Analysis of ferrofluids-nonferrofluids interface instability in microchannels under magnetic field

The stable and clear interface in the microchannel is an important basis for further particle screening. Using the ferrofluid as the core flow and the non-magnetic fluid on both sides as the sheath flow is conducive to microfluidic focusing of particles under magnetic field. This paper is based on the experimental analysis of the ferrofluid-water interface in three-phase laminar microfluidic chip and the solution of the mechanical model. The dimensionless numbers Pe, Bom, Ca, We, Re, and the time tT, td, tito represent the movement state of the particles at the interface were introduced, and it obtained d/h∝(X/Pe)0.633~0.852. The effect of each force on the interface was in the order of magnetic force greater than interfacial tension, inertial force, and viscous force. When Qf/Qw=2, Qf=15μL/min, the convective effect was obviously greater than the diffusion effect. In this case, the viscous dissipation effect of particles was small, and the interface was stable at the center of the channel. The diffusion time td∝(X/Pe)0.523~0.872 oscillated violently at the entrance stage, accelerating fluid mixing. Meanwhile, the increase of magnetic field gradient and fluid diffusion velocity will lead to a drastic change in interfacial time ti∝(X/Pe)0.778~1.172. When X=225—250 in the middle of the magnetic field, tT>ti>td, and the screening efficiency of magnetic swimming was the highest. © 2024 Chemical Industry Press Co., Ltd.. All rights reserved.