Study on the effect of drag force on the particle motion of coir pith in rotary drying

Abstract

This study investigates the effect of drag force on the free-fall motion of coir pith particles under varying moisture contents and particle sizes. Particle-air interactions play a vital role in drying efficiency. Understanding these dynamics is critical for optimizing rotary drying operations. The main objective was to analyze how moisture content affects the drag coefficient and velocity profiles of coir pith particles. A simple experimental setup was used, where particles of three average diameters and five different moisture contents were dropped from varying heights, and their fall times were recorded. Drag coefficients were estimated numerically using measured fall times and calculated velocities. The velocity-time profiles were analyzed to assess whether particles approached terminal velocity during the available fall distances. Results obtained indicate that increased moisture content leads to higher drag coefficients, which delays the attainment of terminal velocity. Additionally, drag coefficients increased with particle diameter. These results provide deep insights into particle-fluid interactions relevant to rotary drying.