## 1 Introduction
The frozen mass fraction improved using small metallic capsules with smaller heat transfer fluid temperatures and greater volume flow rates. [PERSON] et al. [12] examined the melting behavior of a fatty-acid-based PCM with functionalized graphene nanoplatelets ranging from 0.1% to 0.5% by volume in a spherical capsule. The results showed that adding graphene nanoplatelets to PCM changed its Newtonian to non-Newtonian behavior at low shear rates. Adding 0.5 vol% graphene nanoplatelets to PCM nanocomposite decreased melting time by 26% and 21% at 10 \({}^{\circ}\)C and 2 \({}^{\circ}\)C, respectively  
Researchers studied the helical, conical, and twin coils in energy storage systems. The use of a coiled heat exchanger for ice storage has been studied by [PERSON] et al. [13] using both numerical and theoretical methods. Recently, [PERSON] et al. [14] accomplished an experimental examination of paraffin wax in a tapering coil used as a storage unit. Compared with the standard coil, the findings suggested a maximum increase in melting rate of about 28.32% at a fluid intake temperature of 80 \({}^{\circ}\)C. [PERSON] [15] examined the helical coil thermal presentation and pressure fall with and devoid of helical-crimped fins. The results illustrated that the inlet operating conditions for hot and cold water considerably influenced the heat exchanger's effectiveness. [PERSON] et al. [16] presented experimental examinations on an ice storage system utilizing a twin concentric helical coil (TCHC). The outcomes disclosed that about 90% of energy stored was attained at 59% to 74% of the total charging time. [PERSON] and [PERSON] [17] numerically analyzed ice-on-coil thermal storage phase variations using many parameters. Ice formation was performed in a hollow space with a refrigerant transporter. The results discovered that increasing fin height increased the freezing rate. Table 1 represents the merits and demerits of different coils used in cool thermal energy storage. Recently, some studies used nano-PCM as a HTF in the energy storage system. [PERSON] and [PERSON] [18] examined the impact of HTF intake temperature and volumetric flow rates on the overall charging and discharging time of a low-capacity energy storage tank (nano-PCM). HTF settings minimize charging and discharging time by 18.26% to 22.8%. Discharging restores 85.89% of the stored energy, or 2637 kJ (3070 kJ). At 4 \({}^{\circ}\)C HTF, f-GNP dispersion reduces nano-PCM SEC by 28%. The performance of a low-capacity energy storage tank filled with nano-PCM-containing spherical capsules was assessed by [PERSON] et al. [19]. The findings showed that by adjusting to the HTF parameters, charging and discharging times were reduced by 18.26% to 22.8%. The melting rate was raised by 42% at 31 \({}^{\circ}\)C and 63% at 36 \({}^{\circ}\)C when 0.5 vol% graphene was added. [PERSON] et al. [20] used organic phase transition materials in a cold thermal energy storage system (A9 and A14). The real-world system contains a heat pump that circulates water via pipes to chill organic material and fan coil units that release their thermal load in the initially cooled storage medium. A staggered heat exchanger immersed in phase change material is within a thermal energy storage tank. The tank absorbed over 6 kWh