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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]

Molten chloride salt is recognized as a promising heat transfer and storage medium in concentrating solar power in recent years, but there is a serious lack for thermal property data of molten chloride salts. In this work, local structures and thermal properties for molten chloride salt—including NaCl, MgCl2, and ZnCl2—were precisely simulated by Born–Mayer–Huggins (BMH) potential in a rigid ion model (RIM) and a polarizable ion model (PIM). Compared with experimental data, distances between cations, densities, and heat capacities of molten chloride slats calculated from PIM agree remarkably better than those from RIM. The polarization effect brings an extra contribution to screen large repulsive Coulombic interaction of cation–cation, and then it makes shorter distance between cations, larger density and lower heat capacity. For NaCl, MgCl2, and ZnCl2, PIM simulation deviations of distances between cations are respectively 3.8%, 3.7%, and 0.3%. The deviations of density and heat capacity for NaCl between PIM simulation and experiments are only 0.6% and 2.2%, and those for MgCl2 and ZnCl2 are 0.7–10.7%. As the temperature rises, the distance between cations increases and the structure turns into loose state, so the density and thermal conductivity decrease, while the ionic self-diffusion coefficient increases, which also agree well with the experimental results. [ABSTRACT FROM AUTHOR]

[Display omitted] • The agglomeration of nanoparticles results from dominated vdW interactions. • The weak solute–solvent interactions lead to the less stable dispersion. • The ordered interfacial layers can enhance heat transfer and prevent agglomeration. • Small nanoparticles with strong adsorption of molten salt cations are preferred. The nanofluids consisting of molten salt and nanoparticles can gain enhanced thermal performance for heat transfer and energy storage processes. Agglomeration of nanoparticles is ubiquitous in this colloidal dispersion, deteriorating the dispersed states of the nanocomposite interiors, and its microscopic mechanisms are unsatisfactorily explored. In this work, molecular dynamics simulations combined with umbrella sampling technique to capture the relative dispersion state of nanoparticles in molten salts effectively were performed to reveal the free energy landscape of agglomeration and its influence on heat transport. The dominant deep minima in the free energy surface demonstrates that the agglomeration of MgO nanoparticles in the molten NaCl salt is principally induced by van der Waals attractions between MgO nanoparticles and aggravated by large surface area. The unstable dispersion of nanoparticles is the most fatal problem for enhanced thermal conductivity during agglomeration, and the relative distance of MgO nanoparticles has less impacts on the thermal conductivity of the melt. The stronger adsorption of ions around nanoparticles can improve their relative dispersion, and utilize interfacial effects to enhance the thermal conductivity. Combined with the benefit of ordered ionic layer on the surface, the MgO nanoparticles of 10 Å diameter (specific surface area of ∼ 938.80 m2/g) become the optimal choice for molten NaCl. With the mechanisms of interfacial microstructures preventing agglomerated nanoparticles and improving heat transfer of molten salts revealed, this work can enlighten the selection or feasible modification for nanoparticles in various high-temperature molten salts, since the mechanisms are universal to other nanofluids, especially for ionic liquid based nanofluids. [ABSTRACT FROM AUTHOR]

NaCl–CaCl 2 molten salt is considered as a promising high-temperature heat transfer and storage fluid for advanced nuclear power plants and concentrating solar power plants in the field of renewable energy utilization. However, the comprehensive physical properties and their microscopic mechanisms for the molten NaCl–CaCl 2 are failed to be measured accurately due to the extremely measuring condition. In this work, the ab-initio molecular dynamics simulation is used to investigate its microstructures and thermophysical properties for entire operating temperatures. It reveals that ion clusters are formed in terms of three for face-sharing, two for edge-sharing, and one for corner-sharing Cl− ions between the coordination shells of two neighboring cations. The coordination numbers of Na+-Cl- and Ca2+-Cl- ion pairs decrease from 5.88 to 6.46 at 783 K to 5.33 and 6.02 at 1173 K respectively. Meanwhile, the reliable and meaningful values of densities, ion self-diffusion coefficients, viscosities, and thermal conductivities were evaluated from 783 to 1173 K. It suggests that the distances and interactions between ions pairs determine thermodynamic properties directly. The ab-initio molecular dynamics simulation is proved to be an effective way to obtain the essential data for the designs of heat transfer and thermal energy storage systems in practical applications. • Ab-initio molecular dynamics simulations are applied for NaCl–CaCl 2. • Approach-to-equilibrium molecular dynamics method is used for thermal conductivity. • The correlation between microstructures and thermophysical properties are studied. • The distances and interactions between ion pairs determine its properties. [ABSTRACT FROM AUTHOR]

• A workflow to construct solid-molten salt interaction potential is designed. • Deep potential could yield accurate solid-molten salt interaction at ab initio level. • Trends in interfacial heat transfer are correctly described by deep potential model. Interfacial heat and mass transfer properties at molten salt/solid interfaces are crucial for the study of heat storage/transfer properties of molten salt nanocomposite materials as well as the microscopic mechanism of thermophysical property enhancement, but accurate force field parameters for describing molten salt-solid interactions are still lacking. This study has utilized a workflow that could meet the demand of high accuracy and efficiency in molecular dynamics (MD) simulations of molten salt/solid interface with the deep potentials (DPs) trained by deep learning (DL), using SiO 2 /LiCl-KCl interface as a model system. In terms of the short-ranged polarizability and long-ranged correlations of ions, DPs can give accurate description of potential energy surface over wide temperature range at the level of ab initio calculations. Further analysis on interfacial thermal resistance (ITR) and thermal conductivity shows that the slowing down of heat transfer is related to the disordered microstructure of molten salt ions near the SiO 2 surfaces, which also leads to larger ITR. For the mass transfer of molten salt ions on the SiO 2 surfaces, the more active ionic diffusion and permeation through the solid can be observed due to the weaker adsorption between them, which is ascribed primarily to the high temperature. The workflow, of which the feasibility has been verified for molten salt/solid interfaces in this work with rigorous modeling, will be used for building accurate interatomic interaction models and calculating thermophysical properties for various complex interfacial systems containing molten salts. The influence of interfacial microstructure on heat and mass transfer will provide theoretical support for the application of molten salts in energy industry. [ABSTRACT FROM AUTHOR]

• Enrichment of molten salt ions at interface contributes to enhanced heat transfer. • Interfacial thermal resistances are correlated with layering of interfacial ions. • Continuum model with interfacial effect yield good prediction of thermal transport. The solid-liquid interface between molten salt and solid oxides is ubiquitous in the molten salt nanocomposite with enhanced heat storage and transfer properties for concentrating solar power (CSP) systems. Understanding the microscopic mechanisms of interfacial thermal transport on this solid-liquid interface have great significance for evaluating the effective thermal properties of nanocomposites. This study combines equilibrium and non-equilibrium molecular dynamics simulations to explore the thermal transport and its connection with interfacial microstructure at the solid MgO-molten Hitec salt interface. Simulation results indicate that the enhancement of thermal transport can be ascribed primarily to the highly ordered adsorption structure of molten salt ions formed at the MgO surface, and the effect medium model incorporated with the simulated interfacial thermal resistance can reproduce the thermal conductivity of nanocomposite accurately. Further investigation indicates that the stronger adsorption at the MgO (110) surface leads to smaller interfacial thermal resistance than the MgO (100) surface, while the heat transfer parallel to the slab does not show much difference in both surfaces. These findings have illustrated the enrichment of molten salt ions at the solid surface does have a strong enhancement effect on their heat transfer properties and it is also necessary to incorporate the contribution from this interfacial thermal transport enhancement when predicting the thermophysical properties of molten salt nanocomposite materials. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe 2 O 3 promoted AMS-MgO enhanced adsorption capacity (14.86 mmol/g). • Rapid sorption rate of Mg 98 Fe 2 -AMS 10 within 20 min due to the catalysis of Fe. • DFT with Vdw correction was applied to study adsorption mechanism. • Affinity of MgO with CO 2 is increased due to the enhanced potential field by Fe. • AMS and Fe co-promoted MgO achieved the effect of 1 + 1 > 2 on CO 2 adsorption. Rapid and strong CO 2 capture is critical in CO 2 capture and utilization (CCU) techniques to mitigate global warming. Alkali molten salt (AMS) promoted-MgO sorbents with high capacity attracted attention, but their applications suffer from various limitations of low adsorption kinetics and poor stability. Here, AMS-promoted MgO sorbents corporation with Fe 2 O 3 (Mg 100-x Fe x -AMS 10) were fabricated via modified methanol evaporation-induced surface precipitation for use in rapid and stable CO 2 capture. Based on characterization of the sorbents, Mg 98 Fe 2 -AMS 10 showed a loose flake structure, with a large surface area and numerous exposed active sites. Therefore, Mg 98 Fe 2 -AMS 10 exhibited a strong CO 2 capacity (14.86 mmol CO2 /g sorbent at 300 °C) and good cyclic durability. Three kinetic models were explored, and the Avrami model provided a good prediction of the CO 2 adsorption behavior, with Mg 98 Fe 2 -AMS 10 exhibiting rapid adsorption kinetics. The adsorption mechanism was investigated using density functional theory (DFT) calculations. The charge transfer and bonding strengths of the surface O atoms on MgO increased, and these atoms preferentially bonded with activated CO 2 (CO 2 ∙−) under Fe catalysis. This study may provide insights into enhancing the CO 2 capture and kinetics of MgO via combination with 3d transition metals. [ABSTRACT FROM AUTHOR]

Zn−based chloride molten salts have been candidate heat transfer and storage media in solar thermal power attributed to excellent thermal properties and high thermal stability, while associated thermal properties at high temperature are still insufficient in research. In this work, microstructure and thermal properties of NaCl–ZnCl 2 molten salt have been investigated by molecular dynamics simulation based on Born−Mayer−Huggins potential and experimental measurement. Encouragingly, the trends of all properties from simulation are consistent with experimental data, and the errors are 6.97% in density and 7.42% in specific heat, respectively. As temperature increases, the distance between ion clusters centers on cations increases and the internal of ion clusters shrinks, thus density and viscosity decrease with the whole structure of NaCl–ZnCl 2 becoming looser, and thermal conductivity decreases because smaller Zn–Cl distance in [ZnCl n ] structure causes shorter phonon mean free path and larger thermal resistance. As content of ZnCl 2 decreases, density, specific heat capacity and viscosity decrease with the whole structure becoming looser, but thermal conductivity increases due to larger Zn–Cl distance. Besides, the correlation equations for properties−temperature−composition of NaCl–ZnCl 2 (0–100 mol. % ZnCl 2 , 578 K–1073 K) have been further identified for its utilization in advanced thermal storage systems. • NaCl–ZnCl 2 has been studied by molecular dynamics simulation and experiment. • Ion clusters center on cations and stable network structure [ZnCl n ] (n = 5–6) forms. • Density and viscosity decrease as temperature rising or content of ZnCl 2 dropping. • Thermal conductivity drops for shorter Zn–Cl distance and phonon mean free path. • Correlations for properties-temperature-composition of NaCl–ZnCl 2 are identified. [ABSTRACT FROM AUTHOR]