Abstract

Nowadays, solar volumetric absorbers represent a promising alternative to harvest solar radiation. In these devices, the traditional blackened surface where solar radiation is converted into heat and later transferred to a heat transfer fluid is removed. Then, the solar radiation is trapped by direct volumetric absorption on the carrier fluid itself. This reduces the radiative losses and improves the photo-thermal efficiency. From all the technological available options to fabricate volumetric absorbers, "solar nanofluids" that consist of nanoparticles (NPs) suspended in a heat transfer fluid have boost as a promising alternative. Nevertheless, up to now the synthesis of solar nanofluids faces different challenges as the difficulty to create stable nanofluids composed by complex organic oils and metal nanoparticles (MNPs) in an environmental friendly way, without producing chemical waste. In this communication, it is presented the synthesis of a solar nanofluid by an eco-friendly in-situ technique known as Pulsed Laser Ablation in Liquids (PLAL). The synthesis approach is based on the extraction of material from the surface of a tin plate immersed in ethylene glycol (EG) by means of laser ablation. EG is a good base fluid as it presents low absorption in the visible and near infrared range and it is commonly used in industry, residential and commercial applications. On the other hand, MNPs as tin show high efficiency in the absorption process of solar radiation due to its almost flat spectrum in the visible and near infrared ranges. The thermal conductivity of the solar nanofluid sinthesized by PLAL is increased until 140ºC in a 3.6% in comparison with the pure EG. The transmission solar spectral irradiance through the nanofluid is low the first day, but it is increased over time due to the lack of stability in the nanofluid. However, a comparison between a solar nanofluid made with PLAL and the one produced by the two-step method with commercial NPs shows that the laser-assisted nanofluid presents a higher absorption efficiency and an improved stability over the time. After a simple visual inspection of the as-produced nanofluids is possible to notice that in the nanofluid synthesized by PLAL the sedimentation is lower than in the other case.