An experimental investigation on the settling of disk particles in annular region: Wall effect and drag coefficient

Abstract

Settling non-spherical and spherical particles in the annular region is common in many industrial applications. This work shows the intensification of the performance of settling particles in an annular channel by reducing the drag coefficient. The disk/cylinder particles settle in annular channels filled with Newtonian and non-Newtonian fluids. An aqueous solution of different concentrations of glycerin and Carboxymethylcellulose (CMC) was considered as the Newtonian and non-Newtonian fluids. The experimental results reported in the present work covered the 0.17 ≤ blockage ratio ≤0.55, 0.14 ≤ k (flow consistency index) ≤1.81 (Pa.sn), 0.64 ≤ n (flow behavior index) ≤1, and annular channel Reynolds number 0.40 ≤ Re ≤63.44 and 0.05 ≤ Re ≤43.02 in Newtonian and non-Newtonian fluids respectively. The wall factor, f, was increased with the increase in Re and the decrease in blockage ratio. At higher Reynolds numbers (Re), the particle’s wall factor was only influenced by the blockage ratio. The wall factor was reduced due to the particle’s shape change from cylinder to disk, i.e., decreasing the particle’s sphericity. The wall factor of particles is observed to be higher in non-Newtonian than in Newtonian fluids. The critical Reynolds number (Rec ) decreased with the H/d (Height/diameter of disk) ratio and sphericity of the studied particles. Both the drag coefficients, in the absence ( C D ∞ ) and presence ( C D ) of the wall effect, declined with the Reynolds number. Suitable correlations were developed for CD with low values of RMSLD (root mean square logarithmic deviation). The experimentally obtained drag coefficient data were also analyzed successfully using the laminar model available in Ansys (Fluent) −18.1. The computed velocity contours analyzed the wall effect and CD variations successfully. The use of the annular channel as a drag reduction device is encouraged due to the observed higher wall factor and decreased drag coefficient for particle settling in comparison to the non-annular channel.