Fractional Casson nano-encapsulated phase-change material flow and entropy generation in a Y-finned porous cavity using incompressible smoothed particle hydrodynamics

Purpose This study aims to examine transient thermo-solutal convection and entropy generation in a porous tetrahexagonal cavity containing an internal Y-fin and a Casson nano-encapsulated phase-change material (NEPCM) suspension. It examines how porous resistance, buoyancy, magnetic damping and fractional memory alter circulation, latent-heat activation and the spatial distribution of irreversibility. Design/methodology/approach The governing model combines Darcy–Brinkman–Forchheimer resistance, an apparent-viscosity stress formulation for the Casson suspension, reference-time-scaled Caputo derivatives, nonlinear Rosseland radiation, Soret and Dufour cross-diffusion, Arrhenius reaction and viscous dissipation. An incompressible smoothed particle hydrodynamics (ISPH) projection method resolves the irregular enclosure and branched internal surface without body-fitted remeshing. Temperature, concentration, velocity magnitude, the Cr=0.97 latent-activation isostate, entropy components and the Bejan number are evaluated together with averaged Nusselt and Sherwood numbers. Findings Increasing Da from 10−5 to 10−2 reduces porous drag, strengthens recirculation and redistributes the Cr=0.97 latent-activation isostate. Increasing Ha from 0 to 50 suppresses circulation and confines scalar transport near the fin. Raising Ra from 103 to 106 changes broad diffusion-dominated layers into plume-driven transport with localized entropy generation. Increasing Ec intensifies viscous heating, whereas increasing Rd broadens radiative heat penetration. A stronger reaction weakens solutal buoyancy; Soret diffusion redirects species along thermal-gradient pathways; and reducing α to 0.96 delays plume growth, latent-heat activation and entropy-structure migration. Originality/value The distinctive contribution is a geometry-resolved particle analysis of the coupled interaction among Y-fin-induced flow division, non-Darcy porous resistance, fractional thermo-solutal memory and distributed NEPCM latent storage. The documented apparent-viscosity stress formulation, together with the joint interpretation of velocity, temperature, concentration, the Cr=0.97 activation isostate, entropy components and Be, connects the reported patterns to transport near branch tips, corner stagnation and localized irreversibility.