The design of a turbine in a closed cycle setup of electrical power production constitutes the major challenge for the increase of system performance. The preliminary design of an electricity producing turbine, in the range of 100 kW, in a closed low enthalpy Organic Rankine Cycle, powered by either a geothermal and solar thermal field or exhaust emissions of PEM type fuel cells is presented in this paper. For this reason, an extended bibliographic review was performed; on the basis of its findings, an integrated model of equations was developed, aiming in the calculation of the thermodynamic parameters of a closed organic cycle for different working fluids, such as NH3, CO2 and R-134a. Moreover, another mathematical model was developed, in order to calculate the geometrical characteristics of the turbine, as well as the blade geometry, through velocity triangle. After comparison of results for the three working fluids, R-134a was chosen as the best solution, since the system performance index approached 10%. As it is already stated, the main purpose of the paper is the increase of an integrated system performance, which will make use of the wasted energy in the form of heat in order to produce electrical power: therefore, a subsequent study of all components of such a system ( the compressor, the evaporator, the condenser, the gearbox and the bearings) was carried out. Finally, it is worth noting that two versions of the turbine design were developed. In the first version, V2 turbine speed is explicitly subsonic, while in the second V2 turbine speed is equal to Mach, meaning that the flow is choked. Results show that, keeping the crucial parameters for the geometrical formation of the blade constant, turbine volume can be significantly decreased up to 90%.
