The technology of porous bearings is well-known in industry. In classical cases, the porous medium acts as an external reservoir making their use ideal for applications where an external lubricant supply is undesirable or impractical or when fluid has to be delivered on a continual basis. The work considered here looks to extend the benefits of typical porous bearings to allow for the bearing to be sealed, containing, from the onset of operation, all necessary lubricant.
The goal of this work is to demonstrate a bearing that circulates the fluid between a fluid film and an eccentric reservoir, using a porous medium as an intermediary; a system that is capable of supporting a realistic load, while simultaneously pumping the fluid back and forth between the lubricating region and the reservoir.
The method used to investigate such a bearing is a mixture of analytical and numerical techniques. For the analysis, a non-dimensionalization scheme is used to analyze both the momentum and thermal governing equations at their differing orders of magnitude. Upon doing so, the governing momentum equations are reduced considerably which allows for a straight-forward numerical solution procedure. The governing thermal equations are solved using an asymptotic expansion approach, keeping the first and second order terms and equations. This is done so to more accurately model the effects the circulating fluid has on the thermal performance of the bearing.
The phenomenon of cavitation is also discussed, utilizing a method that integrates cavitation into the governing equations and numerical solution procedure. Unlike other cavitation models that decouple cavitation from the governing momentum equations, this model accounts for mass flow continuity which leads to more realistic results.
Practical design considerations, including how to determine the effective permeability and the effective heat transfer coefficient at the exterior wall of the bearing, are discussed. These parameters, used extensively in the analytical and numerical modeling of the bearing, are essentially functions of other physical parameters. Once these relationships are established, their values can be utilized by someone looking to design a bearing considered in this work with a set of performance criteria in mind.
The combination of analytical work and numerical computations produces a comprehensive look at this new type of bearing. A long slider bearing and both long and short journal bearings are discussed in a parametric fashion, whereby the effects of varying the operational and geometric parameters are investigated by examining the accompanying pressure and temperature fields. The model presented here demonstrates the feasibility of a bearing that is capable of supporting a load while eliminating the need for an external lubricant supply and the necessary infrastructure that is required to actively feed a bearing with lubricant. It is shown that the temperatures stay within operating limits utilizing a realistic heat transfer coefficient and a realistic thermal conductivity for the lubricant while generating pressures inside the film that can support a load and simultaneously pump fluid between the film and reservoir regions.