Influences of field conditions on the rupturing instability of a circular thin magnetic film

Cheng

2008

Physics of Fluids

We experimentally investigate the interfacial morphologies of Rosensweig instability on an extremely thin layer of ferrofluid droplets under a constant perpendicular magnetic field. Striking patterns consisting of numerous subscale droplets that developed from Rosensweig instability are observed. For a dry plate, on which surface tension dominates, the breaking pattern of subscale droplets can be characterized by a dimensionless magnetic Bond number Bom. In general, a more pronounced instability, which is evident by a greater number of breaking subscale droplets N, arises with a higher Bom. For a magnetic Bond number that is larger than a critical value, we identify a new mode of interfacial breakup pattern, where the central droplet is torn apart with major mass loss. In addition, we found that the volume fractions of breaking subscale droplets are strongly affected by the height variation of the initial fluid surface and appear unevenly distributed with dominance of a central droplet. On the other hand, for a prewetted plate, a nearly flat fluid surface is achieved due to a smaller contact angle, which then leads to virtually evenly distributed subscale droplets. A global size for all breaking subscale droplets is observed regardless of their initial diameters. The number of breaking subscale droplets (N) and the diameter of the initial droplet (D) can be approximated by a quadratic proportionality of N∼D2.

An experimental study on Rosensweig instability of a ferrofluid droplet

Cheng

2008

Physics of Fluids

Ordered microdroplet formations of thin ferrofluid layer breakups

2010

Physics of Fluids

The ordered breakup pattern of a thin layer of ferrofluid drop subjected to a uniform perpendicular field is experimentally investigated. The results confirm a universal pattern formation containing numerous breaking droplets of a uniform size, which is independent of the initial area of ferrofluid drop and the propagating directions of the formation waves. Two quantitative observations regarding the size and number of breaking droplets are concluded. Both the experiments and theoretical analysis show the correlation between the diameter of breaking droplets ͑d͒ and magnetization strength ͑M͒ can be characterized as d ϰ 1 / M 2 . The uniform size of breaking droplets under a constant field strength results in a linear proportionality between the number of breaking droplets ͑N͒ and the initial area of ferrofluid drop ͑A͒ as N ϰ A, which is verified by the experiments.

Fingering patterns in the lifting flow of a confined miscible ferrofluid

Miranda

2007

Phys. Rev. E

Miscible flow displacements of a ferrofluid droplet subjected to various magnetic field configurations and confined in a time-dependent gap Hele-Shaw cell are examined through highly accurate numerical simulations. The interplay between lifting, miscibility, and applied magnetic fields resulted in complex interfacial pattern formation. By varying the symmetry properties of the applied magnetic fields and by considering the action of Korteweg stresses, a number of interesting droplet morphologies are identified and characterized. The possibility of controlling the degree of fluid mixing and the ultimate shape of the emerging patterns by appropriately adjusting the strength of the applied magnetic fields is also discussed.