Analysis and design optimization of an ejector integrated into an organic Rankine cycle

Abstract The organic Rankine cycle (ORC) is a promising technology to convert low-grade heat to electric power. In this decade, the improvement of the ORC performance is attracting more attention. It has been proven in previous studies that integrating an ejector into an organic Rankine cycle increases the power output capacity. In this study, the impact of both ejector geometry and working characteristics on cycle performance, in particular, the power output capacity is investigated. The ejector functions in the double-choking regime. To this aim, a parameter sensibility study is conducted using some important indicators. Results show that the net power output rises with increasing ejector area ratio or secondary mass flow rate; it falls with increasing throat diameter, primary inlet pressure, or primary inlet temperature. The constant area duct diameter is one of the most important geometrical parameters influencing the power generation and the cycle performance. Power output capacity is found to be independent of the ejector outlet parameters when the ejector operates in the double-choking region. The paper also presents and discusses various energy and exergy metrics as a means of evaluating the cycle performance.