Experimental investigation of dry ice cyclone separator for ultra‐low temperature energy storage using carbon dioxide

Abstract

CO 2 cascade heat pump system has been developed to realize an ultra-low temperature below the triple point of 0.518 MPa and − 56.6 C or less by flowing dry ice solid-gas state of CO 2 in a refrigeration system. Solid CO 2 in the refrigeration system may cause to block the flow in the evaporation process and make the system operation failed. To overcome the blocking phenomena and farther challenging lower refrigeration temperature, the CO 2 cyclone separator was newly proposed instead of the conventional evaporator for ultra-low temperature energy storage. The basic characteristics of CO 2 dry ice cycle separator were investigated by constructing test rigs and visual experiments. The visualization tests were carried out by three type separators: nonswirling type separator, cylindrical, and conical type cyclone separators. The results of visualization test showed that the size of the dry ice particles gets bigger by coalescing together with the strong swirling flow in the cyclone separator. In comparison with three type separators, particularly by using the conical type cyclone separator, the amount of accumulation of dry ice at the bottom of the separator was increased as a result of the growth in dry ice particle size.

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

“…This difference in the number of particles can be attributed to three factors: outflow of particles from the outlet channel, particle coalescence, and particle sublimation. The collection efficiency of particles under the same conditions of pressure difference in the previous study [23] was 62%. Therefore, the main reason for the difference in the number of particles from the region (A) to (B) could be an outflow of particles.…”

“…The size of dry ice particles was determined from the projected area of dry ice particles photographed by a high-speed camera. The previous study [23] showed that dry ice particles coalesce on the walls of the separation chamber and form thin flakes. Therefore, in this study, for all visualization regions (A)-(D), two frames of particles passing through rectangular regions of +30 mm and −35 mm in the z-direction and +1.5 mm vertically in the z-direction from the center of each visualization area were analyzed.…”

“…A detailed schematic diagram of the cyclone separator-evaporator is shown in Figure 2. In this study, a cyclone separator-evaporator with a conical shape was used to achieve the lowest temperature range obtained in the previous study [23]. As seen in the figure, the cyclone chamber is 360 mm long, a length enough to allow the chamber to be used in an actual refrigerator to confirm the required characteristics.…”

“…These studies [17][18][19][20][21][22] are of heat pump systems using horizontal tube evaporators (as a model of conventional tube evaporators) with CO 2 as the refrigerant. As a solution to prevent this blockage phenomenon, in a previous study, we proposed a dry ice-gas separation technology using a cyclone separator-evaporator as an alternative to horizontal tube evaporators for ultra-low temperature energy storage [23]. The cyclone separatorsublimator is expected to be used in place of the conventional evaporator in the CO 2 heat pump system.…”

“…The previous study [23] reported on the collection efficiency and temperature distribution of dry ice particles when using a cyclone separation evaporator. In this study, to further improve the performance of the cyclone separator-evaporator, the behavior of dry ice particles inside the separator-evaporator was visualized and analyzed using a high-speed camera.…”