Optimization of Preparation Methods and Thermal Characterization of Nanofluids Based on Solar Salts for Thermal Energy Storage

Abstract

It is well known that thermal power plants used to generate electricity from heat have an extremely negative impact on the environment. To produce energy, coal, gas, or oil is used, which, after being burned, emit toxic gases. As a result, the accumulation of these greenhouse gases intensifies global warming, contributing to the climate change. For this reason, more and more CSP (Concentrated Solar Power) plants are being developed today to generate energy and serve as a cleaner alternative to replace traditional thermal plants. CSP plants concentrate sunlight to generate heat, which is stored in insulated tanks containing molten salts. The stored heat is later released when electricity needs to be generated. To improve the thermal properties of molten salts, doping with nanoparticles has proven to be the most optimal technique. Several studies have shown that nanofluids containing 1% by weight of nanoparticles significantly increase thermal efficiency and offer major advantages as thermal energy storage (TES) media. However, one of the main disadvantages of nanofluids is the lack of a clear theoretical explanation of their behavior, as existing models do not always fully explain experimental results. For this reason, the aim of this study was to analyze how different parameters, such as the amount of water used to dissolve the salt, sonication time, and water evaporation temperature of the nanofluid affect the thermal properties of a nanofluid composed of NaNO₃ salt and SiO₂ nanoparticles (1% by weight). Two synthesis methods were used: wet and dry. For the wet method, 7 batches were prepared, each containing 9 samples. For the dry method, 4 batches were synthesized, each with 2 samples. Analysis of the results showed that the nanoparticles have a low impact on enthalpy and thermal conductivity but do have a significant influence on increasing the specific heat capacity (cp). The dry method, which involves synthesis through ball milling, stood out as an effective way to create nanofluids with a high specific heat capacity. The main objective of this work was to develop new techniques for the synthesis of nanofluids and to find a way to improve the experimental procedure by optimizing various parameters.