Asymmetric secondary flows for photovoltaic-thermal cooling: a dual-velocity-component topology-optimized cooling device design

• Topology optimization reduces PV/T absorber temperature by 5.5–6.0 K. • Dual‑velocity minimization generates asymmetric secondary flows in PV/T channels. • Secondary y‑ and z‑velocities reach 0.02–0.06 m/s in optimized designs. • Topology‑derived baffles create ≈0.9 K local cooling near vortex wakes. • Optimized channels induce vortices with velocities from 0.01 to 0.085 m/s. This study introduces a Darcy-based topology optimization approach for PV/T cooling channels, in which multiple optimization zones and simultaneous control of multiple velocity components are employed to intentionally generate asymmetric secondary flows, a design strategy not previously explored in PV/T thermal management. The optimization was formulated to minimize the x- and y-components of velocity in selected sub-domains so that secondary flows, vortices, and near-wall mixing would be promoted for improved heat extraction. Five initial layouts were examined by varying the locations and sizes of the minimization regions. Mesh independence was established over seven meshes, and model fidelity was verified against literature temperature profiles with small absolute and relative errors. Through optimization, baffle-like solids were generated that locally slowed core flow and created strong recirculation. Two-dimensional fields showed higher peak velocities and deeper low-velocity pockets in the best design, whereas 3D extrusions confirmed asymmetric y- and z-velocity components that disrupted thermal boundary layers. When the optimum topology (Model V) was embedded in a PV/T module, absorber surface temperatures were reduced in repeated “cool footprints” aligned with baffle locations. Line profiles exhibited a consistent U-shape, with edge temperatures near ∼ 307 K and minima near ∼ 301 K, yielding ≈5.5–6.0 K lateral cooling under the tested condition; lines crossing baffle wakes showed an additional ∼ 0.2–0.4 K dip and up to ∼ 0.9 K difference among minima. It is demonstrated that localized, topology-derived structures can intensify convective exchange and meaningfully reshape the thermal field in PV/T modules, providing a practical route toward future multi-objective electro-thermal optimization that includes pressure losses and operating variability.