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This study delves into the convective heat transfer phenomena within a square cavity that houses a porous medium, analyzing the effects of Darcy (Da) and Rayleigh (Ra) numbers on the thermal and fluid dynamic behavior within the system. Utilizing a combination of computational fluid dynamics (CFD) and the finite element method (FEM), the research focuses on steady-state, laminar flow conditions in two dimensions. The cavity, which is impermeable at its boundaries, contains a centrally located square region filled with a porous, isotropic material. The thermal environment is controlled with insulated horizontal walls and vertically positioned walls that experience sinusoidal temperature variations. The study examines how variations in the permeability of the porous medium (Da numbers ranging from 10−1 to 10−4) and the buoyancy-driven flow strength (Ra numbers spanning from 102 to 105) influence the velocity fields and heat transfer rates, with results expressed through Nusselt number (Nu) distributions. The findings reveal that higher Ra numbers, particularly at 105, significantly intensify convection within the cavity, thereby boosting local rates of heat transfer, especially in the central vertical section. The research identifies that optimal flow resistance in the porous medium occurs within the Da number range of 10−3 to 10−4. These insights are critical for advancing thermal management techniques, particularly in the natural cooling of electronic devices and improving insulation methods. [ABSTRACT FROM AUTHOR]

The hybrid nanofluid is the modified class of nanomaterials with impressive thermal impact and preserves significant applications in extrusion systems, thermal management systems, engineering processes, cooling and heating materials and many more. The aim of this research is to communicate the thermal enhancement of water (H2O) and sodium alginate (C6H9NaO7) base fluids with interaction of hybrid nanofluids. The Casson fluid model is used to endorse the properties of such base liquids. The titanium dioxide and silver nanoparticles incorporate the thermal impact of hybrid nanofluid properties. The fractional simulations are performed by using the Caputo–Fabrizio (CF) time-fractional derivatives. The integration of problem is computed via Laplace technique. It is observed that the velocity profile enhanced the Grashof number. The increasing observations for Nusselt number and wall shear force due to fractional parameters are obtained. [ABSTRACT FROM AUTHOR]

While there are some hydrogen refueling stations (HRS) functioning in different parts of the world, their use is not widespread enough, primarily due to their expensive cost. Hydrogen compression is a main contributor to the capital and operation costs of the HRS. By improving H 2 compression technology, it is possible to optimize the infrastructure for refueling with hydrogen in terms of cost and performance. The use of metal hydride hydrogen compressors (MHHCs), which have the potential to be inexpensive and have the ability to use waste heat and renewable energy sources for the H 2 compression, is a promising solution to overcome this issue. The duration of the H 2 compression cycle is nevertheless a serious challenge due to the metal hydride (MH) bed's low heat conductivity. As a heating technique to improve the performance of MHHCs, electromagnetic induction (EMI) is examined numerically for the first time in this work. The dynamic behavior of a two-stage MHHC with each MH reactor having an external heat exchanger and being ringed by a copper coil traversed by an alternating current is described by a two-dimensional mathematical model, which was established and successfully verified by the reference data. Numerical simulations were performed with the help of this model, and the findings showed that the EMI heating method is faster than the heat transfer fluid (HTF) heating technique. For instance, at a delivery temperature of 373 K and a supply pressure of 20 bar, it is possible to produce 106 NL H 2 per kilogram of HPMH at a pressure of 97 bar with a 74 % shorter compression time than with the HTF heating technique. [ABSTRACT FROM AUTHOR]

The nanofluids became much of interest due to their superior heat mechanism over the conventional fluids. The addition of nanoparticles in the host solvent enhances the internal ability of the liquid to store and transmit heat. Therefore, these fluids are widely used in biomedical engineering, detergents, medication, applied thermal engineering, mechanical, and chemical engineering and so forth. Keeping in mind the significance of nanofluids, this study is conducted to investigate the comparative heat transmission in γAl2O3−H2O${\mathrm{\gamma Al}}_2{{\mathrm{O}}}_3 - {{\mathrm{H}}}_2{\mathrm{O}}$ and γAl2O3−C2H6O2${\mathrm{\gamma Al}}_2{{\mathrm{O}}}_3 - {{\mathrm{C}}}_2{{\mathrm{H}}}_6{{\mathrm{O}}}_2$ under the Effective Prandtl Number Model (EPNM) effects over a vertical permeable cylinder. Formulation of the model is carried out over a vertical cylinder about the stagnation point and the heat transport model is achieved after the successful implementation of the cylindrical stream function, nanofluids effective characteristics, and cylindrical similarity equations. The mathematical treatment was done via RK technique and furnished the results. The nanofluids have the capacity to control the fluid motion more effectively than ordinary fluid and combined convection is better where rapid fluid movement is desired. In the existence of EPNM, higher heat transmission is achieved and is prominent for γAl2O3−C2H6O2${\mathrm{\gamma Al}}_2{{\mathrm{O}}}_3 - {{\mathrm{C}}}_2{{\mathrm{H}}}_6{{\mathrm{O}}}_2$ based on their thermophysical values. Further, the skin friction and Nusselt number are optimum for γAl2O3−C2H6O2${\mathrm{\gamma Al}}_2{{\mathrm{O}}}_3 - {{\mathrm{C}}}_2{{\mathrm{H}}}_6{{\mathrm{O}}}_2$ against α1${\alpha }_1$. [ABSTRACT FROM AUTHOR]

This numerical investigation explores the enhanced control of the 3D natural convection (NC) within a cubic cavity filled with graphene–water nanofluids, utilizing a bottom-center-located tree-shaped obstacle and a horizontal magnetic field (MF). The analysis includes the effects of the Rayleigh number (Ra), the solid volume fraction of graphene ( φ ), the Hartmann number (Ha), and the fins' length (W). The results show complex flow patterns and thermal behavior within the cavity, indicating the interactive effects of nanofluid properties, the tree-shaped obstacle, and magnetic field effects. The MHD effects reduce the convection, while the addition of graphene improves the thermal conductivity of the fluid, which enhances the heat transfer observed with increasing Rayleigh numbers. The increase in the fins' length on the heat transfer efficiency is found to be slightly negative, which is attributed to the complex interplay between the enhanced heat transfer surface area and fluid flow disruption. This study presents an original combination of non-destructive methods (magnetic field) and a destructive method (tree-shaped obstacle) for the control of the fluid flow and heat transfer characteristics in a 3D cavity filled with graphene–water nanofluids. In addition, it provides valuable information for optimizing heat transfer control strategies, with applications in electronic cooling, renewable energy systems, and advanced thermal management solutions. The application of a magnetic field was found to reduce the maximum velocity and total entropy generation by about 82% and 76%, respectively. The addition of graphene nanoparticles was found to reduce the maximum velocity by about 5.5% without the magnetic field and to increase it by 1.12% for Ha = 100. Varying the obstacles' length from W = 0.2 to W = 0.8 led to a reduction in velocity by about 23.6%. [ABSTRACT FROM AUTHOR]

Due to the outstanding thermal properties of nanoparticles, scientists have introduced a range of multidisciplinary applications in fields such as heat transfer systems, thermal management, solar energy, chemical processes, manufacturing, and cooling technologies. The aim of the current paper is to inspect the heat and mass transfer pattern during Maxwell nanofluid flow considering the diffusion phenomenon. The suspension of microorganisms has been considered for bioconvective flow. The inspection of heat transfer is analyzed by adopting the nonlinear radiated effects. The motivations for considering the Maxwell fluid are associated to novel relaxation time features occurring in polymer industry and manufacturing systems. The endorsed flow is caused by periodically oscillating surface with porous medium. The whole mathematical model is developed in terms of partial differential equations (PDE's). A successful analytical solution is presented via homotopy analysis method (HAM). It is observed that solutal concentration reduces due to modified Duffer Lewis number and Deborah number. The surface heating parameter and magneto-porosity constant enhances the temperature profile. The predicted results convey significant impact in enhancing the energy reservoirs, diffusion applications, nuclear systems, oil industry, storage energy, space exploration etc. [ABSTRACT FROM AUTHOR]

The thermal prospective of hybrid nanofluid is more impressive and presents many dynamical applications in solar collectors, thermal systems, machining, extrusion processes, nuclear cooling, heating and cooling devices, desalination. Owing to such motivations in mind, this research communicates thermal impact of carbon nanotubes due to inclined plate under the effect of a magnetic field. Both single-walled carbon nanotubes (SWCNTs) and multiple-walled carbon nanotubes (MWCNTs) are considered as nanoparticles to enhance the thermal mechanism of human blood and water base liquids. The mixed convection phenomenon for natural convective flow is considered. The most recent definition of fractional scheme namely Prabhakar derivatives is used to perform the theoretical outcomes. The integral of problem is supported with Laplace transform. The impact of dimensionless parameters on velocity and temperature profiles is studied and graphs are plotted by the mathematical software. The obtained results are compared numerically and graphically by using different inverse techniques known as Stehfest method and Tzou's methods. It is observed that nanoparticles' volume fraction boosted the thermal phenomenon more effectively for SWCNTs. The improved velocity profile due to interaction of buoyancy forces is observed. [ABSTRACT FROM AUTHOR]

The aim of this work is to examine numerically the effect of using a rotating cylinder and porous layers on the forced convection in a bifurcating grooved channel (BGC) filled with two types of nanofluids (MgO-water, SiO2-water). The semi-implicit finite volumes method was used to solve the governing equations. The effects of Reynolds number, nanoparticles volume fraction, and cylinder rotation speed on hydro-thermal performances have been investigated. According to the obtained results, the rotation direction plays a significant role in the formation of vortices at the branching channel, such that when the cylinder rotates clockwise, the vortex occurs in the vertical channel, and it decreases with increasing Reynolds number. Besides, using BGC with a porous medium enhances the heat transfer rate by 52% and 49% at the vertical and horizontal walls of the porous layer, respectively. On the other hand, the heat transfer rate is improved by 2.6% when using MgO nanoparticles compared to SiO2. Therefore, the use of bifurcating grooved channels can improve the thermal performance of various applications in thermal engineering, from fuel cells to electronic cooling. [ABSTRACT FROM AUTHOR]

In the present investigation, the blood mediated nanofluid flow has been studied in the non-symmetric channel driven by peristaltic mechanism. The influence of radiation, electromagnetohydrodynamics and buoyancy forces have been considered into account. The suitable wave and fixed frame transformations and dimensionless parameters have been used to convert the system of dimensional equations to non-dimensional form. Later, the lubrication approach is utilized to simplify the model. The regular perturbation method has been utilized to find the approximate analytical solutions for the velocity, temperature, stream function, pressure gradient, heat transfer rate and entropy production. It is concluded from the current results that, the blood-graphane based nanofluid velocity declined by 21% from slip parameter 0 to 0.05. There is 34% decrement in Bejan number from radiation parameter 0.1 to 0.4 for blood-diamond nanofluid. The temperature of blood-diamond nanofluid enhances by 5% for suspending blade-shaped nanoparticles as compared with sphere-shaped nanoparticles. [ABSTRACT FROM AUTHOR]

This study numerically investigates the two-dimensional natural convection in a square enclosure with an isothermal diamond elliptic array at Rayleigh numbers of 104 ≤ Ra ≤ 107. Three cases are considered, i.e., case 1 where two pairs of circular heating bodies are used inside the cavity, one is placed on the vertical centerline (VC) of the cavity and the other on the horizontal centerline (HC), case 2 where one pair of horizontal elliptic heating bodies is placed on the VC of the cavity and the other on the HC and case 3 where the horizontal elliptic heating bodies are replaced by vertical elliptic heating bodies. Numerical simulation was carried out based on the mesoscopic approach (LBM). The effects of the horizontally and vertically heated arrays were investigated. We demonstrate that, only when the Rayleigh number increases to Ra = 107, the numerical solutions reach an unsteady state for all cases. The transition of the flow regime from the unsteady state to the steady state depends on the variation in the ratio of the elliptical cylinder. [ABSTRACT FROM AUTHOR]

The present study deals with electrically conductive fluid flow across a heated circular cylinder to examine the oscillatory magnetic flux and heat transfer in the presence of variable surface temperature. The proposed mathematical formulation is time-dependent, which is the source of the amplitude and fluctuation in this analysis. The designed fluctuating nonlinear computational model is associated with the differential equations under specific boundary conditions. The governing equations are converted into dimensionless form by using adequate dimensionless variables. To simplify the resolution of the set of governing equations, it is further reduced. The effects of surface temperature parameter β , magnetic force number ξ , buoyancy parameter λ , Prandtl number Pr, and magnetic Prandtl parameter γ are investigated. The main finding of the current study is related to the determination of the temperature distribution for each inclination angle. It is seen that a higher amplitude of the heat transfer rate occurs as the surface temperature increases. It is also noticed that the oscillatory magnetic flux becomes more important as the magnetic Prandtl number increases at each position. The present magneto-thermal analysis is significantly important in practical applications such as power plants, thermally insulated engines, and nuclear reactor cooling. [ABSTRACT FROM AUTHOR]

The objective of current communication is to study heat transfer phenomenon for slip flow of viscous fluid due to wavy channel with general cosine function boundaries and fixed amplitude. The walls along with slip boundary constraints are kept at different temperatures. The flow is incompressible and Newtonian with AIS as a predicting material being used to check the fluids and thermal properties. The Navier–Stokes expressions with 2D flow regime subject to heat transfer due to convection are used to develop the simulations. A parametric theoretical assumptions analysis is performed for specified range of Reynolds number (100–1000) with upper and lower surface vibration periods of 1 to 6. The results are displayed with graphs, surface and contours plots and first, ever a novel work was done to represent the percentage change in velocity magnitude and local Nusselt number as surface plots and contours, respectively. The results are authentic due to mesh independent study and verification with the experimental correlation. A periodic flow at the lower wall was deducted. The maximum and average rotation rates attain a linear relationship with Reynolds number and their correlation was found. The simulations show the strict relationship of Reynolds number and the geometry of the channel with shear rate. The pressure gradient in y -direction was found minimum in trough and maximum in the crest region. It has been observed that the boundary friction is reduced due to periodic variation of walls surface. [ABSTRACT FROM AUTHOR]

Three-dimensional investigation has been carried out to simulate buoyancy induced heat transfer and fluid flow as well as entropy creation inside C-shaped enclosure charged with based water CNT–Al2O3 (15–85%) hybrid nanofluid. Left side is isothermally heated while the vertical portions of the right wall are isothermally cooled. Effects of various parameters on the flow behavior and the produced irreversibilities, namely the cavity aspect ratio (0.1 ≤ Ar ≤ 0.4), Rayleigh number (103 ≤ Ra ≤ 106) and volumetric fraction of hybrid nanofluid (0 ≤ φ ≤ 0.06) have been examined. It was revealed that the aspect ratio is the main controlling parameter of thermal energy transfer and generated entropy. In addition, for specific Ra, adding hybrid nanoparticles leads to the increase of the average Nusselt number while the highest produced entropy is observed with higher Rayleigh number. Moreover, the maximum Bejan number occurred for a shape factor Ar = 0.1 and Ra = 104 disregarding the hybrid nanoparticles volume fraction showing the dominance of thermal irreversibility over the viscous dissipation irreversibility in such conditions. [ABSTRACT FROM AUTHOR]

The recent progress in nanotechnology developed more stable nanofluid models with ultra-high thermal performances. The immersion of hybrid nanoparticles in the base fluid presents novel applications in the thermal transport processes, solar energy, engineering devices, and heating systems. This continuation identified the thermal outcomes of the hybrid nanofluid model with the water base fluid. The thermal investigation is encountered by utilizing the copper oxide (CuO), silver (Ag), and titanium dioxide (TiO2) nanoparticles. The thermal selection of these three types of nanoparticles is associated with impressive characteristics and stability. To attain the more progressive thermal aspects, thermal radiation consequences are also focused. The inclined infinite configuration is assumed where these nanoparticles and base fluid are specified. The comparative results for the hybrid nanofluid and modified hybrid models are pronounced. The fractional model of dimensionless partial differential leading equations is formulated by following the recent definitions of fractional derivatives, namely, Atangana–Baleanu and Caputo–Fabrizio fractional derivatives. The semi-analytical simulations are performed via the Laplace technique for nanoparticles temperature and velocity inspection. The significances of the fractional parameter and volume fraction are observed for the velocity profile. [ABSTRACT FROM AUTHOR]

The viscoelastic materials are a famous subclass of non-Newtonian fluids that present novel applications in various industrial processes. The most famous applications of viscoelastic fluid are observed in polymer processing. A major activity of the polymer processing industry is the production of thermoplastic polymer sheets and films. However, due to distinct rheology, a complete understanding of such materials is quite necessary for the polymer process. This continuation presents the rheological features of viscoelastic fluid with heat transfer phenomenon near the oblique stagnation point flow. The induced flow is accounted via stretched cylinder. The heat transfer analysis is also taken in the presence of non-linear heat flux. The problem is formulated using cylindrical coordinates in terms of non-linear coupled partial differential equations. Similarity transformation and normalized variables are used to convert the governing system into a set of ordinary differential equations. Due to the highly nonlinear model, the analytical solution of the system seems to be impossible therefore the approximate solution is obtained using the numerically stable and convergent finite difference method known as the Keller Box scheme. The simulated data via numerical algorithm is verified after comparing with already published investigations. The streamlines for the flow problem are presented. [ABSTRACT FROM AUTHOR]

The prime objective of the present article is to investigate the heat and mass transfer impact on the viscous chemically reacting transient fluid flow past an upright surface analytically by employing Prabhakar fractional model. The fractional model has been developed for investigating the transient viscous fluid flow in the presence of inclined magnetic force subject to Newtonian surface heating. The integer order computation techniques for the governing partial differential equations for the formulated flow problem fail to determine the physical behavior of flow parameters with memory effects. To this end, the present model presents the fractional approach based on the Prabhakar fractional derivative. The problem modeled in terms of dimensionless expressions is first transformed into fractional model and later on simulations are performed with Laplace technique. The inverse Laplace transform of the flow characteristics is computed by adopting Stehfest and Tzou's algorithms. For fractional parameters, the increasing trend in the velocity and temperature profiles has been observed. The increasing behavior of velocity subject to increasing values of heat Grashof number and mass Grashof number is observed. [ABSTRACT FROM AUTHOR]

The advances in nanotechnology led to the development of new kinds of engineered fluids called nanofluids. Nanofluids have several industrial and engineering applications, such as solar energy systems, heat conduction processes, nuclear systems, chemical processes, etc. The motivation of the present work is to analyze and explore the thermal and dynamic behaviors of a non-Newtonian fluid flow under time retardation effects. The flow is unsteady and caused by a bidirectional, periodically moving surface. In addition to the convective heat transfer and fluid flow, the radiation and chemical reactions have also been considered. The governing equations are established based on the modified Cattaneo–Christov heat flux formulation. It was found that the bidirectional velocities oscillate periodically, and that the magnitude of the oscillation increases with the retardation time. Higher temperatures occur when the porosity parameter is increased, and lower concentrations are encountered for higher values of the concentration relaxation parameter. The current results can be applied in thermal systems, heat transfer enhancement, chemical synthesis, solar systems, power generation, medical applications, the automotive industry, process industries, refrigeration, etc. [ABSTRACT FROM AUTHOR]

Fluids have played and still play a vital role in attaining an optimized output from industrial processes. However, due to technological advancement, fluids with high hydrothermal characteristics are required. In order to overcome these challenges, researchers have developed fluids with dispersed nanoparticles, which are recognized as nanofluids. Various types of nanoparticles can be added to base fluids to produce thermally enhanced liquids. Among these, the addition of multi-walled carbon nanotubes (MWCNTs) is considered the best due to the considerable enhancement of thermophysical properties and the stability of the solution. Thus, in the present investigation, an analysis of the heat transfer characteristics of an MWCNT–water nanofluid included in a star-shaped cavity equipped with a hot rectangular baffle is conducted. In addition, a uniform magnetic field is applied along the x-direction to oppose the convective flow generated by variations in density. Mathematical formulations under assumed boundary conditions and physical assumptions are established in the form of dimensionless PDEs. The finite-element-method-based software "COMSOL" is used to execute the numerical simulations. PARADISO is employed to resolve the developed non-linear system of equations. The effects of the governing parameters on the velocity and temperature fields are presented through streamlines and isotherms. The Nusselt number is evaluated to depict the impact of the addition of nanoparticles (MWCNTs) on the heat transfer enhancement. Changes in the horizontal and vertical components of velocity are also evaluated against the Rayleigh number and nanoparticle volume fraction via cutline representation. [ABSTRACT FROM AUTHOR]

Metal hydride (MH) hydrogen storage needs an external heat source to release the stored hydrogen. To enhance the thermal performance of MHs, the incorporation of phase change materials (PCM) is a way to preserve reaction heat. This work proposes a new MH-PCM compact disk configuration (i.e., a truncated conical MH bed surrounded by a PCM ring). An optimization method is developed to find the optimal geometrical parameters of the MH truncated cone, which is then compared to a basic configuration (i.e., a cylindrical MH surrounded by a PCM ring). Moreover, a mathematical model is developed and used to optimize the heat transfer in a stack of MH-PCM disks. The optimum geometric parameters found (bottom radius of 0.2, top radius of 0.75 and tilt angle of 58.24) allow the truncated conical MH bed to reach a faster heat transfer rate and a large surface area of higher heat exchange. Compared to a cylindrical configuration, the optimized truncated cone shape enhances the heat transfer rate and the reaction rate in the MH bed by 37.68%. [ABSTRACT FROM AUTHOR]

The bioconvective flow of a Jeffrey fluid conveying tiny particles under the effect of an oscillating stretched bidirectional surface is considered in this paper. The effects of thermal radiation and a porous medium are also investigated. The Cattaneo–Christov diffusion theories are used to analyze the heat and mass transfer phenomena. The activation energy effects are included in the concentration equation. The solved dimensionless equations system is established, based on non-dimensional variables. The analytical findings are evaluated using the homotopic analysis technique. The convergence of solutions is ensured. The results are validated by already available published findings and a good concordance is encountered. The fundamental physical aspect of flow parameters is graphically evaluated. The main results reveal that the velocity is reduced by increasing the permeability of the porous medium. An increase in the temperature occurs when the viscosity of the fluid is varied. The obtained results can be useful in thermal systems, energy production, heat transfer devices, solar systems, biofuels, fertilizers, etc. [ABSTRACT FROM AUTHOR]

In the present study, a CFD simulation of a flow combined an offset jet and a wall jet (noted dual-jet) with the presence of co-flow is carried out. The effect of the intensity of the co-flow CFV (co-flow velocity) as well as its ejection angle α on the heat transfer exchanged in dual-jet flow is also performed. The present simulations are carried out for a Reynolds number Re = 15000, a nozzle-to-nozzle distance equal to 4 times the thickness of the nozzle, a co-flow velocity CFV = 10% − 40 % and a co-flow ejection angle α = 0° − 40°. The results of this computational study clearly show an intensification of the heat transfer exchanged between the flow and the wall by increasing the co-flow velocity CFV as well as its ejection angle α. [ABSTRACT FROM AUTHOR]

The current study deals with the reduced gravity and radiation effects on the magnetohydrodynamic natural convection past a solid sphere. The studied configuration is modeled using coupled and nonlinear partial differential equations. The obtained model is transformed to dimensionless form using suitable scaling variables. The finite difference method is adopted to solve the governing equation and determine the velocity and temperature profiles in addition to the skin friction coefficient and Nusselt number. Furthermore, graphic and tabular presentations of the results are made. The verification of the numerical model is performed by comparing with results presented in the literature and a good concordance is encountered. The main objective of this investigation is to study the effect of the buoyancy force caused by the density variation on natural convective heat transfer past a solid sphere. The results show that the velocity increases with the reduced gravity parameter and solar radiation but decreases with Prandtl number and magnetic field parameter. It is also found that the temperature increases the with solar radiation and magnetic field but decreases with the reduced gravity parameter and Prandtl number. [ABSTRACT FROM AUTHOR]

The current research study is focusing on the investigation of the physical effects of thermal radiation on heat and mass transfer of a nanofluid located around a sphere. The configuration is investigated by solving the partial differential equations governing the phenomenon. By using suitable non-dimensional variables, the governing set of partial differential equations is transformed into a dimensionless form. For numerical simulation, the attained set of dimensionless partial differential equations is discretized by using the finite difference method. The effects of the governing parameters, such as the Brownian motion parameter, the thermophoresis parameter, the radiation parameter, the Prandtl number, and the Schmidt number on the velocity field, temperature distribution, and mass concentration, are presented graphically. Moreover, the impacts of these physical parameters on the skin friction coefficient, the Nusselt number, and the Sherwood number are displayed in the form of tables. Numerical outcomes reflect that the effects of the radiation parameter, thermophoresis parameter, and the Brownian motion parameter intensify the profiles of velocity, temperature, and concentration at different circumferential positions on the sphere. [ABSTRACT FROM AUTHOR]

In this work, double rotating active cylinders and slot nanojet impingement are considered for the cooling system of a conductive panel. Colder surface temperatures of the cylinders are used, while different rotational speeds are assigned for each of the cylinders. The impacts of cylinder rotational speeds, size and distance between them on the cooling performance are evaluated. The rotational effects and size of the cylinders are found to be very effective on the overall thermal performance. At the highest rotational speeds of the cylinders, the average Nusselt number (Nu) rises by about 30.8%, while the panel temperature drops by about 5.84 ° C. When increasing the cylinder sizes, temperature drops become 7 ° C, while they are only 1.75 ° C when varying the distance between the cylinders. Subcooling and nanofluid utilization contributes positively to the cooling performance, while 1.25 ° C and 10 ° C temperature drops are found by varying the subcooled temperature and solid volume fraction. An artificial neural network is used for the estimation of maximum and average panel temperatures when double cylinder parameters are used as the input. [ABSTRACT FROM AUTHOR]

In order to improve the performance of a solar collector in low heat transfer rate zones, a 3-D numerical study of the effects of partially moving wall sections and the use of a water nanofluid (CNT) in a tilted parallelepiped solar collector was performed. Equations governing the mixed convection phenomena occurring in the cavity are developed based on the 3-D potential-vorticity formulation and solved using the finite volume method. Two cases related to the direction of the moving surfaces are considered and compared to the base case (no driven walls). The results are presented in term of flow structures, temperature fields and local and average Nusselt numbers. The Richardson number is varied from 0.001 to 10 and the CNT volume fraction from 0 to 0.045. The results showed that for low Richardson values (less than 1), the motion direction of the moving surfaces has no significant effect on heat transfer rates and becomes effective for higher values. The highest rates of heat transfer are found for high Richardson values and CNT volume fractions, while the enhancement ratio (compared to the base case) occurs for low Richardson values. [ABSTRACT FROM AUTHOR]

This theoretical thermal continuation deals with the radiative flow of Williamson nanofluid subject to the inclusion of microorganisms. The further modification in the bio-convective model is done by incorporating the heat source/sink and activation energy phenomenon. The motivation for the choice of Williamson nanofluid is referred to multidisciplinary rheological impact which may enhance the heating phenomenon upon inclusion of nanoparticles. A bidirectional moving surface is the source of inducing flow patterns. The governing expressions which result via thermal model are numerically simulated with a shooting scheme. The impact of flow parameters is identified for velocity change, heat transfer rate, concentration, and microorganism profile. Moreover, the numerical results in terms of different tables are framed out for observing the fluctuated pattern of heat transfer, concentration impact, and microorganism change. The outcomes simulated from the model reflect that a lower velocity rate is results for the velocity ratio parameter. The external heat source attributed the enhancement of heat transfer. Moreover, the concentration profile improves with activation energy and convection constant. [ABSTRACT FROM AUTHOR]

The present paper focuses on a review recalling the main contributions of studies that involve nanofluids on automotive industry. The novelty of the paper consists on the concise synthesis presented, that highlights new tested nanofluids in several applications in automotive. The review includes critics on the efficiency, the impact on material and the environmental issues when nanofluids are used as fuel. Three main sections are presented, which deploy the use of nanofluids as coolant in a car radiator, addition in the fuel or engine oil and finally the last section reviews the assessment of the wear effects of nanofluids on materials used in a car coolant system and in the car engine. The current review emphasized some major findings and critics: (1) The contradictory conclusions denoted about the effect of volume concentration on pumping power loss and the Nusselt number in a car radiator system. (2) Remarkable discrepancies in the determination of the optimal nanoparticles volume concentration and the precise heat transfer enhancement. (3) The viscosity of a nanolubricant needs a deep analysis to determine the optimal value that ensures the best lubricant film between components in a car engine. (4) Some mechanical problems should be analyzed when using nanofluids in fuel. [ABSTRACT FROM AUTHOR]

The effect of magnetic field inclination and double lid‐driven on the mixed convection in a square cavity is investigated based on the local thermal non‐equilibrium model. The cavity was filled with a copper–water micropolar nanofluid saturated with a porous medium. The top and bottom walls are considered moving to the left or right directions at a constant velocity. In the current work, the ranges of parameters are as follow: Hartmann number (0 ≤ Ha ≤ 50), length of the heat source (0.2 ≤ B ≤ 0.8), Richardson number (0 ≤ Ri ≤ 10), Reynolds number (0 ≤ Re ≤ 100), location of the heat source (0.3 ≤ D ≤ 0.7), vortex to molecular viscosity ratio (0 ≤ Δ ≤ 2), Nield number (1 ≤ Q ≤ 100) and solid volume fraction (0 ≤ φ ≤ 0.1). It was found that the heat transfer decreases as the dimensionless heat source location and the Nield number increase. Also, the growing in the Nield number enhances the rate of the heat transfer for the porous phase and increases the thermal equilibrium state of the system. [ABSTRACT FROM AUTHOR]

In this paper a numerical investigation on the double diffusive natural convection in a finned solar still is performed using the finite volume method. The 3D vector potential-vorticity formalism is used to eliminate the gradient pressure terms and due to the complex shape of the cavity the blocked-off-region method is adopted. After getting the dimensionless governing equations, they are written in a generalised form then discretised. The effects of the buoyancy ratio, conductivity ratio and Rayleigh number of the flow structure, temperature field and heat and mass transfer are studied. The results show that the increase of conductivity ratio and Rayleigh number leads to an enhancement of the heat and mass transfer. [ABSTRACT FROM AUTHOR]

A numerical study was performed to analyze the impact of the combination of several factors on heat transfer rate, flow behavior, and entropy generation in a hybrid nanofluid occupying a porous trapezoid enclosure containing a rotating inner tube. The governing equations were discretized and solved using the Finite Element Method using Comsol multiphysics. The effects of the Darcy and Hartman number, nanoparticle volume fraction (from 0 to 6%), the utilization of various zigzag patterns of the hot wall, and the rotation speed of the inner tube (Ω = 100. 250 and 500) are illustrated and discussed in this work. The outputs reveal that flow intensity has an inverse relationship with Hartman number and a direct relationship with the Darcy number and the velocity of the inner tube, especially at high numbers of undulations of the zigzag hot wall (N = 4); also, intensification of heat transfer occurs with increasing nanoparticle volume fraction, Darcy number and velocity of the inner tube. In addition, entropy generation is strongly affected by the mentioned factors, where increasing the nanoparticle concentration augments the thermal entropy generation and reduces the friction entropy generation; furthermore, the same influence can be obtained by increasing the Hartman number or decreasing the Darcy number. However, the lowest entropy generation was found for the case of Ø = 0, Ha = 0 and Da = 0.01. [ABSTRACT FROM AUTHOR]

This article discusses the heat transfer characteristics of the mixed convection of NEPCM-fluid (Polyurethane/ Nonadecane dispersed in water) contained within a wavy-sided walls cavity. Mixed convection is caused by an adiabatic rotating cylinder located in the cavity center, while natural convection results from deferential heating of side walls. The upper and lower walls of the cavity are insulated. The Galerkin finite element method (GFEM) implemented in COMSOL CFD package is employed to solve the governing equations. The influence of the nanoparticles volume fraction (Ø = 0.02, and 0.05), cylinder radius (R = 0.05, 0.15, and 0.25), cylinder rotating speed (Ω = 100, −500, 500, and 1000), the dimensionless fusion temperature (θ fu = 0.1, 0.25, and 0.5), wavy side walls undulation peaks number (N = 1 to 4) on the flow pattern and temperature field are presented. The results revealed that the heat transfer enhances by increasing the angular speed of the cylinder and its radius, also an enhancement in heat transfer is obtained by upgrading the volume fraction of NEPCM, however, it was noticed that for small cylinders, the counterclockwise rotation of the cylinder reduced the heat transfer rate as the rotation opposed the direction of natural heat convection. In addition, the waviness pattern has a specific impact on each case, for example, N = 4 denotes the best result for only the cases Ω = -500 or 500 when R = 0.25 and Ø = 0.05, while the heat transfer is negatively affected by increasing N for the other cases. On another hand, the impact of θ fu on the heat transfer rate was found to be insignificant. Globally, at the biggest cylinder radius, higher Ø and highest angular speed an enhancement by more than 900 % can be achieved. [ABSTRACT FROM AUTHOR]

The current research presents a numerical investigation of the mixed convection inside a horizontal rectangular duct combined with an open trapezoidal cavity. The region in the bottom wall of the cavity is heated by using two discrete heat sources. The cold airflow enters the duct horizontally at a fixed velocity and a constant temperature. All the other walls of the duct and the cavity are adiabatic. Throughout this study, four various cases were investigated depending on the driven walls. The effects of the Richardson number and Reynolds number ratio are studied under various cases related to the lid-driven sidewalls. The results are presented in terms of the flow and thermal fields and the average Nusselt number. The yielded data show that the average Nusselt number rises as the Richardson number and Reynolds number ratio increases. Furthermore, the Reynolds number ratio and the movement of the cavity sidewall(s) have a significant effect on the velocity and temperature contours. By the end of the study, it is shown that the maximum rates of heat transfer are related to Case 1 where the left sidewall moves downward and heater 2, which is placed near the left sidewall. [ABSTRACT FROM AUTHOR]

• The heat and mass transfer in a solar still embedded with PCM is studied. • The Finite volume method is used to solve the governing equations. • An external water stream is used to enhance the heat and mass transfer. • The effects of the buoyancy ratio and the Rayleigh number have been investigated. The increase demand of water for irrigation and human activities leads to a global development of alternative methods to produce distillate water especially from sea. In this context, the use of solar distiller instead of the classic distillation process is a good solution to preserve environment and reduce the use of fuel. This study explores the advantages of the classic solar still by studying the effect of the PCM-RT42. Hence, a detailed investigation of the heat and mass transfer of a single slope solar still incorporation PCM-RT42 as heat storage system will be presented. The governing equations are solved numerically with employing the finite volume method. The next scopes of parameters are utilized in the computations: dimensionless time (τ = 4.2×10–3, 25.2×10–3, and 50.4×10–3), Rayleigh number (104 ≤ Ra ≤ 106), buoyancy ratio (1 ≤ N ≤ 5). Mixture Prandtl number (Pr m), Schmidt number (Sc) and Lewis number (Le) are presumed as fixed to 0.705, 0.613 and 0.869, respectively. The results show the good effect of the PCM-RT42 on the transfer of heat and mass compared to the initial time for low Ra. However, for Ra=105 and 106, a reduction in the efficiency of condensation and the performance of the solar distiller is observed. [Display omitted] [ABSTRACT FROM AUTHOR]

This study deals with mixed convection of Al 2 O 3 –Cu–water hybrid nanofluid in a wavy channel having a circular cylinder. A two-dimensional system of partial differential equations has been discretized by employing Galerkin finite element method. Numerical simulations are carried out for different ranges of the governing parameters such as Reynolds number ( 10 ≤ Re ≤ 200 ), nanoparticle volume fraction ( 0.01 ≤ ϕ ≤ 0.05 ) and wave amplitude ( 0.05 ≤ A ≤ 0.25 ). It is inferred that Reynolds number is a key factor in this study. As it rises, the fluid behavior switches from slower to faster mode. Average Nusselt number rises at lower wavy wall and with lift coefficient ( C L ). The highest average Nusselt number is achieved at A = 0.05 , which is promoting the heat transfer by roughly 200 % . Furthermore, an enhancement in the nanoparticle volume fraction leads to the decrease in the local Nusselt number on upper wavy wall. The flow philosophy is presented in the form of isotherm contours, streamline contours and some appropriate plots. [ABSTRACT FROM AUTHOR]

This study presents a two and three-dimensional numerical simulations of a flow-through a sudden expansion and contraction microchannels. The finite element method was used to discretize the equations governing the physical model. By carrying out the numerical simulations, results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the microchannel for low Reynolds numbers. For high values of Reynolds number and expansion ratios, the vortex separation length increases. Also, the three-dimensional character of the flow is more pronounced for higher Reynolds numbers. [ABSTRACT FROM AUTHOR]

This study presents 2-D simulations of a flow-through a sudden expansion/contraction micro-channel with the existence of obstacles. The bottom wall is maintained at constant flux, while the other walls are adiabatic. Rectangular adiabatic obstacles are mounted before the expansion region on the upper and lower wall of the channel used. The finite element method was used to discretize the equations that govern the physical model. Results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the micro-channel for low Reynolds numbers. For higher values and expansion ratios, the vortex separation length increases. The obtained results show that the obstacles have a considerable effect on the dynamics of the flow and enhancement of heat transfer. [ABSTRACT FROM AUTHOR]

The electro-thermo-convection in a square cavity with incorporated hot solid body is numerically investigated. The finite volume method associated with Patankar's "blocked-off-regions" technique is applied. A potential difference is applied between the hot obstacle and the horizontal walls in order to eliminate the so-called dead zone created at the bottom of the cavity. The flow movement is induced not only by thermal buoyancy forces but also by the electric Coulomb force. Calculations are made for several injection levels (1 ≤ C ≤ 10), various obstacle shape factors (1 ≤ l/w ≤ 9), different number of electric Rayleigh (0 ≤ T ≤ 800), multiple thermal Rayleigh numbers (2000 ≤ Ra≤ 30,000) and 03 obstacle positions. The results show that according to the intensity of the applied electrical forces, two types of regimes are identified: a thermally dominated regime characterized by a low heat exchange at the bottom of the obstacle and conversely an electrically dominated regime with an excellent heat exchange over the entire cavity. It has been demonstrated that it is possible to improve the heat transfer up to: 43% by changing the shape factor of the obstacle; 82% by varying the injection level and 532% by applying electrical forces. [ABSTRACT FROM AUTHOR]

The present study summarizes a two-dimensional (2D) numerical simulation of a phase change material (PCM) melting/solidification processes in a square cavity. The objectives of this study are to study and compare the effect of the application of different applied thermal boundary conditions such as constant or variable thermal flux during the melting and solidification processes of a PCM. Here, the convective heat transfer is taken into account according to the Boussinesq approximation. The commercial code COMSOL Multiphysics is used, and the "Voller model" based on the enthalpy-porosity technique is applied on a fixed computational grid. Results presented in terms of solid–liquid fraction, flow structure, isotherms, and stored and released thermal energy have shown that the melting time for the applied variable heat flux is reduced compared to that of constant heat applied flux. In addition, it was found that the PCM melting time was shorter than the solidification time. Therefore, the use of variable (sinusoidal) heat flux conditions can be useful in engineering applications such as thermal energy storage applications (PCM life cycle test, solar energy where a variable heat flow is involved due to the change of day). [ABSTRACT FROM AUTHOR]

Three-dimensional numerical simulation on natural convection inside the T-shaped cavity, filled with water-based hybrid nanofluid of CNT–aluminum oxide is performed by vorticity–vector potential formalism. The variables considered are size of enclosure (0.1 < L < 0.9), volumetric percentage of nanoparticles (0 < φ < 4%), fraction of CNT composites (0 < fr < 1), and Rayleigh number (103 < Ra < 106). The heat transfer is increased with the increase in size, volumetric percentage of nanoparticles, fraction of CNT composites, and Rayleigh number. [ABSTRACT FROM AUTHOR]

The heat transfer phenomena inside a horizontal channel with an open trapezoidal enclosure subjected to a heat source of different lengths was investigated numerically in the present work. The heat source is considered as a local heating element of varying length, which is embedded at the bottom wall of the enclosure and maintained at a constant temperature. The air flow enters the channel horizontally at a constant cold temperature and a fixed velocity. The other walls of the enclosure and the channel are kept thermally insulated. The flow is assumed laminar, incompressible, and two‐dimensional, whereas the fluid is considered Newtonian. The results are presented in the form of the contours of velocity, isotherms, and Nusselt numbers profiles for various values of the dimensionless heat source lengths (0.16 ≤ ε ≤ 1). while, both Prandtl and Reynolds numbers are kept constant at (Pr = 0.71) and (Re = 100), respectively. The results indicated that the distribution of the isotherms depends significantly on the length of the heat source. Also, it was noted that both the local and the average Nusselt numbers increase as the local heat source length increases. Moreover, the maximum temperature is located near the heat source location. [ABSTRACT FROM AUTHOR]

A steady laminar two-dimensional magneto-hydrodynamics mixed convection flow in a square inclined cavity filled with Cu–water nanofluid is investigated numerically by using the finite difference method. The left and right vertical sidewalls of the cavity are considered adiabatic and move upward, while a partial slip flow condition is imposed on these walls. The horizontal top wall is considered cold and stationary, while a part of the stationary bottom wall is subjected to a uniform heat source and the remaining parts of it are considered adiabatic. An adiabatic obstacle is located in the center of the cavity and an external magnetic field is applied parallel to the horizontal x-axis. Parametric studies of the influence of various parameters such as Hartmann number, inclination angle of the cavity, dimensionless heat generation/absorption coefficient, obstacle aspect ratio, dimensionless length and location of the heat source, and solid volume fraction on the fluid flow and heat transfer have been performed. Comparisons with previously published numerical work are performed, and good agreements between the results are observed. It is found that the nanofluid was better than water to enhance the heat transfer when the effect of the magnetic field is weak, while the water is better than the nanofluid when its effect is strong. Moreover, the results indicated that the partial slip has a significant effect on the above-mentioned parameters. [ABSTRACT FROM AUTHOR]

A computational study has been performed to investigate the effects of partially active magnetic field on natural convection heat transfer in CNT-nanofluid filled and three-dimensional differentially heated closed space. Two cases are considered to see this effect as magnetic field is applied to upper half (Case I) and lower half (Case II) while remaining walls are insulated. The finite volume method is used to solve governing equations and results are obtained for different governing parameters as Hartmann number (0 ≤ Ha ≤ 100), nanoparticle volume fraction (0 ≤ φ ≤ 0.05) and height of the active zone (0 ≤ L B  ≤ 1). It is found that location of magnetic field plays an important role even at the same Hartmann number. Thus, it can be a good parameter to control heat and fluid flow inside the closed space. [ABSTRACT FROM AUTHOR]

A computational analysis of the natural ventilation process and entropy generation in 3-D prismatic greenhouse was performed using CFD. The aim of the study is to investigate how buoyancy forces influence air-flow and temperature patterns inside the greenhouse having lower level opening in its right heated façade and also upper level opening near the roof top in the opposite cooled façade. The bottom and all other walls are assumed to be perfect thermal insulators. Rayleigh number is the main parameter which changes from 10³ to 106 and Prandtl number is fixed at Pr = 0.71. Results are reported in terms of particles trajectories, iso-surfaces of temperature, mean Nusselt number, and entropy generation. It has been found that the flow structure is sensitive to the value of Rayleigh number and that heat transfer increases with increasing this parameter. Also, it have been noticed that, using asymmetric opening positions improve the natural ventilation and facilitate the occurrence of buoyancy induced upward cross air-flow (low-level supply and upper-level extraction) inside the greenhouse. [ABSTRACT FROM AUTHOR]

A numerical study of the 3-D double-diffusive natural convection in an inclined solar distiller was established. The flow is considered laminar and caused by the interaction of thermal energy and the chemical species diffusions. The governing equations of the problem, are formulated using vector potential-vorticity formalism in its 3-D form, then solved by the finite volumes method. The Rayleigh number is fixed at Ra = 105 and effects of the buoyancy ratio and inclination are studied for opposed temperature and concentration gradients. The main purpose of the study is to find the optimum inclination angle of the distiller which promotes the maximum mass and heat transfer. [ABSTRACT FROM AUTHOR]