Abstract
Some nanoparticles (NPs) possess an outstanding photothermal conversion under optical illumination. For this reason, these NPs are under research in a wide variety of light-induced heating applications such as solar nanofluids, which could be used for direct light absorption in solar collectors. Experimental characterisation of solar nanofluids for their application to light-to-heat conversion processes requires a considerable amount of resources to determine the properties of this mixture, at the nanoscale level. On this ground, an inverse problem based on a high-frequency and light-to-heat finite element model is proposed in the present work to numerically predict the optical properties of these nanofluids. In particular, a cost function based on a L2 norm is formulated to compare experimental measurements and numerical predictions. Then, this function is minimised by means of heuristic techniques –specifically, genetic algorithms- and the desired properties can be determined. In conclusion, the current work presents a numerical tool that could help in the characterisation of properties of solar nanofluids and contribute to reduce the number of experiments to be conducted for this purpose.
Highlights
The consumption of energy is continuously increasing worldwide since nowadays human lifestyle permanently demands energy to ensure the current life standards
With regard to temperature boundary conditions (BCs), the domain surfaces are left unconstrained so that the average temperature of the nanofluid can evolve with the dissipation of solar irradiation
This work presents a numerical tool with the aim of helping in the characterisation of optical properties of NPs for their application in solar nanofluids
Summary
The consumption of energy is continuously increasing worldwide since nowadays human lifestyle permanently demands energy to ensure the current life standards. The solution of an inverse problem depends on the minimisation of a cost function (CF) measuring the discrepancy between experimental and numerical results These numerical results (forward problem) are obtained in the present work through the evaluation of a high-frequency and light-to-heat Finite Element (FE) model, which predicts the thermal increase undergone by the nanofluid when optically excited [7]. With regard to the experimental results for the formulation of the inverse problem, these were directly measured in a laboratory by making use of the experimental setup described in the work of GimenoFurió et al [8] To sum up, this experimental setup (see Figure 1) consists of a quartz glass tube in which the nanofluids were placed and which was irradiated by an artificial sunlight simulator. The numerical tool is applied to determine the optical properties (namely, imaginary part of relative permittivity and electrical conductivity) of water-based nanofluids with Au NPs dispersed in it and for different sizes of NPs within the base fluid
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