Thermal performance of a hybrid pulsed nanofluid flow in a channel with obstacles formed using a dual MRT–LBM approach

Abstract

• Novel synergistic approach: Combines hybrid nanofluids, flow pulsation, and optimized obstacle geometry for enhanced microchannel cooling. • Advanced DMRT-LBM simulations: High-fidelity modeling of complex, unsteady thermo-fluid dynamics. • Optimal pulsation identified: Peak heat transfer occurs at Strouhal number ≈ 0.8, with a 13.2% Nusselt number increase. • Hybrid nanofluid superiority: Cu–Al 2 O 3 /water (4% vol., 75% Cu) boosts heat transfer by 28%. • Geometry impact: Trapezoidal obstacles improve thermal performance by 7.93% and achieve a PEC of 1.35. • Practical design guidance: Coordination of nanoparticle mixture, pulsation frequency, and obstacle shape is key for optimal performance. The multiple relaxation time lattice Boltzmann method (MRT-LBM) was used to study the flow of a pulsating hybrid nanofluid of copper and aluminium (Cu–Al 2 O 3 ) and water containing two internal obstacles inside a heated microchannel. The effects of the Reynolds number (Re), Strouhal number (St), total nanoparticle volume fraction (φ), copper mixing ratio, and obstacle shape (rectangular vs. trapezoidal) were determined using the mean Nusselt number (Nu), friction factor (f), and performance evaluation criterion (PEC). Increases in φ and copper ratio enhanced effective heat transfer, resulting in an increase in Nū. Under identical operating conditions, this reached a maximum of 28% compared to water for φ = 4% and 75% copper. The inlet pulse produced a non-uniform response, with the optimal result occurring near St ≈ 0.8. Within this region, the periodic disturbance of the boundary layer and the regeneration of the thermal fluid near the wall were more effective. Increasing St led to a further decrease in net gain due to phase lag and incomplete thermal redevelopment within the cycle. Replacing the rectangular obstacle with a trapezoidal coil suppresses stagnation recirculation and promotes smoother reattachment. This improves the hydrodynamic thermal equilibrium, resulting in a maximum PEC≈1.35. These results provide design guidelines for the coordinated selection of hybrid configuration, pulse frequency, and barrier shape in microchannel heat sinks.