Thermal Property Prediction of Eicosane‐Fatty Acid Eutectic Phase Change Materials Using the Modified <scp>UNIFAC</scp> Model for Thermal Energy Storage Technology

ABSTRACT Eutectic phase change materials (PCMs) have shown great potential for thermal energy storage applications due to their distinct melting behavior and high latent heat capacities. However, experimental determination of thermophysical properties is time‐consuming, costly, and resource‐intensive, and accurately predicting their phase behavior and thermal properties during phase transitions remains challenging. This study systematically employs a thermodynamic framework based on the Modified UNIFAC model to predict the thermal properties of binary eutectic systems of eicosane and various fatty acids, including lauric acid, myristic acid, and palmitic acid. The interplay between combinatorial and residual parts of the activity coefficient suggests that the dominance of molecular size/shape difference over energetic interactions influences the overall behavior. The total activity coefficient of less than 1 indicates negative deviations from Raoult's Law. The theoretical predictions for thermal properties are validated against experimental data obtained via Differential Scanning Calorimetry (DSC). The results demonstrate a good agreement between the predicted and experimentally measured values, with errors of just 1.4 wt% in composition, 2.8°C in melting point, and 2 J/g in latent heat of fusion and 0.76 wt%, 3.1°C, and 8.7 J/g for freezing parameters. Eutectic PCMs exhibit a latent heat of approximately 214–236 J/g at a melting range of 31°C–34°C. This unified approach highlights the potential of the Modified UNIFAC model as a reliable tool for estimating the thermal properties of complex eutectic systems, significantly reducing experimental effort and providing a cost‐effective pathway for next‐generation thermal energy storage design and optimization.