Theoretical Analysis of Hydrodynamic Water-Lubricated Plain Bearings for High-Speed Applications

Oil is usually used for the lubrication of plain bearings due to its high viscosity, which is the essential parameter in the bearing designing process. However, the oil-free operation seems desirable in a growing number of industrial applications to eliminate complex separation processes of the lubricant from the working fluid after the compressor or various disadvantages of the lubricant in the process downstream of the compressor, e.g. oil traps and reduced heat transfer in the heat exchangers. In addition to the dry-running approach familiar to the process gas industry, the use of the working fluid itself as a lubricant is a possible approach to solve this problem. This paper analyses the feasibility of using a plain radial bearing for a high-speed spindle screw compressor that uses water as a working fluid, internal coolant, and lubricant. Based on calculations, this paper discusses the possible rotational speed and temperature range as well as other challenges and their impact on the minimum acceptable water film thickness and flow in the plain bearing gap.