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Introduction
Improving the adaptability, performance and durability of a wide range of energy systems for energy storage is crucial because it eliminates irregularity between energy supply and demand through the use of proper thermal energy storage (TES) technologies [1,2]. Nowadays, phase change materials (PCMs) have received a lot of interest in the field of TES due to their high heat enthalpy and nearly isothermal operating characteristic during phase transition [3,4]. Among numerous types of PCM (hydrate salts, paraffin, esters, fatty acids, etc.), paraffin is the most promising one because of its high energy storage capability, low supercooling, non-toxicity, non-corrosiveness, vapour pressure and cheaper cost [5]. However, the low thermal conductivity of paraffin makes it unfit for some applications [6]. There have been several attempts to boost the thermal conductivity of paraffin wax. Researchers employed metal foams, carbon additives and fins to improve the charging and discharging rates of paraffin waxes [7,8]. However, these enhancers increase the weight and cost of the TES systems, and few of them are not compatible with PCMs. Carbon materials (graphene oxide (GO), expanded graphite, graphene and others) have recently been investigated for improved heat transfer in PCMs due to their high thermal conductivity, low bulk density and chemical inertness [9,10].
Besides this, these porous carbon materials have an open cell structure coupled with the high thermal conductivity of graphitic ligaments, allowing them to quickly transport heat throughout the PCM [3]. As a result, researchers have attempted to incorporate carbon additive nanoparticles with paraffin at various mass fractions. If the mass fraction of nanoparticles in the base material (i.e., in this case, paraffin) is more than 1%, it is referred to as a high mass fraction; while if it is less than 1%, it is generally considered a low mass fraction [11]. In this study, a comparative analysis of low mass fraction impregnation with high mass fraction impregnation of graphite fillers in paraffin was done after the literature survey.
Li et al [12] found that adding low and high mass fractions of graphite additives (0.5–2.0 wt%) to paraffin increases the thermal conductivity and improves the heat transfer characteristics. Mills et al [13] had enhanced the thermal conductivity of paraffin about 20–130 times by adding a lower mass fraction (<1 wt%)...