Thermal degradation investigation with machine learning modeling of arachis hypogaea shell derived biochar enhanced phase change material for thermal energy storage

Various organic, inorganic, and metal-based nanoparticles have been incorporated into phase change materials (PCMs) to improve their thermal conductivity. However, these nanoparticles are expensive and do not prevent leakage during phase transitions. To address these issues and further enhance thermal conductivity, the inclusion of bio-based, carbon-rich porous materials has been explored. Additionally, the management of solid waste and the disposal of organic PCMs after prolonged use remain critical concerns. This study introduces a novel approach by utilizing green-synthesized, sustainable materials derived from Arachis hypogaea shells, which are agro based solid waste. XRD, FTIR, and SEM analyses show that Arachis hypogaea biochar (AHB) particles are uniformly distributed within the PCM, enhancing its chemical stability. The phase transition temperature and latent heat values of both pure PCM and its composite forms are determined experimentally using Differential Scanning Calorimetry. Thermal conductivity measurements of the prepared PCM composites, conducted using a thermal conductivity analyzer, reveals that the conductivity increases with the addition of AHB particle loading. Thermal degradation kinetics are assessed using model-free kinetic methods, including Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and Starink techniques, to determine the activation energy (AE) at different conversion levels. The degradation temperature of the composite PCM samples at various heating rates and conversion rates is estimated using several machine learning (ML) models, including polynomial regression, decision tree, random forest, Gaussian process, and gradient boost regression models. The polynomial regression model demonstrated superior predictive accuracy, with an RMSE of 0.029179 and an R 2 value of 0.967. These findings indicate that biochar incorporation improves the thermal stability of the PCM, increases the energy barrier for degradation. The increased degradation temperature and activation energy (i.e., PCM + 60% AHB sample) suggest trade-offs in material stability that should be considered when designing thermal energy storage (TES) systems. This study provides valuable insights for optimizing PCM based TES systems for solar water heating applications, balancing enhanced thermal performance with long-term durability, and guiding future research into stable, high thermal conductivity PCM composites.