Investigation of Granular Flow Dynamics by Hyperpolarized-Gas and Pulsed-Field-Gradient NMR

本文的目标是利用非局部核磁共振（NMR）来获得几个颗粒系统的颗粒位移信息，以便与理论预测进行比较。系统将包括一个垂直振荡的容器，充满颗粒固体，流化床和重力驱动的颗粒流沿着垂直通道。利用超极化诺贝尔气体核磁共振（PFG-NMR）表征间隙气体的运动，利用脉冲场梯度核磁共振（pulsed-field gradient NMR）监测颗粒的微观运动。PFG-NMR技术允许在100纳米或更大的距离尺度和毫秒到秒的时间尺度上测量分子的运动。对于小尺度的波动以及较大的特征，如边界上的剪切层、一维和二维密度波以及流化床气泡中的气体流动模式，都有详细的预测。由于现有模型的复杂性，必须简化假设以获得数值结果。提出的实验将检验模型预测的有效性。如果成功，这项工作将导致对模式形成的更好理解，并可能应用于重要的系统，如流化床。

The goal of this proposal is to employ non-local nuclear magnetic resonance (NMR) to obtain particle displacement information on several granular systems for comparison with theoretical predictions. Systems will include a vertically oscillating container filled with granular solids, a fluidized bed, and a gravity driven granular flow down a vertical channel. The motion of the interstitial gas will be characterized using hyperpolarized nobel-gas NMR (PFG-NMR), and the microscopic motion of the grains will be monitored with pulsed-field gradient NMR. The PFG-NMR technique permits the measurement of the motion of molecules over distance scales of 100nm or greater and time scales of milliseconds to seconds. Detailed predictions exist for small scale fluctuations as well as for larger features such as shear layers at boundaries, one- and two-dimensional density waves, and the gas flow pattern in fluidized-bed bubbles. Because of the complexity of current models, simplifying assumptions must be made to obtain numerical results. The proposed experiments will test the validity of the model predictions. If successful, this work should lead to a better understanding of pattern formations and may be applied to important systems such as fluidized beds.