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Metal hydrides (MH) are an attractive option for solid hydrogen storage with the large thermal effects of their hydrogen absorption and desorption processes when used in reactors. Phase-change materials (PCM) have been used as thermal management media in the MH reactor. To further improve the performance of the reactor, this study proposed a novel PCM-based MH reactor with array layouts, aiming to construct a heat transfer interface with a high specific surface area. A mathematical model was constructed to elucidate the phenomenon of heat transmission and absorption reaction. It was found that an increase in the number of array units significantly increased the heat transfer area but had a limited impact on enhancing the absorption rate and heat transfer. Nevertheless, the array reactor with seven units had a significant 1.0 times increase in the absorption rate compared to the traditional reactor with only one array unit. Furthermore, the enhancement of thermal conductivity in MH/PCM and the elevation of hydrogen supply pressure have the potential to accelerate the reaction rate and heat transfer during absorption. The enhanced absorption pressure not only enhances the driving force of the reaction directly but also amplifies the temperature difference in heat transfer between PCM and MH. Consequently, this leads to a further improvement in heat transfer and reaction efficiency.

The operating temperature limit of molten chloride salts mainly depend on thermal stabilities in thermal energy storage applications. In this work, the thermal stability resulted from liquid-vapor transitions of NaCl-KCl-ZnCl2molten salt were studied. Firstly, mass loss curves in an open testing condition were obtained by thermogravimetric analysis, and a phase change activation energy of 37.44 kJ/mol was calculated successfully using the Arrhenius equation. Secondly, molecular dynamics simulations were applied to explore the liquid-vapor interface and transition properties in the closed system. The structural evolution during phase transition was also revealed, it was found that anions and cations mainly existed in the form of molecule or ion clusters with coordination number of 2– 3 in the vapor phase. The layer thickness, stress tensors, surface tensions, density distributions, ion accumulations, and temperature distributions at liquid-vapor interface were analyzed detailly. And a thermodynamic non-equilibrium phenomenon was found at the interface on a microscale of <5 nm. A mass loss of 0.25 % was observed at 1000 °C when Vliquid = Vvaporin the closed system, indicating that the upper limit of operating temperature can be greatly improved to 1000 °C for NaCl-KCl-ZnCl2by using a well-sealed storage tank and pipeline.

Molten salts play a key role in the heat transfer and thermal energy storage processes of concentrated solar power plants. A novel composite material was prepared in this work by adding micron-sized magnesium particles into Li2CO3-Na2CO3-K2CO3molten salt, the heat transfer and thermal energy storage properties of the composites were studied experimentally. A stable composite nanofluid can be obtained, and a thermal conductivity of 0.728 W/(m·K) at 973 K with an enhancement of 31% is achieved for the Mg/molten carbonate nanofluid. And the strengthening mechanism of thermal conductivity was revealed by using ab-initio molecular dynamics method. It is found that the main bonding interactions exist between Mg and O atoms at the surface of Mg particles. A compressed ion layer with a more compact and ordered ionic structure is formed around Mg particles, and the Brownian motions of Mg particles lead to the micro-convections of carbonate ions around them. These factors are helpful to the enhancement of thermal conduction with the improved probability and frequency of ion collisions. This work can provide a guidance for further studies and applications on metal/molten salt composites with enhanced heat transfer and thermal energy storage capacity.