Saturated Water Journal Bearings of a Turbo Compressor

We have developed a water lubricated journal bearing for water vapor turbo compressor. Utilizing working fluid as liquid lubricant has advantages on high efficiency and structural simplicity of oil-free system. But the evaporation of lubricant effects on various kinds of dynamic properties which must be considered during the development of turbo compressors. The loss, stability, and heat transfer of water lubricated bearings, and the effects of cavitation were studied. When the sub-cool of lubricant water is small, vaporous cavitation is likely to appear. Vaporous cavitation is essentially different from gaseous cavitation of general oil-lubricated bearings in that the evaporation of lubricant occurs which involves latent heat. Because the vaporous cavitation reduces the viscosity loss, and the bearing is cooled not only by sensible heat but also by latent heat, the bearing temperature elevation is suppressed. Another effect of cavitation is stabilization of half speed whirl. We conducted two experiments. Firstly, a sub-scale bearing experiment which consists of 2 conical journal bearings, to investigate the above effects quantitatively and develop a prediction method. Secondly, a full-scale bearing experiment to demonstrate the bearings. As a result, we could drive a 28kg rotor at 31,000rpm stably and efficiently with water lubricated journal bearings.