This paper presents the parametric studies conducted on a packed-bed phase change material (PCM) encapsulated in spheres using the effectiveness-number of transfer units (ɛ-NTU) method for optimisation purposes. In order to maximise the energy storage effectiveness within a packed-bed PCM system, the numerical study on the impact of different parameters was implemented by varying the length (L) and radius (R) of the TES tank, number of spheres (n1) in the tank, and sphere diameter (r3) while maintaining the compactness factor (γ) within the range of 0.3442 ± 0.02 m. The modified charging efficiency (ε*) of the PCM and the modified energy storage effectiveness (α*) of the tested configurations were calculated and compared. As a result, the ‘optimum design’ of the tank yielding the maximum energy storage effectiveness was identified at the optimum length and radius of 1.42 and 0.475 m, respectively, filled with 4098 PCM spheres. The study found that a low L/R value resulted in higher phase-change effectiveness, and the storage effectiveness was maximised at an optimum sphere diameter of 0.03475 m. The investigation led to the conclusion that by concurrently modifying L, R, and n1 during the charging process was advantageous in increasing the heat transfer surface area using small balls, reducing the mass flow rates, and utilising spheres with small diameters.
