Effect of nanoparticles on heat capacity of nanofluids based on molten salts as PCM for thermal energy storage
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NANO EXPRESS
Open Access
Effect of nanoparticles on heat capacity of nanofluids based on molten salts as PCM for thermal energy storage Manila Chieruzzi1*, Gian F Cerritelli1, Adio Miliozzi2 and José M Kenny1,3
Abstract In this study, different nanofluids with phase change behavior were developed by mixing a molten salt base fluid (selected as phase change material) with nanoparticles using the direct-synthesis method. The thermal properties of the nanofluids obtained were investigated. These nanofluids can be used in concentrating solar plants with a reduction of storage material if an improvement in the specific heat is achieved. The base salt mixture was a NaNO3KNO3 (60:40 ratio) binary salt. The nanoparticles used were silica (SiO2), alumina (Al2O3), titania (TiO2), and a mix of silica-alumina (SiO2-Al2O3). Three weight fractions were evaluated: 0.5, 1.0, and 1.5 wt.%. Each nanofluid was prepared in water solution, sonicated, and evaporated. Measurements on thermophysical properties were performed by differential scanning calorimetry analysis and the dispersion of the nanoparticles was analyzed by scanning electron microscopy (SEM). The results obtained show that the addition of 1.0 wt.% of nanoparticles to the base salt increases the specific heat of 15% to 57% in the solid phase and of 1% to 22% in the liquid phase. In particular, this research shows that the addition of silica-alumina nanoparticles has a significant potential for enhancing the thermal storage characteristics of the NaNO3-KNO3 binary salt. These results deviated from the predictions of the theoretical model used. SEM suggests a greater interaction between these nanoparticles and the salt. Keywords: Phase change materials; Nanofluid; Thermal energy storage; Nanoparticles; Heat capacity; Molten salt; Nanocomposite
Background The growing world energy demand [1] is increasing the burning of fossil fuels and, consequently, the carbon dioxide emissions. In order to limit these emissions, it is necessary to make better use of the produced thermal energy by increasing the energy efficiency of industrial processes (heat recovery) and buildings and the use of renewable sources such as solar energy [2]. Economic storage of thermal energy (thermal energy storage - TES) is a key technological issue for solar thermal power plants and industrial waste heat recovery [3-5]. The overall objectives of heat storage integration are to increase the solar contribution, to improve efficiency, and to reduce the levelized energy cost (LEC). TES systems can be used at high temperature (T > 400°C) or at lower * Correspondence: [email protected] 1 Civil and Environmental Engineering Department, UdR INSTM, University of Perugia, Strada di Pentima, 4, 05100 Terni, Italy Full list of author information is available at the end of the article
temperature (ranging from 100°C to about 300°C) for heat and solar cooling. Low-temperature storage systems are based almost entirely on sensible heat storage using liquid water [3], but for temperatures exceeding 100°C (con
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