(22h) Modeling and Numerical Investigations of Stretching Liquid Bridges

Rupture characterization of a liquid bridge connecting wetted solid particles and the distribution of a liquid bridge between the particles plays a key role in many industrial particle processing systems. This work is aimed to provide a fundamental understanding of stretching liquid bridges. The work was applied to fluid cokers by investigating coke particle interaction with liquid bitumen; coating of particles and bridge formation.

A simplified mathematical model and numerical simulation of Navier-Stokes equations have been used to predict the shape evolution, rupture distance, and liquid distribution of pendular liquid bridges between two spherical solid particles. In the simplified model, the problem has been modeled using a parabolic assumption for the bridge shape. It is also assumed that surface tension forces are dominant over viscous, inertia, and gravitational forces. For numerical simulations, a commercial computational fluid dynamics software ? FLUENT ? has been employed. Numerical simulations have been based on Navier?Stokes equations; therefore, viscous, inertia and gravitational forces along with the surface tension forces have been taken into consideration. The use of numerical investigation has the following advantages to the simplified model: 1) Capability to solve more general rupture problems and 2) Capability to study the impact of operating conditions and liquid properties on the dynamics of the liquid bridge.

Results obtained with both the simplified model and numerical simulation for rupture distance have been validated with the experimental data available in the literature. It has been observed that both methods and experimental data were in reasonable agreement, provided the non-dimensional numbers were within a certain range. In order to study the effects of liquid properties (i.e. surface tension and viscosity) and operating conditions (i.e. separation velocity and gravity) numerous computations have been performed. As a general trend, the numerical simulation results show that as the importance of viscous forces relative to the surface tension forces increases, the rupture distance increases. On the other hand, increasing the importance of gravitational effects with respect to the surface tension effects reduces the rupture distance. Moreover, the numerical investigations show that the distribution of a liquid bridge between the two particles is strongly affected by the relative importance of the viscous, inertial, gravitational, and surface tension forces. It has been found that the simplified model provides results comparable to the predictions of the numerical simulation with Bond numbers less than 0.1 and capillary numbers less than 10-3. The simplified model has significant limitations, and is not applicable for non-dimensional numbers outside a certain range.

In conclusion, the simplified model and numerical simulation of Navier-Stokes equations are complementary when modeling the rupture distance and liquid distribution of liquid bridges: if the key dimensionless numbers are within a certain range, the simplified model can be used; otherwise, numerical simulation of Navier-Stokes equations has to be performed. The models presented in this work can be used to predict the rupture and post?rupture evolution of liquid bridges; ultimately, their results can be incorporated in numerical investigations of wet particulate processing systems.