Boron compound nanoparticle-enhanced molten salts and production method for concentrated solar energy systems

Abstract

The invention relates to boron compound nanoparticle-enhanced molten salts and their production method, which increase thermal conductivity, enhance low specific heat capacity, and reduce the supercooling degree for concentrated solar energy systems.

Description

[0001] BORON COMPOUND NANOPARTICLE-ENHANCED MOLTEN SALTS AND PRODUCTION METHOD FOR CONCENTRATED SOLAR ENERGY SYSTEMS

[0002] TECHNICAL FIELD

[0003] The invention relates to boron compound nanoparticle-enhanced molten salts and their production method, which increase thermal conductivity, enhance low specific heat capacity, and reduce supercooling degree for concentrated solar energy systems.

[0004] PRIOR ART

[0005] With the continuous growth of the global economy, the escalation of the 1970 energy crisis, and the excessive increase in energy demand (fossil-based energy), challenges such as global warming caused by fossil fuel consumption, limited reserves, availability issues, and energy security have emerged. Consequently, the need for alternative renewable energy sources to reduce dependence on fossil fuels is increasing daily. Moreover, considering the anticipated 60% increase in energy demand by 2030, renewable energy sources present a promising alternative to replace oil resources. Therefore, research on alternative energy sources is increasingly attracting the attention of researchers and nations. Among various alternative energy sources, solar energy is the most abundant renewable energy source and holds significant potential for meeting the rising energy demand with minimal or no environmental pollution. Furthermore, it is expected that solar energy will meet 70% of the world’s energy demand by 2100.

[0006] The simplest way to convert solar energy into thermal energy is through solar thermal systems. This thermal energy can be utilized in various energy applications such as domestic and industrial hot water supply, industrial heat processes, electricity generation in concentrated solar energy (CSE) technology, and desalination plants that convert seawater into potable water. Capturing solar energy using solar thermal systems depends on the efficient conversion of solar thermal energy. The broad operational temperature range of solar thermal systems can be achieved by improving efficient light-to-heat conversion processes at high temperatures (above 300°C).

[0007] In these systems, thermal energy storage (TES) media and heat transfer fluids (HTFs) play a crucial role as they facilitate the storage and transfer of thermal energy. Enhancing the efficiency of solar thermal systems can be achieved by using nanofluids and TES media as promising HTF and TES materials for absorbing solar radiation. In recent years, conventional HTFs and TES media, such as water and industrial oils with added nanoparticles, have been extensively studied for their thermal storage and conductivity properties. However, due to the operational temperature limitations of conventional HTFs and TES media, they are not suitable for applications in various industrial processes and CSE thermal systems that require higher temperatures.

[0008] Moreover, the low thermal stability of these conventional HTFs and TES media up to 400°C is another significant disadvantage. To achieve higher temperatures for TES, CSE systems capable of focusing solar radiation can reach temperatures above 600°C, where TES and HTF materials are of paramount importance. In CSE systems, molten salts are the most commonly preferred TES and HTF thermal energy media due to their wide temperature application range, high-temperature stability, stable phase transition temperatures, natural abundance, low cost, and environmentally friendly properties. By using molten salts in CSE plants, thermodynamic efficiency can be significantly improved, and the cost of electricity generation can be substantially reduced. However, the further application of molten salts in CSE plants is severely limited by their poor thermal properties, such as low thermal conductivity, low specific heat capacities (Cp < 2 kJ / kg°C), and high supercooling degree.

[0009] Enhancing the thermal properties of molten salts is, therefore, of great importance for the development and efficiency improvement of CSE plants. Adding nanoparticles to an HTF or TES material is one of the most effective methods for controlling their specific heat capacities and thermal conductivity. Consequently, the thermal performance of molten salts can be improved by adding nanomaterials with unique physical and chemical properties. To create composite nano-fluids with enhanced thermal performance, molten salts can incorporate zero-dimensional (OD) nanoparticles, one-dimensional (1 D) nanowires, nanorods, and nanoribbons, metallic / semi-metallic particles, oxides, carbides, sulfides, and two-dimensional (2D) hexagonal boron nitride (hBN) and graphene.

[0010] Additionally, one of the molten salts considered as TES and / or HTF in CSE systems consists of 53% potassium nitrate (KNO3), 7% sodium nitrate (NaNO3), and 40% sodium nitrite (NaNO2) by weight. However, the broader application of molten salts in CSE plants is significantly constrained by their poor thermal properties, such as low thermal conductivity, low specific heat capacities (Cp < 2 kJ / kg°C), and high supercooling degree. Therefore, improving the thermal properties of solar salts is of paramount importance for the development and efficiency enhancement of CSE plants. Furthermore, adding nanoparticles to an HTF or TES material has the potential to be one of the most effective methods for controlling their specific heat capacities and thermal conductivity.

[0011] BRIEF DESCRIPTION OF THE INVENTION

[0012] The invention relates to boron compound nanoparticle-enhanced molten salts and their production method, which increase thermal conductivity, enhance low specific heat capacity, and reduce supercooling degree for concentrated solar energy systems.

[0013] In the invention, molten salts are doped with 1 -50% by weight of B4C, Ti B2, HfB2, ZrB2, or SiB6nanoparticles individually. This results in molten salts with improved thermal properties.

[0014] The boron carbide (B4C) nanoparticles used in the invention exhibit high- temperature stability, high melting point, excellent corrosion resistance, low density, and superior thermal and optical properties. Another boron compound nanoparticle, titanium diboride (TiB2), demonstrates oxidation stability, high melting point, excellent corrosion resistance, and thermal conductivity comparable to that of highly conductive metals like copper (Cu) or aluminum (Al).

[0015] Hafnium diboride (HfB2) and zirconium diboride (ZrB2) nanoparticles possess high melting points, high thermal conductivity, excellent chemical stability, and oxidation resistance, making them suitable for high-temperature thermal applications. Additionally, silicon hexaboride (SiB6) nanomaterials exhibit high melting points, excellent chemical stability, and oxidation resistance at high temperatures, despite having lower thermal conductivity.

[0016] LIST OF FIGURES

[0017] Figure 1. Diagram of the Production Method of Boron Compound Nanoparticle Doped Molten Salts DETAILED DESCRIPTION OF THE INVENTION

[0018] In our invention, molten salts are doped with 1 -50% by weight of B4C, TiB2, HfB2, ZrB2, or SiB6nanoparticles, either individually or in combination with at least one of these nanoparticles. This results in the production of boron compound nanoparticle- enhanced molten salts with improved thermal properties.

[0019] In our invention, molten salts composed of 53% by weight potassium nitrate (KNO3), 7% by weight sodium nitrate (NaNO3), and 40% by weight sodium nitrite (NaNO2) are placed into a beaker and mixed with at least one solvent, such as alcohol (ethanol, methanol, isopropyl alcohol), pure water, or deionized water, using a magnetic or mechanical stirrer to produce Mixture-1. In a second beaker, 1 -50% by weight of at least one boron compound nanoparticle (B4C, TiB2, HfB2, ZrB2, or SiB6) is dissolved in alkyl sulfonic acid using an ultrasonic bath and sonicator to produce Mixture-2. Mixture-1 and Mixture-2 are combined in a third beaker and mixed in an ultrasonic bath and sonicator for at least one minute to produce Mixture-3. Subsequently, Mixture-3 is evaporated, melted, and solidified to produce boron compound nanoparticle-enhanced molten salts.

[0020] The boron compound nanoparticle-enhanced molten salts are obtained as follows (by weight); 99-50% (7% NaNO3- 53% KNO3- 40% NaNO2) / 1-50% B4C, 99-50% (7% NaNO3- 53% KNO3- 40% NaNO2) / 1 -50% TiB2, 99-50% (7% NaNO3- 53% KNO3- 40% NaNO2) / 1 -50% HfB2, 99-50% (7% NaNO3- 53% KNO3- 40% NaNO2) / 1 -50% ZrB2, 99-50% (7% NaNO3- 53% KNO3- 40% NaNO2) / 1 -50% SiB6.

[0021] The optimal conditions for the boron compound nanoparticle-enhanced molten salts are as follows (by weight); 98% (7% NaNO3- 53% KNO3- 40% NaNO2) / 2% B4C, 97% (7% NaNO3- 53% KNO3- 40% NaNO2) / 3% B4C, 90% (7% NaNO3- 53% KNO3- 40% NaNO2) / 10% B4C, 50% (7% NaNO3- 53% KNO3- 40% NaNO2) / 50% B4C, 50% (7% NaNO3- 53% KNO3- 40% NaNO2) / 50% TiB2, 90% (7% NaNO3- 53% KNO3- 40% NaNO2) / 10% TiB2, 95% (7% NaNO3- 53% KNO3- 40% NaNO2) I 5% TiB2, 99% (7% NaNO3- 53% KNO3- 40% NaNO2) / 1 % TiB2, 60% (7% NaNO3- 53% KNO3-40% NaNO2) / 40% HfB2, 98% (7% NaNO3- 53% KNO3- 40% NaNO2) 12% ZrB2, 90% (7% NaNO3- 53% KNO3- 40% NaNO2) / 10% SiB6.

Claims

CLAIMS1. Molten salts with nanoparticle additives for concentrated solar energy systems that increase thermal conductivity, enhance low specific heat capacity, and reduce the supercooling degree, characterized by containing at least one of B4C, TiB2, HfB2, ZrB2, and SiB6nanoparticles in a proportion of 1 -50% by weight.

2. A production method for boron compound nanoparticle-enhanced molten salts for concentrated solar energy systems that increase thermal conductivity, enhance low specific heat capacity, and reduce the supercooling degree, characterized by the following steps:- preparing Mixture-1 by placing molten salts consisting of 53% by weight potassium nitrate (KNO3), 7% by weight sodium nitrate (NaNO3), and 40% by weight sodium nitrite (NaNO2) in a beaker and mixing with a solvent alcohol (such as ethanol, methanol, or isopropyl alcohol), pure water, or deionized water using a magnetic stirrer,- preparing Mixture-2 by dissolving at least one boron compound nanoparticle (B4C, TiB2, HfB2, ZrB2, or SiB6) in a proportion of 1-50% by weight in alkyl sulfonic acid using an ultrasonic bath and a sonicator for at least one minute,- combining Mixture-1 and Mixture-2 in a third beaker and mixing them in an ultrasonic bath and sonicator for at least one minute to form Mixture-3,- subjecting Mixture-3 to an evaporation process,- performing melting and solidification processes after evaporation.

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