pressureviscosity

Pressureviscosity refers to the way a liquid’s viscosity changes in response to applied pressure. In many liquids, including lubricants and oils, viscosity increases as pressure rises. This effect is especially important in high-load applications such as bearings and gears, where the pressure within the lubricating film can become very large and significantly alter film formation and load-carrying capacity.

The relationship between viscosity and pressure is often described by the Barus equation: μ(p) = μ0 exp(β p). Here μ(p) is the viscosity at pressure p, μ0 is the viscosity at ambient pressure, and β is the pressure-viscosity coefficient, a material-specific parameter typically determined experimentally. The Barus coefficient is commonly expressed in units of 1/pressure (for example 1/MPa). While Barus provides a convenient approximation, real fluids can exhibit nonlinear or temperature-dependent behavior, and other models may be used to cover broader pressure ranges.

Applications and measurement: Knowledge of pressureviscosity is crucial in elastohydrodynamic lubrication, where high pressures and film thinning interact to determine load support and wear characteristics. Engineers determine μ0 and β at a reference temperature through high-pressure viscometry, enabling predictions of film thickness and performance under operating conditions. Temperature, temperature dependence of β, and shear-rate effects also influence viscosity under pressure, so comprehensive data are often needed for accurate lubrication simulations and component design.