Heat Transfer in Slow Granular Flows

缓慢的颗粒流中，持久的接触是常见的，在从食品到造纸到制药到陶瓷等行业中发挥着重要作用。尽管（微观结构静态）多孔材料中传导的伴随情况已经得到了很好的研究，但即使是最简单的慢颗粒流中的传热也知之甚少。虽然很明显，电导率很大程度上取决于大块材料的微观结构，但在这些缓慢流动中，微观结构随着时间的推移而变化，因此接触时间变得至关重要，颗粒混合/偏析（即“对流”传热）的作用很快就会显现出来。这项工作使用简单的实验和热粒子动力学（TPD）来检查两种典型的慢颗粒流的热流：一个简单的剪切细胞和（在有限程度上）一个滚筒式。TPD是最近引入的一种计算技术，它已经被证明能够从拉格朗日的角度捕捉静态床中粒子的热学和力学行为。在这项工作中，我们将这项技术扩展到缓慢流动的颗粒床，以解决宏观颗粒系统中颗粒接触/碰撞如何影响均匀性和电导大小的基本问题。该提案的主要知识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的传热率的工业相关性。

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.