S-Gamma Particle Size Distribution
The S-Gamma model was developed by Lo and Rao, and Lo and Zhang, and assumes a log-normal distribution of particle sizes.
Particles change size due to breakup and coalescence as they interact with each other. Additional models are provided to account for this interaction between phases. These models are selected on the multiphase interaction node for a pair of Eulerian phases.
The log-normal size distribution is defined by a mean particle diameter and its variance. The mean particle diameter is always updated in the calculation. However, the variance is updated only when the zeroth moment is solved in addition to the second moment, and breakup and/or coalescence is active. If the zeroth moment is not solved, the variance of the distribution remains at the initial value that you provide. This initial value could be zero.
S-Gamma Breakup Model
For breakup, the S-Gamma model considers the balance between disruptive forces (due to shear and turbulence) and restoring forces (due to surface tension) on the particle (such as a droplet). In laminar flows, the viscous effects dominate hence this regime is named “viscous breakup”. In turbulent flows, the interactions with turbulence eddies dominate and this regime is named “inertial breakup”.
See Discrete Quadrature S-Gamma Phase Interaction Model Reference and Pre-Integrated S-Gamma Phase Interaction Model Reference.
S-Gamma Coalescence Model
For coalescence, the S-Gamma model considers the probability of collisions of the particles (such as droplets), the contact time of two colliding particles and the drainage time of liquid film between the particles. Similar to the breakup model, there is the “viscous collision” (or viscous coalescence) regime and the “inertial collision” (or inertial coalescence) regime. The drainage time is a function of the state of the particle surface, whether it is fully or partially mobile or immobile. The model therefore considers the breakup and coalescence processes in great detail.
It is possible to post-process certain results through field functions that these models activate.
See Discrete Quadrature S-Gamma Phase Interaction Model Reference and Pre-Integrated S-Gamma Phase Interaction Model Reference.
S-Gamma Entrainment Model
The S-Gamma Entrainment model models the size distribution of newly created bubbles or droplets. The methods for modeling bubble entrainment are based on the balance of bubble creation energy and turbulent dissipation at the free surface. The S-Gamma entrainment model accounts for the creation of the new dispersed phase by first identifying the large scale interface, followed by identifying the high turbulent dissipation rate cells at the interface. Bubble entrainment is permitted when the turbulent dissipation rate at the large scale interface reaches a specific critical value, determining the upper and lower bound of the bubble radius. A user-defined method for droplet or bubble entrainment can also be implemented using field functions. The S-Gamma Entrainment model predicts a single mean value for nucleation per cell, but the value can vary within the domain.It is possible to post-process certain results through field functions that these models activate.
See Discrete Quadrature S-Gamma Phase Interaction Model Reference.