Agglomeration effects in rotating ferrofluids

Abstract

Abstract We study flow structure modifications due to agglomeration, aggregation and chain formation, also known as elongational flow effect for the flow of a ferrofluid in the gap between two concentric rotating cylinders. The system is subjected to either transverse, axial and oblique magnetic field. Consider elongational flow the torque is found to increase or decrease with variation of elongational flow parameter. Furthermore the 3D flow structures themselves are modified, e.g. resulting in variation of different energy portions/contents and the angular momentum transport. The detected modifications are explained by the fact that real ferrofluids consist of a suspension of particles with a finite size in an almost ellipsoid shape as well as with particle–particle interactions that tend to form chains of various lengths and also have a tendency to agglomerate. To come close to such realistic situation for ferrofluids, we consider elongational flow effects incorporated by the symmetric part of the velocity gradient field tensor, which can be scaled by a so-called transport coefficient λ 2 . The complexity of structures and modifications depend on the magnetic field configuration. In general complexer oblique fields result in stronger interactions and modifications.