Heat Transfer in Slow Granular Flows

在从食品到造纸、制药到陶瓷等行业中，缓慢的颗粒流在持久接触中发挥着重要作用。尽管多孔材料（微观结构静态）中的传导的伴随情况已经得到了很好的研究，但即使是最简单的缓慢颗粒流中的传热也知之甚少。虽然很明显，电导率强烈地取决于本体材料的微观结构，但在这些缓慢流动中，微观结构随时间变化，使得接触持续时间变得至关重要，并且颗粒混合/偏析的作用（即，本文利用简单的实验和热粒子动力学（TPD）研究了两种典型的缓慢颗粒流中的热流：简单的剪切单元和（在有限的程度上）颗粒流。TPD是最近引入的计算技术，其已被证明能够从静态床中的拉格朗日观点捕获颗粒的热行为和力学行为。在这项工作中，我们将这种技术扩展到缓慢流动的颗粒床，以解决粒子-粒子接触/碰撞如何影响宏观颗粒系统中电导的均匀性和大小的根本问题。该提案的主要智力价值在于解决颗粒系统中传导和对流之间竞争的基本问题，以及检查特定设备中传热速率的工业相关性。

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.