The study of magnetorheological fluids sedimentation behaviors based on volume fraction of magnetic particles and the mass fraction of surfactants

Magnetorheological fluids (MRFs) is composed of carbonyl iron (CI) powder distributed in carrier fluid. This paper studied the sedimentation behavior of MRFs in a cylindrical column by using direct visual observation (VO). In order to obtain the settlement law of MRFs with respect to particle concentration and surfactant contents, MRF samples with different particles volume fractions (i.e., 4, 10, 20 and 28 vol%) and with different surfactant mass fractions (i.e., none, 2, 4 and 5 wt%) were prepared, separately. And the commercial MRFs with the same magnetic particles volume fraction was used as the control group. In addition, the morphology of bare CI and surface modified CI particles samples were measured, experimentally, by light microscope. At last, three different settling velocity models (Vesilind model, Dick model, and Richardson and Zaki model) were considered to acquire the sedimentation velocity of magnetic particle concentration of MRF samples. Results present Dick model is more suited to the sedimentation rule of MRF sample in our study. The propagation velocity formula of the volumetric concentration of particles was also established on the basis of sedimentation velocity of particles and the particle setting velocity equation with the variational surfactant contents was also obtained. (paper)