Performance of a small-scale organic rankine cycle system using a regenerative flow turbine: a simulation analysis

Organic Rankine Cycles (ORCs) have an interesting potential in small-scale power production using low-temperature heat sources. Despite their unique applications in power production from low-temperature heat sources, the widespread use of small-scale ORC systems is still challenging especially due to high primary cost resulting in long-term payback periods. The reason goes back to several inherent technical limitations especially related to the available expander machines, which are usually accounted for a significant amount of the total investment cost of such systems. In this paper, a Regenerative Flow Turbine (RFT) adopted in a small-scale ORC prototype is investigated by means of a modelling study. The characteristic curves of the considered turbine have been obtained using CFD analysis to evaluate its performance in an ORC unit working with R245fa. Results of CFD have shown that performance of the RFT has been improved considerably using R245fa and real gas model instead of air and ideal gas model, and total-to-static isentropic efficiency could reach up to 45 % at the best. The system shows an overall performance that is comparable to that of ORC systems despite being penalized because of low isentropic efficiency of the RFT; however, the main advantages of RFTs are considerably low investment costs and high reliability which are important factors in the design of such small-scale power systems.