Chen Q, Restagno F, Langevin D, Salonen A
Université Paris Saclay, CNRS, Laboratoire de Physique des Solides, France.
Université Paris Saclay, CNRS, Laboratoire de Physique des Solides, France.
J Colloid Interface Sci. 2022 Jun 15;616:360-368. doi: 10.1016/j.jcis.2022.02.043. Epub 2022 Feb 12.
Bubbles in a liquid rise under gravity and separate to the top. Bubbly liquids exist commonly in nature and play a significant role in energy-conversion, oil and chemical industries. Therefore, understanding how bubbles rise is of great importance. Rheological properties of the fluid have a strong impact on single bubble rise and have been shown to change collective bubble rise at low gas volume fractions significantly. We expect that a viscoelastic fluid can strongly modify the rise of bubbles in more concentrated suspensions. We generate bubbly liquids up to gas fractions of 30 %. We measure the bubble size and the rise velocity in micellar solutions made of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal), a common system to create shear-thinning solutions. We show that when the NaSal concentration is small and the solutions are Newtonian, the bubble rise velocity decreases with increasing volume fraction of bubbles and the relationship between the two follows the Richardson-Zaki prediction. For the shear thinning viscoelastic solutions, the Richardson-Zaki relation no longer applies. Bubble clustering leads to faster rise velocities and a weaker dependence on the bubble volume fraction. At the largest concentration two rise regimes are observed. A fast one similar to that in the other shear thinning samples, followed by a very slow bubble rise. The slow rise velocity is attributed to the smallest bubbles rising so slowly, that at the shear rates around them, the fluid behaves as a Newtonian fluid. Therefore, bubble rise becomes again comparable to Stokes expectations. We also show that the peculiar dependence of the rise velocity with volume fraction of bubbles in the shear thinning viscoelastic solutions can have important implications in flotation as the area flux changes strongly with bubble volume fraction.
液体中的气泡在重力作用下上升并聚集到顶部。气泡液体在自然界中普遍存在，在能量转换、石油和化学工业中发挥着重要作用。因此，了解气泡如何上升至关重要。流体的流变特性对单个气泡的上升有很大影响，并且已证明在低气体体积分数下会显著改变气泡的集体上升。我们预计粘弹性流体可以在更浓缩的悬浮液中强烈改变气泡的上升。我们生成气体分数高达30%的气泡液体。我们测量了由十六烷基三甲基溴化铵（CTAB）和水杨酸钠（NaSal）制成的胶束溶液中的气泡大小和上升速度，这是一种常见的用于制备剪切变稀溶液的体系。我们表明，当NaSal浓度较低且溶液为牛顿流体时，气泡上升速度随气泡体积分数的增加而降低，两者之间的关系遵循理查森 - 扎基预测。对于剪切变稀的粘弹性溶液，理查森 - 扎基关系不再适用。气泡聚集导致上升速度更快，并且对气泡体积分数的依赖性更弱。在最大浓度下观察到两种上升状态。一种快速上升状态类似于其他剪切变稀样品中的情况，随后是非常缓慢的气泡上升。缓慢的上升速度归因于最小的气泡上升非常缓慢，以至于在它们周围的剪切速率下，流体表现为牛顿流体。因此，气泡上升再次变得与斯托克斯预期相当。我们还表明，剪切变稀的粘弹性溶液中上升速度与气泡体积分数的特殊依赖性在浮选过程中可能具有重要意义，因为面积通量会随着气泡体积分数的变化而强烈变化。
