Croccolo Fabrizio, Bataller Henri
Laboratoire des Fluides Complexes et leurs Réservoirs - UMR5150, Université de Pau et des Pays de l'Adour, 1 Allée du Parc Montaury, 64600, Anglet, France.
Centre National d'Études Spatiales (CNES) 2, Place Maurice Quentin, 75001, Paris, France.
Eur Phys J E Soft Matter. 2016 Dec;39(12):132. doi: 10.1140/epje/i2016-16132-4. Epub 2016 Dec 27.
Fluctuations in the presence of concentration gradients are long-ranged and decay diffusively for small spatial scales. At larger scales fluctuations are influenced by gravity and confinement. The confinement in the direction of the concentration gradient couples to gravity generating a slowing down that ends up in a diffusion-like behavior of fluctuations of size comparable to the vertical extension of the sample. The resulting enhanced diffusion coefficient depends on the solutal Rayleigh number of the system. For small (in modulus) values of the solutal Rayleigh number the apparent diffusion coefficient tends towards the normal one and a simple diffusive behavior is obtained. This is quite similar to what happens in microgravity conditions when the solutal Rayleigh number is drastically reduced because of the reduction of g by about 6 orders of magnitude. Experiments are shown for positive and negative solutal Rayleigh numbers smaller (in modulus) than 1000. The effect of the confinement on the statics is also investigated. Comparison with microgravity data obtained through the GRADFLEX project is performed.
浓度梯度存在时的涨落在小空间尺度上具有长程性且呈扩散衰减。在较大尺度上，涨落受重力和限制作用影响。浓度梯度方向上的限制与重力耦合，导致涨落减缓，最终呈现出与样品垂直延伸尺寸相当的涨落的类似扩散行为。由此产生的增强扩散系数取决于系统的溶质瑞利数。对于溶质瑞利数的小（绝对值）值，表观扩散系数趋向于正常扩散系数，从而得到简单的扩散行为。这与在微重力条件下发生的情况非常相似，此时由于重力g减小约6个数量级，溶质瑞利数大幅降低。展示了溶质瑞利数绝对值小于1000的正负两种情况的实验。还研究了限制对静态特性的影响。与通过GRADFLEX项目获得的微重力数据进行了比较。
