Abstract
This study presents new Nano-enhanced Phase Change Materials, NePCMs, formulated as dispersions of functionalized graphene nanoplatelets in a poly(ethylene glycol) with a mass-average molecular mass of 400 g·mol−1 for possible use in Thermal Energy Storage. Morphology, functionalization, purity, molecular mass and thermal stability of the graphene nanomaterial and/or the poly(ethylene glycol) were characterized. Design parameters of NePCMs were defined on the basis of a temporal stability study of nanoplatelet dispersions using dynamic light scattering. Influence of graphene loading on solid-liquid phase change transition temperature, latent heat of fusion, isobaric heat capacity, thermal conductivity, density, isobaric thermal expansivity, thermal diffusivity and dynamic viscosity were also investigated for designed dispersions. Graphene nanoplatelet loading leads to thermal conductivity enhancements up to 23% while the crystallization temperature reduces up to in 4 K. Finally, the heat storage capacities of base fluid and new designed NePCMs were examined by means of the thermophysical properties through Stefan and Rayleigh numbers. Functionalized graphene nanoplatelets leads to a slight increase in the Stefan number.
Highlights
Thermal energy storage (TES) is considered one of the key technologies for the energy production of the future, especially in the case of renewable systems for which the intermittency and less predictable nature of energy sources are major issues [1,2]
In order to prepare scanning electron microscope (SEM) samples, a drop of graphene in methanol was deposited on the top of a formvar-covered copper transmission electron microscopy grid and the solvent was evaporated at atmospheric conditions
(Solid-liquid) transitions of the PEG 400 used as base material and three NePCMs (0.10, 0.25, 0.50)
Summary
Thermal energy storage (TES) is considered one of the key technologies for the energy production of the future, especially in the case of renewable systems for which the intermittency and less predictable nature of energy sources are major issues [1,2]. Among different types of heat storage, it is worth mentioning the higher densities of energy storage and almost isothermal characteristics of those storage processes that take advantage of the energy involved in a phase change, in comparison to those methods which utilize the sensible heat due to a temperature difference [3,4]. Those materials that use latent heat to store and release energy, increasing thermal inertia of those systems in which are integrated, are known as phase change materials, PCMs [4,5]. In order to overcome this limitation and to develop high-performance phase change materials, the dispersion of nano-sized materials with high thermal conductivity has gained increasing attention, given rise to what is known as Nano-enhanced Phase
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