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不等径颗粒间液桥力学参数及形态的试验研究

THE FORCE PARAMETER AND PROFILE CHANGE OF LIQUID BRIDGE BETWEEN TWO UNEQUAL SPHERES—AN EXPERIMENT STUDY

  • 摘要: 作为一种自然界中广泛存在的力, 液桥力的研究对制药、重金属回收、颗粒分离等领域具有十分重要的意义. 利用纳米多功能拉伸试验机测量不等径颗粒间液桥拉伸过程中的液桥力−位移曲线, 同时配合CCD工业相机记录拉伸全过程液桥形态的变化. 首先分析了液桥力−位移曲线形态、最大液桥力、断裂距离随粒径比及液桥体积的变化规律, 其次基于圆环假设及Y-L方程对本文试验结果的合理性进行验算, 最后针对圆环假设在液桥力计算中存在的不足分析了其原因, 并结合重力对液桥形态的影响对液桥拉伸全过程的形态变化进行了具体分析. 结果表明: 最大液桥力受粒径比的影响较大而受液桥体积的影响较小, 与最大液桥力相反, 断裂距离受液桥体积的影响较大而受粒径比的影响较小; 圆环假设可以较好地预测最大液桥力大小但对拉伸过程中的液桥力预测不准, 这是由于当液桥力达到最大值后液桥的外轮廓已不能用圆环表示; 根据重力对液桥形态的影响, 将拉伸过程液桥外轮廓的变化简化为重力影响可以忽略时的圆环形−抛物线形, 重力影响处于过渡阶段或影响较小时的长轴与短轴之比不断增大的椭圆形, 以及重力影响不可忽略时的“冷却塔形”−双曲线形.

     

    Abstract: The study of liquid force, which is commonly encountered in nature, has a special meaning to crystallization, removal of heavy metals from wastewater, and particle separation in industry. The Nano UTM T150 tensile machine and CCD camera were used respectively to record the force value and the profile change of liquid bridge between two unequal particles during stretching. The influences of radius ratio and liquid volume on the liquid force-displacement curves, maximum liquid force, and rupture distance were analyzed. And the experiment results were then compared with the calculating results according to the circle hypothesis and Y-L equation. Finally, the deficiency of the circle hypothesis in calculating the liquid force was analyzed, meanwhile, combining the influence of gravity, the changes of liquid profile in the whole process of stretch were further analyzed. The results show that the maximum liquid force was greatly influenced by radius ratio while the rupture distance was influenced by liquid volume a lot. What is more, the circle hypothesis can well predict the maximum liquid force, while its prediction of liquid force during the whole stretch is not accurate, this can be attributed to the fact that the liquid profile cannot be expressed as a ring after the liquid force reaches its maximum. Last but not least, based on the influence of gravity, the changes of liquid profile during the experiment were simplified as a circular to a quadratic parabola when the influence of gravity can be neglected; An ellipse which ratio of the long axis to the minor axis gradually increased when the influence of gravity is in the transition stage or has little impact. And a “cooling tower shape” to a hyperbolic, which upper out curvature is small and lower out curvature is large, when the influence of gravity can not be neglected.

     

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