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

该方案的目的是利用非局域核磁共振获得几个颗粒系统上的粒子位移信息，以便与理论预测进行比较。系统将包括一个装满颗粒状固体的垂直振荡容器，一个流态化床，以及沿垂直通道向下的重力驱动颗粒流。间隙气体的运动将用超极化诺贝尔气体核磁共振(PFG-核磁共振)来表征，颗粒的微观运动将用脉冲梯度核磁共振来监测。PFG-核磁共振技术允许测量分子在100纳米或更大距离尺度上的运动，以及毫秒到秒的时间尺度。对于小尺度的波动以及更大的特征，如边界处的剪切层、一维和二维密度波，以及沸腾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，必须进行简化假设才能得到数值结果。拟议的实验将检验模型预测的有效性。如果成功，这项工作将有助于更好地理解模式的形成，并可能应用于重要的系统，如流态化床。

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.