Numerical and Experimental Analysis on the Hydrodynamic Behaviors of Nanoparticle Agglomerates at Moderate Reynolds Numbers

In this study, the hydrodynamic characteristics of agglomerates are studied experimentally for the Reynolds numbers ( Re ) up to ∼200, and their fluid dynamic behaviors are analyzed numerically taking their nonhomogeneous structures into account as 50 ≤ Re ≤ 400. The results show that both the Reynolds number and the fractal dimension ( D f ) of agglomerates significantly affect the flow field around and through the agglomerate. The drag ratios obtained from the numerical simulation show good agreement with the experimental data. The values of drag ratios are all lower than 1 at Re < ∼100 and are all larger than 1 for D f = 2.6 and 2.7 as Re > ∼100. A peak value in drag ratio is observed for D f = 2.6 as Re > 100. A new formula of drag ratio as a function of Re and D f is derived based on the simulated results. Comparisons with the homogeneous permeable sphere show that the effect of the radial variation of permeability on the drag force seems almost negligible in this range of moderate Reynolds numbers.