Thermophysical Properties-Based Evaluation of Nanofluids Laminar Natural Convection Inside Square Enclosure

Abstract

The effect of thermophysical properties on laminar natural convection inside a differentially heated enclosure filled with nanofluids is numerically investigated. Expressions for minimum, average, and maximum values of nanofluid viscosity and thermal conductivity are deduced for an -based nanofluid. The configuration is mathematically simulated using four nonhomogeneous governing field equations: two mass balance equations (one for each phase), a momentum equation, and an energy equation. Brownian motion and thermophoresis are considered as the physical transport mechanisms for the nanoparticles. A numerical finite difference scheme is developed to solve the governing equations. The results of the Nusselt numbers for pure water and nanofluids are found to increase monotonously versus the Rayleigh number in a typical characteristic curve between two asymptotes. Correlations for the Nusselt number are developed. A parametric analysis of the results indicates that the heat transfer effectiveness of nanofluids is highly dependent on the nanofluid viscosity, whereas the nanofluid thermal conductivity has a secondary effect. The minimum values of nanofluid viscosity always lead to heat transfer augmentation, whereas maximum values mostly lead to heat transfer degradation, except for the observed augmentation in very high Grashof number values. Comparative examinations of the results as well as contours for streamlines, isotherms, void fraction distribution, and local apparent Reynolds number are presented.