Particle/Wall and Partical/Boundary-Layer Interactions

本文将研究粒子流动中的两种现象，即粒子与表面碰撞时的传热，以及粒子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至10毫米之间的颗粒，低和高导热性颗粒，层流和湍流进行。流动可视化、粒子追踪和激光多普勒风速测量将用于速度测量。在换热实验中，将测量集热器的感热变化率（粒子/壁面相互作用）和局部表面换热变化率（粒子/边界层相互作用）。此外，弹性冲击的分析/数值研究将通过考虑可变表面积、通过周围气体的传热（间隙贡献）、颗粒和表面之间的材料特性差异、颗粒自旋和表面粗糙度来进行。这些研究将确定颗粒在稀颗粒流（如干燥和流化床干舷部分）的传热中的作用，并将为理解和预测致密相系统提供所需的基础知识。​许多颗粒系统，如干燥机，流化床和颗粒处理（机械或化学回路）需要在流体/颗粒混合物和封闭或淹没表面之间传递热量。两种主要的传热机制是颗粒和这些表面之间的直接传热（传导），以及流体和表面之间的直接传热。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，以及当粒子经历自旋并斜到达表面时，导通贡献尚不清楚。粒子的运动在流场中引起的扰动的程度也还不清楚。本研究旨在提供颗粒对表面传热速率的影响所需要的基础数据。

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.