Meitan kexue jishu (Oct 2023)
Study of slime water mixing process intensification using impingement flow regulation
Abstract
slime water generally contains a large number of highly dispersed suspended particles, making solid-liquid separation difficult. Strengthening fluid mixing and particle collision by regulating turbulence is an effective way to achieve solid-liquid separation. Particle collision flocculation mostly occurs in turbulent environments where the motion of fine particles is strongly influenced by the turbulent minimum vortex scale. In this study, turbulent vortices are modulated by impinging flows to enhance the mixing of two different density suspensions and the collision of fine particles in the suspension. Two different solution models were used to simulate the mixing condition of the suspension and the distribution of the particles in the mixing drum in three dimensions. The water phase entering the mixing drum was considered as a continuous phase and the solid particles were considered as a continuous phase (suspension) or a secondary discrete phase (particles). The effects of different inlet fluid velocity ratios at different feed densities on the turbulent characteristic parameters and particle distribution in the mixing drum were analyzed. The results of the study show that the impact flow formed by the jets colliding vertically with each other can induce turbulent macro-vortices such as hairpin vortices, spanwise vortices and axial vortices. The velocity of particles moving in the turbulent macro-vortex is in the following order: Large particle size and density > Large particle size and small density > Small particle size and high density > Small particle size and density. The interaction between vortex and vortex and between vortex and the main fluid significantly increases the turbulent kinetic energy and decreases the vortex scale, resulting in a minimum scale vortex that is conducive to particle coalescence and collision; the minimum vortex scale generated in the flow field in the mixing drum is mainly smaller than the average minimum vortex scale. The minimum vortex scale tends to increase when the inlet flow rate and flow rate ratio increase from 1.258:1.87 to 1.882:1.258, independent of the inlet density. When the flow rate ratio is similar, the minimum vortex scale decreases only when the flow rate increases. An appropriate increase in the ratio of the upper and side feed flow rates helps fluid mixing and particle aggregation and collision, and the mixing density, apparent viscosity and particle coalescence are all optimal when the ratio of the upper and side feed flow rates is between 1.40 and 1.50. In addition, at the same flow rate ratio, the mixing uniformity and mixing strength are better than the case where the upper inlet feed density is greater than the side inlet feed density, which is more conducive to fluid mixing and particle collision. The study promotes slime water mixing and fine particle coalescence in mixing drums through the regulation of fluid hydraulic conditions, providing a new way of thinking about how to enhance the liquid-liquid mixing and solid-liquid separation process.
Keywords
