Study on the Drag of a Cylinder-Shaped Particle in Steady Upward Gas Flow

Studies on the drag of 28 kinds of cylinder-shaped particles with different sizes and materials were experimentally carried out in steady upward gas flow. The drags were determined by high-resolution digital image processing. Two charge-coupled devices with different frame rates were employed to record the particle movements during experimental investigations. The effects of particle properties (length, diameter, density, and sphericity) and operating conditions (gas velocity and particle Reynolds number) on drag coefficients of single falling cylinder have been systematically tested. The results showed that the drag coefficient first declines sharply and then gradually with increasing particle Reynolds number; finally, it can reach a constant level if the Reynolds number is large enough to exceed a certain value. It was found that the drag coefficient is significantly dependent on particle shape and size for a fixed particle Reynolds number. It increases with increasing particle length and density but decreases with increasing particle diameter and sphericity. In addition, the usability of correlations in publications for predicting the drag coefficient was evaluated by comparing our experimental data. A new correlation considering the effect of particle size, shape, orientation, and density was proposed for predicting the drag coefficient for cylinders, which was in satisfactory agreement with the present experiments and some published experimental results. The correlation is helpful for predicting the drag coefficient for cylinders in ranges of the particle Reynolds number Re(p) = 500-10 500, flatness ratio d(a)/d(v) = 0.95-1.28, and sphericity phi = 0.70-0.87.