The paper presents the results of experimental investigations of the ORC system with two scroll expanders which have been used as a source of electricity. Theworking fluidwas HFE7100 – a newly engineered fluid with a unique heat transfer and favourable environmental properties. In the ORC system three heat exchangers were used (evaporator, regenerator, condenser) and before expanders the droplet separator was installed. As a source of heat an innovative biomass boiler was used. Studies have been carried out for the expanders worked in series and in parallel. The paper presents the thermal and fluidflow properties of the ORC installation for the selected flow rates and different temperatures of the working medium. The characteristics of output electrical power, operating speed and vibrations for scroll expanders were also presented.

The article discusses various types of expanders used in the organic Rankine cycle systems to turn thermal energy into electrical energy. In addition to basic information on scroll, screw, vane, piston, and turbine expanders, the paper also describes the principles of their operation as well as major advantages and disadvantages. The following characteristics of expanders have been developed on the basis of the most recent scientific publications and own experimental research conducted at the IFFM PASci, in Gdansk. The analysis of various expansion devices available on the market, including those that are still in the development phase, revealed a wide variety of problems related to their operation. The design differences between them have a significant impact on their efficiency and reliability when operating with different working fluids. The article is an authoritative compendium of research-based information about designs and performance of various types of expansion devices. It may be useful for people who want to apply such devices in different types of cogeneration systems.

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