Virtual model for ORC – Whole ORC modeling: WOM

In recent years, computational fluid dynamics (CFD) has been applied for the design and analysis of positive displacement machines (both compressors and expanders) used in organic Rankine cycle (ORC) systems, as well as for other components such as heat exchangers. The virtualization of the whole ORC model can be carried out in order to build a virtual test bench: such a device can be useful for testing the off-design conditions, mapping the performance of each component and of the entire ORC system, highlighting particular phenomena like fluid stagnation and the level of the liquid fraction inside the heat exchangers. A virtual test bench could be useful for testing the ORC behavior with different types of fluids. Issues related to compatibility between the organic fluid and the sealing systems or the lubricant oil used in the volumetric displacement machine like pump or expander, do not represent obstacles for the virtual tests. The full 3D numerical simulation of the components can therefore be coupled with a 0D loop that provides boundary condition coming from the outer world (such as thermal and electric loads, environmental conditions, etc.) and transfer the information between machinery somehow simulating the piping system. The resulting 0D-3D approach can be reliably used as virtual model for the ORC system. The present paper reports the framework in which the Whole ORC Modeling (WOM) could be developed. The WOM comprises the CFD analysis of the mains components involved in typical ORC systems like a pump, expander, condenser, evaporator and regenerator. The results show how the WOM could be useful for studying the ORC system highlighting several features that afflict the operation and performance.