Results are presented of a study of heat transfer effects in hydrodynamically lubricated plain journal bearings.
The relevant literature is reviewed along with current procedures for the design of bearings. The computational difficulties associated with a full three-dimensional analysis are discussed.
Recent evidence from related work on pad thrust bearings has shown that the heat conducted to the stationary pads is a consistently small proportion of the total film energy dissipation. On the basis of this evidence a quasi-three-dimensional mathematical model is investigated. This analysis incorporates a quadratic temperature distribution through the film thickness, thereby accounting for heat transfer to and from the moving journal but neglecting heat transfer to and from the bush. The variation of viscosity with temperature is considered along and around the lubricant film.
Tests have been carried out on bearings of diameter 76.2mm, length to diameter ratios 0.5 and 1.0, and clearance ratios 0.001 and 0.002, over the speed range 1000 to 8000 r.p.m.. The heat conducted across the bush wall was deduced from a detailed mapping of the temperature distribution in the bush, and was found to represent around 10% of bearing power loss at high Peclet number, but to account for the removal of the bulk of the power loss at low Peclet number. At low speed the proportion of film cooling provided by bush conduction was significantly dependent upon load.
The test results are compared with results from the mathematical model and a recently published design procedure. Whilst there was good agreement between results from the- two prediction methods, these predictions did not agree well with the experimental results. The most significant discrepancy lay in the lubricant flowrate, which was in general poorly predicted.
Reasons for the discrepancies are discussed, and it is concluded that their source was associated with viscosity variation through the film thickness - a factor not modelled in either of the prediction methods.