Scale formation in orifice plate

• Despite the high local shear rates, scale deposition occurs at sharp orifice edges, driven by heterogeneous nucleation. • The Reynolds number increase reduces the orifice occlusion rate but increases the total deposited mass. • Downstream recirculation zones enhance deposition in view of the low shear conditions and the prevalence of sweep-turbulent events. • PIV-based quadrant analysis identifies sweep-dominated regions as preferential sites for particulate deposition. • Local shear intensity and flow velocity determine the crystal morphology, whether columnar or dendritic. The present work studies scale formation in orifice plates. Mass deposition rates of calcium carbonate under different flow rates in the turbulent regime are experimentally assessed in pipe flows fitted with two types of fixed orifice plates. Despite the increase in total deposited mass with increasing bulk Reynolds number, the orifice occlusion rate decreases, showing a decoupling between global deposition and local constriction blockage. The measurements show that enhanced deposition occurs mainly in the downstream recirculation region, where low shear stresses and increased particle residence time favour crystal growth, and turbulent sweep events promote particle transport toward the wall. The results indicate a monotonic decrease in orifice diameter. Particle Image Velocimetry (PIV) is used to characterize the flow dynamics. The work discusses the morphology and the structure of the deposited crystals.