Stability and discharging performance improvements of modified nano particle enhanced binary alkanes capsule for cold latent heat storage tank

Nanoparticles with high thermal conductivity are often used to enhance the charging/discharging performance of phase change materials (PCMs). In this study, several surface modification methods are employed to enhance the stability of nano-Al 2 O 3 particles in binary alkanes, and their effectiveness is evaluated and compared. Experiments showed that oleic acid-modified nano-Al 2 O 3 (3:1) had the highest stability in binary alkanes within the air-conditioning temperature range, maintaining stability for over 36 h at 3 wt% and 5 wt%. The nano-enhanced phase change material (NEPCM) with the modified nano-Al 2 O 3 exhibited an increase in thermal conductivity, ranging from 20 % to 106 %, with minimal latent heat loss. Based on the properties of NEPCM from previous experiments, a validated numerical model with a dynamic mesh was developed to investigate the discharging performance of NEPCM capsules within a narrow operating temperature range for cold latent heat storage. Compared to pure binary alkanes, adding 1 wt%, 3 wt%, and 5 wt% modified nano-Al 2 O 3 reduced the melting time by 10.9 %, 24.6 %, and 38.3 %, respectively. The convective heat transfer in the four NEPCMs (PCM, nPCM-1 A, nPCM-3 A, nPCM-5 A) accounts for 72 %, 70 %, 68 %, and 67 % of the total heat transfer, respectively, indicating that convective heat transfer is the predominant mode. The percentage of natural convection in total heat transfer decreases with the increasing addition of nanoparticles.