Design of Fly Ash Based Nanocomposites for Improvement Thermal Energy Storage Capacity of the Nitrate Salts

Abstract

In recent years, the demand for sustainability and energy efficiency in the energy sector has been rapidly increasing. Renewable and clean energy sources are needed to meet the world’s growing energy demand. Concentrated solar power (CPS) plants are seen as an environmentally friendly and efficient source of electricity production among alternative energy sources. In CPS plants, the development of fluids with high performance and low cost that can be used as both thermal energy storage (TES) fluids and heat transfer agents (HTA) is crucial. Choosing suitable HTS and TES materials can provide thermodynamic efficiency while minimizing the costs of heat storage tanks solar energy receivers, and heat transfer devices. Today, due to their physicochemical and thermodynamic properties, salt melts and various mixtures are used in CSP plants and many applications. The fact that salt melts are environmentally friendly materials with high chemical stability, low viscosity, low vapor pressure, high energy density, and low cost make them an ideal fluid to be used in the energy sector. However, when molten nitrate salts are used alone, their thermal stability is low, limiting the storage time. Also, due to the high melting points (>200°C) and low decomposition temperatures (at temperatures above 600°C) of molten salt fluids, they can freeze in cold weather conditions and darkness, causing pipes to clog. Therefore, forming nanocomposites by mixing with a material with high thermal conductivity, such as fly ash, contributes to improving the thermodynamic properties of molten salts. Thus, low-cost HTA and TES materials with low melting points, high storage capacity, and high thermal stability will be obtained in CSP plants. In this thesis study, the aim was to design cheap molten salt and fly ash nanostructures with high thermal conductivity, low melting temperature, and high decomposition temperature. The structural and thermal properties of fly ash-potassium nitrate (KNO3) mixtures with different weight percentages of fly ash (0.1%, 0.2%, 1%, 2%, and 5%) were experimentally investigated. The structural properties of the prepared nanofluids were examined with scanning electron microscopy (SEM) and X-ray diffraction (XRD)

thermal characterization was investigated using thermal properties analyzer (TPS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) methods.