Abstract
Abstract The development of aerodynamic bearings applications where ambient conditions cannot be controlled (e.g., for automotive fuel cell compressor) raises the question of the effects of condensation in the humid air on performance. A modified Reynolds equation is obtained in relation to humid air thermodynamic equations, accounting for the variation of compressibility and viscosity in the gas mixture. The load capacity and stability of plain and herringbone-grooved journal bearings is computed on a wide range of operating and ambient conditions. In general, performance metrics show an independence on humid-air effects at moderated temperature, although the stability of the grooved journal bearing exhibits strong variations in particular conditions. In consequence, a safety margin of 25% is suggested for the critical mass.
Highlights
275 A modified form of the Reynolds equation suited for humid-air lubrica276 tion was developed and applied to grooved and plain journal bearings on a wide range of operating conditions
Vapor condensation negatively affects the load capacity of journal bearings, without practical significance at temperature levels met in atmospheric conditions (Ta < 310 K)
The critical mass of plain journal bearings (PJB) is affected in negligible proportions, while herringbone-grooved journal bearings (HGJB) can experience a significantly reduced critical mass at particular compressibility numbers, with a reported reduction up to 25% in realistic atmospheric temperatures
Summary
Eccentricity ratio (-) Circumferential coordinate (rad) Compressibility number (-) Dynamic viscosity (Pa s) Density (kg m−3) Squeeze number (-) Viscosity coefficient (-) Relative humidity (-) Bearing angular velocity (rad s−1) Excitation angular velocity (rad s−1) Superscripts Normalized Saturated Subscripts Ambient condition Air Critical Condensable Groove Non-condensable Ridge, ratio Isothermal Water vapor (gas phase) Water liquid phase x-axis y-axis z-axis Static, unperturbed Perturbed Acronyms Humid air Herringbone grooved journal bearing Plain journal bearing Narrow groove theory
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