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A unifying correlation for laminar particle deposition in 90-degree pipe bends

Inthavong, Kiao
Powder technology 2019 v.345 pp. 99-110
data collection, geometry, models, particle size, powders, turbulent flow
Pipe networks and ducting systems present a myriad of pipe geometry combinations e.g. pipe diameter, bend radius, flowrate − with each of these parameters leading to different flow fields. When particles are suspended in the flow, the fluid-particle dynamics then depend on the particle diameter as well. The literature review showed a variety of particle deposition studies with a prevalence towards turbulent flow studies, and no preference for a specific pipe configuration. This study presents a comprehensive analysis of micron particle deposition in laminar pipe bend flows. The data set consisted of combinations of 8 pipe diameters, 9 bend radii, 3 Reynolds numbers, and 30 particle diameters (from 1μm to 100μm). The secondary flow was visualized by vortex cores and streamlines were seen wrapping around the cores. This depicted the swirling behavior as the flow shifted from a horizontal to vertical direction that influenced the particle deposition. The deposition efficiency for combinations of the pipe geometry, flow condition, and particle diameter were plotted against the particle Stokes number. The deposition profile demonstrated a sigmoidal shape and an arctan function is proposed as the unifying correlation for micron particle deposition in 90-degree bends, given as η=2πtan−1aStb. A limitation of the model is that it doesn't account for sedimentation effects, which could affect the particle locations at the bend entrance, particularly for particles >30μm. For particle <30μm there was inconsistent data for the case where St<0.2 for with bend ratios Ro < 4.0. However, the correlation was very reliable for Ro > 4.0, and Re > 1000.