Influence of Fin Orientation on the Solidification Performance of Bio‐Based Eutectic Phase Change Materials in a Triple‐Tube Thermal Energy Storage System

ABSTRACT This research conducts a computational investigation of the solidification behavior of bio‐based eutectic phase change materials (bEPCMs) in a triple‐tube thermal energy storage (TTTES) system. The proposed configuration employs heat transfer fluid (HTF) flowing through the inner pipe and the outer annulus. In contrast, the intermediate annulus is filled with a eutectic mixture of four different bio‐based PCMs blended in equal proportions—chloroacetic acid–beeswax (97:3), magnesium chloride–manganese chloride (93:7), beeswax–manganese chloride (90:10), and cetyl alcohol–magnesium chloride (93:7). Two fin configurations—longitudinal and radial—are examined to assess their impact on solidification characteristics, energy discharge, and exergetic efficiency. Results reveal that fin geometry plays a crucial role in governing heat transfer and solidification behavior. Longitudinal fins demonstrate superior thermal performance, achieving complete solidification in 1645 s—approximately 4% faster than radial fins. At a St*Fo (product of Stefan and Fourier number) value of 0.01069, the longitudinal configuration exhibited nearly 35% higher energy discharge and 14.2% greater exergy output than the radial configuration. Furthermore, the exergetic efficiency of longitudinal fins exceeded that of radial fins by up to 6.25%, owing to enhanced conductive pathways, reduced thermal resistance, and minimized unused PCM regions. Contour analyses confirm that longitudinal fins promote more uniform and progressive solidification, while radial fins result in trapped liquid cores and uneven freezing fronts. Overall, this work demonstrates the combined potential of bio‐eutectic PCM mixtures and optimized fin geometries to enhance thermal and exergetic efficiency of TTTES systems, offering a viable pathway toward high‐efficiency, sustainable latent heat thermal energy storage technologies.