浮选气泡尺寸对粗颗粒-气泡涡旋湍流脱附机制的影响

Influence of floatation bubble size on detachment mechanism of coarse-grained particles from air bubbles in turbulent vortex

气泡是浮选过程中不可或缺的重要角色,其尺寸对颗粒-气泡间相互作用有着显著影响,然而气泡尺寸对粗颗粒-气泡涡旋湍流脱附机制的影响尚未清晰。为此,采用自制的颗粒-气泡受限湍流脱附测试平台探索了涡旋湍流中不同气泡尺寸的气絮体上颗粒的脱附行为,并运用Image-ProPlus图像处理软件对颗粒脱附过程的动力学参数进行了测量分析。结果表明:在确保气泡浮力的前提下,减小气泡尺寸能够显著提升粗颗粒-气泡的矿化气絮体在涡旋湍流中的稳定性;涡旋湍流中气絮体上颗粒的脱附主要表现为流体剪切、气泡振荡和颗粒离心三种脱附形式,方腔内涡旋结构的改变对气絮体上颗粒的脱附方式至关重要;区别于传统离心脱附理论,涡旋湍流驱使下颗粒并非单独在气泡表面做高速离心运动,而是与气泡一起做离心运动,且小气泡与颗粒在方腔内共同旋转时,位于气泡外缘的颗粒与气泡运动速度接近,相应气絮体稳定性高,颗粒不易发生离心脱附,而大气泡形成的气絮体中,气泡外缘的颗粒与气泡运动速度差异明显增大,颗粒相对于气泡旋转更快,从而使得颗粒所受离心力显著增强,增加了离心脱附的可能性。研究结果有望对涡旋湍流场中粗颗粒的脱附机制提供一个基本认识。

Air bubbles is an indispensable factor that plays an important role in flotation process,and their size has a significant bearing on the interaction between bubbles and particles.However,the influence of bubbles size on mechanism of detachment of coarse-grained particles from bubbles in turbulent vortex still remains unclear.To deal with this situation,a self-made bubble-particle confined turbulent detachment testing platform is utilized to explore the detachment behavior of bubble-particle aggregates at different bubble sizes in turbulent eddies.The dynamic parameters involved in particle detachment during the testing are measured and analyzed using the Image-Pro Plus image processing software.As revealed by test results,while ensuring the bubble buoyance,reducing bubble size can lead to significantly improved stability of mineralized aggregates of bubbles and coarse-grained particles in turbulent vortex flow;the detachment of bubble-particle aggregates in this case takes place as a result of fluid shear or bubble oscillation or particle centrifugation;the change of vortex structure within the wall chamber plays a crucial role in detachment mode of bubble-particle aggregates;opposite from what is assumed in the traditional centrifugal detachment theory,it proves that the particles undergo a highvelocity centrifugal motion on surface of bubbles driven by turbulent eddies together with bubbles rather than an independent action alone;when smaller bubbles and particles rotate together within the wall chamber,the particles at bubble′s periphery tend to move at a velocity close to that of bubble′s core,causing a higher stability of aggregate,and hence less occurrence of centrifugal detachment of particles;conversely,for the aggregate formed with larger bubbles,the significant difference in relative velocity between the particles at the periphery and core of the bubble cause the particles to undergo a faster motion relative to the bubble,allowing the particles to have a more chance to come off the bubble due to the higher centrifugal force to which the particles are subjected.The work made in the paper may offer a basic insight into the mechanism of detachment of coarsegrained particle from bubbles in a turbulent vortex flow field.