Experimental study of a hybrid ferrohydrodynamics instability in miscible ferrofluids: droplet size effects

Ching-Yao Chen¹ - W.-K. Tsai² - J. A. Miranda³

¹ Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of China
² Department of Mechanical Engineering, National Yunlin University of Science and Technology, Yunlin, Taiwan, Republic of China
³ Departamento de Física, LFTC, Universidade Federal de Pernambuco, Recife, Pernambuco 50670-901 Brazil

Abstract
Recently, we have performed a ferrofluid experiment that revealed the existence of a hybrid ferrohydrodynamic situation in which a three-dimensional, collapsing Rosensweig peak and effectively-two-dimensional labyrinthine structures occur simultaneously (C.-Y. Chen et al., Phys. Rev. E., vol. 77 (2008), 056306.) This has been done by immersing a ferrofluid droplet in a thin layer of a miscible nonmagnetic fluid, under the action of a vertically applied magnetic field. We extend the investigation of this new system focusing on the effects produced by ferrofluid droplets of different sizes. It is found that larger droplets result in a more prominent manifestation of both interfacial instabilities. Moreover, the observations of the labyrinthine fingering patterns are extended into very late stages, where the decaying ferrofluid peak has been completely reimmersed into the surrounding nonmagnetic fluid. Figs 9, Refs 29.