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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]

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]

Since the high heat has a bad effect on every electric coolant device performance in small spaces, enhance thermal systems became a challenge to achieve better performance. In the present study, investigate the forced heat transfer and laminar CuO–water nanofluid flow around the sinusoidal cylindrical and cylindrical heat sink, at Reynold number less than 700, and at a constant heat flux. Which is simulated numerically by Galerkin approach finite element methods FEM. The main purpose of the study is to drop the heat spam by enhancing the heat transfer coefficient of laminar flow in different channel types of special shape (corrugate cross-section) using nanofluid. Study the effect of hydraulic diameter of sinusoidal cylindrical to classify the channels depended on (Dh ≤ 3 mm). The new design of heat sink is employed "sinusoidal cylindrical heat sink" varied according to the amplitude values (λ) and the corrugation number (G). A digest of the findings, the best enhance at φ = 0.15%vol of 16.31% and 16.53% for G = 3 and G = 10, respectively. A great drop in wall temperature about 20.47 and 16.58 for λ = 20 of G = 3, and G = 10, respectively, as the volume fraction of CuO–water nanofluid increased at Re = 478 & q″ = 127.3 kW/m2, comparing with water. In conclusion, the sinusoidal heat sink of λ = 20 with CuO–H2O nanofluid of φ = 0.15%vol showed best enhance in heat transfer coefficient. Increased the corrugate number G led to a decrease in the friction factor and thermal resistance. Furthermore, using nanofluid led to reduce the surface wall temperature, the friction factor also the thermal resistance. [ABSTRACT FROM AUTHOR]

The current work investigated numerically the natural convection within a square enclosure filled with nanofluid by examining four different types of attached fins (rigid fins, flexible oscillating in the same and opposing directions) and comparing it to the case without fins. The governing equations of heat and fluid flow (mass, energy and momentum) of fluid had been solved using the finite element scheme. The results are validated with the previous studies and presented in terms of streamlines, isotherm and Nusselt number. The influence of Rayleigh number (104 ≤ Ra ≤ 106), dimensionless time (10–4 ≤ τ ≤ 1), thermal conductivity ratios (1 ≤ ks ≤ 1000), the amplitude of the flexible fins (10–2 ≤ A ≤ 0.1) and frequency (0.05 ≤ λ ≤ 0.5) are studied. The governing parameters have been tested based upon their influence on fluid flow and heat transfer for the current study. The results are shown as contours of vortices, velocity, streamlines and isotherms as well as the local and average Nusselt number (Nuave). It is observed that the larger amounts of heat are transmitted by convection at higher thermal conductivity ratios, and the greater the magnitude of the Nusselt number demonstrates the pronounced effect of the fin oscillation. In addition, when the flexible fins oscillated in the same directions, the Nusselt number increased by 18.34% as compared to the case without fins. Furthermore, increasing the flexible fins' amplitude improves the oscillating motion of the fins inside the cavity, which improves fluid flow and heat transmission strength. [ABSTRACT FROM AUTHOR]

Current article presents a numerical investigation for three dimensional turbulent flow using the MCRT method to simulate solar radiations as a heat flux and the finite volume method in Ansys Fluent to simulate the equations. The fluid in absorber is a synthetic oil having eight hundred index mixed with Aluminium Oxide nanoparticles to enhance the heat transfer process. The study comparing different cases, including different numbers of longitudinal fins assembled inside the absorber with two arrangements and three particular Reynolds number in addition to the testing concentration ratio of the heat flux using the MCRT method. The impact of using three different numbers of fins (2, 4 and 6) at two different arrangements ("a" and "b") were presented. The three Reynolds number used was (18600, 23000 and 28000). Two Rim angles of the collector are tested (80o) and (120o), results showed that (120°) was achieved high outlet temperature with a concentration ratio (CR=82.47). The effects on outlet temperature, friction factor, Nusselt number, and then on the performance evaluation criterion (PEC) of the absorber tube were displayed. The results of the study proved that using nanofluid and finned absorber can increase the absorber hydrothermal performance and using (6) fins of arrangement "b" shows better performance in terms of heat transfer than arrangement "a". [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]

In this paper, numerical Galerkin Finite Element Method (GFEM) is applied for conjugate heat-transfer of a rotating cylinder immersed in Fe3O4-water nanofluid under the heat-flux and magnetic field. The outer boundaries of the cavity were maintained at low temperatures while beside the cylinder were insulated. It is assumed that the cylinder rotates in both clockwise and counter-clockwise directions. The dimensionless governing equations such as velocity, pressure, and temperature formulation were analyzed by the GFEM. The results were evaluated using the governing parameters such as nanoparticles (NPs) volume fraction, Hartmann and Rayleigh numbers, magnetic field angle and NPs shapes. As a main result, the average Nusselt number increases by increasing the NPs volume fraction, inclination angle and thermal conductivity ratios, while increasing the Hartmann number decreased the Nusselt number. Furthermore, platelet NPs had the maximum average Nusselt number and spherical NPs made the minimum values of Nusselt numbers among examined NPs shapes. [ABSTRACT FROM AUTHOR]

In this study, the heat transfer, fluid flow and heat capacity ratio are analyzed in an annulus enclosure filled with porous and saturated by a suspension of nanoencapsulated phase change materials (NEPCMs). It consists of phase change material core and a polymer or non-polymer shell. The presence of nanoparticles in the base fluid and the phase change capability of the nanoparticle's core improve the thermal properties of the base fluid and thermal control process. The inner cylinder wall is reserved at hot temperatures where the encapsulated particles absorb the heat, while the outer cylinder wall is reserved at cold temperatures where the encapsulated particles release the heat. A local thermal non-equilibrium model is adopted for the porous medium. The parameters studied are Rayleigh number (104 ≤ Ra ≤ 106), Stefan number (0.2 ≤ Ste ≤ ∞), melting point temperature of the core (0.05 ≤ θf ≤ 1), the concentration of the NEPCM particles (0% ≤ ϕ ≤ 5%), radius ratio (1.67 ≤ Rr ≤ 2.5), eccentricity (− 0.67 ≤ Ec ≤ 0.67), Darcy number (10−4 ≤ Da ≤ 10−1), porosity (0.3 ≤ ε ≤ 0.9) and interface heat transfer coefficient (1 ≤ H ≤ 1000). The results show that the dimensionless temperature of fusion (θf) plays the main role in the improvement in NEPCM on the heat transfer process. [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]

The natural convection of heat transfer is presented numerically using a temperature gradient from the hot inner corrugated cylinder. Different inner corrugated numbers located inside a cooled wavy-walled enclosure filled with two layers were simulated. The right layer is filled with Ag nanofluid and the left with a fully saturated porous media with similar nanofluid. The porous media with the nanofluid was modeled using the Darcy–Brinkman model. The main dimensionless equations are solved numerically using the method of Galerkin. This study considered the following dimensionless parameters: the Rayleigh number (10 6 ≥ Ra ≥ 10 3 ), the Darcy number (0.1 ≥ Da ≥ 0.00001), the vertical location (0.2 ≥ H ≥ −0.2), the number of sinusoidal inner cylinders (6 ≥ N ≥ 3), fraction volume of the nanoparticle (0.1 ≥ ⱷ ≥ 0), and porous layer thickness (0.8 ≥ X P ≥ 0.2). Results suggest that to increase the fluid flow strength, the internal sinusoidal cylinder must move upward to increase the fluid flow strength. Increasing the thickness of the porous layer reduces the average heat transfer. Results indicate further that highest fluid flow strength occurs at N = 4 when the inner sinusoidal cylinder moves downward vertically. [ABSTRACT FROM AUTHOR]