| Multiphase flow phenomena such as gas-liquid,gas-solid,liquid-solid and gas-liquid-solid are widely present in industrial processes and industrial equipment.Among them,the hydrodynamic behavior of bubbles is particularly prominent in these multiphase flows.Behavioral characteristics such as bubble formation,aggregation,and ascending will cause severe disturbance to the liquid phase or solid phase,which greatly promotes the interaction between phase and phase,thereby improving heat and mass transfer efficiency.It is clear that the hydrodynamic behavior of bubbles is one of the key factors affecting the overall efficiency of many processes and processes.Therefore,it is of great significance to study the behavior of bubbles,and the behavioral characteristics of bubbles in the ascending process are one of the key and difficult points.To this end,this paper uses the visual experimental method to take the rising process of bubbles in the liquid pool as the research object,and compares the bubble rising behavior characteristics under the three nozzle immersion modes,and on this basis,experimentally observes and analyzes the characteristics of formation and rising behavior of bubble in the surface of particles layer.Firstly,this paper uses a self-built visual experiment platform to observe and analyze the rising behavior of bubbles in pure water.The impacts of nozzle immersion mode,nozzle diameter(0.6mm,2.5mm and 7.0mm),gas flow rate and bubble rising height on the bubble rising shape,bubble rising velocity,bubble trajectory and bubble detachment diameter after the bubble has just left the nozzle at normal temperature and pressure conditions.It is found that the evolution of bubble rising morphology and bubble rising velocity,bubble aspect ratio,bubble horizontal displacement,horizontal velocity and vertical velocity with bubble rising height,the variation of bubble rising velocity with gas flow rate under different motion trajectories,the variation of bubble detachment diameter with gas flow rate under the different nozzle diameter,the evolution of bubble rising shape in the three nozzle immersion modes of top immersion,bottom immersion and side immersion,order comparison analysis of bubble rising process and bubble rising behavior characteristics.The results indicated that the shape evolution of the bubble in the top immersion mode is relatively flat,with 108 ms,while the immersion mode of the side and bottom is more severe,with 63 ms and 90 ms,respectively.In three submerged modes,the turning points of the bubbles orderly rising are 0.2L/min,0.3L/min and 0.1L/min,respectively.And when gas flow rate is 0.3L/min,the phenomenon of disorderly rising of bubble is remarkable in the side immersion mode.In the top and bottom immersion modes,the influence of the mutual disturbance of two adjacent bubbles is cyclic,and the periodic variation is the most obvious in the top immersion mod,the rising velocity of the bubble increases sharply with time,then decreases and tends to be gentle.The rising velocity of bubble is the largest in the bottom immersion mode,it is second in the bottom immersion mode,and it is the smallest in the top immersion mode.When the bubble rises linearly under steady state,the horizontal displacement and the horizontal velocity also show a linear change,and the vertical velocity of the bubble is larger in the top and side immersion modes than the bottom immersion mode.When bubble motion trajectories are the line shape and the S shape,the horizontal displacement and the horizontal velocity exhibit periodic changes,and the horizontal displacement maximum and maximum.When the difference between the maximum and minimum values of the horizontal displacement is maximum in top immersion mode,the vertical velocity of the bubble changes more smoothly.Secondly,on the basis of the above experiments,solid particles were added in pure water to form a solid-liquid two phase.The visualized experimental study on the formation characteristics and the evolution of the rising morphology of the bubble-crossing solid-liquid two-phase liquid on the surface of the particle layer was carried out.The effects of gas flow rate,bubble wake,nozzle diameter,particle stack height,particle size range,bubble shape evolution,bubble detachment diameter and adjacent bubble time interval were studied.The formation of the bubble on the surface of the particle layer and the evolution of the rising morphology and the variation of the bubble detachment diameter and the adjacent bubble time interval with the gas flow rate,the nozzle diameter,the particle accumulation height and the particle size range,as well as the comparison of bubble characteristics in pure water and solid-liquid two phase flow.It is found that under a small flow rate,the bubble traversing 150~300?m particles rises on the surface for the longest time,followed by 15~45?m particles,and the shortest is 1500~3000?m particles.Under large flow rate,in the 150~300?m particles,when the gas flow rate is less than Q=0.6L/min(0.8m/s),the single bubble is rising.When the gas flow rate is greater than 0.6L/min,the bubble detaches the particle surface and rapidly convergence and fusion.When the particle stacking height is low,the bubble wake has a weak influence on the shape of the bubble,and the bubble wake has a greater influence on the shape and bubble size.Under the same flow rate,the bubble detachment diameter increases with the increase of the stacking height,and increases with the increase of the particle size.The bubble detachment diameter in the 150~300?m solid-liquid suspension is larger than the bubble detachment diameter in the pure water.Under the same flow rate,the time interval of adjacent bubbles increases with the increase of the nozzle diameter and increases with the increase of the stack height.In pure water,the bubble generation time is faster,and the interval between adjacent bubbles is shorter.In the solid-liquid two-phase liquid pool,the bubble generation time will be slower,and the adjacent bubble time interval is longer. |
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