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The control and improvement of heat transfer in enclosures is very important in several engineering applications. In the current two-dimensional numerical study, the mixed convection and entropy generation of water flowing inside a square vented enclosure that contains four vibrating cylinders with relatively low frequencies fr = 1, 2, 3, 5 Hz in the vertical and horizontal directions are reported. The effects of Reynolds and Richardson numbers, vibration frequency, vibration amplitude, and the direction of the cylinders' vibration on heat transfer and entropy generation are presented for various cases. The horizontal walls of the enclosure are kept adiabatic while the vertical left and right walls are hot and cold, respectively. The linear regression analysis was used to reveal the rate of increase in the Nusselt number with the Reynolds and Richardson numbers number for each cases. Series of analyses show that the existence and the vibration of the cylinders increases heat transfer but the vibration in the horizontal direction is more effective since the top and bottom walls of the enclosure are adiabatic. It is found that the entropy generation due to heat transfer is low at the center of the enclosure. The direct relationship between the heat transfer and both Reynolds and Richardson numbers is reported. In terms of heat transfer, it is found that the critical vibration frequency and amplitude are fr = 4 and A = 0.05L and 0.075L. [ABSTRACT FROM AUTHOR]

A numerical simulation was conducted to study the free convection of Ag/H2O nanofluid between a square cavity with cold walls and an egg shaped cylinder with a hot wall. Utilizing the egg equation, dimensionless governing equations were solved using the Galerkin Finite Element Method (GFEM). In this work, several parameters were studied, i.e. Rayleigh number (10³ ≤ Ra ≤ 106), volume fraction (0 ≤ φ ≤ 0.05), position (-0.2 ≤ Y ≤ 0.2), and orientation angle (-90° ≤ γ ≤ 90°). The numerical results are presented as streamline contours, isotherm contours, and local and average Nusselt numbers. Moreover, the results were used to analyze the fluids' structure, temperature distribution, and heat transfer rate. The numerical results confirmed that the stream intensity value increased with an increase of the Rayleigh number as well as the movement of the cylinder towards the bottom wall for all values of the orientation angle. Variation of the vertical position of the cylinder inside the cavity had a noticeable effect on 𝑁𝑢𝐿, which increased by 50% at γ = -90°, and by 58% at γ = -45°. However, at Y = -0.2, 𝑁𝑢𝐿 increased by 58% at γ = -45° and decreased by 7% at γ = -90°. The highest heat transfer rate was obtained at high Rayleigh number (Ra = 106), volume fraction (φ = 0.05), negative position (Y = -0.2), and the highest positive orientation angle (γ = 90°). [ABSTRACT FROM AUTHOR]

This study numerically investigates the free convective heat transfer of a non-Newtonian nanofluid through an F-shaped porous cavity. The thermal conditions of the walls of the cavity are assigned as TC and TH for the cold right wall and the hot left wall, respectively, and the remaining walls of the cavity are assigned as insulated walls. The model for this investigation is designed, implemented, and analyzed by COMSOL Multiphysics. The Galerkin finite element method is used to model and solve the governing equations of the flow and heat transfer process inside the porous media. Physical parameters are presented in the following order: 6 × 10 0.0, ≥ ≥ φ -2 0.4 AR 0.1, 10 10, 1.4 ≥ ≥ ≥≥ -1 Da -3 ≥n ≥ 0.6, and 10 10 ≥ ≥ Ra 6. The goal of this study is to study the influence of geometry configuration (F shape) and the above parameters on the flow structure, isotherms, and heat transfer. These parameters have been taken into account to investigate their effects on this kind of heat transfer mechanism. Results show that the addition of nanoparticles plays a significant role in changing heat transfer rates. In addition, an increase in the aspect ratio (AR) leads to create narrow areas, which promotes the stagnation zones, thus decreasing the distance between cold and hot walls. This, in turn, enhances the flow uniformity. Moreover, it has been generally concluded that the Nusselt number and velocity rates are directly proportional to the AR, Darcy number (Da), and Rayleigh number (Ra), and negatively proportional to the power-law index (n); however, there are some exceptions and unusual behaviors noticed and explained through the paper. [ABSTRACT FROM AUTHOR]