Development and validation of an advanced simulation model for ORC-based systems

Low-grade heat recovery from solar or geothermal energy may be an eco-friendly resource for electric and thermal energy recovery. The Organic Rankine Cycle (ORC) is one of the main candidates to exploit low-temperature heat sources, otherwise difficult to access using conventional power generation systems. In this paper, an advanced thermodynamic model of an ORC is developed, with the final aim to optimize ORC conversion efficiency, especially for micro-CHP applications. First, a thorough review of issues related to ORC system modeling is presented by analyzing the state-of-the-art experience and advancements. Subsequently, an advanced simulation model is developed, by taking advantage of all the key characteristics of the models presented in the literature. The simulation model is developed in Matlab®/AMESim® environment, which allows system modeling both for steady and transient analysis. The heat source is coupled with the system through a plate heat exchanger, which is modeled using an iterative sub-heat exchanger modeling approach. A scroll expander, modeled in detail by decomposing the behavior of the fluid stream into several steps, is used to extract the useful work. Finally, model predictions for the evaporator and the expander are validated against both numerical and experimental data published in literature. The simulation model of the entire ORC system is also validated against literature data taken on a test bench