ABSTRACTLatent heat energy storage systems (LHESS) using phase change materials (PCMs) offer high thermal energy storage density and effective temperature regulation due to their ability to absorb and release heat at nearly constant temperatures. However, accurately simulating the melting process of PCMs remains challenging due to the nonlinear nature of heat transfer and phase transition mechanisms. In this study, the Lattice Boltzmann Method (LBM), implemented via the OpenLB framework, is employed to simulate the melting behavior of lauric acid material inside a finned rectangular cavity. The primary objective is to validate a new OpenLB numerical model against benchmark experimental data. The simulation results show excellent agreement with experimental observations in terms of liquid fraction evolution over time, particularly for the case with higher spatial and temporal resolution. Additionally, temperature measurements obtained from thermocouples at multiple locations within the cavity display the same trend in temperature evolution as observed in the numerical model, further supporting the model's reproducibility. Following validation, the model is used to study 12 additional configurations involving variations in fin aspect ratio and position. The simulations reveal that longer, thinner fins placed near the bottom of the cavity can reduce the total melting time. Between the minimum and maximum melting times obtained in this study, the fin aspect ratio and position showed a difference of 63.7%. Compared to upper fin placements, lower‐position fins consistently maintained increased melting rates, with improvements ranging from 11% to 26% depending on the fin aspect ratio. In fact, higher melting rates were observed in longer and thinner fins for all positions studied, with improvements ranging from 1% to 25% depending on the position.