چكيده به لاتين
Abstract:
The use of magnetic field for the emulsion breaking has been raised during last decades, as an alternative of electrostatic field, with the aim of increase of efficiency and decrease of hazards. Although the first studies on the magnetic aided separation of emulsions were reported in 1960s, but the commercialization and industrialization of this tecknique was limited due to the limitations of the fluid magnetization. Nowadays due to the fast growing developments in the nanotechnology the synthesis of the approperiate nano magnetic fluids has been possible and therefore the suitable conditions are provided for the development of the technology of magnetic aided breaking of the emulsions. The magnetostatic coalescence of droplets is the main key phenomena in the emulsion breaking, which is not yet clearly understood due to the lack of studies in the magnetostatic coalescence of droplets. Hence this study was aimed to investigate the effects of magnetic field on the coalescence of the magnetic droplets. For this aim the dynamic behavior of water based ferrofluid droplets under the effect of magnetic field was investigated by means of CFD simulation and also by experiments. The equilibrium shape of ferrofluid droplets and the collision of two droplets under the effect of uniform magnetic field was simulated by CFD technique. Furthermore, the movement and deformation of ferrofluid droplet under the effect of non-uniform magnetic field was experimentally investigated and also it was simulated. For the simulation, a finite volume based solver was 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 (VOF) and Level-Set (LS) methods was applied for interface capturing. The effects of different parameters, such as magnetic field intensity, magnetic susceptibility, initial size of droplets, surface tension and viscosity on the deformation of magnetic droplets and their coalescence were investigated. It was concluded from simulations that in order to minimize the collision time there will be a need to decrease the values of viscosity and surface tension while the magnetic field intensity and/or magnetic susceptibility to be increased. A non-dimensional correlation was obtained to formulate the dependency of Aspect ratio of droplet at the equilibrium state to the magnetic Bond number and magnetic susceptibility. Furthuremore in order to evaluate the effect of parameters on the magnetic induced coalescence of ferrofluid droplets a new correlation was proposed which is capable to predict the collision time for two ferrofluid droplets in a relatively wide range of properties and operating conditions. The experimental results obtained in this work were compared with the simulation results and a good consistency was observed. It was concluded that the droplets under the effect of non-uniform magnetic field have more setteling velocity in compared to the droplets under the effect of uniform magnetic field. The experimental result revealed that it is possible to increase the velocity of droplets up to four times.
Key Words: Coalescence, Ferrofluid Droplet, Interface Capturing, CFD simulation, ferrohydrodynamics
