Magnetic field-enhanced orifice traversal of droplets: Minimizing surface adhesion for improved efficiency

In this article, we propose the feasibility of replacing traditional materials with ferrofluid droplets to actively regulate their behavior as they traverse an orifice in the presence of an external magnetic field. The traversal behavior of the droplet is investigated using both rectangular and curved orifice boundaries. We employed a simplified multiphase lattice Boltzmann method (SMLBM) to simulate the flow field and interface, which considerably improves computational efficiency. For magnetic field generation, a self-correction procedure is coupled with SMLBM. For curved boundaries, we used our recently developed immersed boundary approach, which can specify wetting boundary conditions for both stationary and moving boundaries, in the same way as flat boundaries are handled. To check the validity of our methods, we first simulated three benchmark phenomena and compared our results with experimental and numerical findings. This research includes orifice geometries, including straight and curved boundaries, and investigates the dynamic behavior of droplets traversing through narrow opening, increased orifice thicknesses, and large diameter droplets passing through confined and multiple orifices. All simulations are initially carried out without the use of magnetic fields, then the experiments are repeated and compared with the addition of a uniform magnetic field. It is found that, in the absence of a magnetic field, the droplets can successfully pass only through wide orifices. However, for narrow or thick orifices, a significant portion of droplet volume adheres to the orifice walls, causing an apparent decrease in falling velocity. In contrast, the addition of a magnetic field enables the droplet to efficiently traverse through even narrower and thicker orifices, attaining faster speeds and reduced mass loss. Furthermore, the influence of Reynold number and magnetic field strengths on the droplet velocity, its wetting dynamics, and relative shedding area are also discussed in detail.