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To investigate the effect of frother concentration on bubbles and their tail vortex zone characteristics in flotation is an important prerequisite for predicting the probability of particle coiling in the trailing vortex zone of flotation bubbles. The flow field characteristics of the bubble trailing vortex region under different sec-octyl alcohol (2-octanol) foaming agents were studied by the laboratory homemade proposed rising bubble device and particle image velocimetry system. The fluid separation behavior of the bubble surface and the trailing vortex height characteristics were analyzed. The morphological characteristics of the bubbles and the trajectory and distribution probability of the particles in the bubble wake area were observed with the high-speed camera system. The results of the research are as follows: The size of bubbles slightly decreases and the aspect ratio gradually increases with the increase of the frother concentration. The boundary layer separation angle of the bubbles gradually increases with the increase of the frother concentration, and there is a critical separation angle of 196.70°. The vortex caused by the bubble is mainly concentrated in the region where the flow velocity is less than 0.09 m/s. The height of the vortex area gradually decreases with the increase of the frother concentration, and the critical value of the minimum vortex area is 1.06 times the bubble diameter. There are three kinds of trajectories of particles in the bubble trailing vortex area, and the trajectory of particle coiling can be divided into three significant stages, and the force on the particles is the critical factor leading to the difference in their coiling types. The range and probability of particles being coiled gradually decreased with the increase of frother concentration. The critical concentration affecting both the bubble trailing vortex and particle motion was 1.6×10-4 mol/L. The results of the study clarified the mechanism of frother concentration on mineral particle entrainment in the bubble trailing vortex and provided valuable guidance for the development of microfine mineral flotation technology.

BACKGROUND: Understanding the effect of ions on collector generation characteristics is crucial for adjusting the oil/water interface and enhancing mineral flotation. METHODS: We conducted a study of the kerosene droplet generation process in the presence of NaCl, MgCl2, and AlCl3 using a high‐speed motion acquisition system. RESULTS AND CONCLUSIONS: The results showed that the generation process of kerosene droplets could be divided into two stages, droplet expansion and column contraction, according to variations of the droplet width. With the increasing capillary inner diameter, the generation time of the kerosene droplet increased, while the w/h value (column width/column height) of the kerosene column decreased. When the w/h value decreased to 0, the droplet column ruptured, and the droplet separated from the capillary. As the ion valence increased, the equivalent diameter (d) of the kerosene droplet increased due to the ionic hydration and followed the order dAl3+ > dMg2+ > dNa+. Furthermore, as the ion concentration increased, the equivalent diameter increased with the same capillary inner diameter, and the w/h value decreased. A model of the kerosene column height and capillary inner diameter (R) was established to predict the characteristics of the generated kerosene droplet. © 2023 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

To deal with the reflective cracks and wet foundation surface in asphalt pavement construction of immersed tube tunnel, the shrinkage and differential settlement of structural joints and construction joints in different types of immersed tube tunnels are analyzed, and the factors affecting tunnel humidity are studied. The test results show that: (1) The reflective cracks of tunnel pavement can be effectively prevented by adopting seamless expansion joints for immersed pipe joints, App waterproof coil + filling joints for deformation joints, and polyester glass fiber cloth + filling joints for construction joints; (2) Through the rational use of natural temperature changes and the use of mechanical ventilation, the tunnel humidity can be effectively reduced to ensure dry base surface, and the working environment can be improved; (3) By blasting the base surface and selecting a reasonable asphalt structure layer, the waterproofing and durability of asphalt pavement surface of immersed tube tunnel can be effectively improved. [ABSTRACT FROM AUTHOR]

Wind barrier is an effective countermeasure to protect vehicles from the lateral wind on sea-crossing bridges. Previous studies focused on the sheltering efficiency of wind barriers and their effects on the aerodynamic/aeroelastic characteristics but ignored the analysis of intrinsic mechanism for dynamic stability, especially for flutter instability, which results only in a vague understanding of the role of wind barriers in flutter. Hence, this study paid attention to the effect mechanism of wind barriers on the flutter characteristics to generate a comprehensive understanding of the coupled relationship between wind barriers and the main structure. Wind tunnel experiments of closed box girders with different aspect ratios were first conducted to unearth the sensitivity of wind-barrier location, wind-barrier shape, wind-barrier porosity, and aspect ratios of main girders to flutter performance. The positive function of wind barriers was discovered, which was contrary to the common view that wind barriers had an adverse effect on streamlined structures. Then, the overall evolution of flutter process affected by wind barriers was investigated in detail from the flutter derivative contribution and modal participation. Simultaneously, local-region responses on the bridge surface to the installation of wind barriers were also studied by a proposed simplified local effect model based on surface fluctuating pressure. Also, the reason for the different influences of wind barriers was revealed according to the analysis from both overall and local levels. Wind barrier is an effective countermeasure to protect vehicles from the lateral wind on sea-crossing bridges. However, a modification of structural aerodynamic shape affected by wind barriers may have an adverse effect on aerodynamic stability, especially flutter instability. This study focuses on the wind-barrier effects on the flutter characteristics of closed box girders with different aspect ratios. The model test shows that there is no obvious positive or negative correspondence between wind barriers and structural flutter performance. If we can make full use of wind barriers, the flutter critical wind velocity can be improved by even 40%. Then, the flutter mechanism of wind barriers is investigated in detail based on the analysis of global derivatives, local derivatives, and unsteady pressure. Finally, the key flutter derivatives and the key function region of the deck surface are obtained, which may provide some references for the application of closed box girders in super long-span bridges. [ABSTRACT FROM AUTHOR]

At present, there is a common problem that the mixing mode is single and it is difficult to overcome the inherent bottleneck of multiphase mixing. A mixing device combining the advantages of jet entrainment and mixing dispersion was designed and built. In an effort to determine the mixing degree of two phases, the mixing coefficient of gas–liquid charging was measured using the cylinder method with the optimal working parameters. To explore the optimization of the mixing conditions and control mechanism of multiphase materials, the law of gas–liquid shear mixing in the process of multi-force field synergistic change was revealed. Based on the testing of the gas injection capacity under different working conditions and the calculation of the gas–liquid two-phase mixing coefficient, it was concluded that the flow rate was the direct key factor affecting the gas injection capacity. The working speed also had a certain impact on the gas injection capacity. When working at a high speed and high flow rate, the jet beam broke through the cutting barrier and presented a superposition effect. The jet impact assisted the rotation, and the suction performance of the device was significantly improved, which was conducive to the mixing of the gas and liquid phases. According to the test results of the measuring cylinder method, the calculated average inflation volume is 0.01 m 3 / (m 2 · m i n) , the inflation uniformity coefficient is 77.51, and the mixing coefficient of the gas and liquid phases is 0.12. [ABSTRACT FROM AUTHOR]