Bubbles bouncing

Similar assemblies have been extensively characterized for the ion pair cetyltrimethylammonium-salicylate. In both cases the micellar fibers produce slightly viscous solutions and the effect of viscoelasticity is observed if one rotates such a solution and suddenly stops the rotation, smalt particles in the solution (e.g., air bubbles) bounce back. While the bulk water is still rotating in the nonviscous solutions, the inertia of the high molecular weight threads builds up an elastic wall for the suspended particles and pushes them back. Lithium and sodium ricinolates produce helical micellar fibers of opposing chirality in toluene (Tachibaona, 1970,1978). 

It is known that a bubble bounces off a flat plate of good wettability for a Weber number. We, larger than 0.3 [43]. Under the experimental conditions considered here, a bubble of approximately 2x 10 m in diameter was observed to bounce off a poorly wetted plate. For example, the Weber number for the bubble shown... 

In Fig. 1.4a, an example of the radius-time curve for a stably pulsating bubble calculated by the modified Keller equation is shown for one acoustic cycle [43]. After the bubble expansion during the rarefaction phase of ultrasound, a bubble strongly collapses, which is the inertial or Rayleigh collapse. After the collapse, there is a bouncing radial motion of a bubble. In Fig. 1.4b, the calculated flux of OH... 

A spherical bubble being bounced off a disc of soap film. 

Once an anti-bubble has been formed it will move, under its own momentum, down into the bulk of the fluid. The buoyancy of the surrounding air will provide an upthrust which will cause it to slow down and eventually rise to the surface. On reaching the surface it will either bounce back into the fluid or come to rest nder the surface as a sphere or a hemisphere. 

Bubble ascends with repeated bouncing but never attaches to the plate. 

The mechanism of the bouncing of a bubble from a plate can be explained as follows. Before the bubble comes in contact with the plate, the water just above the bubble first collides with the plate. Consequently, the pressure in the thin water layer between the plate and the bubble is thereby elevated. When the diameter of the bubble is small, such as 2 x 10 m, the force acting downwards on the bubble due to the pressure increase inside the water layer is higher than the buoyancy force, and the surface tension force is sufficiently large to prevent a breakup of the bubble. This results in the bouncing of the bubble off the plate. This phenomenon occurs irrespective of wettability of the plate. The implication of this result is that the bouncing of a bubble off a plate is always accompanied by the existence of a thin liquid layer between the bubble and the plate even if the plate is not wetted by the liquid. 

A requirement of the DSMC method is that expressions are available for the postcoUisional velocities of two particles, given their precolUsional positions and velocities. For solid particles, there are well-known expressions in terms of normal and tangential coefficients of restitution and fiiction coefficients (Van der Hoef et al, 2008). However, for droplets and bubbles (as well as wet particles), additional correlations are needed detailing the outcome of a binary collision, such as bouncing, coalescence, or breakup. In the topical sections, we will discuss these correlations for some representative systems. 

In the DBM, the centers of mass and volumes of individual bubbles are tracked. The outcome of a binary coUision between two such bubbles is bounce or coalescence, depending on many factors including the surface tension and relative velocity. Under sufficiently strong deformations, bubbles can even break up into a number of smaUer bubbles. At larger bubble volume fractions, the bubble motion leads to a strong mixing of the continuous fluid and therefore a large dispersion of dissolved chemicals. 

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