A numerical investigation was conducted to study the forced and mixed convection of nanofluid in a horizontal channel with a built-in-heated square cylinder. The nanofluid considered in this study is composed of metal nanoparticles suspended in water (base fluid). The governing equations are solved using the finite volume method based SIMPLER algorithm. Different Reynolds numbers and volume fractions of nanoparticles ranging respectively from 85 to 200 and from 0%to12%, have been considered. The effect of the nanoparticles volume fraction on the critical Reynolds number value defining the transition between two flow regimes (stationary and periodic)as well as on the overall flow coefficients is firstly studied. In the thermal study, we have established correlations to evaluate the heat flux transferred from the obstacle to the flow for different nanoparticles volume fractions. Results show a marked improvement in heat transfer compared to the base fluid. This improvement is more pronounced for higher Richardson numbers and higher nanoparticles volume fractions.

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A numerical investigation was conducted to analyze the effect of the presence of a square obstacle placed behind the first primary recirculation zone on the flow field and heat transfer over a backward-facing step using copper-water nanofluid. Computations were performed over a range of Richardson number from 0 to 2.85 and volume fraction of nanoparticles φ from 0 to 15% at a fixed Reynolds number Re = 450 and Prandtl number Pr = 6.2. A discussion about the buoyancy effect on the heat transfer exchanged between the horizontal walls of the channel as well as on the heat flux transferred from the obstacle to the flow for different φ. Results show that, the presence of heated square obstacle is effective in augmenting the heat transfer. In fact, in presence of the square obstacle, enhancements in the maximum values of the Nusselt number of 194% and 153% are obtained at the lower and the upper walls of the channel, respectively. Furthermore, the heat transfer reaches its maximum at the emplacement of the square cylinder. On the other hand, results show a marked improvement in heat transfer compared to the base fluid. This improvement is more pronounced for higher and φ. Finally, the effect of the buoyancy forces is found less important on the heat transfer enhancements when Ri increases. This can be explained by the thermophoresis forces effect near the hot walls of the obstacle.

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