Numerical Investigation of TiO₂-Water Nanofluid Flow and Heat Transfer in Rectangular Cavities: Effects of Aspect Ratio

In the present study, the flow and thermal behavior of TiO₂-water nanofluid is numerically studied in rectangular cavity of various aspect ratios (AR). The goal is to understand the effect of the cavity shape on the velocity field and temperature distribution of the nanofluid. A numerical model using a single-phase model is used to describe the thermo-fluid characteristic of the nanofluid and the governing equations are solved for five aspect ratios of 0.5, 1, 2, 4 and 8. Convergence analysis, grid-independence test and comparisons with previously published results are used to test the reliability of the numerical results. The results show that the aspect ratio is a significant factor that influences the flow structure inside the cavity. The flow is more strongly horizontally circulative and has greater horizontal velocity component variations at low aspect ratios. As the aspect ratio increases the flow is increasingly dominated by vertical motion and the variations in horizontal velocity are decreased. The cavity geometry has also a great influence on the temperature profiles. When the aspect ratio of the cavities is low, the temperature changes are large in the centerline investigated, but with increasing aspect ratio the temperature profiles are more uniform and the temperature field is more uniform in the cavity. Overall, it can be concluded from the results that the aspect ratio is one of the important geometric parameters to control the flow and the heat transfer characteristics of TiO₂-water nanofluid in confined cavities.