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The cavitation phenomenon is well known to lead to deagglomeration and uniform dispersion of nanoparticles in liquid metal. The nature of flow leading to deagglomeration, the rate of deagglomeration, and the effect of frequency of them has been systematically investigated. It is extremely difficult to experimentally know about them and thus modeling the phenomenon is indispensable. The same has been attempted in the present study. The present study attempts to model the process of deagglomeration and dispersion of ceramic nanoparticles in the vicinity of cavitation using FLUENT 6.2.16. For this a simple representative volume element has been modeled.

The phenomenon of bubble cavitation has been found to be useful for de-agglomeration and uniform dispersion of nano-particles in liquid metal. There are many researchers who have described the bubble dynamics in details [

A two-dimensional representative volume element (RVE), which is shown in Figure

Schematic diagram of the domain with semicircular bubble wall.

Although during the collapse the dimension of the bubble changes, for simplicity it has been kept static. Since the size of bubble is small compared to the representative volume element and through the mathematical model only a rough estimate of the dispersion time is aimed at, the assumption is justified. Also convective movement of the bubble has been ignored. The assumption of negligible flow at the boundaries does not make the problem far away from reality because the pushing effect of cavitation of different bubbles will be resulting in cancellation of flow along a boundary line surrounding each of the bubble.

It has been further assumed that size distribution is not present in the nanoparticles, that is, all the particles are of same size. Eulerian multiphase granular flow was assumed and solved using FLUENT 6.2.16. The volume element was divided into

The Eulerian granular multiphase model solves a set of momentum and continuity equations for each phase. Coupling is achieved through the pressure and interphase exchange coefficients. In this problem, a combination of two phases, namely, fluid and solid has been taken. This is called granular flow problem. In granular flows, the properties are obtained from application of kinetic theory [

The Shyamlal et al. Equation [

Since Al is most widely used material as a matrix in composites, for the modeling of the nanoparticle deagglomeration we have chosen Aluminum as matrix material. The reinforcement in the matrix has been taken as SiC nanoparticles of 30 nm size. Along with this we have assumed that about 15 ppm air is entrapped in the aluminum melt.

FLUENT 6.2.16 was run to simulate the mathematical model. The computational time step for solving the unsteady state problem was 0.1

The contours of volume fraction of particulate were plotted from the saved data files. Figure

Contour of particulate volume fraction at time

(a) Contour of particulate volume fraction at time

After the formation of spiral bands, as shown in Figures

The contour of magnitude of velocity (liquid Al) is shown in Figure

Contour of magnitude of velocity (liquid Al) at time

A flow within a representative volume element with a single agglomerated lump of the nanoparticles, as a result of periodic cavitation, has been simulated. After ~4.2 s significant dispersion took place and the distribution of nanoparticles was almost uniform. Thus the phenomenon of deagglomeration due to cavitation could be simulated at mesoscale. Intense convective flow with significantly large gradient in the velocity fields, at the mesoscale, results in the dispersion.