A new partitioned 1D LTNE continuum model for the simulation of 3D-shaped honeycomb absorbers

Kurzfassung

Porous absorber structures intended for open volumetric receivers of central tower power plants are receiving significant attention in current research. Due to the geometric complexity, volume-averaged continuum models are a common tool for the simulation of volumetric absorbers. Widely established for the investigation of ceramic foams, existing continuum models are less suitable for the simulation of honeycomb absorbers. 3Dshaped honeycomb absorber designs, i.e. absorbers with varying cross-sections, can pose additional challenges in the form of internal front-like surfaces, which are oriented perpendicular to the main channel axis. Due to the importance of the internal front-like surfaces w.r.t. absorption of solar radiation and convective heat transfer, a new partitioned 1D LTNE continuum model is proposed. The key innovation is the division of the absorber geometries into distinct sections forming a set of coupled LTNE models. The new 1D continuum model has been successfully validated against a 3D CFD model. For nine compared simulation cases, the calculated thermal absorber efficiencies differ on average 0.81 percentage points between the two models. Simulations have been conducted for the state-of-the-art HiTRec absorber and two new absorber geometries. The StepRec absorber, a monolithic channel design with characteristic step-pins created, via ceramic 3D screen printing out of SiSiC, reaches a thermal efficiency of up to 89.5 % for an air outlet temperature of 700 °C. A volumetric effect is predicted by for the new Emitec absorber, a channel geometry made of thin metal sheets, depending on the incident irradiation with efficiencies of up to 85.8 % at 700 °C.