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A new correlation model for predicting the melting and boiling temperatures of the Lennard-Jones systems
No full textThe Lennard-Jones (LJ) potential function is widely employed in molecular dynamics simulations. In this study, the LJ potentials under different characteristic diameter sigma and characteristic energy epsilon were simulated, and the changes in properties such as number density, total energy, phase transition latent heat, and phase transition temperature were detailed. With the increase of sigma, the melting and boiling temperatures of the LJ systems and the thermodynamic temperature range corresponding to liquid decrease, while with the increase of epsilon, the melting and boiling temperatures and the thermodynamic temperature range of liquid increase. Moreover, the phase transition latent heat hardly changes with the increase of sigma, but significantly increases with epsilon. The number densities at the melting and boiling temperatures are only dependent on sigma, and are not nearly influenced by epsilon. Furthermore, based on a modified Lindemann's melting criterion, a new empirical correlation model is proposed to predict the melting and boiling temperatures of the LJ systems, where the phase transition points are in good agreement with the experimental values. For the melting point, the absolute error between the formula and the experimental measurement for inert gas and methane is no more than 10 K, and for the boiling point, the absolute error is less than 15 K. By this new presented model, some thermophysical properties of the LJ potential systems can be quickly obtained and evaluated
Preparation and characterization of steel slag-based low, medium, and high-temperature composite phase change energy storage materials
No full textIn this study, industrial solid waste steel slag was used as supporting material for the first time, and polyethylene glycol (PEG), sodium nitrate (NaNO3), and sodium sulfate (Na2SO4) were used as low, medium, and high -temperature phase change materials (PCMs). A series of shape-stable composite phase change materials (C-PCMs) were prepared by vacuum impregnation and mixing-sintering methods. The morphology, thermal prop-erties, and thermal reliability of C-PCMs were characterized by scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC). The results show that the three PCMs are uniformly dispersed in the pores of steel slag, and the maximum loading is 35 %, 40 %, and 50 %, respectively, and they have good chemical compatibility with steel slag. Compared with their pure PCMs, the three prepared C-PCMs showed a reduction in subcooling of 2.64 degrees C, 4.53 degrees C and 0.79 degrees C, respectively, and an increase in thermal conductivity of 172 %, 54.9 % and 82.4 %, respectively, all with good phase change thermal storage properties. Even after 100 thermal cycles, the latent heat retention rate was more than 97 %, which had good thermal reliability. Therefore, it can be concluded that the three kinds of low, medium, and high -temperature C-PCMs have considerable application potential in different temperature areas, such as building latent heat storage, solar energy storage systems, and industrial waste heat recovery system
Confinement amorphous cobalt-nickel oxide polyhedral yolk-shell structures for enhanced oxygen evolution performance
No full textMulti-scale regulation strategies ranging from electronic behavior regulation to crystal structure modulation to micro-nano structure construction can effectively improve the properties of materials, thereby bringing about significant improvements in performance. In this paper, we successfully constructed (Co1-xNix)3O4 with Ni substitution (x) unique polyhedral yolk-shell structure (PYSSs) electrocatalysts with confined amorphous regions, and achieved a significant improvement in the performance of oxygen evolution reaction (OER). The substitution of Ni can regulate the electronic coupling between metal sites, thereby optimizing the electronic configuration, creating abundant vacancy defects and enhancing the Co 3d-O 2p covalency. Meantime, the creation of confined amorphous regions can further increase the number of oxygen vacancies and unsaturated metal sites. Especially, the construction of the unique PYSSs structure can increase the effective specific surface area, hold the reaction intermediates for deeper reaction, accelerate the infiltration and transport of the electrolyte, prevent the adhesion of bubbles and accelerate the gas diffusion
