Development of Correlations of the Charging and Discharging Times of Carboxyl-Functionalized Multi-Walled Carbon Nanotubes (MWCNT-COOH) and Water with and without Polyethylene Glycol in Spherical Encapsulation

This investigation shows the results of a coupled numerical and experimental study on the solidification and melting of spherical capsules and the development of correlations for solidification time and melting time with parameters that impact the complete phase change time of nanofluids and water with and without polyethylene glycol inside plastic spherical capsules. Experiments included the investigation of different configurations of plastic spherical capsule diameters, external temperature, the initial temperature of phase change material (PCM), and PCMs. The PCMs used were water, water with a concentration of polyethylene glycol from 10% to 50%, and multi-wall carbon nanotubes functionalized with carboxylic acid group (COOH-MWCNT) with MWCNT at 0.125, 0.25, 0.5, and 1.0%. The simplified model was validated with available experimental results from the present work and from the literature, showing maximum deviations in the range of 0.25 to 12%. The simulation results showed that the use of nanoparticles in the base fluid increased the velocity of the solidification and melting processes and shortened the time for complete solidification and melting. The correlations for the complete solidification time and complete melting time followed the experimental results, with a maximum deviation of about 6%, which proves an excellent concordance of the correlations with the experiments.