The Motion Characteristic Study And Drag Model Correction Of The Particle-Laden Bubbles

As an efficient separation method,flotation is widely used in the field of micro mineral separation.In flotation process industry,air exists in the pulp of the equipment in the form of bubbles with suitable size.As a carrier,it is easy to collide and adhere with the hydrophobic mineral particles in the pulp to form a bubble-particle aggregate whose density is less than that of water.Then,under the influence of buoyancy,the target minerals are brought to the liquid surface to achieve the purpose of mineral separation.At present,many studies only focus on the motion of bare bubbles,and the research on the rising movement of bubble-particle aggregate is less,but the behavior of the aggregate in the floating process will affect the performance of the flotation equipment.It will provide a theoretical basis for improving the separation efficiency of flotation minerals to systematically study the movement characteristics of the bubble carrying particles in the liquid and establish the relationship between the different particle carrying amount and the movement characteristics of the bubble.In this study,hydrophobic polymethylmethacrylate(PMMA)spherical particles were used to simulate minerals,and the single particle-laden bubble rising in deionized water was taken as the research object.High-speed dynamic photography technology and related image processing software were used to measure and extract the characteristic parameters of bubbles,and the movement characteristics of particle-laden bubble with different sizes,particle size and particle coverage were studied.Five kinds of particle size classification for PMMA were carried out,and the size and contact angle of PMMA were measured by laser particle size analyzer S3500 and Kruss k100 surface tensiometer,respectively.The results show that after the free falling particles collide with the bubble,the particles were monolayered on the surface of bubble from the bottom to the top of the bubble.The arrangement of the particles on the surface of bubble is regular hexagon,and the corresponding plane filling factor is 0.907.Within 4ms after the bubble leaves the needle,a small number of particles fall off,and then the particles can stably attach to the bubble surface to form particle-laden bubble.The bubble deformation can be reduced by covering the bubble with particles.With the increase of particle coverage,the bubble shape gradually changes from flat to ellipsoid.After the bare bubble and particle-laden bubble separated from the needle,it first accelerated to the maximum velocity along a straight line,then the velocity began to decline,and finally,the instantaneous velocity and deformation of bubbles showed periodic fluctuations.The velocity and deformation of the particle-laden bubble decrease with the increase of the coverage rate,but when the coverage rate exceeds 50%,the influence on the velocity and deformation is very small with the increase of the coverage rate.With the increase of particle coverage,the terminal velocity of bubble decreases and the average aspect ratio increases,which indicates that bubble deformation affects the rising velocity of bubble.The rising trajectory of bubble changes from zigzag to straight line with the increase of coverage rate,and the larger the particle size is,the closer the trajectory is to a straight line.Clift,Mendelson,Fan and Tomiyama classical formulas were used to predict the terminal velocity of particle-laden bubbles.It was found that the prediction error of the above formula is large,and only the trend of Tomiyama formula is consistent with the experimental value.Therefore,based on the Tomiyama formula and the introduction of the surface tension correction,a new velocity prediction formula is obtained to predict the terminal velocity of the bubble with different particle coverage,and the maximum absolute average value of the prediction error is 6.54%.Based on the experimental values of drag coefficient of particle-laden bubbles with different particle coverage,the prediction formula for the drag coefficient of particle-laden bubbles was derived,which is consistent with the experimental values.The ratio of the two is basically around 1.When predicting small size particle-laden bubbles,the accuracy is higher and the error is smaller.There are 52 figures,9 tables and 104 references in this thesis.