Investigation of the effect of adding nano-encapsulated phase change material to water in natural convection inside a rectangular cavity

•Free convection in nano-encapsulated phase change material (NEPCM).•The core and shell parts are made of n-nonadecane and polyurethane.•Adding NEPCM to the water enhances its heat transfer up to 48%. The present simulation aims to investigate adding NEPCM nanoparticles to water in the natural convection inside a cavity by using FVM method and SIMPLE algorithm. Nano-encapsulated phase change material (NEPCM) consists of a shell and core with phase change property. The NEPCM particles in base fluid have the ability to transfer heat by absorbing and dissipating heat in the liquid-solid phase change state. In this study, the energy wall phenomenon due to the phase change of NEPCM core has appeared that the whose energy transfer strength is proportional to the latent heat of NEPCM core and the thickness of the energy wall. Moreover, the relationship between the energy wall and the heat transfer rate is payed attention, and the effects of the energy wall parameters including strength, thickness, and event location of energy wall and volume fraction are studied on the energy wall and heat transfer rate. According to the obtained results, adding NEPCM to the water enhances its heat transfer up to 48% in order to increase heat capacity of water-NEPCM mixture. Also, best heat transfer rate happens when the energy wall is at the center of the cavity. Moreover, a relation is presented for the thermal expansion coefficient of NEPCM, which considers the effects of the thermal expansion coefficient of the core and shell material.