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This work proposes and validates a novel idea of using plasmonic nanoparticles (PNP) to improve the solar thermal conversion efficiency. Gold nanoparticle (GNP) is synthesized from an improved citrate-reduction method, and used as an example to illustrate the photothermal conversion characteristics of PNPs under a solar simulator. The experimental results show that GNP has the best photo-thermal conversion capability comparing to other reported materials. At the lowest particle concentration examined (i.e., 0.15 ppm), GNP increases the photo-thermal conversion efficiency of the base fluid by 20% and reaches a specific absorption rate (SAR) of ~10 kW/g. The photo-thermal conversion efficiency increases with increasing particle concentrations, but the SAR shows a reverse trend, which is unexpected as all GNPs should be still in the independent scattering regime.

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A new class of 2D materials named “MXene” has recently received significant research interest as they have demonstrated great potential for the applications in batteries, supercapacitors, and electronic devices. However, the research on their thermal properties is still very limited. In this work, Ti3C2Tx films were prepared by the vacuum-assisted filtration of delaminated nano-flake Ti3C2Tx MXenes. The thermal and electrical conductivity of the Ti3C2Tx films were measured by the state-of-the-art T-type method. The results showed that the effective thermal conductivity of the films increased from 1.26 W·m−1·K−1 at 80 K to 2.84 W·m−1·K−1 at 290 K, while the electrical conductivity remained at 12,800 Ω−1·m−1 for the same temperature range. Thermal resistance model was applied to evaluate the inherent thermal conductivity of the Ti3C2Tx flakes, which was estimated to be in the range of tens to hundreds W·m−1·K−1.

This paper reviews briefly the definition of heat capacity and clarifies the defined specific heat capacity and volumetric heat capacity. The specific heat capacity and volumetric heat capacity, with our measured experimental data for CuO nanofluids, are discussed as an illustrating example. The result indicates that the specific heat capacity of CuO nanofluid decreases gradually with increasing volume concentration of nanoparticles. The measurement and the prediction from the thermal equilibrium model exhibit good agreement. The other simple mixing model fails to predict the specific heat capacity of CuO nanofluid. The nanoparticle size effect and solid-liquid interface effect on the specific heat capacity of nanofluid are discussed.

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