Integrated Optimization Study of Axial Expander Applied to Waste Heat Recovery System
Guilherme Leibsohn Martins1; Sérgio Leal Braga2; Sandro barros Ferreira3
1 Petrobras; 2 PUC-RIO; 3 GT2 Energia
doi:10.20906/CPS/COB-2015-0225
Resumo
An analysis of the application of an organic Rankine cycle (ORC) to recover the heat rejected by an internal combustion engine is presented. The selected fluid is R245fa, whose real gas behavior is relevant under the studied conditions, as modeled by the Redlich-Kwong-Soave equation of state. A single stage partial admission axial expander is assumed to directly drive a synchronous two pole generator. The loss model for the flow through the axial blades adopted in this work is based on the boundary layer theory, the concept of diffusion factor, wind tunnel cascade tests available in literature and the conservation equations for compressible flow. The basic geometry and dimensions needed to achieve maximum expander efficiency are determined under several subcritical and supercritical cycle conditions by means of a restrained design optimization algorithm. The optimum value for the evaporator temperature is stablished so as to obtain the maximum net output from the subcritical cycle, according the constructive alternatives considered. The single stage expander design is shown to be greatly influenced by media compressibility and the use of convergent-divergent profiled nozzles is promising to achieve the highest possible performance potential, especially at high pressure steam generator conditions.
Palavras-chave: organic Rankine cycle; waste heat recovery; dense gases; design optimization; axial stage efficiency