Tailoring the Spectral Absorption Coefficient of a Blended Plasmonic Nanofluid Using a Customized Genetic Algorithm

Abstract

Recently, plasmonic nanofluids (i.e., a suspension of plasmonic nanoparticles in a base fluid) have been widely employed in direct-absorption solar collectors because the localized surface plasmon supported by plasmonic nanoparticles can greatly improve the direct solar thermal conversion performance. Considering that the surface plasmon resonance frequency of metallic nanoparticles, such as gold, silver, and aluminum, is usually located in the ultraviolet to visible range, the absorption coefficient of a plasmonic nanofluid must be spectrally tuned for full utilization of the solar radiation in a broad spectrum. In the present study, a modern design process in the form of a genetic algorithm (GA) is applied to the tailoring of the spectral absorption coefficient of a plasmonic nanofluid. To do this, the major components of a conventional GA, such as the gene description, fitness function for the evaluation, crossover, and mutation function, are modified to be suitable for the inverse problem of tailoring the spectral absorption coefficient of a plasmonic nanofluid. By applying the customized GA, we obtained an optimal combination for a blended nanofluid with the desired spectral distribution of the absorption coefficient, specifically a uniform distribution, solar-spectrum-like distribution, and a step-function-like distribution. The resulting absorption coefficient of the designed plasmonic nanofluid is in good agreement with the prescribed spectral distribution within about 10% to 20% of error when six types of nanoparticles are blended. Finally, we also investigate how the inhomogeneous broadening effect caused by the fabrication uncertainty of the nanoparticles changes their optimal combination. Plasmonic nanofluids, which contain a suspension of plasmonic nanoparticles in a base fluid, have been proposed as effective working fluids to directly convert solar radiation to thermal energy 1. Owing to the resonance characteristics of the localized surface plasmon (LSP), the absorption efficiency of the nanoparticles can be greatly enhanced with the excitation of the LSP, offering great potential in solar thermal applications. For instance, a direct-absorption solar collector (DASC) combined with a plasmonic nanofluid has drawn much attention for solar thermal energy harvesting in recent decades 1-5. Recently, Qin et al. 6 showed how the spectral absorption coefficient of a plasmonic nanoparticle should be tuned (i.e., either uniformly or following the solar spectrum) by engineering nanoparticle suspensions to exploit the solar radiation maximally with the given constraint of the total particle concentration. Therefore, the effective tuning of the spectral absorption coefficients of plasmonic nanofluids is crucial for improving the thermal performance capabilities of DASCs. As suggested by Lee et al. 1 , broadband absorption spectra can be designed by blending multiple types of nanoparticles given that the resonance wavelength of the LSP depends on the material, size and shape of the nanoparticles. The simplest a...

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