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Fluidisation of yield stress fluids under vibration
Journal of Non-Newtonian Fluid Mechanics ( IF 2.7 ) Pub Date : 2021-06-16 , DOI: 10.1016/j.jnnfm.2021.104595
Ashish Garg , Nico Bergemann , Beccy Smith , Matthias Heil , Anne Juel

Motivated by the industrial processing of chocolate, we study experimentally the fluidisation of a sessile drop of yield-stress fluid on a pre-existing layer of the same fluid under vertical sinusoidal oscillations. We compare the behaviours of molten chocolate and Carbopol which are both shear-thinning with a similar yield stress but exhibit very different elastic properties. We find that these materials spread when the forcing acceleration exceeds the same threshold which is determined by the initial deposition process. However, the height reduction due to spreading is typically at least three times greater in chocolate than in Carbopol under similar forcing. Moreover, the two materials exhibit very different spreading behaviours: whereas chocolate exhibits slow long-term spreading, the Carbopol drop rapidly relaxes its stress by spreading to a new equilibrium shape with an enlarged footprint. This spreading is insensitive to the history of the forcing. In addition, the Carbopol drop performs large-amplitude oscillations with the forcing frequency, both above and below the threshold. We investigate these viscoelastic oscillations and provide evidence of complex nonlinear viscoelastic behaviour in the vicinity of the spreading threshold. In fact, for forcing accelerations greater than the spreading threshold, our drop automatically adjusts its shape to remain at the yield stress. We discuss how our vibrated-drop experiment offers a new and powerful approach to probing the yield transition in elastoviscoplastic fluids.



中文翻译:

振动下屈服应力流体的流化

受巧克力工业加工的启发,我们通过实验研究了在垂直正弦振荡下,屈服应力流体的固着滴在相同流体的预先存在层上的流化。我们比较了熔融巧克力和 Carbopol 的行为,它们都具有相似的屈服应力,但表现出非常不同的弹性特性。我们发现当强制加速度超过由初始沉积过程确定的相同阈值时,这些材料会扩散。然而,在类似的压力下,巧克力中由于铺展导致的高度降低通常至少是 Carbopol 的三倍。此外,这两种材料表现出非常不同的铺展行为:而巧克力则表现出缓慢的长期铺展,Carbopol 下降通过扩展到具有扩大足迹的新平衡形状来快速放松其应力。这种传播对强迫的历史不敏感。此外,Carbopol drop 以高于和低于阈值的强迫频率执行大振幅振荡。我们研究了这些粘弹性振荡,并提供了扩散阈值附近复杂非线性粘弹性行为的证据。事实上,为了迫使加速度大于扩展阈值,我们的水滴会自动调整其形状以保持屈服应力。我们讨论了我们的振动跌落实验如何提供一种新的、强大的方法来探测弹粘塑性流体中的屈服转变。此外,Carbopol drop 以高于和低于阈值的强迫频率执行大振幅振荡。我们研究了这些粘弹性振荡,并提供了扩散阈值附近复杂非线性粘弹性行为的证据。事实上,为了迫使加速度大于扩展阈值,我们的水滴会自动调整其形状以保持屈服应力。我们讨论了我们的振动跌落实验如何提供一种新的、强大的方法来探测弹粘塑性流体中的屈服转变。此外,Carbopol drop 以高于和低于阈值的强迫频率执行大振幅振荡。我们研究了这些粘弹性振荡,并提供了扩散阈值附近复杂非线性粘弹性行为的证据。事实上,为了迫使加速度大于扩展阈值,我们的水滴会自动调整其形状以保持屈服应力。我们讨论了我们的振动跌落实验如何提供一种新的、强大的方法来探测弹粘塑性流体的屈服转变。我们研究了这些粘弹性振荡,并提供了扩散阈值附近复杂非线性粘弹性行为的证据。事实上,为了迫使加速度大于扩展阈值,我们的水滴会自动调整其形状以保持屈服应力。我们讨论了我们的振动跌落实验如何提供一种新的、强大的方法来探测弹粘塑性流体的屈服转变。我们研究了这些粘弹性振荡,并提供了扩散阈值附近复杂非线性粘弹性行为的证据。事实上,为了迫使加速度大于扩展阈值,我们的水滴会自动调整其形状以保持屈服应力。我们讨论了我们的振动跌落实验如何提供一种新的、强大的方法来探测弹粘塑性流体的屈服转变。

更新日期:2021-07-06
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