Search

Chloride molten salts have become a potential heat storage material for the design of a new generation of concentrating solar power (CSP) (>700 °C) due to its abundant reserves and low cost. The difficulty of measuring the high-temperature thermal properties of chlorides can be effectively solved by using molecular dynamics simulation. However, it is challenging to get the thermophysical properties of multi-component molten salts containing CaCl2 due to the lack of Born–Mayer–Huggins (BMH) potential parameters of CaCl2. Through comparative analysis of the structure and thermal properties of CaCl2, including density and thermal conductivity, a set of Born–Mayer–Huggins (BMH) potential parameters of CaCl2 named SP2 is determined in this study. The density, specific heat capacity, and thermal conductivity of nine eutectic molten salts are simulated, including NaCl-CaCl2, KCl-CaCl2, NaCl-CaCl2-MgCl2, and NaCl-CaCl2-KCl, and the simulation results are found to be in good agreement with the experimental results. It is also found that the SP2 parameters are able to predict the thermal properties and structure of molten multicomponent chlorides including calcium. [ABSTRACT FROM AUTHOR]

The specific heat of molten salts plays a key role to reduce the costs of thermal storage for concentrating solar power plants. In this study, two different mass concentrations Mg particles were dispersed in a binary chloride molten salt to improve its specific heat used as a high temperature heat storage and transportation medium. The influence of Mg particle morphologies and mass concentrations on the specific heat of nanosalts were investigated. Results showed that Mg particles dissolved as elemental metal and dispersed as stone-like blocky in molten salt. The melting temperature of the molten salt had almost no change. The average value of specific heat was obviously improved up to 3% (1.0 wt% Mg) and 7% (2.0 wt% Mg) in solid phase, respectively. [ABSTRACT FROM AUTHOR]

Molten salts have been widely used as a kind of high-temperature thermal energy storage materials taking its advantage of high heat storage density and good stability. In this paper, the eutectic chloride salt (NaCl–CaCl 2 , 52-48mol.%) was prepared by a statically mixing method assessing its thermal energy storage performance for concentrating solar power (CSP) plants. The thermal properties were all determined experimentally by thermal analysis methods including melting temperature, latent heat, specific heat capacity, density, thermal expansion coefficient, thermal diffusivity and thermal conductivity. The measurement results showed that the eutectic salt has a suitable melting temperature of 512.8 °C and high latent heat of 178.4 J/g. Moreover, it exhibited an excellent thermal stability below 858 °C with no significant mass changes. Both high heat storage density and low cost price promoted its potential application for high-temperature thermal energy storage. • The binary chloride salts have good thermal stability under 858 °C. • Thermo-physical properties of the binary chloride salt are experimentally studied. • The heat storage density of the binary chloride salts is as high as 1484.14 MJ/m3. • The binary chloride salts had a potential use for high-temperature heat storage. [ABSTRACT FROM AUTHOR]

Molten salt LiNO3-NaNO3-KNO3 has been investigated as heat transfer and thermal storage media for its low melting point and good thermal performance. In this paper, nanofluids were synthesized by dispersing MgO nanoparticles into LiNO3-NaNO3-KNO3, and the effects of nanoparticles on thermal properties were studied with different sizes (20–100 nm) and mass percent concentrations (0.5–2.0 wt.%). The addition of nanoparticles had little effect on melting temperature, and led to a slight increase in enthalpy of fusion by 2.0–5.5%. Compared with base salt, the density of nanofluid increased a little by 0.22–1.15%. The scanning electron microscope (SEM) test implied that nubby and punctate microstructures were responsible for larger surface area and interfacial energy, which could lead to the improvement of specific heat capacity reaching 2.6–10.6%. The heat transfer characteristics remarkably increased with the addition of nanoparticles, and the enhancement of average thermal diffusivity and conductivity of salt with 1 wt.% nano-MgO could be 5.3–11.7% and 11.3–21.2%, respectively. Besides, the viscosities of nanofluids slightly increased for 3.3–8.1%. As a conclusion, nano-MgO was positively influential on the thermal properties of LiNO3-NaNO3-KNO3 base salt. [ABSTRACT FROM AUTHOR]

• Bi-Sn-In alloy/Ag/copper foam was proposed and prepared for rapid thermal management. • Present composite with optimal aperture of 0.42 mm had excellent shape stability. • Thermal conductivity is improved by Ag strips and copper foam synergistic effect. • Higher specific heat capacity and good chemical stability was performed. With the increasing challenge of heat dissipation in electronic device, the development of rapid thermal storage and management materials with high thermal conductivity becomes an important topic. This study developed a novel low melting point metal composite phase change material composed of Bi-Sn-In alloy, Ag particles (1–4 wt%) and copper foam (apertures 0.25–0.64 mm) using high thermal conductivity synergetic enhanced effect. The Ag particles were uniformly distributed in Bi-Sn-In alloy and they changed to Ag strips with high Ag content, and Bi-Sn-In alloy/Ag can be evenly filled in apertures of copper foam. Bi-Sn-In alloy/Ag/copper foam composite with optimal aperture of 0.42 mm exhibited highest shape stability, because it avoided molten alloy leakage for larger apertures and residual alloy which was not pressed into copper foam for small apertures. As Ag content increases, the melting points of Bi-Sn-In alloy/Ag and Bi-Sn-In alloy/Ag/copper foam with Ag content of 4 wt% respectively increased by 4.91 % and 2.46 %, while their enthalpy slightly decreases by 10.9 % and 2.49 %. More importantly, the synergistic effect of Ag strips and copper skeleton addition formed continuous channels for heat transfer. The thermal conductivities of alloy/Ag (4 wt%) and alloy/Ag (4 wt%)/copper foam were respectively 22.4 and 42.7 Wm−1 °C−1, and they were remarkably higher than that of Bi-Sn-In alloy (16.4 Wm−1 °C−1). Furthermore, thermal management test showed that Bi-Sn-In alloy/Ag/foam copper had the most prominent endothermic and exothermic properties. The outstanding performance of present Bi-Sn-In alloy/Ag/copper foam demonstrates a promising prospect for solving the thermal management problems of contemporary electronic devices. [ABSTRACT FROM AUTHOR]

In this work, a series of solar salt nano-fluids with 2.5 wt%, 3.5 wt%, 4.5 wt%, 5.0 wt% and 10.0 wt% MgO nanoparticles (∼60 nm, 18 W/m·K[24]) have been prepared and their thermal properties over 220 °C have been studied. The viscosity (η), density (ρ), specific heat capacity (c p) and thermal diffusivity (α) of the nano-fluids have been measured by rotary viscometer, Archimedean technique, differential scanning calorimeter (DSC) and laser flash analysis (LFA) respectively. The thermal conductivity (λ) is determined by ρ, c p and α. The results show that the viscosity and density of nano-fluids are about 5.1 cp∼2.4 cp and 1.96 g/cm3∼1.83 g/cm3 at 240 °C–380 °C which is close to that of solar salt fluid. The average c p of the fluids with nano-MgO from zero to 5.0 wt% is 1.442–1.613 J/(g·K), and the λ of fluids is 0.37–0.60 W/(m·K) at 375 °C. The enhancement of c p and λ of nano-fluids reaches 11.9% and 62.1%, which increases the Nusselt number with improved heat transfer performance. It is suggested that the nano-fluid with 5.0 wt% MgO in solar salt is a promising fluid for application of heat transfer and thermal storage in a CSP system. • A series of MgO doped solar salt nanofluids have been prepared. • The nanofluids have the nearly same viscosity and similar density as solar salt fluid. • The nanofluids have enhanced thermal conductivity and specific heat capacity. • The mechanisms of enhancement of thermal conductivity and specific heat capacity are analyzed. [ABSTRACT FROM AUTHOR]

The NaCl–CaCl 2 based composite is a novel high-temperature heat transfer and solar thermal storage material with enhanced specific heat capacity by dissolving metallic magnesium in the molten salt. However, the enhancement mechanism and the interactions between Mg atoms and various ions in the molten NaCl–CaCl 2 are not clear. In this work, the interfacial effects of local coordination structures around the nano Mg particle and the bonding characteristics between Mg atoms and molten salt ions were studied from both the chemical and physical points of view by using the ab-initio molecular dynamics simulations. The results indicate that [MgNa m ] n + and [MgCa x ] y + clusters are formed at the interface according to the analysis of calculated Mayer bond orders. A compressed ion layer with higer ion densities of Na+ and Cl− ions is formed around the nano Mg particle. Moreover, a calculated specific heat capacity of 1.387 J g−1 K−1 is obtained with an enhancement of 25.98% for the Mg/NaCl–CaCl 2 system, which is mainly resulted from the formed compressed ion layer and decreased potential energy due to the interfacial effect. And a theoretical thermal energy storage density with an enhancement of 29.59% is achieved for the Mg/NaCl–CaCl 2 composite at 873 K compared to the pure molten salt. [Display omitted] ● Bonding interactions and microstructure evolutions at the interface are revealed. ● The doped Mg atoms can react with Na+ and Ca2+ ions instead of Cl− ions. ● A compressed ion layer of Na+ and Cl− ions is formed around the nano Mg particle. ● Specific heat capacity of 1.387 J g−1 K−1 of the composite is enhanced by 25.98%. [ABSTRACT FROM AUTHOR]

Molten chloride salt is recognized as a promising heat transfer and storage medium in concentrating solar power (CSP) in recent years, but there is a serious lack for thermal property data of molten chloride salts under high-temperature condition. In this work, temperature and component dependence of local structure and physical properties for binary KCl–MgCl 2 mixture were computed by molecular dynamics simulations (MD) method based on Born–Mayer–Huggins (BMH) potential. As the temperature rises, the distances between ions change and the structures turn into loose state, thus the density, thermal conductivity and the shear viscosity decrease, which also agree well with the experimental results. The calculation errors of thermal properties are mainly within 8%. The results show that density and thermal conductivity have negative linear correlation with temperature. Specific heat capacity is invariant with temperature at a constant pressure. When K+ increases in the salt, thermal conductivity is significantly improved, and shear viscosity and specific heat capacity decrease. The formulas of temperature-thermal properties-component correlations are obtained, which provide the fundamental property database for the precise design of high-temperature thermal storage system. ● Structures and thermal properties of KCl–MgCl 2 were calculated by MD simulations. ● Properties of KCl–MgCl 2 were influenced by component and temperature. ● With increasing K+, coordination structures became looser and densities decreased. ● The correlations of properties and component/temperature were obtained. [ABSTRACT FROM AUTHOR]

Molten binary chloride salts are considered as promising heat transfer and storage mediums in a Concentrating Solar Power (CSP) Station. The properties of them over the entire operating temperature are required to be calculated, since they are difficult to be measured under high-temperature conditions. Reliable numerical method is an alternative tool to accurately predict thermal properties of molten salts from the viewpoint of micro-structure. Based on the effective Born-Mayer-Huggins (BMH) pair potential model, the local structures and thermodynamic properties of lithium-potassium chloride were computed by using Molecular Dynamics simulations (MD) and the results are consistent with available experimental literature data. The simulation results prove that BMH force field is reasonable to be adopted to predict the properties of various molten chloride salts and their mixtures. The minimum errors of thermal properties above are all within 11.1%, which is accurate and reliable. The results show that Li+ promotes the diffusion of the system efficiently. In addition, the specific heat capacity and thermal conductivity are significantly improved with the increase of Li+. The database of thermal properties and structures of this work are significant for accurate design of material structure and regulation of thermal storage system performance. • Temperature/component dependence on properties of molten lithium-potassium chloride. • Reverse non-equilibrium molecular dynamics methods were reported. • Lithium ion promotes the diffusion of the system efficiently. • Thermal conductivity/specific heat capacity improved with increasing lithium chloride. • Accurate material structure design and thermal storage system performance regulation. [ABSTRACT FROM AUTHOR]

• Molecular simulation is used to compute structures-properties of Na 2 CO 3 -K 2 CO 3. • Temperature and component dependence are studied from microscopic view. • The temperature-thermophysical properties-composition correlation are obtained. Molten carbonate eutectic salts are promising thermal storage and heat transfer fluid materials in solar thermal power plant with the feature of large specific heat capacity, wide operating temperature range and little corrosive. The high-temperature properties of molten carbonates should be determined accurately over the entire operating temperature for energy system design. In this paper, molecular dynamic simulation is used to study temperature and component dependence of microstructures and thermophysical properties of the binary carbonate molten salt. Negative linear temperature dependence of densities and thermal conductivities of binary mixtures of different components is confirmed with respect to the distances of ion clusters. Besides, positive linear temperature dependence of self-diffusion coefficient is also obtained. When temperature is constant, densities and thermal conductivities of binary mixtures are linearly related with components. Self-diffusion coefficients of CO 3 2− firstly increase and then decrease with increasing mole fraction of Na 2 CO 3. The temperature-thermophysical properties-composition correlation formulas are obtained, and the database of thermophysical properties of molten carbonate salts over the entire operating temperature is complemented, which will provide the essential data for heat transfer and storage system design, operation, and optimization in CSP. [ABSTRACT FROM AUTHOR]