Lubrication theory

About: Lubrication theory is a research topic. Over the lifetime, 1713 publications have been published within this topic receiving 50261 citations. The topic is also known as: Fluid bearing.

Impact of slippage on the morphology and stability of a dewetting rim.

Abstract: In this study lubrication theory is used to describe the stability and morphology of the rim that forms as a thin polymer film dewets from a hydrophobized silicon wafer. Thin film equations are derived from the governing hydrodynamic equations for the polymer to enable the systematic mathematical and numerical analysis of the properties of the solutions for different regimes of slippage and for a range of timescales. Dewetting rates and the cross sectional profiles of the evolving rims are derived for these models and compared to experimental results. Experiments also show that the rim is typically unstable in the spanwise direction and develops thicker and thinner parts that may grow into 'fingers'. Linear stability analysis as well as nonlinear numerical solutions are presented to investigate shape and growth rate of the rim instability. It is demonstrated that the difference in morphology and the rate at which the instability develops can be directly attributed to the magnitude of slippage. Finally, a derivation is given for the dominant wavelength of the bulges along the unstable rim.

Modelling of elastohydrodynamic lubrication and fatigue of rough surfaces: The effect of lambda ratio:

Abstract: The article describes a numerical model for the analysis of elastohydrodynamic lubrication under conditions in which the nominal lubricant film thickness is small compared to the roughness present on the surfaces (lambda ratio less than unity). These conditions occur in most types of gear tooth contacts and in many other heavily loaded machine elements. In these situations, lubrication occurs at the roughness asperity level (micro-elastohydrodynamic lubrication), and in extreme cases ‘mixed’ lubrication behaviour occurs in which momentary solid contacts between the surfaces take place. In both micro-elastohydrodynamic lubrication and mixed lubrication regimes high, localised pressures are applied cyclically to asperity features as they move through the nominal contact leading to fatigue at the asperity level, which culminates in micropitting wear. Results of the modelling show the effect of lambda ratio in lubricated gear tooth contacts, and demonstrate the transition from full-film to micro-elastohydrodynamic lubrication and mixed lubrication, and the consequences in terms of predicted fatigue damage.

Dispersion coefficient in an electro-osmotic flow of a viscoelastic fluid through a microchannel with a slowly varying wall zeta potential

Abstract: The dispersion coefficient of a passive solute in a steady-state pure electro-osmotic flow (EOF) of a viscoelastic liquid, whose rheological behaviour follows the simplified Phan-Thien–Tanner (sPTT) model, along a parallel flat plate microchannel, is studied. The walls of the microchannel are assumed to have modulated and low potentials, which vary slowly in the axial direction in a sinusoidal manner. The flow field required to obtain the dispersion coefficient was solved using the lubrication approximation theory (LAT). The solution of the electric potential is based on the Debye–Huckel approximation for a symmetric electrolyte. The viscoelasticity of the fluid is observed to notably amplify the axial distribution of the effective dispersion coefficients due to the variation in the potentials of the walls. The problem was formulated for two cases: when the Debye layer thickness (EDL) was on the order of unity (thick EDL) and in the limit where the thickness of the EDL was very small compared with the height of the microchannel (thin EDL limit). Due to the coupling between the nonlinear governing equations and the sPTT fluid model, they were replaced by their approximate linearized forms and solved in the limit of using the regular perturbation technique. Here is the amplitude of the sinusoidal function of the potentials. Additionally, the numerical solution of the simplified governing equations was also obtained for and compared with the approximate solution, showing excellent agreement for . Note that the dispersion coefficient primarily depends on the Deborah number, on the ratio of the half-height of the microchannel to the Debye length, and on the assumed variation in the potentials of the walls.