Paraffin wax–water nanoemulsion: A superior thermal energy storage medium providing higher rate of thermal energy storage per unit heat exchanger volume than water and paraffin wax

•Phase change nanoemulsions with 10–50 wt% paraffin wax prepared and characterized.•Thermal energy storage performance of phase change nanoemulsions evaluated.•Nanoemulsions possess a blend of desirable characteristics.•Nanoemulsion containing 10 wt% paraffin wax provided the best storage performance.•Best nanoemulsion provided 23% enhancement in storage performance than paraffin wax. Experimental investigations have been carried out to identify an appropriate concentration of paraffin wax in paraffin wax–water nanoemulsions, for use as thermal energy storage media. For this purpose, paraffin wax–water nanoemulsions containing different concentrations of paraffin wax (10 wt%, 20 wt%, 33 wt% and 50 wt%) were prepared, with the size of dispersed phase ranging between 200 and 600 nm. Specific heat of nanoemulsions increased with paraffin wax concentration, with 50% paraffin wax–water nanoemulsion possessing 47% higher specific heat than that of water. The variation of viscosity of paraffin wax–emulsions was similar to that of pure liquid, with a reduction in viscosity at elevated temperatures. The performances of paraffin wax–water emulsions and those of water and pure paraffin wax were evaluated during charging cycle of thermal energy storage in an experimental setup. The experiments revealed that the energy stored per unit time per unit heat exchanger volume was the highest for paraffin wax–water emulsion containing 10% paraffin wax, exceeding those of water and pure paraffin wax by 11% and 23% respectively.