To address the problem of high-efficient heat dissipation in the insulated gate bipolar transistor (IGBT) modules used in high-speed trains, a pin-fin heat sink was designed and applied to dry ice particle spray cooling. Three sets of different pin-fin parameter models are established, and the influence of the pin-fin number, diameter, and height on the heat dissipation effect is analyzed by numerical simulation. The optimal pin-fin heat sink has 64 pin-fins, a diameter of 12 mm, and a height of 45 mm. Compared with the baseline heat sink without fins, the surface temperature of the heat transfer substrate is reduced by 10.57 ℃, and the sublimation rate of dry ice inside the radiator is increased by 17.2%. The flow state of the dry ice particle cooling fluid in the pipeline and the disturbance and collision processes of the dry ice particles inside the heat sink are observed experimentally, and the simulation results are verified. The dry ice particle spray cooling keeps the IGBT module with a heat source power of 1.6 kW at approximately 25 ℃ to meet its heat dissipation requirements. Therefore, it is necessary to provide guidance for in-depth research on dry ice particle spray cooling technology.

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.

Freezing and thawing are often required for the preservation and market value of seedless lychee. However, the traditional freezing and thawing have severely limited the quality of fruits and vegetables, due to the time-consuming, inefficient, and damage rate. Fortunately, dry ice jet quick freezing and microwave thawing have emerged to gain much attention in recent years. Therefore, this study aims to explore the effects of different quick-freezing and thawing on the quality of the seedless lychees. Two freezing modes (dry ice jet quick freezing and conventional quick freezing) were combined with four thawing modes (room temperature, water bath, microwave, and refrigerated thawing). A series of experiments were designed for the dry ice jet quick freezing of seedless lychee. A comparison was made on some indicators, such as the freezing time, thawing time, vitamin C content, drip loss rate, pH value, titratable acidity (TA), texture properties (hardness, elasticity, and chewiness), total phenolic content, and total soluble solids (TSS) content. A systematic evaluation was also made on the effects of different freezing-thawing on the quality of seedless lychee. The experimental results demonstrated that the dry ice jet quick freezing with microwave thawing (DM) performed best across all indicators. The freezing time of DM was only 181 s, significantly shorter than the 2.2 h required for conventional freezing. The thawing time of DM was only 2.86 min, far faster than the rest, and greatly saving time costs. In terms of quality preservation, the DM exhibited the lowest drip loss rate (4.87%) and the least vitamin C loss (0.42×10^-2 mg/g), significantly outperforming the rest treatments. Additionally, the DM effectively maintained the pH value and titratable acidity (TA) of lychee fruits. The pH value of DM-treated lychee was 3.83, close to that of fresh lychee (3.81), with only a 0.52% increase. The TA of DM-treated lychee was 0.66%, similar to the 0.64% of fresh lychee, with only a 3.13% increase. In terms of the texture properties, the DM-treated lychee showed elasticity (2.38 mm), hardness (8.37 N), and chewiness (10.13 MJ) close to those of fresh lychee, with reductions of only 2.9%, 1.5%, and 1.1%, respectively. A significant advantage was maintained in the fruit texture. Furthermore, the TSS content of DM-treated lychee was 17.86 °Bx, closest to the 18.00 °Bx of fresh lychee, while the total phenolic content was 0.94 mg/g, significantly higher than the rest treatments, indicating its excellent performance in retaining the nutritional components. Sensory evaluation results showed that the DM-treated seedless lychee was ranked the highest in appearance, texture, aroma, taste, and flavor, with scores of 8.7, 8.5, 8.8, 8.6, and 8.7, respectively, close to the 9.0, 8.8, 9.0, 8.9, and 9.0 of fresh lychee and significantly higher than the rest (P< 0.05). The microstructural analysis further validated that the DM treatment shared minimal damage to cell walls and membranes, as well as uniform and fine ice crystal distribution, effectively maintaining the fruit cell integrity and water retention capacity. In conclusion, the dry ice jet quick freezing with microwave thawing can be expected to maximize the preservation of seedless lychee quality. This finding can also provide important theoretical insights for the more efficient freezing preservation, storage, and transportation of seedless lychee.