Longitudinal fins cooled by advanced nanofluids have emerged as an effective solution for enhancing heat transfer in modern thermal systems. This study presents a novel transient thermal analysis and fin efficiency of wetted longitudinal porous fin cooled by a trihybrid nanofluid under the influence of a magnetic field, which has not been previously explored. The longitudinal fin with rectangular, convex and triangular profiles employing trihybrid nanofluid composed of \(Fe_{3} O_{4} , Au\) , and \(Zn\) nanoparticles suspended in blood has been investigated. It incorporates internal heat generation and magnetic field effects with Darcy’s law describing the porous medium. The governing nonlinear partial differential equation is solved numerically via the finite difference method after being nondimensionalized. A comprehensive parametric analysis is carried out to investigate the influence of key dimensionless parameters on the fin’s temperature distribution and thermal efficiency, including the Peclet number, wet porous parameter, convective parameter, radiative parameter, power index, generation number, internal heat generation, Hartmann number and ambient temperature. A 400% increase in internal heat generation slightly raises fin temperatures by 0.257%, 0.298% and 0.295% for rectangular, convex and triangular profiles. Conversely, a 200% rise in the Hartmann number improves heat transfer, lowering fin temperatures by 11.2%, 12.5% and 12.1% for the respective profiles. The findings indicate significant thermal performance enhancements achieved through the combined effects of the trihybrid nanofluid and optimized fin geometries, demonstrating the effectiveness of the proposed configuration for improved heat dissipation.
