Synergistic effects of nano-enhanced phase change material (NePCM) and fin shape on heat storage performance of a finned shell-and-tube unit: An experimental study

•Melting and heat storage of NePCM in shell-and-tube LHTES unit were investigated.•Synergistic effects of NePCM and fin shape were studied by volume expansion method.•Sufficient preheating time can promote occurrence of close-contact melting (CCM).•The negative effect of additive loading on convection is greater than that on CCM.•Suitable combinations of fin shape and additive loading were proposed for applications.