Flow characteristics and micro—bubble behaviour in a rotating pipe section with an abrupt enlargement

Abstract

The¯ow characteristics and dynamic behaviour of micro-bubbles were investigated experimentally and numerically for swirling¯ow within rotating pipe sections. In the present investigation, three types of rotating pipe section were used in order to study the eVects of geometric con®guration upon the¯ow®eld. Experimental data were obtained for locations of the stagnation point and pro®les of the parabolic surface. The results obtained from experiments were examined and veri®ed with the aid of numerical analysis. It was found that the air pocket formed at the stagnation point was moved upstream by the eVect of the suddenly expanded part when pipe rotation was increased. The reattachment point did not shift downstream as a result of an increase in the Reynolds number. This is due to the fact that the vortex zone at the expanded corner expands or shrinks, depending on the speed of rotation. NOTATIONA aspect ratio C a virtual mass coe cient C D drag coe cient C L lift coe cient d bubble diameter (mm) d c critical bubble diameter (mm) d s simple mean bubble diameter (mm) D inner pipe diameter (D 1 and D 2 ) (mm) E expansion ratio g gravity acceleration (m/s 2 ) L ! length of the rotating pipe section (mm) L ¤ normalized length based on L ! L ¤ 0 normalized length from the stagnation point m b mass of the bubble (kg) m L liquid mass of the exclusion volume of the bubble (kg) N number density (1/m 3 ) p isotropic pressure (Pa) p ¤ dimensionless pressureˆp=…» L U 2 ave † r ¤ normalized length based on R R pipe radius (mm) Re axial Reynolds number Re b bubble Reynolds number Re ! rotational Reynolds number u liquid¯ow velocity vector (m/s) u b bubble velocity vector (m/s) U ave mean axial velocity (m/s) V b volume of bubble (m 3 )

Review on swirl-type microbubble generator: Concept, technology, and applications

“…It represents a flow with a spiral motion on the tangential axis, in addition to the axial and radial directions [33]. There are several methods for generating swirl [42], [43], such as using twisted tape, where tape inserts are attached to a shaft as illustrated in Figure 2 [4], [41], [44]- [46]; fixed-blade impellers attached to a shaft [33], [47]- [50]; rotating pipes [51], [52]; and tangential injection [2], [28]- [32], [53]- [56]. The swirl number, which can be employed to quantify the strength of swirl, is defined as the ratio of the azimuthal momentum flux to the axial momentum flux, expressed by Eq.…”

Characterization of the Fluid Deaeration Device for a Hydraulic Hybrid Vehicle System

“…Suzuki et al [9,13] explored cyclone deaeration through modeling and experimentation. Yamaguchi et al [14,15,16] studied the motions of bubbles in a rotating pipe and broadly stated that cyclone deaerators have difficulty removing small bubbles in viscous fluid. However, the research to quantify the efficiency for cyclone deaeration devices is lacking and is the goal of this research.…”

Micro-Bubbly Flows in Rotating Pipe Sections with Abrupt Expansion and Contraction

“…In the present study, a fundamental approach of the numerical analysis is that the motion of a bubble is calculated by solving its equation of motion in the known flow field, which is obtained for the rotating pipe situation by numerical analysis, neglecting the mutual interaction between the dynamical motion of the bubble and the flow field (4), (5) . This was thought by the reason that bubbles in fluid are minute and highly dispersed, and resultantly the rheological characteristic of two-phase flow is almost the same as the base fluid (as indicated in Table 1), so that in investigating individual bubble dynamics the bulk fluid can be treated as simple Newtonian single phase flow.…”