Comment on "Consistent hydrodynamics of ferrofluids"
We demonstrate that the theory presented by A. Fang (Phys. Fluids, v. 34, 013319, 2022) violates the law of conservation of angular momentum, and is therefore false.
physics.flu-dyn↗
arXiv subjects
Mark I. Shliomis
Publications and source records attributed to Mark I. Shliomis.
Comment on "Novel Convective Instabilities in a Magnetic Fluid"
Comment on the paper "Novel Convective Instabilities in a Magnetic Fluid" by W. Luo, T. Du, and J. Huang, Phys. Rev. Lett., v.82, p.4134 (1999).
cond-mat.soft↗
Convective Instability of Magnetized Ferrofluids: Influence of Magnetophoresis and Soret Effect
Convective instability in a ferrofluid layer heated from below or from above in the presence of a uniform vertical magnetic field is investigated theoretically. Convection is caused by a magnetic mechanism based on the temperature and concentration dependence of magnetization. An imposed temperature gradient establishes (by the Soret effect) a concentration gradient of magnetic particles of which the ferrofluid is composed. Both these gradients cause a spatial variation in magnetization, which induces a gradient of magnetic field intensity within the fluid layer. The field gradient induces in its turn an additional redistribution of magnetic grains due to magnetophoresis. Resulting self-consistent magnetic force tries to mix the fluid. A linear stability analysis predicts oscillatory instability in a certain region of the magnetic field strength and the fluid parameters. The instability owes magneto- and thermophoresis its origin: were the particle diffusion not operative, then only stationary instability would occur. A discovery of predicted convective oscillations is expected in ferrofluid layers about 1 mm thick, where the buoyancy mechanism is negligible and the characteristic diffusion time is not too long.
cond-mat.soft↗
Ferrohydrodynamics: testing a new magnetization equation
A new magnetization equation recently derived from irreversible thermodynamics is employed to the calculation of an increase of ferrofluid viscosity in a magnetic field. Results of the calculations are compared with those obtained on the basis of two well-known magnetization equations. One of the two was obtained phenomenologically, another one was derived microscopically from the Fokker-Planck equation. It is shown that the new magnetization equation yields a quite satisfactory description of magnetiviscosity in the entire region of magnetic field strength and the flow vorticity. This equation turns out to be valid -- like the microscopically derived equation but unlike the former phenomenological equation -- even far from equilibrium, and so it should be recommended for further applications.
cond-mat.soft↗
Comment on "Magnetoviscosity and relaxation in ferrofluids"
It is shown and discussed how the conventional system of hydrodynamic equations for ferrofluids was derived. The set consists of the equation of fluid motion, the Maxwell equations, and the magnetization equation. The latter was recently revised by Felderhof [Phys. Rev. E, v.62, p.3848 (2000)]. His phenomenological magnetization equation looks rather like corresponding Shliomis' equation, but leads to wrong consequences for the dependence of ferrofluid viscosity and magnetization relaxation time on magnetic field.
cond-mat.soft↗