Experimental study of wall effect on hollow cylindrical particle settling in Newtonian and non-Newtonian fluids in cylindrical channels

Abstract

Experimental studies are carried out to assess the confined wall's impact on the terminal velocity of hollow cylindrical particles settling in Newtonian and non-Newtonian fluids. The three different diameter flow channels are considered to calculate the wall effect on the particles. The presences of finite boundaries impose additional retardation on the particle motion and affect the particle's terminal velocity(V). The experimental results cover the following conditions range from 0.08 ≤ deq/D ≤ 0.47, 0.2 ≤ di/do ≤ 0.8, 0.64 ≤ n ≤ 1, and 0.14 ≤ K ≤ 1.81. The variation of terminal velocity is observed by changing the hollow particle's flow channel diameter and inner-to-outer diameter of the hollow cylindrical particle. Increasing the diameter of the flow channels and reducing the di/do ratio raises the terminal velocity of hollow particles. The wall effect is quantified using the wall factor against the diameter ratio and the Reynolds number, and at high Reynolds numbers (Re), the diameter ratio solely determines the wall factor. In both Newtonian and non-Newtonian fluids, it is found that the wall effect is greater for hollow cylinders than for solid cylinders. Simple relationships between the wall effect and diameter ratio are developed. The present study also focuses on the relationship between the drag coefficient (CD) and the Reynolds number (Re). The Reynolds number varies from 0.126 ≤ Re∞ ≤ 118 for Newtonian fluids and 0.004 ≤ Re∞ ≤ 78 for non-Newtonian fluids. The developed correlations for drag coefficients successfully predicted the estimated data for the hollow cylindrical particles.