Magnetocoalescence of ferrofluid droplets in a flat microfluidic channel

Department of Physics, Faculty of Sciences, Persian Gulf University - 75168 Bushehr, Iran and Max Planck Institute for Dynamics and Self-Organization - Am Fassberg 17, D-37077 Göttingen, Germany

Received: 16 January 2014
Accepted: 3 April 2014

Abstract

In this work we present the numerical study of the deformation and the coalescence of two ferrofluid droplets in a uniform applied magnetic field. Employing the boundary element method (BEM), we numerically solve the Darcy equation in a flat microfluidic channel by applying the magnetic normal stress as a boundary condition at the interfaces of droplets. The occurrence of different numerical regimes is summarized in the two phase diagrams scanned by the distance between two droplets, magnetic capillary number, and magnetic permeability. We also show the existence of the critical separation of two droplets where the coalescence of the droplets is inhibited. This critical value is independent of the applied-magnetic-field intensity, although it depends on the permeability ratio of droplet and continuous phase.