Rajesh C. Shah

Impact of various and arbitrary porous structure in the study of squeeze step bearing lubricated with magnetic fluid considering variable magnetic field

The aim of this paper is to study the impact of various and arbitrary porous structure on the performance of the step bearing lubricated with magnetic fluid. The paper also studied about the effect of squeeze velocity which appears when two lubricated surfaces approaches to each other with a normal velocity. The porous layer (region or wall or matrix) is attached to the lower flat impermeable plate (surface or disc). Two porous structure models given by Kozeny-Carman (a globular sphere model) and Irmay (a capillary fissures model) are considered for the study. The upper surface is a step surface approaching to lower one. The magnetic field considered here is variable and oblique to the lower plate. Expressions for pressure under the step surfaces and load-carrying capacity are obtained. The dimensionless load-carrying capacity W ¯ is calculated for various values of permeability, porous width, length of first step of the bearing, width of the film region, and strength of magnetic field. From the results it is observed that W ¯ increases with the increase of the length of the first step and with the increase of K (which leads increase of H) for both the models. It is also observed that permeability and width of porous matrix have almost no effect on W ¯ . In the case of width of the film region, it is observed that W ¯ attains same behavior whether film thickness is small or large. Moreover, calculation shows that globular sphere model have better performance for W ¯ than capillary fissures model. Thus, it is suggested to have a design of porous squeeze step bearing with globular spheres in the porous region considering variable magnetic field strength H of order 104.

Analysis and comparative study of ferrofluid lubricated circular porous squeeze film-bearings

Based on ferrohydrodynamic theory by R. E. Rosensweig and continuity equation for film as well as upper and lower porous regions, a general modified Reynolds equation for ferrofluid (FF) lubricated circular discs porous squeeze film-bearings is derived by assuming the validity of the Darcy’s law in the porous regions. The effects of porosity, slip velocity, anisotropic permeability and rotation at both the discs are also included for the study. Here, the FF is controlled by oblique and radially variable magnetic field. The effect of porosity is included because of its advantageous property of self-lubrication, and oblique variable magnetic field is important because of its advantage of generating maximum field at the required active contact zone of the bearing design systems. Using Reynolds equation, different circular porous squeeze film-bearing design systems (e.g. exponential, secant and parallel (flat)) are studied and compared for load-carrying capacity. During the course of investigation, it is observed that uniform magnetic field does not affect on the performances of the bearing systems.

Ferrofluid lubrication of circular squeeze film bearings controlled by variable magnetic field with rotations of the discs, porosity and slip velocity

Based on the Shliomis ferrofluid flow model (SFFM) and continuity equation for the film as well as porous region, modified Reynolds equation for lubrication of circular squeeze film bearings is derived by considering the effects of oblique radially variable magnetic field (VMF), slip velocity at the film–porous interface and rotations of both the discs. The squeeze film bearings are made up of circular porous upper disc of different shapes (exponential, secant, mirror image of secant and parallel) and circular impermeable flat lower disc. The validity of Darcys Law is assumed in the porous region. The SFFM is important because it includes the effects of rotations of the carrier liquid as well as magnetic particles. The VMF is used because of its advantage of generating maximum field at the required active contact area of the bearing design system. Also, the effect of porosity is included because of its advantageous property of self-lubrication. Using Reynolds equation, general form of pressure equation is derived and expression for dimensionless load-carrying capacity is obtained. Using this expression, results for different bearing design systems (due to different shapes of the upper disc) are computed and compared for variation of different parameters.

Some porous squeeze film-bearings using ferrofluid lubricant: A review with contributions

Based on ferrofluid flow model given by R.E. Rosensweig, a general equation for different slider squeeze film-bearing design systems, formed by solid upper surface and lower porous plate, is theoretically derived considering the effects of porosity, permeability, squeeze velocity, tangential velocity and oblique variable magnetic field. While deriving the general equation, continuity equation and Darcy’s law are also considered. Expressions for pressure and load-carrying capacity for different squeeze film-bearing design systems are obtained. The results for dimensionless load-carrying capacity are computed and compared with previous results in some cases. The results indicate the better performance of different bearing systems when ferrofluid is used as lubricant. Further, some important conclusions are also made. Two permeability models – globular sphere and capillary fissures are discussed. The variable magnetic field is considered because uniform magnetic field does not enhance bearing performances.