Three-dimensional measurements of bubble size, and velocity are presented along with the associated statistics for dilute bubbly flow in a vertical pipe. These measurements were obtained through a combination of precise index-of-refraction matching and a stereoscopic high-speed imaging system. An image-processing algorithm has been developed and used to extract instantaneous bubble size, shape, velocity and trajectory information and statistics corrected for magnification errors (maximum of 2%). The experiments have been conducted at a Reynolds of 14,600 in vertical pipe-flow and a volumetric gas flow ratio of 0.29%. Bubble sizes ranged from sub millimeter to several millimeters. The results indicate that bubbles less than approximately 20 wall units with very low ratios of rise velocity-to-liquid-average-velocity occupy the full breadth of the test section, while bubbles in the range between 20 and 60 wall units with ratios of rise-velocity-to-liquid-average-velocity greater than 0.5 are efficiently trapped by the wall and are almost exclusively found in the inner wall region (y+ < 30). Bubbles larger than 60 wall units with ratios of rise-velocity-to-liquid-average-velocity less than 0.5 are found throughout the pipe cross-section although with a strong preference to the wall neighborhood. This bubble behavior is put in perspective considering four mechanisms of bubble migration: (a) turbulent dispersion due to near-wall large scale structure, (b) inviscid transverse forces (Magnus), (c) viscous transverse forces (Saffman), and (d) unsteady transverse forces because of vortex shedding and bubble shape deformation.
Bubble Size Effects on Dispersed Phase Motion in Vertical Bubbly Pipe Flow
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Nikitopoulos, DE, Fiedler, J, Dowden, M, & Evans, E. "Bubble Size Effects on Dispersed Phase Motion in Vertical Bubbly Pipe Flow." Proceedings of the ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. Volume 1: Fora, Parts A, B, C, and D. Honolulu, Hawaii, USA. July 6–10, 2003. pp. 1757-1763. ASME. https://doi.org/10.1115/FEDSM2003-45553
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