Experimental investigation of the effect of solid-gas two-phase flow in CO₂ cascade refrigeration system

The dry ice sublimation process of CO₂ is a unique technique in which temperature ranges below the triple point of −56 °C can be achieved in a CO₂ refrigeration system. However, during the evaporation process of the actual refrigeration system, the dry-ice blockage maybe happens in the evaporator, which causes a risk of system failure in the suction of the compressor. In order to overcome this problem, in this study, an ultra-low temperature CO₂ cascade refrigeration system with a novel tapered evaporator/sublimator was designed and constructed. The novel evaporator/sublimator included a swirl promoter, which induces the swirling flow of solid-gas two-phase flow. Experiments were conducted for the investigation of solid-gas two-phase flow heat transfer characteristics in the evaporator/sublimator. According to the experimental results, it is verified that the CO₂ refrigeration system can operate consistently and steadily without dry ice blockage in the evaporator/sublimator. In addition, the dry ice particles are uniformly distributed along the inner wall of the evaporator/sublimator by the installation of the swirl promoter, and the heat transfer coefficient is considerably improved. © 2020, © 2020 Taylor & Francis Group, LLC