High Rayleigh Number Convection in Laboratory Porous Media

目的：确定地下多孔介质中高瑞利数（Ra）热对流演化的长度和时间尺度。将被测试的具体假设是，流动模式有几个相互作用的运动尺度，同时发生，相互影响。最小的尺度是从热边界层剥离的单个羽流，而最大的尺度是实验装置的大小。运动的长度和时间尺度以及时间传热可以用局部（边界层）和全局（系统）瑞利数、努塞尔数、佩莱特数以及介质的非均质性来理解。科学价值：热对流是一种重要的传输过程，它可以导致地壳区域的高热流率。虽然多孔介质中的许多焦点都集中在封闭对流细胞上，这种细胞会导致低瑞利数的受限介质，但在参数空间中进行的研究很少，也没有基础实验，在参数空间中，细胞本身变得不稳定并过渡到湍流状态。方法：一系列实验将在一个高1米×宽1米×厚2厘米的实验室试验室内进行。层理图案将使用不同尺寸的半透明硅砂(100 ？M ~ 7mm)。大约75个热电偶阵列将安装在电池中心周围，以捕获厘米尺度的温度（因此流动）运动。通过将热致变色液晶溶解在工作溶液（水）中，可以看到大规模的运动；这些晶体会随着温度的变化而变色（红绿蓝）。更广泛的影响：这项研究将形成内华达大学里诺分校博士生课程的论文部分。这项研究是C. Cooper更大目标的一部分，该目标是开发方法来理解地下流体力学作为地质因素的重要性。

0309618CooperObjectives: The objective of the proposed research is to determine the length and time scales of evolving high Rayleigh number (Ra) thermal convection in subsurface porous media. The specific hypothesis that will be tested is that flow patterns have several interacting scales of motion occurring simultaneously that influence each other. The smallest scales are individual plumes that peel away from a thermal boundary layer, while the largest scales are on the order of the size of the experimental apparatus. The length and time scales of motion, as well as temporal heat transfer can be understood in terms of the local (boundary layer) and global (system) Rayleigh numbers, the Nusselt number, the Peclet number, as well as the heterogeneity of the media. Scientific merit: Thermal convection is an important transport process that can result in high heat flow rates in regions of the Earth's crust. While much focus in porous media has been on the closed convection cells that result in confined media at low Rayleigh numbers, little research, and no fundamental experiments, have been conducted in parameter space where the cells themselves become unstable and transition to a turbulent regime. Methods: A series of experiments will be conducted in a sand-filled laboratory test cell with dimensions 1 m tall x 1 m wide x 2 cm thick. Bedding patterns will be constructed using translucent silica sands of varying sizes (100 ?m to 7 mm). An array of approximately 75 thermocouples will be installed around the center of the cell to capture cm-scale temperature (hence flow) motion. Large-scale motion will be visualized by dissolving thermochromic liquid crystals in the working solution (water); these crystals change color (red-green-blue) as a function of temperature. Broader impacts: This research will form the dissertation portion of a Ph.D. student's curricula at the University of Nevada, Reno. This research is part of a larger goal of C. Cooper to develop methods to understand the importance of subsurface fluid mechanics as a geologic agent.