Experimental and numerical estimation of wall effect and drag coefficient on hollow frustum settling in annular and non-annular channels

Abstract

The wall effect and drag coefficient of hollow frustum particles (Tapered hollow cylinders) settling in cylindrical non-annular and annular channels were experimentally investigated. The terminal velocity, V, of the hollow frustum particles is measured by considering flow channels of different diameters filled with various working fluids. The present work deals with the study of drag coefficient for a range of 0.12 ≤ deq/D ≤ 0.44, 0.22 ≤ deq/L ≤ 0.43, and 0.22 ≤ di/do ≤ 0.77. The hollow frustum particle's terminal velocity, V, decreases with increased blockage ratios and di/do ratios. The experiment revealed that the frustum attains a steady-state orientation. The hollow frustum particle is affected by the wall's retardation, which is described by the wall factor. The hollow frustum particle's wall factor (f) depends on the Reynolds number (Re) and blockage ratio. The wall factor increases with increasing Reynolds number up to a certain point called critical Reynolds number, Rec; after that, the wall factor remains constant with increasing Reynolds number. The hollow frustum particles settling in the cylindrical non-annular channel were more subjected to wall effects than those in the annular channel. Simple correlations between the wall factor and the blockage ratio are developed. The current research also focuses on the relationship between Reynolds number (Re) and drag coefficient (CD). The wall effect is considered while estimating the hollow frustum particle's drag coefficient (CD). The numerical estimate of the experimental drag coefficient is made using Ansys- fluent 18.1, and the experimental and numerical results are consistent with each other.