for low-temperature freezers in the future.