Visualization and Measurement of Swirling Flow of Dry Ice Particles in Cyclone Separator-Sublimator

Abstract

The dry ice sublimation process of carbon dioxide (CO2) is a unique, environmentally friendly technology that can achieve a temperature of −56 °C or lower, which is a triple point of CO2 in CO2 refrigeration systems. In this study, a cyclone separator-evaporator was proposed to separate dry ice particles in an evaporator. As an initial step before introducing the cyclone separator-evaporator into an actual refrigeration system, a prototype cyclone separator-evaporator was constructed to visualize dry ice particles in a separation chamber. A high-speed camera was used to visualize the non-uniform flow of dry ice particles that repeatedly coalescence and collision in a swirl section. Consequently, the dry ice particle size and the circumferential and axial velocities of dry ice were measured. The results show that the equivalent diameter of the most abundant dry ice particles in the cyclone separation chamber is 2.0 mm. As the inner diameter of the separation section decreases, dry ice particles coalesce and grow from an equivalent diameter of 4 mm to a maximum of 40 mm. In addition, the comparison of the experimental and simulation results shows that the drag force due to CO2 gas flow is dominant in the circumferential velocity of dry ice particles.