Investigation of magnetorheological grease flow under the influence of a magnetic field

Abstract

In this work, we present a novel magnetohydrodynamic flow study using micro-Particle Image Velocimetry (m-PIV) in a rectangular channel under the effect of a uniform transverse magnetic field. This study is the first of its kind to explore the use of magnetorheological grease in machine components such as bearings. Rheological characterisation of grease samples establishes the non-linear relationship between the shear rate and shear stress and thus confirms the non-Newtonian behaviour of the grease. The flow follows a parabolic path away from the magnetic field. Experimental studies reveal that the flow velocities reduce considerably from 11.9 m/s to 1.7 m/s in the vicinity of the magnetic zone due to the formation of strong field-induced chains. These chains are responsible for an increase in localized yield stress of grease thereby causing a surge in the resistance to flow. Further, numerical and analytical models are developed to predict the velocity field under a magnetic field. The analytical model can accurately predict the flow velocity for different magnetic field strengths. It can be deduced that the obtained correlation is a suitable model for estimating the velocity values at different magnetic field strengths for flow in similar configurations. Numerical results predicted by a finite volume method-based solver are in good agreement with the experiments on the upstream side. Flow velocities increase with flow rate and decrease with the onset of the magnetic field. Pressure drop along the channel length shows an abrupt change in the magnetic zone. This is because of the disturbance of the normal flow regime due to the presence of the magnetic field. The grease flow disturbs the distribution of magnetic field lines resulting in flow-induced field strength of B = 0.1 T against an applied external magnetic field strength value of B = 0.3 T. The present study analyses the effects of an external field on the flow patterns of magnetorheological grease. It confirms that magnetorheological grease provides controllability in applications, because flow properties can be varied by tuning the magnetic field strength.