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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]

Heat transfer by natural convection for a centered inner adiabatic circular cylinder inside a trapezoidal enclosure filled with Ag-water nanofluid superposed saturated porous-nanofluid layer is numerically investigated. The inclined left and right walls of the trapezoidal enclosure are insulated. The bottom wall is partially heated at isotherm hot temperature, while the top wall is maintained at isotherm cold temperature. Finite element technique is used to numerically solve dimensionless Navier-Stoke equations for the nanofluid and porous-nanofluid media between inner adiabatic circular cylinder and trapezoidal enclosure. The numerical results are validated with those of Kim et al. [2008] in terms of streamlines and isotherms to check the accuracy of the present program. The validation illustrates a favorable agreement between the present work and Kim et al. The following parameters are studied: Rayleigh number (103 ≤ Ra ≤ 106 ), Darcy number (10-1 ≥ Da ≥ 10-5), nanoparticle volume fraction (0 ≤ ph ≤ 0.1), and porous layer thickness (0 ≤ Yp ≤ 100%).

In this numerical study, the heat transfers of two types of fuels, namely kerosene and gasoline, were studied within a wavy channel with pulsed flow. The CFD module at COMSOL Multiphysics was used in this study. Several variables were used and applied to both types of fuel and compared between them. These variables included the values of Reynolds numbers between 200 to 800, as well as several values of Strouhal Numbers between 0 to 0.25. Different variable values were also used for the wavy channel, including the wave numbers (0, 2, 4, 6, 8, 10) as well as variable values of the wave amplitude (0, 0.1, 0.2, 0.3). Through this study, it was observed that as Strouhal Numbers increase, there is an increase in the Nusselt Number value. It was also observed that as the number of waves increases, there is an improvement in the heat transfer values. The numerical results showed that the values of heat transfer improved with an increase in the amplitude of the wave.. [ABSTRACT FROM AUTHOR]

Enhancing thermal performance and lowering heat loss in energy conversion systems are essential, especially for new and complicated products that make this requirement worse. In order to address this difficulty, this study looks at fluid flow and heat transmission using hybrid nanofluid and nanoporous materials in combination cavities. The numerical simulation of natural convection within a hollow two-dimensional cavity comprised of two connected tilted squares with a circular hollow at the center is investigated. The inner heated square is filled with a nanoporous material, whereas the rest of the cavity is filled with Cu-Al2O3 hybrid nanofluid. The COMSOL Multiphysics software is utilized to simulate the dimensionless governing equations. A comparison with previously published research showed a good agreement. Calculations are performed for different values of Ra number (Ra: 103, 104, 105, and 106), Darcy number (Da: 10–1, 10–2, 10–3, 10–4, and 10–5), volume fraction (φ: 0, 0.02, 0.04, and 0.06), width (W: 0, 0.1, 0.2, 0.3, and 0.4), and uniform porosity (ε: 0.2, 0.4, 0.6, and 0.8). The results demonstrated that the increase of the porosity leads to a decrease in the Nu number with the Rayleigh number increase. Darcy and Rayleigh numbers have a significant impact on the width (W) between the hybrid nanofluid and nanoporous layers. In addition to the above, the fluid flow slows down at Ra = 103, which causes S ˙ gen , T ⌣ and Be to increase. The rising of Ra from 104 to 105 causes no change in the S ˙ gen , T ⌣ because heat is primarily transported by conduction, but the maximum Be number is reduced. [ABSTRACT FROM AUTHOR]

Convective flowing and heat transference of non-Newtonian liquid comprising nano-encapsulated phase-changing material (NEPCM) suspensions, filled in a square cavity, is numerically investigated. The molecules of NEPCM are cored with n-octadecane, shelled by polymethyl-methacrylate, and suspended in non-Newtonian fluid. The enclosure is insulated horizontally and heated vertically. Finite element method (FEM) is implemented for the numerical solution under different variables such as nanoparticles volume fraction (0 < ∅ < 0. 0 5), Stefan number (Ste = 0. 2 , 0. 3 1 3 , 0. 5), the heat capacity ratio (λ) of about (0.4), the temperature of fusion of the NEPCM (0 < θ f < 1) and the density ratio ( ρ P ∕ ρ f ) (0. 7 < ρ P ∕ ρ f ≤ 0. 9). The results show that the Nusselt quantity is related to the fusion temperature. An improvement in heat transference is observed when the fusion temperature deviates from the wall temperature, which is in the range of 0. 2 5 < θ f < 0. 7 5. For all power law index values (n), a linear increase of the Nusselt number with the solid volume fraction is detected. The shear-thinning nanofluid (n = 0. 6) demonstrates higher Nusselt number values than those of n = 1 and 1.4. [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]

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AbstractThis study utilizes numerical analysis to investigate laminar flow and natural convective heat transfer of nanofluids (NFs) within dome-shaped enclosures (DSEs). The horizontal walls of the enclosure are adiabatic, while the vertical walls on the right and left are maintained at isothermal conditions with low and high temperatures, respectively. The study focuses on examining the impact of DSEs on flow patterns and natural convection (N.C.) under varying parameters, including Rayleigh numbers (Ra), Lewis numbers (Le), enclosure inclination angles, dome angles, and buoyancy ratio number (Nr). The Prandtl number (Pr) and nanoparticle volume fraction are consistently maintained at 10 and 0.05, respectively. The governing equations have been resolved by applying the Eulerian–Eulerian two-phase model. The study reveals that the DSE significantly influences flow dynamics, leading to smoother circulation patterns that intensify convection currents. This movement of hot fluid toward cooler regions within the enclosure enhances natural convective heat transfer. Across all enclosure inclination angles, the average Nusselt number (Nu) increases with higher Ra, while the Le remains constant at 4. Significantly, due to its robust convective currents, the average Nu in the DSE with a 45° dome angle surpasses those of corresponding square and rectangular enclosures. [ABSTRACT FROM AUTHOR]

Abstract This study investigates the consequences of introducing a pair of oscillating elliptical obstacles on the natural convection and entropy generation within a quarter-circle cavity that is filled with a water-based hybrid nanofluid. The Galerkin Finite Element Method was utilized to perform numerical simulations on a 2-dimensional cavity, where the outer wall was set to a low temperature and the inner wall was kept at a high temperature, while the other walls were adiabatic. The hybrid nanofluid containing Cu-Al2O3 nanoparticles was used. The impact of changes in the values of dimensionless parameters, such as the Rayleigh number, heated wall length, oscillation frequency, oscillation amplitude, and oscillation period, on the flow and heat transfer within the cavity was examined. Results showed that an increase in the length of the hot source resulted in a decrease in heat transfer rate and that increasing the Rayleigh number led to a significant increase in total entropy generation and heat transfer irreversibility. A drop in the average Bejan number was noted as the Rayleigh number increased, demonstrating the prevalence of entropy caused by fluid friction. The effect of changing the amplitude had a higher impact on the average Nusselt number compared to the frequency value. At low Rayleigh numbers, the average Nusselt number was higher when the elliptical obstacles oscillated in the same direction, while the opposite trend was observed at higher Rayleigh numbers. [ABSTRACT FROM AUTHOR]