CO2 solid–gas two-phase flow is investigated in an ultra-low temperature cascade refrigeration system. Visualization test shows that dry ice sedimentation occurs in low mass flow rate. The sedimentation also occurs at low condensation temperature and low heating power input. On the basis of the present investigation, it is found that the present ultra-low temperature cascade refrigeration system works better at a heating power input above 900 W and condensation temperature above ?20°C. Under suitable operating conditions, the present ultra-low temperature cascade refrigeration system has shown the capability of achieving an ultra-low temperature of ?62°C continuously and stably.
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