Statistical characterization of the forces on spheres in an upflow of air

TL;DR

This study investigates the forces acting on spheres in an upflow of air, analyzing how these forces scale with various parameters and exploring the interaction potential between two spheres, extending understanding of fluidized particle dynamics.

Contribution

It provides a detailed statistical characterization of forces on spheres in air upflows and examines how these forces depend on experimental conditions, offering new insights into fluidized particle interactions.

Findings

Force terms scale with air flow speed, sphere radius, and density.

Effective interaction potential between two spheres characterized.

Force behavior consistent with a Langevin equation model.

Abstract

The dynamics of a sphere fluidized in a nearly-levitating upflow of air were previously found to be identical to those of a Brownian particle in a two-dimensional harmonic trap, consistent with a Langevin equation [Ojha {\it et al.}, Nature {\bf 427}, 521 (2004)]. The random forcing, the drag, and the trapping potential represent different aspects of the interaction of the sphere with the air flow. In this paper we vary the experimental conditions for a single sphere, and report on how the force terms in the Langevin equation scale with air flow speed, sphere radius, sphere density, and system size. We also report on the effective interaction potential between two spheres in an upflow of air.