Heat transfer framework for selecting the structure of open volumetric air receivers

摘要

During the last 10 years, the interest of several authors in the use of compressible gases (as CO_2 and Air) as working fluid in concentrated solar power systems (CSP) has increased significantly. These fluids allow to increase the upper limit of the operating temperatures and achieve higher conversion efficiencies. Nevertheless, achieving temperatures higher than 700°C requires the use of volumetric absorbers, which design presents two scientific challenges. The first related to the computational modeling of the transport phenomena inside the porous media, coupling the viscous effects, compressibility, the convective heat transfer and the extinction-propagation of the concentered radiation in the solid media. And the second, related to the design process regarding the configuration, distribution and material selection of the solid media, aiming to deal with the challenging operating conditions. In that context, the present study presents a performance analysis of an open volumetric absorber using atmospheric Air as working fluid, comparing honeycomb mini-channel (HC) and ceramic foam (CF) as exchange solid media. The results show that the ceramic foam is the better option for the total range of porosity analyzed, accordingly to the novel figure of merit proposed in this document. The proposed benefit factor considers the benefit related to the capacity of heat exchange and the power losses by pressure drop inherent of each design in study.