Heat Transfer in Slow Granular Flows

缓慢的颗粒流在从食品到造纸、制药到陶瓷的各种行业中扮演着重要角色，持续接触是常见的。尽管(微结构静态)多孔材料中的导热伴随情况已经被很好地研究了，但即使是最简单的慢速颗粒流动中的热传递也是鲜为人知的。虽然很明显，电导率强烈依赖于块体材料的微观结构，但在这些慢流中，微观结构随着时间的变化而变化，因此接触持续时间变得关键，颗粒混合/分离(即对流换热)的作用迅速显现出来。本工作使用简单的实验和热粒子动力学(TPD)来研究两种典型的慢颗粒流中的热流：简单的剪切单元和(在一定程度上)滚筒。TPD是最近引入的一种计算技术，已被证明能够从拉格朗日观点捕捉颗粒在静态床中的热行为和力学行为。在这项工作中，我们将这项技术扩展到缓慢流动的颗粒床，以解决颗粒-颗粒接触/碰撞如何影响宏观颗粒系统中电导的均匀性和大小这一根本问题。该建议的主要学术价值在于解决了颗粒系统中传导和对流之间的竞争这一根本问题，以及检查特定设备中的热传输率的工业相关性。

Slow granular flows where lasting contacts are common play an important role in industries ranging from food to paper to pharmaceuticals to ceramics. Despite the fact that the companion case of conduction in (micro-structurally static) porous materials has been well studied, heat transfer in even the simplest slow particle flows is poorly understood. While it is clear that the conductivity depends strongly on the micro-structure of the bulk material, in these slow flows, the micro-structure changes with time so that the contact duration becomes critical and the role of particle mixing/segregation (i.e., "convective" heat transfer) quickly comes to the fore.This work uses simple experiments and Thermal Particle Dynamics (TPD) to examine heat flow in two prototypical slow granular flows: a simple shear cell and (to a limited extent) a tumbler. TPD is a recently introduced computational technique that has been shown to be capable of capturing both thermal and mechanical behavior of particles from a Lagrangian viewpoint in static beds. In this work, we extend this technique to slowly flowing granular beds in order to addresses the fundamental issue of how particle-particle contacts/collisions affect both the uniformity and magnitude of the conductance in macroscopic particulate systems. The primary intellectual merit of the proposal lies in addressing the fundamental issue of the competition between conduction and convection in granular systems, as well as the industrial relevance of examining heat transfer rates in specific devices.