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AbstractA numerical study of the natural convection flow and heat transfer characteristics of different nanofluids within a square enclosure is conducted by using a two-phase Eulerian–Eulerian model. In this study, the Cu-H2O and Al2O3-H2O nanofluids are considered because of their good stability. The Eulerian–Eulerian model considers the governing equations of the liquid and solid phases separately, and the coupling between the phases is done with interfacial interaction forces. Finite difference methods are used to discretize the governing equations. Additionally, sixth-order compact schemes are used to evaluate the non-linear convective terms. The current Fortran-based solver is validated by using experimental and numerical results from the literature. The effect of Grashof number (Gr = 103 to Gr = 106) and volume fraction (1–3%) of nanoparticles on the flow field and heat transfer are discussed in detail through stream function contours, isotherms, velocity and temperature profiles at the midsection of the enclosure, and average Nusselt number values. The results demonstrated that the incorporation of nanoparticles into the base fluid augmented the flow intensity and heat transfer. Moreover, this effect is more significant with Cu nanoparticles than Al2O3 nanoparticles. At Grashof number, Gr = 106 and volume fraction, ϕs = 2% the average Nusselt number values for the Cu-H2O nanofluid and Al2O3-H2O nanofluid are enhanced by 32.04% and 19.47% respectively, compared to the base fluid water. The findings also indicate that increasing the Grashof number and volume fraction leads to a substantial improvement in the heat transfer rate. Finally, a new correlation is developed to predict the average Nusselt number along the heated wall of a square enclosure filled with nanofluids. [ABSTRACT FROM AUTHOR]

Ice storage sphere systems are favored in the field of energy storage, however, the poor thermal conductivity of phase change materials (PCM) seriously weakens their wide application. Metal foam has been shown to enhance its heat transfer. In this paper, we investigate the impact of varying the filling radius ratio of foam metal to further improve energy storage performance and reduce costs in ice storage spheres. Computational fluid dynamics are employed to analyze the heat transfer and solidification processes. The enthalpy-porosity method is used to describe PCM solidification, while the local equilibrium thermal (LET) model characterizes heat transfer between the PCM and foam metal. The study explores temperature field variations, solid phase fraction changes, solidification times, and cold storage volumes, accounting for natural convection. By comparing solidification rates and other relevant parameters, the effect of foam metal filling on the solidification process is explored. Moreover, a new evaluation index is proposed, which can assess the overall performance of ice storage systems in real-time, considering market prices. The results show that natural convection is the primary heat transfer mode in pure PCM-ffild ice storage spheres, whereas smaller foam metal filling radii significantly inhibit natural convection, resulting in heat conduction as the dominant mode. Without specific requirements, an optimal fill radius ratio of 9/13 is determined. This paper offers a comprehensive understanding of cold storage employing various foam metal filling radios, contributing to advancements in efficient thermal energy storage systems. [ABSTRACT FROM AUTHOR]

Heat transfer by convection is widely used in many engineering applications such as in heat exchangers, combustion devices or gas processing. In Buildings, the use of rough surfaces allows enhancing heat transfer rates. Practically, in this study, a rough surface is obtained by using protuberances on the vertical left wall. In this perspective, the originality of this research is to study the influence of the protuberance geometric shapes on the heat transfer using 2D numerical simulations as a tool investigation. The homotopic transformation is used to reach a flat plate. The system of equations with the boundary conditions is solved using the finite volume method. A simple algorithm is chosen for the integration of algebraic equations. The governing equations are figured out using ANSYS FLUENT commercial software with SIMPLE algorithm in order to solve pressure-velocity coupling. The numerical simulations have been performed for different shapes of the protuberances (battlement, triangular and sinusoidal). The boundary conditions are based on a uniform heat flux applied to the vertical wall. On the other hand, the horizontal walls are subject to the adiabatic condition. It can be noticed that the effect of the wavy geometry induces a noticeable improvement of the heat transfer rate compared to an enclosure without protuberances. It can also conclude that the wavy configuration exhibits a Nusselt average slightly higher than that of the square cavity, particularly the triangular configuration, by approximately 20%. [ABSTRACT FROM AUTHOR]

The current paper has the objective of exploring the thermophysical properties (TPPs) of single walled carbon nanotube (SWCNT) nanofluids (NFs) for heat transfer applications. The effect of dispersing the nanotubes in conventional heat transfer fluids (HTFs) has been investigated. Carbon nanotubes (CNTs) have exceptionally high thermal conductivities. Using the effective medium theory, density, specific heat, thermal conductivity, and viscosity has been evaluated as functions of volume fractions. The base fluids considered in this work are water, ethylene glycol, engine oil, and kerosene oil as these are the commonly used HTFs for industrial applications. Theoretical predictions from this study show an increase in density, thermal conductivity, and viscosity with volume fraction while there is a decrease in specific heat with volume fraction. The effect of the aspect ratio (AR) of CNTs on the thermal conductivity of NF is also investigated. For low volume fractions of SWCNT, the thermal conductivity has been found to increase with AR. Further, this study has been extended for a real‐world application of heat transfer using SWCNT. In this paper, a numerical investigation of heat transfer in a square enclosure with differentially heated vertical walls, filled with SWCNT‐water NF under natural convection is carried out. Due to low concentrations of SWCNT in water, single phase flow is assumed. Velocity and temperature distributions are obtained as solutions to the energy and Navier–Stoke's equations. A comparison of the temperature and velocity profile has been represented by simulating the system over a range of Rayleigh numbers. [ABSTRACT FROM AUTHOR]

Radon exhaled from building materials infiltrates the indoor atmosphere and is transported into the indoor space by buoyancy-driven airflow. This paper investigated the dynamic coupling of radon concentration in the building wall area and indoor space. An indoor radon migration model under natural convection caused by temperature gradient was established. The radon exhalation rate, average Nusselt number, and average Sherwood number at the building wall and indoor space interface were quantified. The mechanism of radon migration from building materials into the indoor atmosphere was elucidated. Results show that natural convection influences the flow of indoor air and the radon concentration distribution, which increases with the increase of temperature gradient. [ABSTRACT FROM AUTHOR]

In this work, diurnal heating, by solar radiation, and cooling in a sloping water body with vegetated shallow regions are investigated numerically. The sloping water body consists of a vegetated region with a bottom slope equal to 0.1 and a deep region with a horizontal bottom. The Volume-Averaged Navier-Stokes equations together with the Volume-Averaged Energy equation are solved numerically in the vegetated region. The latter has porosity equal to 0.85 (typical of aquatic plants found in lakes) and a length equal to the total length of the sloping region. At the top free surface, a time-dependent thermal forcing is applied, which is reduced in the vegetated region. Shallow water is considered with a maximum water depth being less than the penetration depth of the solar radiation. The non-vegetated sloping water body is also considered for validation purposes. The results (isotherms, streamlines, exchange flow rate), after ten full thermal forcing cycles, indicate significant vegetation effects on the daytime and night circulation and the exchange flow rates. [ABSTRACT FROM AUTHOR]

The main objective of the present analysis is to characterize the transient buoyancy-motivated free convection turbulent flow and heat transfer characteristic features of an incompressible viscous fluid past a vertical cylinder with low-Reynolds-number (LRN) k–ε turbulence model in a two-dimensional coordinate system numerically. The Reynolds averaged Navier–Stokes equations (RANS) such as continuity, momentum, and energy are considered in terms of cylindrical coordinate system. The extra stress tensors obtained from the RANS model are closed using the eddy diffusive model. The local value of turbulent kinematic viscosity ( ν t ) is determined by utilizing the kinetic energy (k) and dissipation rate (ϵ) equations. The resulting system of partial differential equations (PDEs) with high nonlinearity, governing the turbulent boundary layer flow are solved using the implicit Crank–Nicolson technique. The discretized set of dimensionless tridiagonal algebraic equations are simplified by utilizing Thomas algorithm. Also, the simulated results are expressed in terms of graphs to analyse the average velocity, temperature, kinetic energy, dissipation rate, and also average momentum and heat transfer rates for the varying values of turbulent Prandtl ( Pr t ), Grashof (G r t) and Reynolds ( Re t ) numbers. It is noted that the average velocity, kinetic energy, dissipation rate of kinetic energy fields suppressed, and temperature field enhanced with increasing Re t . Also, the rising turbulent Prandtl parameter decreased the average velocity, temperature, turbulent kinetic energy, and dissipation rate profiles. Further, the increasing turbulent Grashof number decreased the kinetic energy and dissipation rate profiles. Further, the obtained results from the present turbulent investigation are compared with the existing results and observed an excellent agreement. [ABSTRACT FROM AUTHOR]

In this piece of communication, numerical heat transfer and fluid flow in a Darcy porous enclosure are investigated. The right wavy wall is maintained at a constant low temperature, with the top and bottom preserved thermally insulated, while the left vertical wall is uniformly heated. The governing equations for non-dimensional systems are solved using the Galerkin finite element method; a local thermal non-equilibrium appears between the base fluid and porous matrix. The effects of interface heat transfer parameter (0 ≤ N h s ≤ 10 3) along with porosity of porous media (0.1 ≤ ϵ ≤ 0.9) , Rayleigh-Darcy number (10 ≤ R a ≤ 10 3) , and parameters involving waviness of cavities, such as the number of undulations in a unit length (1 ≤ N ≤ 5) and amplitude of the wave (0.05 ≤ a ≤ 0.25) are investigated. The results show that increment waviness augments heat transfer enhancement for fluid and solid phases. The local thermal equilibrium cases for various parameters are pointed out at a 5% significance level of the average temperature difference between the two phases. [ABSTRACT FROM AUTHOR]

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Although natural convection is frequently encountered in various chemical processes, Rayleigh number (Ra) cannot be defined fully in shear‐thinning fluid systems. In particular, the velocity scale, which is necessary to estimate the effective viscosity of the system, should be discussed carefully. Thus, in this study, the representative velocity scale of Rayleigh‐Bénard (RB) convection, which is a typical example of natural convection, with shear‐thinning fluids was investigated based on the velocity fields obtained using computational fluid dynamics. Numerical simulations revealed that the critical temperature difference at which RB convection starts to fully develop decreases with an increase in the shear‐thinning property. The shear‐thinning property also induced subcritical bifurcation. In addition, the velocity scale of convection increases with an increase in the shear‐thinning property. Thus, the shear‐thinning property is considered to accelerate convection. Compared with several types of velocity scales used by other researchers, significant deviations from the actual scale were observed. Therefore, a new type of velocity scale, including the buoyant to viscous force ratio, arbitrary parameter, and thermal diffusivity, was proposed. The proposed velocity scale allowed an approximate estimation of the actual velocity scale. Although further investigation of the validity is necessary with varying geometries and rheological parameters, this velocity scale will be useful for controlling RB convection with Newtonian/shear‐thinning fluids. [ABSTRACT FROM AUTHOR]

AbstractIn day-to-day life, heat transfer has several applications and hence we have many research areas of interest to learn new things. Nanoparticles improve the characteristics of heat transfer due to the random motion of particles. In this study, a computational approach is used to study natural convection in a porous enclosure with nanofluid. The convective term is solved by the QUICK scheme, and the finite difference method is used to solve the stream function with a 60 × 60 mesh size. CuO-water nanofluid is used in this work since nanoparticles are widely used in almost all engineering fields. In this study, we considered a two-dimensional complex cavity which is solved mathematically by using the Boussinesq approximation method. For validation of the software code, the obtained results are compared with the existing results in the literature and are found to be in good agreement. We see distortion of isotherms increases with an increase in the Rayleigh number and the nanoparticle content. That is, heat transfer takes place by natural convection very fast. Nusselt number increases with increasing nanofluid particles and the Rayleigh number. Also, it can be concluded that the heat transfer is a strong function of the Darcy number and The Rayleigh number. [ABSTRACT FROM AUTHOR]

Combined buoyancy shifts from temperature and concentricity gradients create double-diffusive convection. Complex Crown form enclosure with heat and mass source brings originality and practicality by enhancing use in a broad variety of technical, industrial, and geophysical operations. Current artifact is to explore thermosolutal diffusion in buoyantly driven flowing of viscid liquid contained in a crown enclosure with the installation of a uniformly heated and soluted circular cylinder. Novel physical characteristics of inclining magnetic field are introduced, and distributions affected by cylinder radius change are compared. Dimensionless PDEs are solved numerically using finite elements. Grid independence test ensures simulation mesh level. Hybrid meshing with triangular and rectangular components discretizes domain. Linear interpolating polynomials approximate pressure, whereas quadratic polynomials approach velocity, temperature, and concentricity. PARDISO solves a non-linear system of equations efficiently. Average Nusselt and Sherwood numbers are estimated by comparing relevant parameters to cylinder radius change. Heat transference rate rises to 40% and mass transport upsurges to 60% when radius of cylinder is increased from 0.1 to 0.2. Hartmann number tends to affect a decline in Nusselt and Sherwood quantities. Reduction in thermal and solutal boundary layers near surface of the cylinder is observed against the improve in radius of cylinder. [ABSTRACT FROM AUTHOR]

The analysis of non-Newtonian fluid flow over an oscillating surface often involves numerical simulations and experimental investigations. Computational fluid dynamics method including finite difference or finite element techniques can be used to crack the governing equations of the fluid flow. In this work, we used the Crank–Nicolson numerical technique to analyze the numerical behavior of unsteady boundary layer flow of Casson fluid with natural convection past an oscillating vertical plate. The temperature-dependent viscosity is assumed for the flow analysis. The impact of chemical reaction and heat generation coefficient is used to examine the mass and heat transferal rates. The investigation of non-Newtonian fluid flow over an oscillating surface is crucial for a wide range of industrial, biomedical, and scientific applications. The governing model of equations occurs in the form of nondimensional PDEs and then we use the dimensionless variables in order to achieve the dimensional PDEs. These equations are numerically solved by using the Crank–Nicolson technique. The Crank–Nicolson scheme is used because it has the ability to provide accurate and stable solutions and make it a valuable numerical technique in various scientific and engineering disciplines. The findings indicate the significance of numerous parameters on the mass, velocity and energy regions. The numerical outcomes of skin friction are observed due to fluid parameter, viscosity parameter, Grashof numbers of heat and solutal rates. [ABSTRACT FROM AUTHOR]

AbstractIn order to study the effect of porous fin parameters on the natural convection heat transfer in the side-heated cavity containing the internal heat source, the influence of the structural parameters of porous fins (length of porous fins l, installation position of porous fins s, Installation angle of porous fins θ) and the physical property parameters of porous fins (effective thermal conductivity Ke, Darcy number Da) on the natural convection heat transfer in the cavity was numerically analyzed by arranging a porous fin on the hot wall. The effect of the coupling effect of the structure parameters of porous fins was analyzed by the response surface method, and it was found that the coupling effect of the installation position and installation angle of porous fins had the most significant effect on the convective heat transfer in the cavity, the combination of the structural parameters of porous fins with the optimal convective heat transfer effect is l = 0.053 H, s = 0.373 H, and θ = 93.21°, which increases the average Nusselt number of the hot wall by 38.72% compared with no-fin structure; The effect of Darcy number and effective thermal conductivity of porous fins on the average Nusselt number of the hot wall surface is analyzed. The results of the study can guide the study of solar radiation in buildings, the internal temperature control of automobiles, and the study of the thermal performance of electronic components. [ABSTRACT FROM AUTHOR]

AbstractMetallic ligaments in open-cell metal foams have effectively improved the heat conduction of phase change materials (PCMs). However, when the gradient direction of porosity is perpendicular to the direction of heat conduction, the mechanism by which graded foam (GF) influences the phase transition of PCM remains elusive. To address this issue, this study employs the pore-scale numerical simulation and develops a numerical model to study the impact of GF on the charging of PCM-foam composites. The analysis identifies the local convection and heat conduction as the most crucial factors influencing heat transfer during phase transition. To effectively examine the role of metallic ligaments in the phase transition, simplified tetrakaidecahedron cells are adopted. The results demonstrate that the GF delays the charging of PCM. Specifically, compared to the homogeneous foam, the full melting time (FMT) of PCM in the GF increases by over 29%. Additionally, the integral-mean temperature response rate (ITRR) of PCM in the GF decreases by 20.2% to 22.1%. Within the GF, the PCM requires more time to melt completely in the tetrakaidecahedron cells with high porosity. Moreover, local convection plays a pivotal role, considerably reducing the FMTs of PCMs by over 85% and increasing the ITRRs of these structures by 588.1% to 599.0%. [ABSTRACT FROM AUTHOR]

Phase change material (PCM) are characterized by their high latent heat and low density. Combining PCM with building walls, aircraft fuselages, and other structures can significantly enhance the thermal sink capability of these structures. In order to address the issue of low heat storage efficiency resulting from the low thermal conductivity of PCM, a novel integrated thermal protection structure (ITPS) architecture with a supportive structure based on a porous lattice has been designed. Experimental and numerical methods were employed to investigate the thermal response characteristics of the ITPS with and without PCM, the melting behavior of PCM within the porous lattice, and the effects of lattice configuration and pore size on the PCM melting rate. The current ITPS study includes evaluation of two types of lattice configurations and three different pore sizes. The results indicate that the inclusion of PCM reduces the internal panel temperature of the ITPS by approximately 15%. The melting of PCM occurs primarily at the central region of the porous lattice and gradually spreads towards the periphery until complete melting is achieved. Specifically, the Gibson–Ashby lattice configuration enhances the PCM melting rate by 43.5%, while the tetradecahedron lattice configuration yields a 53.1% improvement. Furthermore, for PCM with different pore sizes, smaller pores exhibit faster melting rates during the early and intermediate stages, whereas larger pores exhibit faster melting rates in the later stages as the proportion of liquid PCM increases. The conclusions of this study provide valuable insights for the application of PCM in the field of thermal management. [ABSTRACT FROM AUTHOR]

AbstractThe influence of the local thermal nonequilibrium (LTNE) state on steady-state natural convection due to the heating and cooling of the side walls of the slender porous cavity has been addressed analytically and numerically. The porous medium is assumed to be hydrodynamically anisotropic. The Darcy model has been adopted. A closed-form solution, based on a parallel hypothesis, is reported for a slender cavity. The combined impact of media anisotropy and LTNE state on the heat transfer rate, as well as flow dynamics, have been analyzed. The help of boundary layer analysis is taken to report the boundary layer thickness and heat transfer rate of fluid flow analytically. It has been found that the maximum (minimum) heat transfer rate of the fluid phase as well as solid phase takes place at orientation angle, ϕ, equal to π/2 when permeability along the horizontal (vertical) direction is higher than the same along vertical (horizontal) direction. [ABSTRACT FROM AUTHOR]

The primary goal of this study is to perform the analysis of heat transfer in free convection flow of micropolar nanofluid along a complex roughened surface. A micropolar nanofluid is made by adding nanoparticles namely SWCNTs (single-walled carbon nanotubes) in ethylene glycol (EG) base micropolar fluid. A mathematical model for micropolar nanofluid can be developed in terms of nonlinear partial differential equations by extending Navier-Stokes equations along with micro inertia effects, angular momentum equation and Tiwari and Das model. After using the suitable transformation, the resulting nonlinear PDEs are made dimensionless and solved numerically using finite difference scheme. Micropolar nanofluids have a capability to improve the thermophysical properties and heat transportation capacity instead of base fluids. The impacts of numerous pertinent parameters on velocity, microrotation and temperature profiles also on physical quantities namely wall couple stress, local and average Nusselt numbers, total heat transfer and skin friction coefficient are discussed graphically. It is noted that total heat transfer rate becomes high in case of dominant amplitude of harmonic wave as compared to fundamental. It is also noted that total heat transfer rate decreases by increasing micropolar parameter and can be enhanced by adding SWCNTs in EG based micropolar fluid and that enhancement is reported approximately 27 and 26% in dominant amplitude of fundamental and harmonic waves as compared to ethylene glycol fluid. [ABSTRACT FROM AUTHOR]

AbstractNumerical analysis is performed to deduce the effect of aspect ratio (AR) and inclination of a rough-walled cavity on heat transfer, fluid flow, and entropy generation due to natural convection for Rayleigh number (Ra = 105). The cavity is filled with Al2O3-water nanofluid of 0.05 solid volume fraction. The natural convection process is caused by the temperature difference between the left hot wall and the right cold wall of the cavity. The walls are subjected to slip boundary conditions and the slip velocity is characterized by the Knudsen number (Kn = 0.5). The profile of the rough surface is generated by Weierstrass-Mandelbrot (W-M) function. Numerical simulations have been performed using Finite Element based software COMSOL Multiphysics 6.0. The AR is varied in the range of 0.5 to 4, and the inclination of the cavity is kept at 0°, 30°, and 60°. The numerical results are exhibited in terms of isotherms, streamlines, entropy generation due to heat transfer, and fluid friction irreversibilities. It is observed that the slip velocity on the walls has a strong influence on the fluid flow. Entropy generation due to fluid friction is found to increase with the rise in AR up to 2 and then it starts declining. The entropy generation due to fluid friction irreversibility at the center of the cavity is minimal, so the Bejan number is close to unity. Cavity with an inclination of 30° gives the maximum Nusselt number at any value of AR. Notably, the total entropy generation is observed to reach its maximum at α = 60° and minimum at α = 30°, offering comprehensive insights into the interplay of geometric and flow parameters within the cavity. [ABSTRACT FROM AUTHOR]

Thermally-driven natural convection is theoretically explored in the present work within a porous layer with respect to the Darcy's law. The usual non circulating basic cellular flow between two infinitely long horizontal Darcy porous plates leads to generalized basic state considering the isothermal boundary conditions leading to the Hadley flow configuration. Such a motion is governed by a circulatory flow together with a temperature both varying along the horizontal axis. Hence, besides the buoyancy Rayleigh parameter, yet another parameter appears dominating the evolution of basic cellular circulation and thermal progress. Instability onset of this basic state is targeted based on the linear stability analysis of small normal modes. The resulting 3D instability system of equations is treated numerically and the stationary modes leading to convective neutral stability are determined. The found eigenvalues are also justified to be those deviating from the well-known no-flow Darcy porous solution through an asymptotic perturbation method in the special circumstances. The bounds of neutral stability curves in regard to the longitudinal, oblique and transverse modes are thoroughly investigated and it is shown that longitudinal modes are always the most unstable ones, while the transverse and oblique modes having finite encapsulated zone of instability can undergo a complete stability after a threshold value of horizontal temperature gradient parameter. [ABSTRACT FROM AUTHOR]

In this research, the effect of different models of thermal conductivity and dynamic viscosity has been investigated by considering the effect of Brownian motion of nanoparticles on the flow field and heat transfer of nanofluids. This study was performed numerically in a square cavity with water/aluminum-oxide nanofluid in three modes of natural, mixed and forced convection by changing the independent variable such as nanoparticle volume fraction, Rayleigh number, Richardson number, and Reynolds number. The governing equations with certain boundary conditions are solved using the finite volume method. Also, according to the obtained numerical results, Nusselt number has been investigated for different conditions with and without considering Brownian motion. The results showed that for all the studied models, in all three modes of natural, mixed and forced convection, the average Nusselt number when the effect of Brownian motion is considered, is more than the case that the effect of this motion is not considered. In all cases, the Koo & Kleinstreuer and Li & Kleinstreuer models show approximately the same values for the maximum mean Nusselt number. The similar results are obtained employing the Wajjha & Das and Xiao et al. models. For mixed convection, the highest and lowest increases of Nusselt number, considering Brownian motion are 17.68% and 14.84%, respectively. While referred values for forced convection are 30.46% and 17.94 %, respectively. [ABSTRACT FROM AUTHOR]

This study aims to look into the temperature distribution on a vertical flat plate with a variable temperature boundary condition. As a novelty, the variable temperature is considered on the wall, and coupled momentum and energy equation are solved. Moreover, a novel variable change transforms the infinite boundary condition into the finite one. The partial differential governing equations were introduced and transformed into ordinary differential equations form using the similarity solution. The obtained equations were numerically solved and validated using previous research. The results showed that for a constant variable temperature index (n), increasing the Prandtl number (Pr) from 0.1 to 2 reduces the dimensionless maximum velocity by less than half and the skin friction coefficient by about 32%. In this case, the dimensionless temperature approaches zero faster; as a result, the thermal boundary layer thickness declines, and the Nusselt number (Nu) rises. Furthermore, for a constant Pr, when n increases from 0 to 1.5, the dimensionless maximum velocity and the skin friction decrease by about 38% and 23%, respectively. Since the dimensionless temperature continues to descending trend, Nu still rises in this case. [ABSTRACT FROM AUTHOR]

• A ROM methodology is proposed to solve convective-dominant conjugate heat transfer flows. • Numerical validation of the methodology is done exhaustively with benchmark solutions. • A mesh-based hyper-ROM approach is used to assess fast numerical approximations. • The use of ROM in all the unknown fields or only in the velocity and pressure is compared. • Speed-up of three hundred times is obtained through the use of ROM methodologies. This article presents a full and reduced-order methodology based on the finite element method that allows the characterization of convective-dominant conjugate heat transfer flows. Reduced-order modeling (ROM) allows the description of several degrees of freedom problems, referred to as full-order modeling (FOM), through a reduced-order surrogate representation based on a Petrov-Galerkin projection onto a reduced subspace. The FOM and ROM problems are stabilized through the Variational Multi-Scale (VMS) method, which ensures stability in dominant convective problems and allows equal interpolation spaces for the pressure, velocity, and temperature. The proposed methodology is validated solving natural heat convection in a differentially heated square cavity, considering air as the working fluid and Rayleigh numbers in the interval 10 4 ≤ Ra ≤ 10 8. In this problem, the benefit of using a ROM approximation for the three unknown fields, i.e., velocity, pressure, and temperature, is compared against ROM approximation only in the velocity and pressure fields and a FOM type approximation for temperature. The benefit of using mesh-based hyperreduction and its computational performance and precision are also analyzed. Subsequently, the method simulates a conjugate heat transfer problem that includes natural heat convection, allowing the inclusion of different rheologies between the working fluids. The results verify the precision and speed up of the calculations by more than three hundred times with respect to the time necessary to solve a full-order formulation, emerging it as a great potential tool in the resolution of thermally coupled flows. [ABSTRACT FROM AUTHOR]

The aim of this study is to better understand the behavior of the nanofluid in a specific configuration, aiding in the creation of new models and designs for heat transfer systems, by investigating the MHD natural convection in an annular partially porous metal space between two vertical concentric cylinders, which is saturated by (Cu–water) nanofluid. The inside cylinder undergoes a regular heat flux, whereas the outer cylinder maintains a uniform temperature. The upper and lower walls are impermeable and insulated. In the upward direction, an exterior magnetic field with constant intensity is used. The nonlinear coupled conservation equations with specified boundary conditions in the vorticity-stream function form are solved using the finites differences method in conjunction with the successive over relaxation method. The numerical results obtained are presented to show the impact of a variety of control parameters depicted in Darcy number 10 - 5 ≤ Da ≤ 10 - 1 , Rayleigh number 10 4 ≤ Ra ≤ 10 6 , Hartmann number 0 ≤ Ha ≤ 100 , heater size, the porous layer thickness 0.25 ≤ Xp ≤ 0.75 , and nanoparticle concentration 0.01 ≤ ϕ ≤ 0.05 . From this study, the increase in the Ra number from 10 4 to 10 6 causes a thermal energy transmission improvement of 50%. Furthermore, a rise in the Da number from Da = 10 - 5 to Da = 10 - 1 enhances the thermal energy transport by approximately 30 % , while it reduces by 4.8% when we increase the Hartmann number from 0 to 100. Also, the rise in nanoparticle concentration leads to an enhancement of the average Nusselt number, while the heat transfer rate is reduced by extending the heater size. The numerical results also show a significant improvement in the thermal energy transport in active walls by using an optimum thickness layer of stainless steel porous medium, according to the Da number. Furthermore, this study demonstrates that there is a critical value of porosity for a given nanoparticle concentration and porous layer thickness for better heat transfer enhancement. [ABSTRACT FROM AUTHOR]

In power applications, convection plays a dominant position in the transport of strength for the proper design to attain higher warmth transfer quotes. Where in the fluid movement is genuinely induced via density gradients. This has a look at what is involved with transient convection in an isosceles-superimposed triangular enclo sure. The walls were angled at θ = 45°. Critical Rayleigh numbers have been obtained: Ra = 106, especially for the fluid crushed between the two triangles where we can visualize the critical convection transaction between the air and water. The consequences in the quantitative dimension of average Nusselt quantity change and qualitative visualization of streamline and isotherms are examined. The air and water streamlines and the temperature fields had been obtained for the Rayleigh numbers 10³ ≤ Ra ≤ 108. Furthermore, the water fluid's natural convection case has the best heat transfer performance at the water fluid, whereas the dilatant fluid exhibits the lowest heat transfer performance. Heat transfer from the bottom to the top can be significantly improved by the triangle shape at first in a smooth and harmonious manner, and then it turns into a more complex and disorderly shape when the water reaches high temperatures. [ABSTRACT FROM AUTHOR]

This study employs finite difference modelling to investigate the natural convection of a two-phase hybrid nanofluid consisting of Al2O3 and Cu nanoparticles dispersed in water along a vertically heated wavy surface. The hybrid nanofluid has unique features that influence convective heat transfer. Numerical solutions analyze fluid flow patterns and temperature distributions, providing insights into heat exchange and thermal management. The research highlights the importance of hybrid nanofluids, notably those containing Al2O3 and Cu in a water base, in improving overall heat transfer efficiency. The mathematical model accounts for laminar and incompressible fluid flow with a Prandtl number of Pr = 6.2, Lewis number Le = 10, and maximum 10% concentration of hybrid nanoparticles. After transforming the governing equations into a non-dimensional form, the implicit finite difference method is used to solve them. The solution employs the in-house FORTRAN 90 code and compares its outcomes with the bench-mark results. Various parameters, such as the Schmidt number (Sc = 1 to 10), volume fraction of nanoparticles (φ = 0.0 to 0.1), wavy amplitude (A = 0.0 to 0.3), and NBT = (0.05 to 0.2), are investigated regarding temperature, velocity, local skin friction coefficient (Cf), local Nusselt number (Nu), streamlines, and isotherms. Elevated volume fraction generally decreases skin friction, increases temperature, and may reduce velocity. Meanwhile, higher skin friction, temperature, velocity, and local Nusselt numbers often correlate with elevated Schmidt numbers. Changes in amplitude and NBT affect skin friction, temperature, velocity, and local Nusselt numbers, providing information on the dynamics of fluid systems. For example, when the volume fraction (φ) increases from 0 to 0.1 at Y = 2, the temperature rises by 75%, while the velocity gradually decreases by 11.11%. This is in contrast to findings according to when the NBT rises from 0.05 to 0.2 at Y = 1. In this case, the temperature drops by 18.75%, followed by a 9.68% fall in fluid velocity. Understanding these interactions enhances comprehension of heat transfer and fluid dynamics. By investigating these interactions, we not only improve our understanding of heat transfer and fluid dynamics, but also open the door to new strategies for improving thermal systems and manufacturing procedures. [ABSTRACT FROM AUTHOR]

It was found that the injection of bubbles into liquid can effectively improve heat transfer efficiency, so it is important for industrial applications to investigate the effect of bubble injection on heat transfer. The effect of bubble injection on natural convective heat transfer in steady laminar flows in a vertical channel is investigated using the volume of fluid (VOF) method, and the effects of bubble diameter, Eötvös number (Eo), bubble arrangement, and bubble distance from a hot wall on the heat transfer between the hot wall and liquid are studied, respectively. The results show that bubble injection can effectively improve the heat transfer between the hot wall and liquid; an increase in bubble diameter and Eo can improve the enhancement effect of heat transfer and can expand the enhancement area of heat transfer; the closer to the hot wall a bubble is, the better the enhancement of heat transfer is; and the spacing and arrangement of bubbles also have important effects on the heat transfer between the hot wall and liquid. The comparison shows that the enhancement of heat transfer is the best for the vertical arrangement of double bubbles, which increases the local heat transfer coefficient by 3.2 times. The enhancement of heat transfer generated by bubble injection is related to the degree of disturbance of the local liquid phase caused by bubble injection. The more strongly the local liquid is disturbed, the thinner the local temperature boundary layer becomes, and the better the enhancement of heat transfer is. [ABSTRACT FROM AUTHOR]

Experimental studies were conducted to investigate the effect of varying torque loads on the temperature distribution on the surface of lithium-ion batteries (72 volts–20 Ah) in real commercial two-wheeler electric vehicles as part of our previous research. An electric vehicle engine was installed in a dyno testing laboratory and used as the main load for the battery. Ambient temperature and relative humidity were controlled using an air conditioning system. The test results are presented as surface temperature distributions on each side of the battery at various torque loads. The highest temperature on the battery's surface was found to be approximately 40 °C at a torque load of 100%. Unfortunately, the heat generated by the battery during testing could not be measured for further research. This paper presents a numerical study of battery heat generation at 100% torque load using Ansys Fluent 2020 R1©. This tool is employed to calculate the heat flux from the battery surface to the ambient air. The CFD tool was initially validated against available experimental data and commonly used correlations for natural convection along a vertically heated wall. Good agreements between the current predictions and experimental data were observed for laminar flow regimes. Convective heat transfer between the battery surface and ambient air was simulated. The results indicate that the commonly used heat transfer correlation for vertical plates accurately predicts the heat transfer rate on the battery surface, and it was found that the heat generation rate is 1199 W/m3. [ABSTRACT FROM AUTHOR]

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In this article, we report on numerical simulations of laminar Rayleigh–Bénard convection of air in cuboids. We provide numerical evidence of the existence of multiple steady states when the aspect ratio of the cuboid is sufficiently large. In our simulations, the Rayleigh number is fixed at R a = 1.7 × 10 4 . The gas in the cube is initially at rest but subject to random small-amplitude velocity perturbations and an adverse temperature gradient. When the flow domain is a cube, i.e., the aspect ratio is equal to unity, there is only one steady state. This state is characterized by the development of a single convective roll and by a symmetric normalized temperature profile with respect to the mid-height. On the contrary, when the aspect ratio is equal to 2, there are five different steady states. Only one of them exhibits a symmetric temperature profile and flow structure. The other four steady states are characterized by two-roll configurations and asymmetric temperature profiles. [ABSTRACT FROM AUTHOR]

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To provide food supply chains, reduce losses from various crops after the harvesting process, and also to preserve vegetable and fruit crops purchased for consumption from rotting and not being wasted. The drying process is one of the most appropriate ways to solve such problems. In this research, several simple thermal modeling methods were proposed to perform the drying process through open sun drying (OSD) under forced pressure (FGD) and natural convection (NGD). This study was conducted at the King Faisal University Training and Research Station (25.4° latitude). North, longitude 49.6° east, height 142 meters above sea level). The thermal performance analysis of the models was evaluated by calculating the amount of solar radiation, air temperature, product temperature, moisture evaporation rate, and wind speed. The results obtained showed that drying inside the greenhouse is the best alternative to drying under direct sunlight, so that the maximum temperatures were obtained, ranging between 55 to 52 in FGD and 40−45 inside NGD. Also, the heat transfer coefficient was highest in the amount of moisture removed from the product, reaching its maximum. The weight of the product was reduced to 83%, 80 and 73%, in GFD, NGD and OSD, respectively Accordingly, it was found that drying gave the highest expected results, and the temperature of the product ranged between 9.25 to 14.36 and 4.93 to 10.32, and the correlation coefficient ranged between 0.95−0.52 and 0.95. −0.89 at OSD and NGD respectively. Moisture evaporation from the product is 28.92−2.77 at NGD and moisture evaporation exerted for FGD is 31.35 and the correlation coefficient for the product at FGD ranges from 0.93−0.84. The product and greenhouse temperature range are between 0.99−0.96. The moisture evaporation rate indicating that the values obtained were well matched. Finally, the economic analysis of the different methods of drying was done through a mathematical model.

A natural convection heat transfer inside rhombic square cavity partially filled with porous material have been numerically investigated. A constant heat flux has been applied to the left wall with a right wall kept in constant cold temperature while thermally insulated the top and bottom walls. Finite volume technique with Simple algorithm have been used to simulate the governing equations of fluid flow and heat transfer coupled with Darcy-Brinkman model to simulate the flow of the air inside the main cavity and the open cells of the porous media. Three factors were chosen to study their effects on the natural air velocity and the mechanism of the free convection inside the enclosure. The inclined angle of the sidewall of the rhombic (q = 90o, 80o and 70o), the thickness of the metal foam (t = 5 cm, 10 cm, and 15 cm) and the amount of heat flux (q = 150 to 600 w/m2). Copper metal foam with 0.9 porosity was chosen as porous media with open cell filled by air (Prandtl number =0.7) and 10 as pore density. The results showed that using a layer of porous metal foam with open cells will increase the heat transfer rate. It was 41.3% enhancement when use 5 cm of porous media and 68% for 15 cm. Acute inclined angle will decrease local Nusselt number and led to form vorticities. Furthermore, high heat flux increased the average Nusselt number and improved the heat transfer rate.

This research provides information on the heat transfer in the cavity by natural convection which has a partially open side with a ratio (A = 1, 0.75, 0.5, 0.25) to the surroundings for cooling. It is filled with porous media (glass beads) and saturated with air. The bottom wall was heated with a constant heat flux (q = 1500, 3000, 4500, 6000) W/m2 while the top and other walls of the cavity were well insulated. The porous media had small porosity (0.418), a range of Rayleigh number Ra (57.6-1470). The distribution of temperatures, the local Nusselt number, and the average Nusselt number were all extracted from the testing rig's temperature data. It is clear that the fluid flow and heat transfer are affected by heat flux and the ratio of partially open side. Observed that, the greatest temperature values at maximum heat flux (q) and minimum open ratio (A). Thus, the temperature rising at all values of the constant heat flux and the enhancement of the local Nusselt number at (q = 6000) W/m2 about (5.47%, 3.85%, 1.76%) for (A = 1, 0.75, 0.5) respectively, when compared with (A = 0.25). The enhancement of the average Nusselt number at (q = 6000) W/m2 is about (7.28%, 4.55%, 2.27%) for (A = 1, 0.75, 0.5) respectively, compared with (A = 0.25).

The present work deals with thermal aspect and entropy of ternary hybrid nanofluid (Graphene, Al2O3, and MWCNT as nanoparticles and water as base fluid) inside an inclined domain considering heat generation/absorption. The domain possesses triangle-shaped corrugated walls with variable height and a semi-circular heater located on its bottom wall. Finite element method (FEM) is employed to acquire a well-defined solution of the non-dimensional governing equations along with the boundary conditions. The influence of the pertinent parameters along with their ranges (0.2≤b≤0.3), (105≤Ra≤106), (0o≤η≤90o), (−1≤Hs≤1) has been studied. Some striking outcomes of the present investigation are that streamlines and entropy generation (EnT) peter out while local Nusselt number (Nuloc) and average Bejan number (Beave) ameliorate with rise in dimensionless height of the corrugated wall (b). The absolute maximum values of vertical and horizontal velocities of ternary hybrid nanofluid enhance by 96.47 % and 29.5 %, respectively, when inclination angle (η) increases from 45o to 90o. It is visualized that Nusselt number is maximum subject to heat sink while it attains a minimum value in response to heat source. Because of triangle shaped corrugated walls and ternary hybrid nanofluid, the present problem contributes superior cooling in thermal systems featured with such complex geometry in industries.

This numerical analysis investigates the behavior of magnetohydrodynamics (MHD) thermosolutal convection in a hybrid nanofluid made up of multi-wall carbon nanotube (MWCNT)-Fe3O4 and water along a vertical wavy surface with wall heat and mass flux conditions. The mathematical model is developed using the conservation equations of mass, momentum, energy, and energy. The governing equations are converted into a non-dimensional form using the appropriate transformation, and the implicit finite difference technique is used to solve them. The effects of various parameters, such as the Schmidt number (Sc), nanoparticles volume fraction (ϕ), wavy amplitude (a), magnetic parameter (M), buoyancy ratio (Br), on the velocity, temperature, concentration distribution (Φ), streamlines, isotherms, local skin friction coefficient (Cf), local Nusselt (Nu) number, local Sherwood number (Sh) are investigated. Results show that higher amplitude and the addition of hybrid nanofluids volume fraction slow down the heat and mass transport rate, as indicated by declining local Nusselt and Sherwood numbers. However, enhancing the buoyancy ratio increases the fluid flow’s skin friction, heat, and mass transport. The velocity, temperature, concentration distribution, skin friction, and convective heat transport within the wavy surface is weakened by the addition of the magnetic parameter M.

Natural convection in a porous, rectangular hollow full of saturated air was investigated numerically in the current study. The bottom side was warmed with a continuous heat flux, the right side's temperature was kept at (Tc), the left wall was opened to the surroundings, and the top side was insulated. The pertinent filled-out research parameters in the current experiment were four heat flux values (1500, 3000, 4500, and 6000 W/m²) and three Darcy’s numbers (Da1=4.025×10-10, Da2=4.025×10-8, Da3=4.025×10-6). COMSOL Multiphysics 5.5a, using finite elements and a relying Brinkman-Darcy extended model, was employed to resolve government equations. Local thermal balance simulation was assumed in this solution. Energy transfer and momentum were studied using isotherms and streamlines. The findings appeared that the flow velocity improved with the rising Darcy number, especially in the case of Da3, as well as increasing the average Nusselt number about 110 % and 45% for Da3 and Da2 compared with Da1. Additionally, the increase in heat flux will increase the heat transfer, especially with Da3.

This work develops a model for natural convection in annuli with internal heat sources based on Graph Convolution Network (GCN), achieving rapid prediction by directly establishing the mapping relationship between the geometric features and the temperature field. The GCN learns node features and connections between nodes in data structures. Compared with traditional machine learning networks, GCN exhibits greater advantages in handling complex geometric shapes and unstructured nodes. In this study, numerous data samples were constructed with various geometric features, e.g., varying sizes, positions, and quantities of internal heat sources. The results indicate that a fully trained GCN was capable to adaptively predict temperature field distributions with arbitrary heat source sizes, positions, and quantities. The mean prediction errors of GCN for the temperature field are around 0.17 %, 0.32 %, and 0.85 %, for the single, double, and triple heat sources cases, respectively. Furthermore, the GCN prediction performance was also compared with surrogate models by the convolutional, and fully connected neural networks (CNN and FNN), which shows an improvement of 88.1 % and 84.8 %, respectively. Therefore, compared with numerical results and other surrogate models, the proposed model presents superior geometric adaptability, high prediction accuracy and a remarkable enhancement in computational efficiency (three orders of magnitude).

The Lattice Boltzmann Method (LBM) is one of the suggested numerical approaches that has been shown to accurately estimate the increase in heat transfer caused by nanofluids. Several approaches to the prediction of the characteristics of nanofluids are investigated, and it is shown to what degree the classical models are accurate representations of the experimental data. The first thing that was done in this study was to explain the thermophysical parameters of the Ethylene Glycol (EG)-iron nanofluid that was employed. The effect of the Rayleigh number, the volume fraction of nanoparticles (φ), and the cavity angle (θ) on the isotherms and the average Nusselt number (Nuavg) are investigated. Finally, the effect of the adiabatic fin on the flow is investigated, and it is demonstrated in which scenario the adiabatic vane will be the most effective. The findings demonstrate that raising the Rayleigh number to 105 and 106 causes the heat to be transferred under the adiabatic fin. This finding suggests that the buoyancy force has a stronger influence on the heat transfer process when it is carried out close to the source of the cold. In general, if the Rayleigh number is increased, the rate of heat transfer in the fluid will rise as well. The Nu avg is increased by 44 % when the Ra number is increased from 103 to 105, and it is increased by 118 % when the Ra number is increased from 105 to 106. The chances of heat entering the cold source are reduced when the adiabatic fin is longer and situated lower. There is a wider cold zone within the hollow when Lf = 80 and Hf = 20, indicating that less heat is entering the cold source.

A computational analysis due to the thermal performance of combined effects of solar radiation and variable density around a laminar vertical jet is carried out. For this purpose, a mathematical model in terms of nonlinear coupled partial differential equations, keeping in view the coordinate system of the proposed problem, is established. Further, to get insight to the physical significance of the proposed problem, numerical data is obtained. For this purpose, the finite difference method is used to integrate the primitive form of the partial differential equations. The coefficient matrices of the unknown variables involved in the model are solved by using the Gaussian elimination technique with the help of Fortran-Laher 90. The obtained numerical results for different parameters involved in the flow model, that is density parameter m, Prandtl number Pr, radiation parameter Rd, and fluid's absorption parameter D, are highlighted graphically by using Techplot-360. The primary findings show that enhancing values of the density variation parameter m leads to an increase in the velocity profile and a decrease in the thermal profile. On the other hand, for increasing values of Rd, the boundary layer profiles decline. Also, the heat transfer rate prominently declines with the rise in numeric value of m, Rd, and D. The main novelty of the current work is to improve the thermal performance of natural convection heat transfer with the inclusion of solar energy and variable density.

Decreasing the freezing time of the cold storage heat exchanger was an effective way to reduce the risk of cold chain breakage and the fluctuation of cold chain temperature. A validated unsteady mathematical model of the cold storage heat exchanger was established to analyze the transient evolution of temperature, velocity, ice distribution, and heat transfer coefficient for different diameters of heat transfer tubes and coolant temperatures. The results showed that there were four stages of temperature in the cold storage heat exchanger, namely the primary cooling stage, the freezing stage, the secondary cooling stage, and the constant temperature stage. The ice fraction distribution and the heat transfer coefficient were inextricably linked to the water's natural convection. The average heat transfer coefficient decreased with decreasing coolant temperature and increasing heat transfer tube diameters. The freezing time decreased with the coolant temperature and the diameter of the heat transfer tubes decreasing. The tendency of the inhomogeneity of ice distribution first increased with the ice fraction up to 0.75 and then decreased with the ice fraction over 0.75. The inhomogeneity decreased with the coolant temperature increasing when the diameter of the heat transfer tubes was greater than 2 mm.

Our study focuses on numerically investigating natural convection within a three-dimensional trapezoidal cavity featuring a corrugated hot bottom wall, with a particular emphasis on enhancing heat exchange using a water-based hybrid nanofluid. Employing a steady-state regime assumption, the study considers laminar and incompressible three-dimensional flow. The Darcy-Forchheimer model is incorporated to account for inertial advection effects within the porous layer. Predictions of the thermal and hydrodynamic behaviors of the system are achieved by solving dimensionless equations utilizing the Galerkin Finite Element Method (GFEM). Notably, a range of influential parameters, including the volume fraction of nanoparticles (φ), Darcy number (Da) spanning from 10−5 to 10−2, Hartman number (Ha) across the range of 0–100, φ within the range of 0–0.08, porosity (ε) ranging from 0.2 to 0.9, and Rayleigh numbers (Ra) varying from 103 to 106 was explored. The investigation also evaluates the geometrical impact of the enclosure by considering undulation numbers (N) of the warm bottom ranging from 1 to 4. Our results provide novel quantitative insights. Specifically, we observe an inverse relationship between undulation number (N), Hartman number (Ha), and porosity (ε) with large Rayleigh (Ra) flows, significantly influencing effective heat transfer. Notably, this influence diminishes at lower Ra flows. At the highest Ra, we find that increasing Da, ε, and φ enhances the Nusselt number (Nuavg) by 26 %, 17 %, and 23.5 %, respectively. Conversely, increasing Ha and N reduces Nuavg by 13 % and 40 %, respectively. These findings highlight the nuanced interplay of parameters and offer valuable quantitative data for optimizing heat transfer processes in similar systems.

In order to study the influence of the nature of the mining airspace on the natural convection heat transfer in the unventilated working face, we establish a numerical model of natural convection in a composite cavity containing porous media by CFD method. The effects of different Rayleigh numbers (Ra), porous media thicknesses, and porosities ε on the natural convection temperature and velocity fields and heat dissipation from the heat source were comparatively analyzed. The results show that the larger Ra is, the stronger the natural convection flow and heat transfer in the composite cavity; when the thickness of porous media increases from 0.2 to 0.75, the average Nussel number (Nuave) of the high-temperature wall surface decreases by 40.38%, the Nuave of the interfaces decreases by 6.15%, the maximum dimensionless velocity of the boundary layer in the porous region decreases from 10,771 to 3775, and the dimensionless horizontal line in the center of cavity decreases by 0.05, indicating that the natural convection temperature and velocity fields and heat dissipation from the heat source are affected by different Ra. Temperature decreased by 0.05, demonstrating that the increase in the thickness of porous media will weaken the strength of the fluid side of the flow and heat transfer; porosity increased from 0.2 to 0.8, and the interfacial Nuave increased by 5.61%, demonstrating that the larger porosity makes the porous media area flow and heat transfer enhancement, but has a certain weakening effect on the flow and heat transfer in the fluid domain. The results of the study can be used for the natural convection flow and heat transfer in the unventilated coal mining face, and provide some reference value for avoiding the thermal damage of mechanical equipment.

This article investigates the effect of Rayleigh numbers, Hartmann numbers, and magnetic fields on nanofluid flow behavior and heat transfer. The flow behavior has been analyzed based on the contours and values of the flow function and heat transfer based on the temperature distribution contours and local and average Nusselt number values. Since the effects of the magnetic field are an important parameter in many technical and engineering applications such as cooling of nuclear reactors, extraction of geothermal energy, and induction casting of metals, in this study, its effect on aluminum oxide nanoparticle, Al2O3, and water, H2O, has been analyzed. The governing equations of nanofluid flow, continuity, momentum, and energy equations have been solved using the Galerkin finite element method and coded and simulated using FlexPDE software. The results obtained for both octagonal cavities containing horizontal and vertical Cassini oval barriers with specific boundary conditions show that with the Rayleigh number and nanoparticle volume fraction being constant, the value of the maximum stream function decreases with the increase of the Hartmann number, and when the Hartmann number and nanoparticle volume fraction is constant, with increasing Rayleigh number, its value increases significantly.

This paper is dedicated to a numerical study of natural convection through a cavity with finned surface where its base temperature is variable with linear profile. An approach based on modelling of internal fluid flow around a finned surface in laminar and at steady state conditions is used. Thermal and hydrodynamic aspects of the fluid flow were analyzed through the numerical resolution of equations of fluid dynamics. For this purpose, we have developed a computer code (in Fortran 90) based on the finite volume method. The studied model consists of a rectangular cavity where vertical walls are thermally insulated, the horizontal ones are maintained at different temperatures: cold and constant temperature on the upper wall and hot temperature with linear profile on the lower wall. The Rayleigh number used is in the range of 103 to 106 and the Prandtl number is fixed at 0.71. The plotted results are related to temperature distribution, streamlines, velocity fields as well as the mean Nusselt number.

This study aims to determine the effect of the geometry shape of the copper material heat sink fins on the surface temperature distribution of the heat sink. The material used in this research is pure copper, the shape of the heat sink fins is made rippled with the addition of the number of fins 5, 6, and 7 and the input temperature is varied from 40 C to 80 C with airflow variations from 0.2 m/s to 1 m/s. The first step is to create a heat sink design with Autodesk Inventor. Then the plan is simulated with Autodesk CFD to solve the continuity, momentum, turbulence, and energy equations. Based on the method that has been carried out, it is found that the addition of variations in the number of fins affects the decrease in surface temperature. The highest temperature drop on fin 5 ripples is 24.1 C. The heat energy transfer rate increased by 0.4657 W. The convection heat transfer coefficient increased by 3.47 W/m²C. Nusselt number shows an increase of 271. Fin performance has increased efficiency by 63.4 %, and effectiveness by 1.61. The results of this study are expected to provide practical alternatives that can be widely adopted on a heatsink plate that is very promising for future thermal developments.

Metal hydride (MH) systems can be used for storage in stationary facilities of hydrogen with a high volume density at temperatures and pressures close to ambient ones. Recently, the possibility of using passive heating/cooling systems or regenerative heat exchangers has been studied to improve the energy efficiency of MH systems for hydrogen storage without the need for forced circulation of a heating/cooling fluid. Natural convection of air may be used to passively remove/add heat as required for proper operation of a MH reactor. Under these conditions, the MH reactor can operate at a constant ambient air temperature and be driven by a difference in pressure between the source and the consumer of hydrogen. Since operation of MH systems with natural convective heating/cooling has not been systematically investigated as yet, a tubular MH reactor based on this principle is examined in this paper. Two-thirds of the internal volume of ø25.4 × 1 mm tube is occupied by a composition of LaNi5 and aluminium foam (one linear metre contains 1.1 kg of LaNi5 with a hydrogen capacity of 153 NL H2). Annular fins are used to increase heat transfer to air. Detailed and simplified mathematical models of the systems of this class are proposed and validated. It is shown that acceptable hydrogen charging/discharging rates in such systems are achieved with proper selection of fining characteristics. Charging from a hydrogen source at a pressure of 10 atm and an ambient air temperature of 10 to 30 °C takes 15 min. A reactor with a length of 1 m can desorb almost all stored hydrogen at a minimum outlet pressure of 0.45 bar to feed 30–300 W fuel cells.

This paper examined the role of suction/injection on time-dependent electromagnetohydrodynamics (EMHD) natural (free) convection flow in a vertical microchannel with electroosmotic effect. With the aid of Laplace transformation method, the governing energy and momentum equations are converted from partial differential equation (PDE) into ordinary differential equation (ODE) to obtain fluid temperature and velocity in Laplace domain. The semi-analytical solutions of the velocity profile and temperature distribution have been derived using the Riemann sum approximation. After which a MATLAB program was written to study the effects of Prandlt number Pr, Hartmann number Ha, electric field strength on x and z directions (Ex and Sz) and Grashof number Gr in fluid velocity, temperature, skin-friction and mass flow rate in terms of line graphs. Result shows the role of suction/injection parameter alters the temperature distribution and velocity profile, so also how effective the governing parameters contribute to the flow formation. .