Parameter study and CFD analysis of head on collision and dynamic behavior of two colliding ferrofluid droplets

In the present study a computational fluid dynamics  approach is implemented to investigate the dynamic behavior of two freely suspended ferrofluid droplets under the effect of uniform magnetic field. The colliding droplets are tracked from their initial state to a new equilibrium state which will be obtained for the new produced droplet after the coalescence. During collision time the shape of each droplet and also the variations of their energies are investigated and discussed. For the simulation, a finite volume based solver is modified based on the open source solver library (OpenFOAM^®) which is capable of coupling the flow field and magnetostatic equations. A coupled scheme of volume of fluid and level-set  methods is applied for interface capturing. The simulation results are validated based on the available numerical and experimental results reported in the literature. In order to evaluate the effect of parameters on the magnetic induced coalescence of ferrofluid droplets a dimensional analysis based on the Buckingham π theorem is implemented. Based on the simulation results and dimensional analysis a new correlation is proposed which is capable to predict the collision time for two ferrofluid droplets in a relatively wide range of properties and operating conditions. (paper)