Three-dimensional temporal imaging of X-ray CT imaging of dissolution-driven convection in glass beads

The images in this dataset show the mixing of two liquid solutions in a random bead pack as a function of time and in three-dimensions. The working fluids used in this study are solutions of methanol and ethylene-glycol (MEG, fluid 1) and brine (fluid 2). In particular, three mixtures of ethylene-glycol and methanol were prepared that differ in wt% ethylene-glycol, namely 55 wt% (MEG55), 57 wt% (MEG57) and 59 wt% (MEG59). Measurements are conducted using in the regime of Rayleigh numbers, Ra = 2000-5000. X-ray Computed Tomography is applied to image the spatial and temporal evolution of the solute plume non -invasively. The tomograms are used to compute macroscopic quantities including the rate of dissolution and horizontally averaged concentration profiles, and enable the visualisation of the ow patterns that arise upon mixing at a spatial resolution of about (2x2x2) mm3. We observe that the mixing process evolves systematically through three stages, starting from pure diffusion, followed by convection-dominated and shutdown. A modified diffusion equation is applied to model the convective process with an onset time of convection that compares favourably with literature data and an effective diffusion coefficient that is almost two orders of magnitude larger than the molecular diffusivity of the solute. The comparison of the experimental observations of convective mixing against their numerical counterparts of the purely diffusive scenario enables the estimation of a non-dimensional convective mass flux in terms of the Sherwood number, Sh = 0.025Ra. We observe that the latter scales linearly with Ra, in agreement with observations from both experimental and numerical studies on thermal convection over the same Ra regime.

本数据集展示了两种液体溶液在随机珠子填充层中的混合过程，该过程随时间变化并在三维空间中进行。本研究所采用的工质为甲醇与乙二醇（MEG，流体1）的溶液以及卤水（流体2）。具体而言，制备了三种不同乙二醇含量的混合物，分别为55 wt%（MEG55）、57 wt%（MEG57）和59 wt%（MEG59）。实验在雷利数范围内进行，雷利数 Ra = 2000-5000。采用X射线计算机断层扫描技术对溶质羽流的时空演化进行非侵入性成像。断层扫描图像被用于计算宏观量，包括溶解速率和水平方向上的平均浓度分布，并能够以约（2x2x2）mm³的空间分辨率可视化混合过程中产生的流动模式。观察到混合过程系统性地经历了三个阶段，从纯粹扩散开始，随后为对流主导阶段，最后进入关闭阶段。对扩散方程进行修正，以模拟对流过程，其对流启动时间与文献数据相符，有效扩散系数比溶质的分子扩散系数大两个数量级。通过对实验观察到的对流混合与纯扩散场景的数值模拟进行对比，估算出无量纲对流质量通量，以舍伍德数 Sh = 0.025Ra 表示。观察到后者与 Ra 呈线性关系，与在相同 Ra 范围内进行的实验和数值研究关于热对流的观察结果一致。