Bubbles clusters

Very often multiphase flow systems show inherent oscillatory behavior that necessitates the use of transient solution algorithms. Examples of such flows are encountered in bubbling gas-fluidized beds, circulating gas-fluidized beds, and bubble columns where, respectively, bubbles, clusters, or strands and bubble plumes are present that continuously change the flow pattern. 

The underlying premise of the cloud collapse theory is that the first bubbles to collapse are those at the periphery of a cavitation cloud, and they in turn transfer collapse energy to the core of the bubble cluster, thus intensifying water hammer pressures. 

A rise in the discharge pressure and hence the final recovery pressure results in reduced bubble cluster life and hence a decrease in the cavitationally active volume downstream of the throat of the venturi where the cavitational effects can be observed though the cavitation intensity in this reduced volume represented by the magnitude of the collapse pressure pulse is higher. This phenomenon can be used for more stubborn chemical reactions. 

The cavitation development process is the formation of a cloud of vapour-gas bubbles (bubbly cluster) under the action of a rarefaction phase in the liquid containing microinhomogeneities, such as microbubbles of free gas, solid particles or combinations of them. Under an intense development of cavitation the liquid physically transforms into a two-phase state changing substantially the structure and parameters of the applied field. In order to construct a mathematical model of this process, one should know, first of all, the state of real liquid and the mechanism of the bubbly cluster formation. 

MODELING COALESCENCE OF BUBBLE CLUSTERS RISING FREELY IN LOW-VISCOSITY LIQUIDS... 

Modeling Coalescence of Bubble Clusters 423 Exponential Model... 

Bubble interaction in swarms is a complex process. Bubble clusters commonly form that coalesce more or less simultaneously into very large bubbles. Recent experiments have revealed some of the details behind this behavior. A bubble contacts another only by following its wake to an overtaking collision. Coalescence or breakup occurs only after the collision, when one bubble is pulled into the near wake of the other. Interaction of three or more bubbles in clusters leads to increased coalescence rates. We have also shown analytically that bubbles do not collide like solid particles, but rather are drawn together by the dynamics of the surrounding fluid. Gravity and fluid acceleration drive bubble motion small-scale turbulence tends to prevent rather than enhance coalescence. 

Besides progressive pressure waves it is possible to deal with standing waves (with bubbles clustering at pressure antinodes, p. 38) provided that low acoustic... 

As discussed above, depending on the combined effects of material properties and operating conditions, the mesoscale structures take the forms of bubbles, clusters, and so on. All these mesoscale structures are found to obey the bimodal distribution, and thus, we can estabhsh the generalized conservation... 

Bubbles, clusters and nonuniform flow structures are inherent characteristics of the gas-solid fluidization systems, which greatly influence the performance of fluidized beds in many applications. Thus an understanding of the inherent flow structures is essential for introducing internal tubes and baffles with clear... 

Sheet cavitation is also known as fixed, attached, cavity or pocket cavitation. Sheet cavitation is stable in a quasi-steady sense. The liquid vapor interface becomes wavy and breaks down in the closure region of the cavity. Downstream flow, which contains large scale eddies, is dominated by bubble clusters. 

---