Selection of the Bearing System for a 1 kW ORC Microturbine

The article describes an analysis of various bearing systems for the rotor of an ORC turbine with an electric power of 1 kW. The nominal rotational speed of the newly designed single-stage axial-flow turbine is 100,000 rpm. The turbine is supplied with a low-boiling medium’s vapor and this medium is not compatible with all typical materials used for constructing power turbines. Additionally, the turbine must be an oil-free machine. In one of the design variants, the turbine rotor disk is to be made of plastic and the temperature of the working medium directed to the vanes will be approx. 150°C (at a pressure of 10 bar). Three different bearing systems were considered: 1. bearings lubricated with a low-boiling medium’s liquid; 2. gas bearings lubricated with a low-boiling medium’s vapor; 3. rolling bearings. After initial analysis, it was found that hydrodynamic bearings lubricated with a low-boiling medium did not work properly in this case and it was decided to conduct a detailed analysis of the second and third type of bearings. The two bearing systems are associated with changes in the geometry of the rotor, which in turn strongly affect the dynamic performance of the entire rotating system. The dynamic analysis of the rotor is the subject of the conducted research and constitutes part of the bearing selection process. This article presents the process of selecting and optimizing the bearing system for the rotor of a 1 kW turbine.