Particle/Wall and Partical/Boundary-Layer Interactions

研究颗粒流动中的两种现象，即颗粒与表面碰撞时的换热以及颗粒与动量边界层和热边界层的相互作用。实验将使用直径在1到10毫米之间的颗粒、低导热系数和高导热颗粒以及层流和湍流进行。流动显示、粒子示踪和激光多普勒测速将被用于速度测量。在传热学实验中，将测量集热器的感热变化率(颗粒/壁面相互作用)和局部表面换热速率(颗粒/边界层相互作用)。此外，还将通过考虑可变表面积、通过周围气体的换热(间隙贡献)、颗粒与表面之间的材料特性差异、颗粒自旋和表面粗糙度来对弹性冲击进行分析/数值研究。这些研究将确定颗粒在稀相颗粒流动中的热传递中的作用(例如在干燥和床层的干舷部)，并将提供理解和预测密相系统所需的基本知识。许多颗粒系统，如干燥机、流态化床和颗粒加工(机械或化学回路)，都需要在流体/颗粒混合物和封闭或浸没表面之间传递热量。两种主要的热传递机制是颗粒和这些表面之间的直接热传递(传导)，以及流体和表面之间的直接热。后者受粒子运动的影响。目前，对于粒子表面不光滑的实际情况，当粒子经历旋转并倾斜到达表面时，传导贡献尚不清楚。颗粒运动在流场中造成的扰动的程度也尚不清楚。本研究旨在为颗粒对表面换热速率的影响提供必要的基础数据。

Two phenomena occurring in particulate flows, namely, heat transfer during collisions between particles and surfaces, and the interaction of the particles with the momentum and thermal boundary layers will be studied. Experiments will be performed using particle diameters between 1 to 10 mm, low and high thermal conductivity particles, and laminar and turbulent flows. Flow visualization, particle tracing, and Laser Doppler Anemometry will be used for the velocity measurements. The rate of change of sensible heat of a collector (particle/wall interaction) and the change in local rate of surface heat transfer (particle/boundary-layer interaction) will be measured in the heat transfer experiments. In addition, analytical/numerical study of the elastic impact will be made by allowing for variable surface areas, heat transfer through the surrounding gas (gap contribution), material property differences between the particle and the surface, particle spin, and surface roughness. These studies will determine the role of particles in heat transfer from dilute particulate flows (such as in drying and the freeboard portion of the fluidized beds) and will supply the fundamental knowledge needed for understanding and prediction of dense phase systems. Many particle systems, such as dryers, fluidized beds and particle processing (mechanical or chemical loops) require transfer of heat between fluid/particle mixtures and confining or submerged surfaces. Two of the major heat transfer mechanisms are the direct transfer of heat between the particles and these surfaces (conduction), and direct heat between the fluid and the surfaces. The latter is influenced by the motion of the particles. Presently, the conduction contribution is not known for practical cases where the particle surface is not smooth, and when the particle undergoes a spin and arrives at the surface obliquely. The extent of the disturbances caused in the flow field, by the motion of the particles, is also not yet known. This study aims at furnishing these needed fundamental data on the influence of particles on surface heat transfer rates.