Flow and Heat Transfer Characteristics of Jet-Assisted Non-Newtonian Nanofluids in Backward-Facing Step Channels

Abstract

This study numerically investigates the thermal-hydraulic performance of a jet-assisted backward-facing step channel using a non-Newtonian Al₂O₃/carboxymethyl cellulose (CMC) nanofluid under steady-state, laminar, incompressible, and two-dimensional flow conditions. The governing equations of mass, momentum, and energy are solved using the finite volume method, while the rheological behavior of the CMC solution is modeled using the Power-Law model. The numerical model is validated against previously published experimental and numerical data, demonstrating good agreement with benchmark results. The effects of Reynolds number, nanoparticle volume fraction, fluid rheology, jet injection angle, and jet momentum ratio on the flow structure and thermal-hydraulic performance of the channel are systematically investigated. The results reveal that increasing the Reynolds number significantly enhances convective heat transfer by strengthening fluid mixing and reducing the thermal boundary layer thickness. The incorporation of Al₂O₃ nanoparticles improves the overall thermal performance owing to the enhanced effective thermal conductivity of the nanofluid. Furthermore, the shear-thinning behavior of the non-Newtonian CMC solution provides superior heat transfer characteristics compared with Newtonian water. The jet injection parameters are also found to play a critical role in controlling the flow structure and thermal performance of the system. Appropriate jet injection angles and momentum ratios improve fluid mixing and significantly enhance heat transfer while maintaining favorable thermal-hydraulic characteristics. The performance evaluation criterion (PEC) confirms that the combined application of jet injection and non-Newtonian nanofluids offers considerable thermal enhancement with acceptable hydraulic penalties. The findings demonstrate the potential of jet-assisted non-Newtonian Al₂O₃/CMC nanofluids for advanced cooling and thermal management applications involving separated flow configurations.