Multi-condition operating characteristics and optimization of a small-scale ORC system

Abstract

The multi-condition operating characteristics of an organic Rankine cycle (ORC) are crucial to the development of the practical unit. This work developed a steady-state model of a small-scale ORC prototype built and tested in the lab. The influence of heat source/sink parameters, component design, and operation strategies are analyzed. It is found that the optimal output power and thermal efficiency correspond to the similar expander rotating speed but diverse working fluid mass flow rate. The higher mass flow rate is beneficial to the output power whereas deteriorates the thermal efficiency. Heat source temperature and flow rates mainly affect the unit output power while the ambient temperature and humidity influence both the output power and thermal efficiency. The condenser fouling resistance leads to a significant reduction of expander output power and system thermal efficiency. However, the effect of the evaporator fouling resistance could be neglected due to its sufficient redundant area. The long-term climate conditions and operating strategies profoundly impact the unit's off-design performance. The annual constant output power operation can be achieved by adjusting the working fluid mass flow rate. The thermal efficiency of the unit is damaged while pursuing the output power stability in winter and spring.