Application of a Heat Resistant Plastic in a High-speed microturbine Designed for the Domestic ORC System

orc2019 Tracking Number 101

ORC (organic Rankine cycle) systems have gained popularity in recent years. They are used in many new economic sectors. This is due to numerous advantages of this technology as well as the possibility to adjust operation parameters and output power to an available heat source and the user’s demand. One example of a successful attempt to apply ORC systems are single-family houses, where there is a great demand for heat and electricity. The high price of small ORC systems is one of the main factors that hamper their development (the cost of a single kilowatt of installed power increases considerably with a decrease in the power rating of the system). This article discusses research works aimed at applying modern plastics to build a high-speed microturbine that is intended for use in a domestic ORC system. Because of the high production cost of the rotor disc, it was decided to make it from plastic. The nominal electric power of the microturbine is 1 kW and the maximum rotational speed of the rotor is 120,000 rpm. It turned out that some plastics can be usefully applied to the microturbine because they are able to withstand such operating conditions. Machining of these plastics is easier and faster as compared to conventional metallic alloys, which could decrease the overall production costs. Preliminary analyses covered several plastics that met the adopted criteria, which are related to the operating conditions of the ORC system. Selected plastics were subjected to further tests such as chemical compatibility and dimensional stability when exposed to the contact with the ORC system’s working medium. Then, for selected materials, strength calculations were carried out, taking into account the full geometry of the rotor disc. The purpose of these calculations was to determine maximum stresses and deformations. Based on the results of the analyses performed, several rotor discs were made of one carefully selected type of plastic. Already after the first tentative series of plastic blade systems was manufactured, it became clear that it is possible to significantly shorten the machining time and reduce production costs. The rotor disc made of plastic was then installed in the turbogenerator that has passed preliminary tests under laboratory conditions. The conducted research and its results could be of interest for those scientists and engineers who are looking for new material solutions that can enable shortening the production time and lowering the production costs of microturbines employed in ORC systems. The research carried out so far demonstrated that well-chosen heat resistant plastics can be successful in replacing constructional materials used to date.