Enhancement of Heat Transfer in a Cavity Containing a Periodically Moving Flexible Fin: Application of NEPCM

This study investigates the enhancement of natural convection heat transfer in a differentially heated square cavity by coupling fluid–structure interaction (FSI) with a nanofluid containing nanoencapsulated phase change material (NEPCM). This configuration is important for improving passive cooling in energy‐efficient technologies, such as electronics, buildings, and electric vehicles. The novelty of this study lies in the integration of a sinusoidal oscillating flexible fin with latent‐heat‐enhanced nanofluids in a fully coupled FSI framework. A finite element method is used to solve the governing equations for fluid flow, heat transfer, and structural motion, with validation through grid independence tests and comparison against benchmark numerical and experimental data. Parametric studies were performed for fin oscillation amplitude (0.05–0.15), oscillation period (0.1–0.7), Rayleigh number (10⁴–10⁶), and Stefan number (0.2–0.7). Results show that increasing the amplitude to 0.15 enhances the mean Nusselt number by up to 10%; lower periods ( τ fin = 0.1) and Stefan numbers ( Ste = 0.2) reduce heat transfer; higher Rayleigh numbers promote stronger convective currents and better thermal uniformity. These findings offer quantitative insights for optimizing thermally responsive structures using NEPCM fluids and flexible fins, enabling efficient heat transfer.