Parallel-expander Organic Rankine cycle using dual expanders with different capacities

•A novel ORC with multi expanders in parallel (PE-ORC) was proposed for varied heat.•The proposed PE-ORC were experimentally evaluated with two different expanders.•The experimental results show three clearly separated operation regions with high efficiency.•Better heat recovery capability over a wider range of heat input compared to a basic ORC system.•A control strategy for the system is proposed to maintain superheated state at the expander inlet.

This study reports on a parallel-expander Organic Rankine cycle (PE-ORC) using dual expanders with different capacities. This system is applicable to waste heat sources that have large variation, such as distributed power plants with varying electricity demand. The test bench for the experimental investigation consists of a PE-ORC loop with two different scroll expanders, an electrical water heating system, and an air-cooled chiller. The tested performance characteristics for each operating mode are presented. The experimental results show three clearly separated operation regions with high efficiency, two possible switching points of the operating mode, and good heat recovery capability over a wider range of heat input compared to a PE-ORC system with two identical expanders. A control strategy for the system is proposed to maintain superheated state at the inlet of expander and to obtain high performance after changing the operating mode.