Oscillatory instability of convection in ferromagnetic nanofluid and in transformer oil

Abstract

Stability of a mechanical equilibrium of ferromagnetic nanofluid and transformer oil in a spherical cavity carved inside a Plexiglas block heated from below is investigated experimentally. It is shown that in a fluid left at rest prior to the start of experiment the onset of convection is delayed and the convective motion arises abruptly acquiring a finite equilibrium amplitude at supercritical temperature differences. Convection has an oscillatory character associated with a precession of a vortex axis in the equatorial plane. A hysteresis is detected in the reverse transition to a quiescent state. Oscillations in the investigated ferro-nanofluid have been observed during the complete experimental runs (up to several weeks). Similar oscillations in transformer oil have been detected only in the beginning of experimental runs. They were observed to eventually decay resulting in a stationary convection.

The Effect of Viscous Dissipation and Thermal Radiation in Siskoferronanofluid Flow over a Porous Medium

“…[23] Ferrofluid flow and convective heat transfer effects studied for Ferro hydrodynamic and Magnetohydrodynamics effects. Stability of a mechanical equilibrium of ferromagnetic nanofluid and transformer oil is tested experimentally in a spherical cavity [24]. Under the influence of magnetic dipole with Soret and suction effects the influence of chemical reaction and heat transfer study of Maxwell saturated ferrofluid flow over a stretching surface is investigated [25].…”

The influence of uniform external magnetic field on heat transfer in ferrofluids

“…where µ 0 = 4π ×10 −7 H/m is the magnetic constant, η, λ and χ are the coefficients of dynamic viscosity, thermal diffusivity and magnetic susceptibility, respectively, and ∆T is the temperature difference between the poles of a sphere of diameter d. Thus, to achieve large values of Rm in a uniform external field, large temperature differences need to be applied to fluids with large pyromagnetic coefficients. Under such conditions, thermomagnetic convection can be induced by applying a uniform vertical magnetic field even if the fluid is heated from above and remains in a stable mechanical equilibrium with respect to gravitational buoyancy [3]. The thermomagnetic parameter characterizing the dependence of the magnetic Rayleigh number on the magnetic field for a given type of FF is K 2 /(1 + χ), which was described in detail in the case of a flat fluid layer in [4].…”

“…Instead the temperature measurements were made for detecting and quantifying the strength of convection flows. In a spherical cavity they take the form of a vortex with the axis located in the equatorial plane of the cavity [3,8]. When they arise, the symmetry of the temperature distribution breaks, and this fact can be used to detect the onset of convection.…”