| description abstract | Abstract. The advancement of thermal management technologies necessitates improved heat transfer performance, particularly in low-Reynolds-number flow regimes. This study presents a comprehensive three-dimensional numerical investigation of laminar mixed convection heat transfer in noncircular ducts using aluminum oxide (Al2O3)/water nanofluid. Simulations are performed in an equilateral triangular duct and five additional duct geometries relevant to solar water heating (SWH) systems, including rectangular and isosceles trapezoidal ducts with base angles ranging from 60 deg to 100 deg. Using ansys fluent 18.1 and a single-phase model, simulations are conducted under a uniform wall heat flux of 1000 W/m2, with a fixed Reynolds number of 100, Richardson numbers ranging from 0 to 5, and nanoparticle volume concentrations from 0% to 5%. Results show that increasing both the Richardson number and nanoparticle loading enhances convective heat transfer. At 5% nanoparticle volume concentration and a Richardson number of 5, the average convective heat transfer coefficient increases by approximately 13.9% compared to pure water. Similarly, increasing the duct base angle from 60 deg to 100 deg at high buoyancy levels yields a Nusselt number enhancement of about 13%. However, these thermal benefits are accompanied by increased wall shear stress and pumping power, which rise up to 4.2 times compared to the baseline case. Flow field analysis indicates that ducts with larger base angles promote stronger vortex formation and improved thermal mixing. The findings highlight the trade-off between heat transfer enhancement and pressure drop, with the performance evaluation criterion (PEC) revealing diminishing returns beyond 3% nanoparticle concentration. | |
