High Rayleigh Number Convection in Laboratory Porous Media

研究目标：本研究的目的是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。将要检验的具体假设是，流动模式有几个相互影响的相互作用的运动尺度同时发生。最小的尺度是从热边界层剥离的单个羽流，而最大的尺度大约是实验仪器的大小。根据局部(边界层)和整体(系统)Rayleigh数、Nusselt数、Peclet数以及介质的非均质性，可以理解运动的长度和时间尺度以及时间尺度的热传递。科学价值：热对流是一种重要的传输过程，可导致地壳区域的高热流率。虽然在多孔介质中，人们的大部分注意力都集中在导致低瑞利数受限介质的封闭对流胞上，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，胞体本身变得不稳定，并过渡到湍流区域。方法：在高1m×宽1m×厚2 cm的充砂实验室试验室中进行一系列实验。床铺图案将使用不同大小(100米至7毫米)的半透明硅砂建造。一个由大约75个热电偶组成的阵列将安装在电池的中心周围，以捕捉厘米级的温度(因此流动)运动。大规模的运动将通过在工作溶液(水)中溶解热致变色液晶来可视化；这些晶体随着温度的变化而改变颜色(红-绿-蓝)。更广泛的影响：这项研究将成为内华达大学雷诺分校一名博士生课程的论文部分。这项研究是C·库珀更大目标的一部分，目的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.