Energy Reports 7 (2021) 4930–4940 Contents lists available at ScienceDirect Energy Reports journal homepage: www.elsevier.com/locate/egyr Research paper Heat transfer enhancement of microencapsulated phase change material by addition of nanoparticles for a latent heat thermal energy storage system Samaneh Sami, Nasrin Etesami ∗ Department of Chemical Engineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran article info Article history: Received 24 March 2021 Received in revised form 18 June 2021 Accepted 26 July 2021 Available online xxxx Keywords: Phase change material Microencapsulation Thermal energy storage Nanoparticles Thermal conductivity Thermal performance abstract In the present study, nanoparticles of MgO, TiO 2 , and Graphite with mass ratios of 3, 5, 7, and 10% were added to the structure of the synthesized Lauric acid (LA) microcapsules, and the effect of nanoparticles on the thermal properties of microencapsulated Lauric acid as non-toxic phase change material for energy storage applications was investigated. The microcapsules containing nanoparticles were prepared by emulsion polymerization of Styrene as the shell. The microencapsulation ratio (E.R) of LA increases with the amount of MgO and TiO 2 . However, the microencapsulation ratio was reduced by increasing the mass ratio of nano graphite. The highest microencapsulation ratio (69.90%) belonged to the microcapsules containing 10% of titanium oxide nanoparticles. Scanning electron microscopy (SEM) images showed that microcapsules obtained containing TiO 2 were spherical with a smooth surface and narrow particle size distribution. The thermal stability and thermal conductivity coefficient for the pure LA, microencapsulated LA with/without nanoparticles were examined. The thermal stability improved with the increasing mass ratio of the nanoparticles, no considerably. The microcapsules with 10% of TiO 2 nanoparticles had higher thermal stability. The weight loss temperatures in the first and second steps are 287 ◦ C and 435 ◦ C, respectively. The thermal conductivity of the lauric acid was increased by microencapsulation from 0.146 W/m.K to 0.149 W/m.K. The thermal conductivity coefficient of microcapsules increased by adding nanoparticles. Finally, the thermal energy storage performance of the obtained samples was evaluated in a designed experimental setup. The decrement percentage of the onset of the melting process time for lauric acid microcapsules and the microcapsules containing graphite nanoparticles, titanium oxide, and magnesium oxide were 1.2, 4.7, 8.5, and 16.7%, respectively. © 2021 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction Nowadays, the effective use of renewable energy sources is needed due to the increase in energy demand, the limited fos- sil fuels, and the emission of greenhouse gases. However, an important limitation associated with some renewable energies like solar energy is that it is only available for a limited time period, and there is always no balance between energy demand and energy supply (Du et al., 2018; Li et al., 2019). Thermal energy storage for the short or long term can solve this contra- diction (Jankowski and McCluskey, 2014; Ling et al., 2015; Jiang et al., 2017). Phase change materials (PCMs) with the unique ability of thermal energy storage can help to balance between demand and consumption. Improvement of thermal properties of PCMs can affect on reduction of energy consumption and cost. ∗ Corresponding author. E-mail address: netesami@iut.ac.ir (N. Etesami). Microencapsulation is one of the methods used to improve the properties of phase change materials due to the increase of the specific surface, the heat transfer rate, and the thermal stability of the phase change materials (Zhaoa et al., 2018). The microcapsules have low leakage and no reactivity with the ex- ternal environment (Chen et al., 2018; Alva et al., 2017). These properties are essential during various thermal cycles and they have been investigated in various studies. However, most phase change materials have low thermal conductivity, limiting their applications (Lei et al., 2017). Yu et al. (2014) synthesized micro- capsules based on n-octadecane core and calcium carbonate shell were through a self-assembly method to enhance the thermal conductivity and durability. The shell material was obtained by removing the n-octadecane core from microcapsules. The thermal conductivity of the shell was found 2.467 W/m K. Such a value is much higher than that of polymeric wall materials around 0.20 W/m K. Thermal characteristics and stability of TiO 2 /paraffin compos- ites with and without sodium stearoyl lactylate (SSL) as a surfac- tant were evaluated by Sami and Etesami (2017). An increase https://doi.org/10.1016/j.egyr.2021.07.080 2352-4847/© 2021 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).