Optimized volumetric solar receiver: Thermal performance prediction and experimental validation

In the last decade, different absorber geometries, such as foams and honeycombs, have been tested at laboratory or industrial scale in order to achieve high performance in the conversion of the solar radiation into usable heat, with the current state-of-the-art, the HiTRec-II monolithic honeycomb, characterized by a square-channel section and made out of siliconized silicon carbide (SiSiC). Such geometry has been so far the best compromise for large-scale application thanks to the low production costs, easy manufacturability through extrusion procedure and overall acceptable performance. However, it does present some drawbacks, since the geometry is not able to contain the radiative heat losses, especially from the front surface. An optimized absorber geometry, capable to reduce overall thermal losses, is presented in this work, being able to increase the final thermal efficiency of more than 12% compared to the current state-of-the-art and showing the presence of the so-called volumetric effect, since the outlet fluid temperature is higher than the solid inlet temperature. A test sample has been produced for laboratory-scale experiments, in the form of a 3:1 scaled prototype through additive manufacturing procedure, using a titanium-aluminium alloy (Ti6Al4V) and the experimental results were in good agreement with the numerical calculation, with a deviation of 3%, computed considering a 3:1 Ti6Al4V scaled-up sample. As the manufacturing technology will progress and become cheaper in the near future, it will be possible to improve the overall Solar Power Tower (SPT) plants performance using advanced micro-geometry for open volumetric receivers.