Abstract
In the motion of two spherical bubbles rising side by side, the bubbles are known to attract each other at a high Reynolds number (Re = ρUd/μ). Furthermore, spherical bubbles kiss and bounce under certain conditions; however, deformable bubbles repel each other without kissing. This paper experimentally and numerically presents the flow structures and shape of the nonkissing repulsion of deformable bubbles. For the experimental analysis, we organized bubble behaviors by Galilei number (Ga = ρg1/2d3/2/μ) and Bond number (Bo = ρgd2/σ). The bubbles repelled each other without kissing near the unstable critical curve of a single bubble. The curvature inside the gap, which is similar to the shape of a zigzag behavior bubble, was large. For the numerical analysis, the velocity of the equatorial plane inside the gap was larger due to the potential interaction, although the velocity behind was the opposite due to the strengthened vorticity generated at the surface. Furthermore, the double-threaded wake emerged behind the interacting bubbles, and it showed that the rotation direction was repulsion regardless of whether the bubbles attracted or repelled each other. The streamline behind the bubbles in the 2D plane was from the outside to the inside.
Highlights
Flows are widely observed in many industrial types of equipment, such as in chemical reactors and blast furnaces because of gas injection for mass transfer enhancement [1]
Bubble-driven liquid flow structures depend on the void fraction and bubble size distribution [2]
For two spherical bubbles rising side by side, the numerical simulation by Legendre et al [3] showed that the bubbles attract each other due to the increasing velocity of the equatorial plane inside the gap with the Reynolds number (Re = ρUd/μ) being larger than the transition region 30 ≤ Re ≤ 100
Summary
Flows are widely observed in many industrial types of equipment, such as in chemical reactors and blast furnaces because of gas injection for mass transfer enhancement [1]. The approaching/repelling hydrodynamic interaction between bubbles is an essential factor when determining these factors. Many studies examining the interaction between two bubbles, which is the most simplified condition, were conducted. For two spherical bubbles rising side by side, the numerical simulation by Legendre et al [3] showed that the bubbles attract each other due to the increasing velocity of the equatorial plane inside the gap with the Reynolds number (Re = ρUd/μ) being larger than the transition region 30 ≤ Re ≤ 100. We confirmed bouncing with kissing and found repulsion without kissing and weak hydrodynamic attraction/repulsion [6]; spherical interaction hardly explains the bouncing without kissing and weak repulsion, because the Re is O(102 )
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