Heat Transfer in Slow Granular Flows

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

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.