Abstract
We report mea.sUICJD.CD.ts of two-dimensional (B/D::S) fully tw:bulent and developed duct flows (overall length/depth. IlD=60; D-based Reynolds number Re>104) for inclinations to 30 degrees from vertical at low voidagcs (<5% sectional average) representative of disperse regime using tap water bubbles ( 4-6 mm) and smaller bubbles (2 mm) stabilised in ionic solution. Pitot and static probe instrumentation, primitive but validated, provided adequate (10% local value) discrimination of main aspects of Che mean velocity and voidage profiles at representative streamwise station i.e IlD =40. Our results can be divided into three categories of behavionr. For vertical flow (0 degrees) the evidence is inconclusive as to whether bubbles are preferentially trapped within the wall-layer as found in some, may be most, earlier experimental work. Thus the 4 mm bubbles showed indication of voidage retention but Che 2 mm bubbles did not. For nearly vertical flow (5 degrees) there was pronounced profiling of voidage especially with 4 mm bubbles but the Transvm e transport was not suppressed sufficiently to induce any obvious layering. In Chis context, we also refer to similarities wieh previous work on one-phase vertical and nearly vertical mixed convection flows displaying buoyancy inhibited mean shear turbulence. However, with inclined flow (10+ degrees) a distinctively layered pattem was invariably manifested in which voidage confinement increased with increasing inclination. In this paper we address flow behaviour at near vertical conditions.
Khairuddin Sanaullah, N. H. Thomas. (2008) Buoyancy Profile Inhibition of Turbulence in Nearly Vertical Bubbly Shear Flow, NUST Journal of Engineering Sciences , Volume 1, Issue 1.
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