Experimental tests and modelization of a domestic-scale ORC (Organic Rankine Cycle)

The work deals with the realization of a prototype, the experimental testing and the modelization of a small-size Organic Rankine Cycle. The components of the circuit, filled by the refrigerant R245fa, are an inverter-driven diaphragm pump, a plate condenser, an electric boiler and a scroll expander. The latter is a hermetic device, derived from a commercial HVAC compressor, and expected to deliver a power of about 1.5 kW. The rotating speed of the expander, and of the electric generator contained in the same sealed vessel, is free, and the three-phase variable-frequency alternating current is converted into a direct current by a rectifier. The system is controlled regulating the feed pump speed and the vapor temperature at the boiler exit, while the imposed braking torque is varied adjusting the resistance of the electric load connected to the generator. Some performance parameters of the whole cycle and of the plant components have been investigated with a series of experimental tests, whose results are discussed in the paper. The registered working parameters and efficiencies are comparable with those expected from previous studies and reported in literature, even if the system is not yet optimized. These results are the basis for the numerical modelization of the cycle, realized with the simulation software LMS Imagine.Lab AMESim®. This has been chosen for its wide libraries of fluid properties and cycle mechanical and electric components and for its capacity to simulate systems also in transient conditions. Such a feature will be needed in the future developments of the work. Once the numerical model has been realized and calibrated on the basis of the experimental measurements, it will be used to achieve a better knowledge of the physical system, to understand which are the main problems to solve in order to achieve better performances, and finally to choose a more suitable control strategy for the prototype.