Influence of surface dimpling on pressure drop in a monolayer sphere configuration under confined flow conditions

This study investigates the influence of surface dimpling on pressure drop in a confined monolayer of spheres under low diameter-ratio conditions (Dtube/dsphere≈1.17). An integrated experimental and computational fluid dynamics approach is employed to analyze the hydraulic performance of smooth and dimpled spheres arranged in a single row within a horizontal pipe, across a range of inter-particle spacing ratios (δ/Dp=1.0–2.0) and superficial velocities (Us=2–16 m/s). Experimental results reveal that dimpled spheres consistently exhibit higher pressure drops than smooth spheres, with the relative increase quantified by the ratio Ψ=(ΔP/L)dimpled/(ΔP/L)smooth. This ratio shows a non-monotonic dependence on Us, reaching a minimum of approximately 1.02 near Us=9–10 m/s, and is systematically reduced by increasing δ/Dp. Normalization of pressure drop per particle (ΔP/Np) collapses data onto single power-law trends for each surface type, indicating that individual particle contributions are largely independent of packing density. The increased resistance for dimpled spheres is attributed to enhanced surface area, promoted flow separation, and earlier boundary layer transition. These findings demonstrate that surface texture significantly alters flow resistance in confined arrays, where wall effects and particle proximity dominate, offering insights for applications in filtration, catalytic beds, and narrow-channel flows.