Porous array nozzle of dry ice spray quick-freezing blueberry

More cost-saving and efficient freezing is required to enhance the performance of quick freezing for blueberries. In this study, a new system was proposed to utilize a multi-outlet array nozzle for spraying blueberries with dry ice particles. Experimental tests were conducted to investigate the variations in the thermal properties of blueberries with temperature during the freezing process. These parameters were then input into Fluent software. A quick-freezing model was established for the dry ice particle spray inside the chamber. Numerical simulation was conducted to simulate the blueberry quick freezing using Fluent software. The optimal inlet flow velocity was successfully obtained to optimize the nozzle outlet diameter after the simulation. The results indicate that the better precooling of blueberries in cold water was to a temperature of 1 ℃. The nozzle was designed with six outlets in a circular array, where the central lines of the outlets were inclined at a 60° angle from the central line of the nozzle inlet, while the aperture size was 5.2 mm, and the nozzle was designed in a circular aperture shape with a contraction form. Additionally, four outlets were arranged at the center position of the nozzle's entrance axis, each with a diameter of 2 mm. The nozzle was configured with a spraying height of 120 mm, an entrance aperture measuring 30 mm, and an inlet velocity of 0.25 m/s. The center temperature of all the blueberries decreased from 1 ℃ to −18 ℃ in a total of 129 s, indicating the more uniform and quick freezing of the blueberries. Experimental testing was conducted to validate the simulation. An optimal combination was achieved in the freezing process of 127 s at the slowest cooling rate, with a time of 36 s for the formation of the maximum ice crystal generation zone. The cooling curves of the experimental process and the simulation process match well. The thawed blueberries were then subjected to physicochemical property testing after three days of storage. The results show that the blueberries subjected to quick freezing using dry ice particle spraying exhibited superior changes in their quality before and after freezing, compared with the CXS 103-1981 standard for frozen blueberries. A comparative experiment show that the blueberries were subsequently subjected to quick freezing using direct spraying of liquid nitrogen at −80 ℃. However, the dry ice cost much less for the quick freezing of blueberries, compared with the direct spraying with −80 ℃ liquid nitrogen. This low cost further enhanced the feasibility and economic viability of dry ice for blueberry freezing. The physicochemical property tests showed that there was almost no difference with the dry ice. The research findings can provide a solid foundation for the widespread application of the quick freezing of blueberries using dry ice spray.