Experimental findings and analysis of terminal velocity and drag coefficient of Raschig Ring in vertical and inclined channel

Abstract

Hollow particle-drag coefficient data is valuable for designing many transport processes. However, limited published work in this regard has motivated us to perform the present work. The present work encompasses experimental terminal velocity, V and estimated drag coefficient, CD of Raschig Ring settling under gravity in Newtonian fluids for 0.2984 ≤ Re ≤ 13, 0.19 ≤ di/do ≤ 0.33, 0.22 ≤ do/D ≤ 0.83 and 40° ≤ θ ≤ 90°. The influence of inner diameter to outer diameter ratio, di/do of the Raschig Ring and the ratio of outer the diameter of the ring to channel diameter, do/D (blockage ratio) on the terminal velocity and drag coefficient are analyzed. The variation of the terminal velocity shows an increasing trend at lower di/do and higher do/D ratios. The terminal velocity becomes higher for higher angle of inclination, θ of the flow channel. The Predictive relation for the drag coefficient is developed as a function of Re, sphericity and the channel inclination. The reliability of the developed models is confirmed by the error analysis. The Raschig Ring experiences higher drag forces than the solid cylinder. The blockage ratio is identified as responsible factor for the appearance of the difference between the present and the litrature drag coefficient data for the vertical channel. The authenticity of the present drag coefficients are therefore examined by comparing it with the theoretical values obtained by numerical simulation using Ansys Fluent v15.0 software. An excellent agreement between the predictive and the current experimental results assures the viability of the RSM model of the simulator.