New Insight into Pseudo-Thermal Convection in Vibrofluidised Granular Systems

Abstract

Utilising a combination of experimental results obtained via positron emission particle tracking (PEPT) and numerical simulations, we study the influence of a system’s geometric and elastic properties on the convective behaviours of a dilute, vibrofluidised granular assembly. Through the use of a novel, ‘modular’ system geometry, we demonstrate the existence of several previously undocumented convection-inducing mechanisms and compare their relative strengths across a broad, multi-dimensional parameter space, providing criteria through which the dominant mechanism within a given system – and hence its expected dynamics – may be predicted. We demonstrate a range of manners through which the manipulation of a system’s geometry, material properties and imposed motion may be exploited in order to induce, suppress, strengthen, weaken or even invert granular convection. The sum of our results demonstrates that boundary-layer effects due to wall (in)elasticity or directional impulses due to ‘rough’ boundaries exert only a secondary influence on the system’s behaviour. Rather, the direction and strength of convective motion is predominantly determined by the energy flux in the vicinity of the system’s lateral boundaries, demonstrating unequivocally that pseudo-thermal granular convection is decidedly a collective phenomenon.

Intruder trajectory tracking in a three-dimensional vibration-driven granular system: Unveiling the mechanism of the Brazil nut effect

“…The complexity of granular segregation arises from the interplay of diverse influencing factors, including particle size, density, interaction between interstitial fluid and particles, and friction between particles and container walls. [4,24,25] Various segregation mechanisms, such as convection, [26,27] voidfilling, [28] buoyancy, [29,30] inertia, [31] and cohesion, [10,13] have been identified, each inducing gradients in different ways. [32,33] Given the complexity, physicists have attempted to simplify the problem by studying the motion of a single large particle embedded in a granular bed [34,35] to infer the mechanisms underlying the bulk particle segregation.…”

Zero-gravity thermal convection in granular gases

“…More specifically, thermal convection induced by sidewall energy leaks is well known in molecular fluids [30]. For granular materials, a similar mechanism is triggered by wall-particle inelastic collisions, rather than a thermal leak [31][32][33][34].…”