Numerical Investigation of the Effect of Chirality of Carbon Nanotube on the Interfacial Thermal Resistance

Abstract

Concentrated Solar Power (CSP) systems are used widely as a stable and reliable renewable source of energy. However, intermittency of this power source and the variability in demand for electrical power creates challenges that necessitate the integration with energy storage for reliable dispatch of power. Thermal Energy Storage (TES) systems provide a cheap, cost-effective and reliable option for energy storage in renewable power delivery systems. Due to their low vapor pressures at elevated temperatures, molten salts and their eutectics are used in conventional high temperature thermal energy storage (TES) systems and also as coolants for energy conversion, such as in power tower configurations that are typically used in CSP applications. A major drawback of the molten salts is their relatively poor thermo-physical properties, which may lead to lower systemic efficiencies in CSP/TES. Recent reports in the literature have shown that doping molten salts with nanoparticles at minute concentrations (typically less than 5% mass fraction and ideally at less than 1-2% mass fraction) can significantly enhance the thermo-physical properties of these nanomaterial (also termed as "nanocomposites" in solid state and "nanofluids" in liquid state). The dominant factor that controls the resultant thermo-physical properties of these nanomaterials is the interfacial thermal resistance (or Kapitza Resistance "R k ") that impedes the heat transfer between the nanoparticle surface and the bulk solvent molecules.ii In this study, the interfacial thermal resistance between a carbon nanotube (CNT) and carbonate molten salt eutectics were calculated by using numerical models that were then implemented in Molecular Dynamics (MD) simulations. The estimates for "R k " obtained from these simulations enabled the prediction of the optimum dimensions of the nanoparticles for maximizing the thermo-physical properties of the mixture, i.e. thermal conductivity and specific heat capacity values of these nanomaterial. The simulations were restricted to the carbonate salt eutectic, which is composed of a molar ratio of 62:38 for lithium carbonate (Li 2 CO 3 ) and potassium carbonate (K 2 CO 3 ). In this study, parametric simulations were performed to estimate the values of "R k " by varying the chirality of a single walled CNT (i.e, for armchair, chiral, and zig-zag CNT). The results show that the Kapitza resistance of the CNT is significantly affected by the change in the chirality of the CNT.

Increment of specific heat capacity of solar salt with SiO2 nanoparticles

“…Salt ions are ordered around nanoparticles due to electrostatical interactions, forming fractal-like structures. The semisolid layering approach is in accordance with the increment observed in Cp and the available nanoparticle surface area; however, more experimental work is needed in order to check and refine the model [ 21 - 23 ].…”

Molecular dynamics simulation of a nanofluidic energy absorption system: effects of the chiral vector of carbon nanotubes

“…[3][4][5] The effects of different types of CNT have been investigated on some fluid properties in some works. [7][8][9][10] The effects of the chiral vector of a CNT on the center of mass mean velocity of a water nanodroplet confined inside the CNT by a thermal gradient along the axis of the CNT were investigated by Zambrano et al 7 It was concluded that the center of mass mean velocity of a water nanodroplet in different thermal gradients is decreased by changing the type of CNT from armchair to chiral and then to zigzag. Binesh and Kamali 8 investigated the effects of chirality of CNTs on single-file water permeation through CNT membranes.…”