<p>This numerical study investigates the coupled effects of fin location and pitch on the melting behavior of nano-enhanced phase change materials in a rectangular enclosure subjected to various orientations. Crescent-shaped fins are positioned at three locations (top, center, and bottom) while the dimensionless fin pitch (Γ) is varied from 0.25 to 0.833 to cover a wide range of geometric configurations. The enclosure inclination angle is varied between 0 and 180° to represent realistic operating conditions in practical thermal energy storage systems. The melting process is simulated using the enthalpy–porosity method, and the numerical model is validated against available experimental and numerical data from the literature. The findings revealed that fin location and pitch strongly affect the melting performance across all inclination angles. The vertical enclosure with center fins at Γ = 0.5 achieved the maximum enhancement ratio of 59% and reached 95% liquid fraction in the shortest time. The optimal design for best passive energy storage corresponds to center fins at Γ = 0.5 for enclosure inclination angles of 0°, 30°, and 180°, while bottom fins at Γ = 0.541 are optimal for enclosure inclination angles of 60°, 90°, and 120°. For an inclination angle of 150°, the optimal configuration is achieved with bottom fins at Γ = 0.583. The optimal crescent-shaped design for the vertical enclosure achieved a 73.6% reduction in total melting time compared to the unfinned enclosure. The proposed design significantly reduces melting time and improves thermal efficiency, demonstrating strong potential for passive thermal management applications.</p>