ABSTRACT This study presents a comprehensive numerical investigation of double‐diffusive natural convection in a pear‐shaped enclosure containing nano‐encapsulated phase‐change materials (NEnPCMs). Internally heated fins are present within the enclosure and are subject to various thermal and solutal boundary conditions. The influences of the important dimensionless parameters Rayleigh number ( Ra = 10 3 –10 6 ), Darcy number ( Da = 10 − 5 –10 − 2 ), Hartmann number ( Ha = 0–100), Lewis number ( Le = 0.1–10), and fin length (XF = 0–0.2) are presented in clear detail to facilitate understanding of the performance in terms of heat and mass transport. Results indicate that as Ra increases, convective forces increase, leading to a higher average Nusselt number ( Nu avg ) from 10.737 to 11.569 and the average Sherwood number ( Sh avg ) from 98.376 to 106.32. A further increase in Da would switch the system from conduction to convection, thereby distorting isotherms and concentration fields considerably. The applied magnetic field suppresses fluid motion, which in turn reduces Nu avg and shifts the transport regime toward diffusion. Increasing Le improves the distribution of species but slightly suppresses the convective flow. The variation in the length of the fins (XF = 0–0.2) demonstrates that longer fins reduce vortex strength and convective transport, resulting in a decrease in Nu avg by 5% and Sh avg by 3%. These findings provide fresh perspectives on optimizing NEnPCM‐based thermal systems for energy storage, electronic cooling, and building envelope design.