Abstract
The article discusses results of the analyses of various bearing systems for the rotor of an ORC (Organic Rankine Cycle) microturbine with an electric power of 30 kW. It is impossible to choose the appropriate bearing system taking into account only basic parameters of the bearings. When designing a new power turbine, it is important to conduct the dynamic and strength analysis of the entire rotor-bearings-supporting structure system. The nominal rotational speed of the newly designed single-stage axial-flow turbine is 40,000 rpm. The turbine will be powered using the vapour of a low-boiling working medium. The chosen working medium cannot be used in combination with all materials that are commonly used for turbine constructions. An additional requirement was that the turbogenerator must be oil-free. The temperature of the working medium directed to the rotor blades could exceed a value of 200 °C. Three bearing systems were considered: bearings lubricated with a low-boiling fluid (in the liquid form), gas bearings lubricated with the vapour of a low-boiling medium and rolling bearings. Since the rotors used in those three systems have different geometries, their dynamic properties vary as well. The rotor dynamics analyses were carried out using computer programs belonging to the MESWIR environment, which had been developed at the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences (IMP PAN) in Gdańsk. The computational model, based on the finite element method, was used to prepare graphs on which are presented vibration amplitudes as functions of the rotational speed. The computational model, based on the finite element method, served to perform calculations on the basis of which graphs presenting vibration amplitudes as functions of the rotational speed were prepared. Moreover, vibration trajectories of individual nodes of the computational model were shown. Besides analyses of the bearings themselves, calculations were also carried out to assess the dynamic properties of the rotors supported by those bearings in a wide range of rotational speeds. As a result of the conducted analyses, the concept of an innovative turbogenerator was created. Its rotor can operate at a very high rotational speed, and the bearings do not require oil lubrication.
Highlights
Micro-cogeneration ORC systems have become increasingly popular in recent years
ORC microturbines can use bearing systems equipped in bearings of many different types, such as, for example, rolling bearings, bearings lubricated with a low-boiling medium in the liquid or gaseous state or foil bearings—which are increasingly considered as potential solutions
The tested rotors were supported by rolling bearings, hydrodynamic bearings and gas bearings
Summary
Micro-cogeneration ORC systems have become increasingly popular in recent years. The growing number of implementations and associated scientific publications is evidence of this. ORC microturbines have blade systems that are designed for specific operating parameters such as the type of working medium and the rotational speed. Numerical simulations of the operation of a 3 kW ORC microturbine, the rotor of which was supported by bearings lubricated with a low-boiling liquid, were presented in paper [5]. ORC microturbines can use bearing systems equipped in bearings of many different types, such as, for example, rolling bearings, bearings lubricated with a low-boiling medium in the liquid or gaseous state or foil bearings—which are increasingly considered as potential solutions. According to the design assumptions, the turbine generator is an oil-free device For this reason, it was necessary to use the working medium of the thermal cycle in a liquid or gaseous form as a bearing lubricant. This limits the number of possible solutions of the bearing system, but on the other hand, it enables designing a very modern, compact and hermetically sealed construction
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
