This paper presents numerical simulation of the heat storage problem via a conductive block containing a phase change material (PCM) placed inside a nanofluid. Energy storage during combined heat transfer using PCMs is a critical issue in modern thermal systems. In this research, natural convection and radiation mechanisms are examined inside the two-dimensional medium filled with water-Al2O3 nanofluid by considering the real radiation properties of nanoparticles in the governing equations. The radiation presence is assumed in the participating medium to investigate its effects on the temperature distribution and phase change propagation. Numerical calculations are carried out utilizing the full lattice Boltzmann method (LBM). The variation of parameters such as the Planck number, Rayleigh number, block size and nanofluid concentration is studied. The results show that volumetric radiation can enhance the phase change by >50 % compared to pure natural convection. However, the radiation effects decrease with increasing Planck number and block size. Moreover, increasing the nanofluid concentration from 0.1 % to 0.3 % reduces the liquid fraction by up to 5.5 % due to its absorbing and scattering properties. The findings confirm that LBM simulation can reveal the influences of integrating volumetric radiation into PCM block-nanofluid systems, providing applicable insights for the design of energy storage and thermal management systems.

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