1Phase change materials (PCM) with their high thermal storage density at almost isothermal conditions 2 and their availability at wide range of phase transitions promote an effective mode of storing thermal energy. 3Literature survey evidently shows that paraffins and salt hydrates provide better thermal performance at 4 competitive cost. This review paper is focused on the classification of various paraffins and salt hydrates. To 5 acquire long term productivity of LHS system, the thermo-physical stability of both paraffins and salt hydrates; 6 and their compatibility with various plastic and metallic container materials play a vital role. Likewise, the 7 lower thermal conductivity of PCMs affects the thermal performance of LHS system. This article reviews the 8 various thermo-physical performance enhancement techniques such as influence of container shape and its 9 orientation, employment of fins and high conductivity additives, multi-PCM approach and PCM encapsulation. 10The performance enhancement techniques are focused to improve the phase transition rate, thermal 11 conductivity, latent heat storage capacity and thermo-physical stability. This review provides an understanding 12 on how to maximize thermal utilization of PCM. This understanding is underpinned by an analysis of PCM- 13Container compatibility and geometrical configuration of the container.

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This article is focused on numerical analyses of commercially available metal-oxides as potential nano-additives for paraffin in thermal storage applications. Technical and economic prospects of metal-oxides based nano-PCMs are evaluated to help formulate selection criterion for nano-additives to achieve optimum thermal performance at acceptable cost. Numerical model based on enthalpy-porosity technique is developed which incorporates natural convection and transient variations in thermo-physical properties of nano-PCM. Numerical model is simulated for charging and discharging cycles of nano-PCMs in shell and tube heat exchanger at controlled temperatures. Transient simulations help in analysing heat transfer categorisation and isotherms distributions, solid-liquid interfaces propagations, charging and discharging rates, and overall thermal enthalpy. Inclusion of nano-particles increase the effective thermal conductivity and surface area for heat transfer, which results in enhanced charging and discharging rates. The conductive heat transfer, peak heat flux, charging and discharging rates are significantly enhanced by increasing volume concentration of nano-particles. The percentage enhancement in charging rates of SiO 2 based nano-PCM samples with 1% and 5% are 29.45% and 41.04%, respectively. Likewise, the discharging rates are improved by 21.09% and 30.08%, respectively. However, an increase in volume concentration reduces natural convection and overall thermal enthalpy, and increases total cost of nano-PCM. For instance, the percentage reductions in total enthalpy of CuO based nano-PCM samples with 1% and 5% volume concentrations are 8.01% and 32.14%, respectively. Likewise, the total costs are increased from 14.26 €/kg for base paraffin to 70.89-309.33 €/kg, respectively. Hence, the significance and originality of this research lies within evaluation and identification of preferable metal-oxides with higher potential for improving thermal performance at reasonable cost. This article will help bring significant impact to large-scale utilisation of low-carbon and clean energy technology in domestic and commercial applications.