In an occupied enclosure space formed by multiple opposing jet outlets, understanding vortex structures is crucial in controlling the spread of viruses and pollutants. In this study, a scaled model of an occupied enclosed space with opposing jet flows was constructed by incorporating a heated floor as a heat source to create thermal plumes under cooling conditions. A particle image velocimetry (PIV) system was employed to measure the flow field under isothermal and cooling conditions. The identification performance of different vortex identification algorithms was compared by studying the turbulent characteristics of the flow field from the perspective of the vortex. The Liutex vortex identification method was applied to analyze the vortex motion within one oscillation period, revealing distinct strengths in counterclockwise and clockwise directions, with maximum intensities of 50 s^-1 and 110 s^-1, respectively. The study concluded that the motion, merging, and annihilation of vortices influenced the flow field structure with a jet oscillation period of approximately 3.67 s. Owing to the trapping effect of vortices on pollutants, areas of pollutant accumulation can be represented using relative frenquency distribution maps of vortex cores. Despite the unsteady flow field, the vortex distribution remained relatively stable. Specifically, on the left side of the CS4 cross-section, the vortex core appeared at the same point up to 21 times. Under cooling conditions, pollutants are confined to smaller regions, which aids in containing the spread of pollutants.

Circulating water is used as the working medium in water-based chillers. Salt ions, such as calcium in circulating water, may precipitate during long-term operation, resulting in the attenuation of heat transfer performance. The application of small-diameter tubes in heat exchangers may lead to more prominent fouling problems. This study developed an accelerated fouling method to evaluate water fouling risk. The most typical operating conditions for water-based chillers were selected as the experimental conditions. The test samples included small diameter (5 mm) smooth tubes, with 7 mm smooth tubes selected for the control experiment. The experimental conditions include a circulating water inlet temperature of 60 ℃, a flow rate of 1 m/s, a foulant mass concentration of 800 mg/L, and a test time of 0-400 h. The results revealed that the total fouling mass was 39.5% higher and required fouling time was 17.6% shorter when comparing the 5 mm and 7 mm smooth tubes; the small diameter tubes had a larger total fouling mass and higher fouling rate. The heat transfer coefficients of the 5 mm and 7 mm tubes after fouling decreased by 12.5% and 9.7%, respectively, and the pressure drops increased by 50.6% and 10.4%, respectively, demonstrating a more severe heat transfer performance deterioration of small diameter tubes after fouling. The microscopic observation results of the fouling layer morphology demonstrated that the fouling layer in 5 mm tubes is a form of compact lamellar scaling, which is more difficult to remove compared with the 7 mm tube; therefore, the fouling risk should be considered when promoting the application of small diameter tubes in chillers.

Microencapsulation technology based on sodium alginate hydrogels can be used to optimize freezing and rewarming procedures and to reduce cryo-damage to cells and tissues. This study first observed the morphology of oocytes of sodium alginate hydrogels at different volume fractions (0.5%, 1.0%, 1.5%, and 2.0%) to determine the safe concentration for their encapsulation. Second, the crystallization temperature and crystallization behavior of sodium alginate hydrogels with different volume fractions were systematically investigated using cryo-microscopy, and the morphology and crystallization of oocytes were compared when they were cooled down/retempered in the base solution (cryoprotectant solution). Finally, the freezing effects of the sodium alginate antifreeze hydrogel-encapsulated oocytes prepared by solvent replacement and physical mixing were compared. The results revealed that oocytes maintained their overall morphology and volume better in sodium alginate gels at volume fractions of 0.5% and 1.0%. Furthermore, oocytes in both the 1.0% sodium alginate group and the cryoprotectant solution group of 12.5% DMSO + 12.5% EG + 0.5 mol/L trehalose did not produce intracellular ice during the cooling process. Additionally, compared with the physical mixture, oocytes in the hydrogel solvent replacement group did not produce intracellular ice during the cooling process, and the cells retained their normal morphology after rewarming.