STRUCTURAL ANALYSIS OF A REGENERATIVE FLOW TURBINE FOR LOW-TEMPERATURE ORGANIC RANKINE CYCLE SYSTEMS

A Regenerative flow turbine (RFT) is an innovative turbomachine based on the momentum exchange between the impeller and the flow resulting in a helical trajectory in the peripheral direction and generating a pulse pressure variation inside the flow. In general, an RFT shows low isentropic efficiencies compared to other kinds of expanders, but the potential low manufacturing cost makes it an alternative expander for low-temperature Organic Rankine Cycle (ORC) applications. In a previous study carried out by some of the authors, the performances of an RFT for low-grade waste heat recovery (WHR) applications in a non-regenerative ORC system have been preliminarily assessed. In this work, a structural analysis of the same RFT geometry has been performed in ANSYS to evaluate the mechanical stress before its potential manufacturing. More precisely, two different low-cost materials have been investigated namely aluminum and polyphenylene sulfide (PPS), and the most critical parts of the expander identified considering the nominal operating conditions of the ORC system. The analysis has shown that the maximum tensile strength is reached during the thermal transient phase and it is about 127.4 MPa and 50.8 MPa for aluminum and PPS respectively. Under thermal steady-state conditions, instead, the maximum stress lowers to 42 MPa for aluminum and 40 MPa for PPS. Hence, together with the evaluation of the mechanical stress of the expander in low-temperature applications, the analysis has provided useful insights into the expected power output and the potential dilation of the material, which may result in the critical operation of the impeller.