Effect of channel width on the sedimentation modes of a cold elliptical particle in hot narrow channels

Many natural and industrial processes involve transport of solid particles. This research reports sedimentation modes of a single cold elliptical particle with an aspect ratio of 2 in narrow hot channels. Prior research on settling of non-isothermal elliptical particles was limited to wide vertical channels. A cold particle with constant non-dimensional temperature of T _p ^∗=0 and an initial orientation of θ ₀=π/3 between its major axis and horizontal axis is released in a hot fluid. Fluid Prandtl number is 7, and its initial temperature is T _f,0 ^∗=1. Simulations are based on an in-house lattice-Boltzmann solver with two distribution functions for fluid flow and heat transfer and using Boussinesq approximation in low density variations. In total, 120 simulations in five channel widths have been run, with enough time for the particle to reach a distinct sedimentation/rising pattern. Effects of channel width (L=12A/13−38A/13), where A is ellipse major diameter, the Grashof number (Gr=100−1000), and particle-to-fluid density ratio (ρ _r=1.0003−1.3) have been studied. Channel width, gravity and heat transfer have been discovered to cause the particle to travel up or down. Seven sedimentation modes have been observed including i) horizontal at centerline, ii) inclined off-center, iii) vertical at center, iv) oscillatory motion around centerline, v) tumbling off-center, vi) horizontal fluttering at centerline, and vii) inclined off-center with oscillations. Three of these patterns (iii, iv, vii) are peculiar to narrow channels, and have not previously been observed for cold elliptic particles in wide channels (L=52A/13). Moreover, the particle has been seen to move upward rather downward in the narrowest channel for small particle-to-fluid density ratios.