Search

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]

The present investigation is on examination of the natural convection and entropy generation considering the heatlines visualization of nanofluid I‐shaped enclosure with two corrugated walls considering inner rectangular heater of three different heights. The influence of Brownian motion along with thermophoresis had been implemented using Inhomogeneous two‐phase model of nanofluid. The governing equations were solved numerically using COMSOL software. Influence of Rayleigh number (103≤Ra≤105) $({10}^{3}\le {Ra}\le {10}^{5})$, Buoyancy ratio number (0.1≤Nr≤4) $(0.1\le {Nr}\le 4)$, Lewis number (2≤Le≤8) $(2\le {Le}\le 8)$, heater length (0.25≤H≤0.75) $(0.25\le H\le 0.75)$. The results indicate that the influence of Lewis number on heat transfer bettering is stronger at high Rayleigh number (Ra=105) $({Ra}={10}^{5})$ while its impact is negligible at a lower value of Rayleigh number (conduction mode). In addition, the total entropy generation gets its highest value at Lewis number (Le=1) $({Le}=1)$. Bejan number, fluid flow strength and heat rate increase as the rectangular heater height increases. Also, higher heat transfer augmentation is taken when the heater height is (H=0.5) $(H=0.5)$ while increasing the heater height to (H=0.75) $(H=0.75)$ leads to more total entropy generation. The impact of heater height on total entropy generation is highly affected by Rayleigh number as increasing the heater height from (H=0.25) $(H=0.25)$ into (H=0.75) $(H=0.75)$, total entropy generation increases by 60% $60 \% $ at Ra=103) ${Ra}={10}^{3})$ while it increases by 74.62% $74.62 \% $ at (Ra=105) $({Ra}={10}^{5})$. [ABSTRACT FROM AUTHOR]

The current study investigates the influence of MHD on the natural heat transfer considering the irreversibility in a complex-shaped cavity with the existence of inner roundish heater with four attached fins utilizing finite element formulation. Three different cases are considered to figure out the major characteristics of temperature, stream function and total generated entropy, Nusselt number in addition to Bejan number. Concentrated attention is directed to the enclosure geometry modifications and the varied length of attached fins and their impacts. The parameters of study are ranged as follows; Rayleigh number 10 3 ≤ Ra ≤ 10 6 , Hartmann number 0 ≤ Ha ≤ 60 , fins' length 0.1 ≤ H ≤ 0.3 . The novelty of the present work is on studying all of these parameters in the complex enclosure considering three different cases of the shape of the outer walls so that the star-shaped enclosure is classified as case 1. With increasing the length that separated between the outer arc of the star enclosure, the octagonal-shaped enclosure will appear as denoted in case 2 and 3. It had been seen that at low Rayleigh number Ra = 10 4 , case one is the best choice in heat transfer bettering while it is the lowest case at high Rayleigh number Ra = 10 6 . Additionally, the influence of Hartmann number on the total entropy generation reduction percentage for case three is 63.57 % while it is 51.11% for case two while Hartmann number had negligible impact of entropy generation reduction for case one. Lastly, the highest Bejan number is at fin length H = 0.3 is recorded for case one. [ABSTRACT FROM AUTHOR]

In line with recent studies, where it has been shown that nanofluids containing graphene have a stronger capacity to boost the heat transfer coefficient with respect to ordinary nanofluids, experiments have been conducted using water with cobalt ferrite/graphene nanoparticles. In particular, a circular channel made of copper subjected to a constant heat flux has been considered. As nanoparticles are sensitive to the presence of a magnetic field, different conditions have been examined, allowing both the strength and the frequency of such a field to span relatively wide ranges and assuming different concentrations of nanoparticles. According to the findings, the addition of nanoparticles to the fluid causes its rotation speed to increase by a factor of two, whereas ultraviolet radiation plays a negligible role. The amount of time required to attain the maximum rotation speed of the nanofluid and the Nusselt number have been measured under both constant and alternating magnetic fields for a ferrofluid with a concentration of 0.5% and at flow Reynolds number of 550 and 1750. [ABSTRACT FROM AUTHOR]

Nanofluids have garnered significant interest as a potential solution to address overheating challenges across diverse industries. Researchers are actively exploring different types of nanofluids to mitigate these issues. In this study, a numerical analysis was conducted using ANSYS software to examine the fluid flow and heat transfer characteristics of nanofluids (ranging from 0 to 4 volume fractions) in a corrugated wavy channel within the turbulent range. Various nanoparticles, including Al2O3, CuO, SiO2, and ZnO, were employed and dispersed in different base fluids such as ethylene glycol, glycerin, and water. The particle size of the nanoparticles ranged from 20 to 70 nm. The results revealed that SiO2/water-based nanofluids provide better heat transfer than all the water-based nanofluids. The maximum average Nusselt number and pressure drop of 200 and 115 Pa, respectively, were observed for SiO2 nanofluid (volume fraction of 0.04) with a particle size of 20 nm. [ABSTRACT FROM AUTHOR]

The present work focuses on investigating magnetohydrodynamic (MHD) natural convection in a complex I-shaped enclosure with corrugated walls, filled with nanofluid and porous media layers. This study analyzes various parameters’ effects on heat transfer and fluid flow. The enclosure’s left and right walls maintain low temperatures, while the other walls are insulated. The inner corrugated cylinder experiences high temperatures. The study examines the impact of Rayleigh number (Ra), Hartman number (Ha), nanofluid volume fraction (φ), Darcy number (Da), MHD inclination angle (γ ), position of the corrugated cylinder (δ) and number of undulations (N) on isotherms, streamlines, velocity profiles and average Nusselt number variations. The results show that higher Ra values increase the average Nusselt number while increasing Da enhances it by 65%. Magnetic source inclination greatly affects heat transfer, with Nusselt at γ = 90° being 15.34 compared to 10.234 at γ = 0°. The study concludes that optimal heat transfer occurs at γ = 90°, Ra = 106, Da = 10−3, Ha = 30 and N = 2. [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]

This study presents an experimental investigation to determine the heat transfer enhancement in a novel heat exchanger known as the "Helicoidal Square-Shaped Heat Exchanger" with and without using a nanofluid. The experiments were performed for the range of Reynolds numbers from 4400 to 8000, using nanofluid (Al2O3-pure water) at the concentrations 0.1, 0.25, and 0.5%. This experimental investigation found that the heat transfer ratio is improved by increasing the nanofluid concentrations and the flow Reynolds number. The highest value of the heat transfer ratio was at Re = 8000, and 0.5% concentration of nanofluids. The corresponding increment in the heat transfer rate was 13.46 %, the heat transfer coefficient augmented by 9.64 %, and the Nusselt number improved by 10.43% compared to the results obtained experimentally with distilled water. The results obtained for the distilled water were verified with the Dittus-Boelter equation and numerical simulation. In addition, all obtained experimental data were compared with the CFD simulation. The use of nanofluids for heat transfer enhancement has a wide range of applications. Therefore, the presented results suggest using Al2O3-water nanofluids to improve the efficiency of many renewable energy plants, including solar and geothermal energy systems. [ABSTRACT FROM AUTHOR]

The present study examines the turbulent flow of mixed convection heat transfer enhancement within a rectangular channel considering three different novel shapes of ribs (smooth, scalene, and curved‐side triangular). The investigations were conducted experimentally by developing a new test facility, while the numerical computations were carried out using the finite volume method. The experimental work involves constructing of the channel, ribs, and all equipment and measurement instruments. The numerical work is based on ANSYS FLUENT considering the k–ε turbulent model. The results are presented and compared in terms of Nusselt number, friction factor, and performance factors for Reynolds numbers ranging between 3000 and 12,000. By comparing the average values of the numerically obtained Nusselt number with experimental measurements, the data showed a close agreement with a maximum difference of 5%. It also found that scalene triangular ribs (STRs) provide better performance in terms of heat transfer, although introducing a slight increase in friction losses. STRs showed (20%) increase in Nusselt number compared with smooth channel, and 3%–6% increase in Nusselt number compared with curved‐side triangular ribs (CTRs). In contrast, CTRs have a lower friction factor value of 5% compared with STRs at a low value of a Reynolds number of 3000. Furthermore, the Nusselt number changes significantly (250% increase) by increasing the value of the Reynolds number from 3000 to 12,000. A thermal performance factor of up to 1.28 was achieved for the STRs at the lowest range of Reynolds' number of 3000. The findings from the present study are of practical importance for industries requiring heat transfer enhancement techniques to improve heat transfer equipment performance. [ABSTRACT FROM AUTHOR]

The principal moot point in this investigation is heat removal from surfaces with high heat flux, which is the use of tabulators and parts with a particular geometry, it has been chosen as a solution to this moot point. The primary hypothesis in this investigation is to increase fluid heat transfer by increasing turbulence and heat transfer by increasing the plane of heat transfer and establishing a vortex flow. The fundamental idea and novelty of this investigation is the simultaneous use of a turbulator (to improve turbulence and provide more effective heat transmission) and increasing the contact surface (through the installation of parts with unique geometry), which can be obtained from different turbulator used in other geometries. In this research, the limited volume method to solve governing equations in three-dimensional space and Cartesian coordinates has been used on the network using Ansys Fluent software. In order of comparison, turbulators SLT and then TRT is compared to other turbulators (TRT, SHT, RET) It has the highest Nusselt number, and in the Reynolds numbers in the turbulent flow regime, they have the most significant reduction in the friction coefficient. [ABSTRACT FROM AUTHOR]

In this work, the numerical investigation was conducted for the MHD natural convection and entropy generation characteristics of water-based hybrid nanofluid (Fe 3 O 4 -MWCNT) in a porous annulus between a cooled circular cylinder and a heated Koch snowflake subjected to a uniform magnetic force. The novelty of this work is presented by the special shape and different studied positions of the hot barrier. The governing equations are explained by employing the Finite Element Method. The impacts of nanoparticle volume fraction (φ = 2 %, 3%,4%, and 5 %), Rayleigh number (Ra = 103 to 106), Hartman number (Ha = 0,25,50,100), Darcy number (Da = 10-2, 10-3, 10-4, and 10-5), and the position of the Koch snowflake (four cases) on the distributions of isotherms, streamlines, average Nusselt number (Nu avg) as well as on total entropy generation and Bejan number are thoroughly examined. The computational outcomes indicate that increasing the Ra number is possible by changing the temperature between the hot and cold sources. By increasing this parameter, the buoyancy force of the fluid is strengthened. As the Da number increases, the penetration of the flow cross-section in the cavity increases, and the flow circulates in the cavity with less depreciation due to the buoyancy force. Applying Lorentz force, if not in the direction of natural flow, causes the flow velocity to be depleted and fluid flow in the cavity to be facilitated. With increasing Ra number, the application of Lorentz force with different intensities becomes important due to the importance of fluid circulation in the cavity. Applying a Lorentz force with a higher Ha number at high Ra numbers reduces heat transfer due to junction balance and flow separation on hot and cold surfaces. In the lower Ra numbers, the Bejan number tends to 1, indicating a significant increase in the temperature gradient in the cavity and the expansion of the thermal boundary layer at low fluid velocities. At the highest Ra, increasing Ha from 0 to 100 decreases Nu avg by 50 %, while decreasing Da from 10−2 to 10−5 reduces Nu avg by 70 %. [ABSTRACT FROM AUTHOR]

The current study focuses on the transient mixed convection within a vented square enclosure with differentially heated vertical walls and a flexible baffle coupled to a circular solid cylinder. In numerical analysis, the COMSOL Multiphysics tool is used to simulate and solve two-dimensional governing equations using the Galerkin finite element approach and the arbitrary Lagrange–Euler (ALE) method, as well as the coupling of structure deflection and fluid flow. This work considered the effects of changing locations of flexible baffles attached to a cylinder on thermal and flow structures. The effect of several parameters, such as Richardson number (10–1 ≤ Ri ≤ 102), Cauchy number (10–12 ≤ Ca ≤ 10–4), and Reynolds numbers, (50 ≤ Re ≤ 250) on convective heat transfer characteristics are investigated for time 0.01 to 10 s. It is observed that changing time steps leads to a continuous change in fluid flow intensity which reflects on the deformation direction of the flexible baffle. The results indicated that the cavity with flexible baffle has the best average Nusselt number compared to cavities with rigid baffle and without baffles, respectively. As Re is raised from 50 to 250, the percentage of the average Nusselt number increased to 40% at Ri = 0.1 and 59% at Ri = 200. [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]

Global technological advancements drive daily energy consumption, generating additional carbon-induced climate challenges. Modifying process parameters, optimizing design, and employing high-performance working fluids are among the techniques offered by researchers for improving the thermal efficiency of heating and cooling systems. This study investigates the heat transfer enhancement of hybrid "Al2O3-Cu/water" nanofluids flowing in a two-dimensional channel with semicircle ribs. The novelty of this research is in employing semicircle ribs combined with hybrid nanofluids in turbulent flow regimes. A computer modeling approach using a finite volume approach with k-ω shear stress transport turbulence model was used in these simulations. Six cases with varying rib step heights and pitch gaps, with Re numbers ranging from 10,000 to 25,000, were explored for various volume concentrations of hybrid nanofluids Al2O3-Cu/water (0.33%, 0.75%, 1%, and 2%). The simulation results showed that the presence of ribs enhanced the heat transfer in the passage. The Nusselt number increased when the solid volume fraction of "Al2O3-Cu/water" hybrid nanofluids and the Re number increased. The Nu number reached its maximum value at a 2 percent solid volume fraction for a Reynolds number of 25,000. The local pressure coefficient also improved as the Re number and volume concentration of "Al2O3-Cu/water" hybrid nanofluids increased. The creation of recirculation zones after and before each rib was observed in the velocity and temperature contours. A higher number of ribs was also shown to result in a larger number of recirculation zones, increasing the thermal performance. [ABSTRACT FROM AUTHOR]

One of the best methods in thermal engineering for cooling a liquid is to use a radiator. Using the radiator mechanism in free convection systems is a successful and first idea to improve performance of natural convection systems, which have various applications in building, energy storage, and cooling systems. Therefore, a radiator with four constant temperature fins on each side was used to contribute to cool a hot plate in this study. The mechanism of this system was free convection of water with Multi-walled carbon nanotubes (MWCNTs), and a complex relationship was used for thermal conductivity nanofluid, respecting the thermal conductivity of MWCNT in radial and longitude directions. A deviated magnetic field also created a Lorentz force on the moving fluid to control natural convection mechanism. This system was modeled using the finite volume method to study the influences of Rayleigh number, volume fraction, and Hartmann number on the flow and heat transfer parameters. Evidences showed that injecting 3% volume fraction of MWCNT in Rayleigh numbers of 10 4 escalated the mean Nusselt number by 48% in all of the Hartmann numbers. [ABSTRACT FROM AUTHOR]

Free convection of F e 3 O 4 -water inside the porous enclosure was investigated in the presence of magnetic fields. The SIMPLE algorithm was employed to solve the equations based on FVM. The inner wall of enclosure was considered in the constant flux and that of outer wall were at a constant temperature, respectively. Also, two other walls are thermal insulation and the radiation reflects to inner semi-annulus. An electric current coil for producing a magnetic field is wrapped around the semi-annulus. The effects of R a p = 10 a n d 1000 , the concentration (φ A v e = 0 , 0.01 a n d 0.03) , porosities (ε = 0.4 a n d 0.7) and magnetic numbers (0 ≤ M n ≤ 8 × 10 7) are investigated considering first laws of thermodynamics. The findings revealed that the mean Nusselt number has direct relation with the magnetic number, porosity, R a p and concentration, respectively. Moreover, increasing volume fraction from 0.01 to 0.03 in high magnetic number enhanced the Nusselt number by 32 %. [ABSTRACT FROM AUTHOR]

In this study, laminar flow & natural convection heat transfer of water/Single Wall Carbon Nanotubes (SWCNT) nanofluid in a triangular cavity is simulated using the finite volume method. The cold temperature of the triangular cavity is due to the forced flow of cool pure water flowing above the cavity, and the hot source with temperature T h is at the bottom of the cavity. The present study aims at cooling triangular cavities with fixed bases and different angles of attack or heights, installed in a rectangular channel. This study is done for the solid nanoparticles volume fraction of φ = 0–0.06, angle of attack of 15–60°, and Rayleigh number of Ra = 10. Results show that the temperature gradient between the hot and cold sources in the cavity increases the temperature gradients. Depending on the dominant heat transfer mechanism in the cavity, the temperature distribution will differ. By increasing the angle of attack, the cavity temperature gradients increase. By adding fluid injection in the cavity & increasing solid nanoparticles volume fraction (φ), it is possible to improve heat transfer. Friction occurs in areas with high-velocity gradients and at the start and end of the warm plate. At the middle of the plate, due to the separation of the vortex from the hot surface, the friction factor is reduced. Increasing φ results in higher cooling fluid viscosity and density which has a higher momentum dissipation rate. The most heat absorption from the hot surface occurs at the point where the cooling fluid reaches the hot surface, and the vortices are symmetric for all angles of attack. By placing the cavity in the channel, changing the cavity angle and increasing heat flux are more effective than increasing solid nanoparticles in higher φ values for improving heat transfer. [ABSTRACT FROM AUTHOR]

In this numerical study, the numerical simulation of laminar free convection of water/silver nanofluid in a circular cavity under the effect of hot water fluid outside the cavity is carried out. The cooling fluid is water silver nanofluid at a volume concentration of φ = 0–0.06. This study was done for Gr = 102, 103 and 104 using the finite volume method. The Reynolds numbers of Re = 1, 10 and 100 were used. The results of the study show that due to the temperature difference between the cavity and the entering fluid, heat transfer occurs between the hot fluid in the channel and the nanofluid in the cavity at the start of the channel. This temperature difference between the surface and the fluid reinforces the buoyancy force and the Grashof number, intensifying the cavity flow and creating a more uniform cavity temperature distribution. For low Gr number, higher φ results in modest temperature gradient reduction. Using a higher fluid flow, the channel-cavity heat transfer increases which elevate dimensionless temperature curves. At a higher φ, due to the higher fluid viscosity and density, a higher momentum is required for flow convection and circulation. As a result, a stronger buoyancy force aids with free convection intensity, which is effective in elevating the Nusselt number curve values. By increasing the Reynolds number, a higher cavity heat transfer occurs due to the stronger circulating fluid's momentum. [ABSTRACT FROM AUTHOR]

In this paper, fully developed turbulent flow and heat transfer behavior in trapezoidal channels using nanofluids are numerically studied. This study evaluates the effects of four different types of nanoparticles, Al 2 O 3 , CuO, SiO 2 and ZnO, with different volume fractions (0–4%) and diameters (20–80 nm) under constant heat flux (6 kW/m 2 ). The effects of geometrical parameters (wavy amplitudes, longitudinal pitch) of the trapezoidal channel on the thermal and flow fields are also examined. The results indicated that SiO 2 has the highest Nusselt number among the nanofluids. Enhancement of heat transfer increases with particle volume concentration, but a slight increase in pressure loss with decreasing nanoparticle diameter is also observed. When nanofluids are used in a forced convection, 10% increase in average Nusselt number is observed for nanoparticles with a diameter of 20 nm and at 4 vol.%. Analysis of the flow and heat transfer in a corrugated trapezoidal channel is made based on the comprehensive evaluation factor J / f. The optimum ( J / f ) enhancement shows that the CuO nanofluid, lower concentration ratio of nanoparticles, trapezoidal height of 2.5 mm and a longitudinal pitch of 6 mm are the most desirable parameters for saving energy. Using nanofluids with a corrugated channel can improve the thermal performance because it can lead to more compact heat exchangers. [ABSTRACT FROM AUTHOR]

The present work examines numerically the natural convection along with the entropy generation within H-shaped enclosure with wavy walls filled by (Ag-MgO/water) hybrid nanofluid considering inner bodies and under the influence of horizontal magnetic field and thermal radiation using finite element scheme. The inner bodies of the circular shapes are kept at a hot temperature, while the two-sided wavy walls are kept at a cold temperature. The rest of the enclosure’s walls are thermally insulated. The influence of many parameters had been examined such as Rayleigh number (103≤Ra≤105)\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$({10}^{3}\le \text{Ra}\le {10}^{5})$$\end{document}, Hartmann number 0≤Ha≤60\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(0\le \text{Ha}\le 60\right)$$\end{document} vertical location of inners bodies 0.2≤δ≤0.8\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(0.2\le \delta \le 0.8\right)$$\end{document}, distance between inner bodies 0.3≤E≤0.9\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(0.3\le E\le 0.9\right)$$\end{document}, height of the enclosure walls 0.2≤B≤0.8\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(0.2\le B\le 0.8\right)$$\end{document} and width of the enclosure wall 0.1≤A≤0.9\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(0.1\le A\le 0.9\right)$$\end{document} in addition to the radiation parameter 0≤Rd≤3\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(0\le \text{Rd}\le 3\right)$$\end{document} on fluid flow, heat transfer and entropy generation. The results of this study had been presented in terms of streamlines, isotherms, entropy generation, Nusselt and Bejan number. The results showed that the Nusselt number will be at its lowest value when the vertical location of the inner bodies is δ=0.8\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(\delta =0.8\right)$$\end{document} and the influence of Hartmann number will be negligible at this value. Also, at high Rayleigh number Ra=105\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(\text{Ra}={10}^{5}\right)$$\end{document} increasing the distance between the inner bodies from E=0.3\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(E=0.3\right)$$\end{document} into E=0.9\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(E=0.9\right)$$\end{document} leads to increasing Nu by 76%\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$76\%$$\end{document}. However, increasing the height of the enclosure’s walls from B=0.2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(B=0.2\right)$$\end{document} into B=0.8\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(B=0.8\right)$$\end{document} leads to enhancing Nu by 0.02%.\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$0.02\%.$$\end{document} However, increasing width of the enclosure wall from A=0.1\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(A=0.1\right)$$\end{document} into A=0.9\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(A=0.9\right)$$\end{document} leads to an obvious reduction in Nusselt number by 20%\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$20\%$$\end{document}. Additionally, it had been obtained that increasing the vertical location of the inner bodies, the distance between them and the width of the enclosure and reduction of the height of the enclosure’s wall lead to increasing Bejan number. Stronger magnetic fields enhance conductive heat transfer; increasing the Bejan number which represents irreversibility as noted at increasing Hartmann number from Ha=0\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(\text{Ha}=0\right)$$\end{document} into Ha=60\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\left(\text{Ha}=60\right)$$\end{document} leads to increasing Bejan number by 79%\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$79\%$$\end{document}. [ABSTRACT FROM AUTHOR]

The present work demonstrates the natural convection of two layers filled the space between inner circular cylinder located within wavy enclosure using finite element scheme. The right layer is filled with Ag nano-fluid while the left layer is filled saturated porous media and the same nanofluid. The governing equations of fluid flow and heat transfer (mass, energy and momentum of the fluid) have been formulated in dimensionless form with related initial and boundary conditions the numerical solution include the subdividing the fluid flow domain to two sets of transport equations. The Darcy-Brinkman model was considered for modeling porous media with nano-fluid. The considered dimensionless parameters are Rayleigh number (106≥Ra≥103), Darcy number (10-1≥Da≥10-5), cylinder’s radius (0.4≥R≥0.2), circular cylinder vertical position (+0.2≥δ≥-0.2), the number of undulation (3≥N≥0) and nano-particle volume fraction (0.1≥φ≥0). The nanofluid is combining of Ag solid particle and water as a main fluid. The results were presented according to the stream-lines, isotherms, local and the mean of Nusselt number. The results have demonstrated the increasing in the value of the Rayleigh and Darcy numbers as well as nanofluid volume fraction enhances both fluid flow strength and average of heat transfer. It has been concluded that when the number of undulations N = 1 gives better heat transfers enhancement. It is recommended that for better heat transfer average to move the internal circular cylinder with radius (R = 0.2) vertically downward (δ=-0.2) with undulations’ number (N=1). [ABSTRACT FROM AUTHOR]

• A novel design of an efficient air-cooling system for improving the performance of lithium-ion batteries. • It is revealed that the average Nusselt numbers (Nu) are an increasing function of Reynolds numbers (Re). • The cells, which receive fresh cold external flow cause a substantial reduction in the cell surface temperature. • Increasing Re also reduces the cooling pack outlet temperature, which leads to the improved life of the batteries. Modern society depends on energy storage systems like Lithium-ion (Li-ion) batteries. Li-ion battery cells are delicate to changes in temperature. Extreme environmental conditions affect their life cycle and performance. Therefore, effective cell temperature management is a must for secure and dependable battery operation. Additionally, the high production costs of electric cars must be countered by the adaptability of the battery pack design for modern electric vehicles. As the chemical reactions generate more heat and raise the battery's temperature, it may cause the battery to explode and cause fires in the workplace. To address this issue, the present work attempts to numerically study a novel design of an efficient air-cooling system for improving the performance of lithium-ion batteries by reducing the operational temperatures under a different coolant flow rate. The main output of the presented study is the analysis of a novel design of an efficient air-cooling system for lithium-ion batteries. The study aims to reduce the operational temperatures of the batteries under different coolant flow rates to improve their performance and service life. The numerical simulations are carried out using a finite volume-based computing tool with the K-epsilon (k-ε) turbulence model. The analysis is performed for various pertinent parametric ranges, including the spacing between the batteries, Reynolds numbers, and average Nusselt numbers. The results indicate that increasing air inlet velocity (Re) substantially reduces the average air temperature of the cooling pack and temperature difference (ΔT) of the battery cells, and the cooling pack's average heat transfer rate (Nu) increases monotonically as the Re increases. [ABSTRACT FROM AUTHOR]

• Three-dimensional numerical simulation of geothermal heat exchanger is done. • The effects of adding nanoparticles on the heat transfer characteristics and entropy generation are investigated. • The diameter ratio is studied, and the best ratio is selected. • The best performance is observed when the thermal resistance of the outer wall is high and the inner wall has the minimum resistance. • Artificial neural networks is used to predict the Nusselt number and entropy generation, and the results are outstanding. Since the world is facing an energy crisis, and the emission of carbon-based fuel combustion is causing global warming, more research has been devoted to studying renewable energies. Due to the broad use of geothermal heat exchangers in central air-conditioning systems and also as a direct source of energy, in the present study, we have conducted a simulation of a geothermal heat exchanger and investigated the optimal diameter and nanoparticle concentration in order to minimize entropy generation. The fluid flow is turbulent, and SST K − ε is utilized as the turbulence model. The results show that as the thermal resistance of the inner wall increases, the outlet temperature rises. The effects of thermal resistance and diameter are thoroughly investigated, and the results have been used for selecting the least entropy generation. The results showed that the diameter in which the entropy is minimized increases by increasing the inner wall's thermal resistance. The best case is high thermal resistance in the outer walls and meager resistance in the inner walls. Using inner walls with high thermal resistance can decrease the adverse effects of entropy generation in large diameters. Also, the addition of nanoparticles is investigated, and the average Nusselt number and entropy generation, respectively, increased and decreased by almost 10%. Artificial neural network models are proposed to predict Nusselt number and entropy generation based on numerical results. The models are able to achieve MAE of lower than 3% and R 2 higher than 0.95. [ABSTRACT FROM AUTHOR]

Taking a more complex engineering geometry into account, magnetohydrodynamic natural convection of nanofluid (Cu-water) in a wavy walled enclosure having a circular hot cylinder inside is investigated by employing Galerkin-weighted residual formulation. In order to investigate the flow and heat transfer characteristics from several perspectives and increase the ability of adaptation to various engineering applications, the influences of the Hartmann number, Ha , Rayleigh number, Ra , and nanoparticle concentration are examined in detail. In addition to that, heat generation and heat absorption situations are also considered within the present work, which are simulated by a heat coefficient in a range of −10 ≤ q ≤ +10. The results revealed that increasing Ha has an insignificant effect on Nusselt number, Nu , at low Ra , however, it significantly pulls Nu down up to 33% for higher Ra , because of restricting convection. It is found that the heat coefficient, q , has a remarkable impact on Nu at low Ra , while its significance is diminished when Ra is increased. For q < 0, the heat absorption creates a heat sink, which increases Nu up to 34%, while the heat generation (q > 0) conversely reduces Nu up to 48%. Besides, variation in heat coefficient does not considerably affect the improvement impact of nanoparticles. • MHD natural convection of nanofluid is studied in a wavy enclosure with a cylinder. • Heat generation and absorption are more significant at low Ra. • Ra and q are the most effective parameters for Nu. • Ha and q considerably loses its significance at high Ra. • High Hartmann numbers may restrict convection by up to 33%. [ABSTRACT FROM AUTHOR]