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In industrial applications, annular fins are commonly made of homogeneous materials such as aluminum, struggling to provide uniform temperature distribution along their length. Recognizing the potential of Functionally Graded Materials (FGMs) to enhance thermal performance by combining two different materials with a gradual variation, this study proposes their use as fin materials to achieve optimum performance. The study consists of three major components: (1) numerical analyses to determine the optimum volume composition of FG fins, (2) the fabrication process of aluminum and FG fins utilizing powder metallurgy and the hot-pressing technique, and (3) experiments to evaluate the thermal performance of FG and aluminum fin arrays attached to a horizontal cylinder of 250 mm length under natural convection. Heat ranging from 25 W to 150 W is applied to the cylinder during these experiments. Based on the experiments, the thermal performances of fins are evaluated in terms of net free convection heat transfer rate, the Nusselt number, and fin effectiveness. Overall, experimental results demonstrate that the net convection heat transfer rate depends on fin spacing, material, and the base-to-ambient temperature difference. Specifically, FG fin arrays enhance the net heat transfer rate by 59%, while aluminum fin arrays increase it by 33% compared to finless cylinders. Moreover, FG fins outperform aluminum fin arrays by 40% in convective heat transfer coefficient h. Due to being the first experimental study, this study sets itself apart. [ABSTRACT FROM AUTHOR]

• 3D ice storage spheres with different metal foam methods and proportions are designed. • Solidification performance of PCMs augmented by partially metal foam is studied. • The competitive mechanism of natural convection and heat conduction is analyzed. • Considering the economic benefit, the optimal filling radius 6/13 is obtained. The advancement of ice-ball thermal energy storage systems is limited by the poor thermal conductivity of phase change materials(PCM). This paper presents a numerical investigation into enhancing heat transfer in ice balls by partially filling them with metal foam. Dynamic temperature changes, solid phase fraction, and cold storage capacity are analyzed for various filling radius ratios (2/13, 4/13, 6/13, 8/13, and 13/13). We quantitatively assess the specific impact of metal foam filling on heat transfer by calculating changes in the comprehensive thermal conductivity coefficient. Our findings reveal that the comprehensive thermal conductivity coefficient increases nonlinearly with the growing metal foam filling radius ratio, indicating that full filling may not the most optimal configuration. Furthermore, the energy storage capacity per unit time, per unit weight and per unit cost of the ice ball filled with metal foam under different radius ratios was evaluated by comprehensive evaluation criteria, and the optimal filling radius ratio was determined to be 6/13. Contrary to prior findings, this research highlights the efficacy of partial filling strategies, offering valuable insights for optimizing ice ball performance in thermal energy storage applications. [ABSTRACT FROM AUTHOR]

Free convective heat transfer created from two aligned cylinders immersed inside a vented air duct is experimentally investigated. The experiments include the measurements of cylinders temperature and the air temperature inside the enclosure under steady, turbulent, and incompressible flow properties by using steady‐state heat equations. The studied parameters include Rayleigh number (105≤Ra≤3.4×106 ${10}^{5}\le {Ra}\le {3.4\times 10}^{6}$), opening sizes at lower and upper enclosure surfaces (0.146≤O≤1 $0.146\le O\le 1$), and space size between cylinders (0.35≤S≤0.532 $0.35\le S\le 0.532$) with the constant ratio of enclosure width to cylinder diameter equal to 6. The findings displayed that the average air temperature inside the enclosure for the low values of S and O is low, and it rises as S is raised. The behaviors of Nu differ with changing Ra values. An interaction between hot cylinder and cold cylinder inside the enclosure is observed that depends on O and S values, and hence, they have a large impact on fluid temperature. The data indicated that Nu ${Nu}$ rises with the Ra ${Ra}$ for all S $S$ and O $O$ values. The value of Nu ${Nu}$ for each cylinder depends on the values of S $S$ and O $O$. The maximum Nu ${Nu}$ value has been obtained when O=0.439 $O=0.439$ and S=0.35 $S=0.35$ with maximum enhancement between 30% and 50% depending on Ra values as compared with O=0.146 $O=0.146$ and S=0.523 $S=0.523$, whereas the minimum average Nu ${Nu}$ has been indicated when O=0.146 $O=0.146$ and S=0.35 $S=0.35$. The profiles of Nu ${Nu}$ reveal that O $O$, Ra ${Ra}$, and S $S$ have a considerable influence on heat transfer. [ABSTRACT FROM AUTHOR]

Analysis of various accident scenarios is vital for the safety assessment of nuclear fuel storage facilities. The accidents in the storage vault due to loss of cooling are generally considered highly uncertain since the accident progression is slow (in comparison to reactors) and allows time for remedial activities to the operator. In the present work, numerical simulations of different accident scenarios have been carried out for a short duration to understand the situation better. Thermal aspects of accident conditions such as failure of the suction blower, drying of cooling water at the chiller, and combined effect of both accidents were investigated. The airflow inside the ventilated enclosures due to the failure of the blower and the rise in inlet air temperature is analyzed numerically. The temperature distributions inside the vault and the rise in temperature of the sub-assemblies and magazines have been studied. The key mechanisms of heat transfer, which take part in nuclear fuel storage vault for post-accident conditions, were identified. The study will be helpful to classify various accident conditions based on their thermal implications and the model developed can be used to design passive cooling systems. [ABSTRACT FROM AUTHOR]

This research aims to enhance convective thermal transport in an inverted T-shaped porous enclosure filled with a water-based hybrid nanofluid, incorporating a circular cylinder at different vertical locations (Case C1-no cylinder, Case C1-cylinder at (0.5, 0.25), Case C2-cylinder at (0.5, 0.5), Case C3-cylinder at (0.5, 0.75)). The numerical investigation employs the penalty finite element technique to simulate the Darcy–Brinkmann–Forchheimer-based mathematical model. Moreover, the complete results of streamlines, isotherms, mean Nusselt number (Num), and thermal enhancement percentage ( En % ) are analyzed at the broad range of flow parameters, including Rayleigh number ( Ra = ( 10 3 − 10 6 ) ), Darcy number ( Da = ( 10 − 5 − 10 − 2 ) ), and porosity value ( ϵ = (0.1 − 0.9) ). Initial comparative investigations of different configurations (C0–C3) at selected Ra values reveal that case C1 exhibits significant potential for enhancing convective heat transport phenomena. Consequently, only case C1 physical domain has been explicitly analyzed for convective heat and fluid flow characteristics at the selected range of flow parameters. Further, it is analyzed that the increasing range of Ra, Da, and ϵ enhances the convective heat and fluid flow phenomena. Furthermore, the comparative study of Num and En % for case C1 against the simple case C0 reveals substantial improvements as Ra, Da, and ϵ increase. The En % for Da and Ra reaches up to 97%, while a maximum of 25% improvement is observed with varying values of ϵ. These findings highlight the promising opportunities to optimize convective thermal transport in the investigated system, mainly through adopting case C1. [ABSTRACT FROM AUTHOR]

The MHD finite element analysis naturally convective flow across an exponentially accelerating plate with viscous dissipation is investigated numerically. In this process dimensional partial differential equations are changed to dimensional less form. The Galerkin finite element method is emerged to solve non-dimensional partial differential equations. Obtained results are effectively depicted through the utilization of graphs, allowing for a comprehensive understanding of the impact that different physical parameters on primary velocity, transverse velocity, temperature, and concentration profiles. The study effectively differentiated between the present and prior findings, ultimately demonstrating a strong consensus of excellent agreement between the results. The key findings of this study are: The primary velocity increases on growing the values of Thermal Grashof number, Solutal Grashof number, Eckert number, and Dufour number and decreases on climb up the values of Magnetic parameter, Prandtl number, Schmidt number, and Hall parameter. The secondary velocity increases on raising the values of Thermal Grashof number and Solutal Grashof number and diminishes on enhancing the value of Hall parameter. The temperature increases on increasing the values Eckert number and Dufour number and decreases on improving the value of Prandtl number. The concentration decreases on increasing the value of Schmidt number. [ABSTRACT FROM AUTHOR]

AbstractThe innovative design of the AP1000 power plant has various layers of passive safety systems aiming to enhance reactor safety during normal and transient conditions. The passive containment cooling system (PCCS) is a safety-related system capable of removing heat from the steel containment vessel (SCV) to the atmosphere and preventing the containment from exceeding the design pressure and temperature following a postulated design-basis accident. The PCCS heat removal mechanisms include condensation on the internal SCV surface, heat conduction, natural convection, evaporation of water film, and radiative heat transfer. In two basic postulated scenarios, the reactor decay heat can ultimately be removed from the SCV only by air natural convection. The first scenario occurs 72 h following a large-break loss-of-coolant accident (LBLOCA) when the passive containment cooling water storage tank becomes unavailable. The second scenario occurs following a postulated loss of shutdown decay heat removal event. Hence, investigating the thermal-hydraulic behavior of the containment under transient conditions is essential to ensure its safety and integrity. In this study, a simplified three-dimensional model using ANSYS FLUENT is developed to investigate the cooling capability of air natural convection outside the SCV during a LBLOCA event. Because of the lack of experimental data, code-to-code validation was performed using the actual results of AP1000 alongside other research findings. The results show good agreement with available data, which can be used for future research. [ABSTRACT FROM AUTHOR]

This paper explores natural convection heat removal performance in accordance with the variation of the baffle size and position in a skewed cavity. In this skewed cavity, the top and bottom walls are considered to be adiabatic. The inclined left wall is deliberated at a sinusoidal cool temperature, and the other wall is treated at a hot temperature. The baffle is connected to the hot temperature wall. The dimensionless governing equations will be solved by the Galerkin weighted residual (GWR) technique of the finite element method. The influence of Rayleigh number (103≤Ra≤106), baffle sizes (L=0.20, 0.35, and 0.50), and baffle positions (B=0.25, 0.50, and 0.75) in a fluid with Pr=1.41 were investigated in this research. The comparisons between the outcome of this work and previously published work in a literature review by Elatar et al.8 have been produced to examine the reliability and consistency of the data. The results of the simulation are represented by streamlines, isotherms, local and mean Nusselt numbers, mean fluid temperature, and baffle effectiveness. The results demonstrate that as the Rayleigh number grows, the heat removal performance rate continues to develop in this study. Also, the results revealed that the heat transport rate decreased when gradually raising the baffle length. Baffles can significantly improve the mixing of fluid inside the enclosure, which can mean reductions in reaction times and operating costs, along with increases in heat exchange and efficiency. [ABSTRACT FROM AUTHOR]

This paper reports the numerical study of natural convection in a square enclosure filled with CNT-water nanofluid and exposed to a uniform external magnetic field. Heating is ensured by twothin fins. Using the control volume method, the effects of the fins position, their length and spacing as well as the solid volume fraction, the Rayleigh number and the Hartmann number on the thermal performance of the cavity were examined. The results obtained show that the heat transfer rate increases with the Rayleigh number, solid volume fraction and fins length; but decreases with Hartmann numbers. A comparison is also carried out between the results obtained from the Maxwell and Xue models. The results prove that the mean Nusselt number is higher based on the Xue model. [ABSTRACT FROM AUTHOR]

This work is devoted to the study of the influence of height and the number of heaters on the nature of the flow and isotherms in a three-dimensional cube filled with Al2O3/H2O nanofluid with a volume fraction of 1% at Pr = 7.06586. Numerical simulation was performed on the base of the numerical finite volume method and the coupled scheme. It simulated the natural convection with nanofluid. Verification of the mathematical model was performed by comparing the results with the results of other authors. Having obtained satisfactory results, numerical results of U and V velocities, temperature contours and calculations of average Nusselt numbers for six cases of the main problems were obtained. [ABSTRACT FROM AUTHOR]

This paper introduces an innovative approach for modelling unsteady incompressible natural convection flow over an inclined oscillating plate with an inclined magnetic effect that employs the Atangana-Baleanu time-fractional derivative (having a non-singular and non-local kernel) and the Mittag-Leffler function. The fractional model, which includes Fourier and Fick's equations, investigates memory effects and is solved using the Laplace transform. The Mittag-Leffler function captures power-law relaxation dynamics, which improves our understanding of thermal and fluid behaviour. Graphical examination shows the influence of fractional and physically involved parameters, leading to the conclusion that concentration, temperature, and velocity profiles initially grow and then decrease asymptotically with time. Moreover, the study emphasizes the impact of effective Prandtl and Schmidt numbers on temperature, concentration, and velocity levels in the fluid. [ABSTRACT FROM AUTHOR]

This computational study looks at the dynamics of free convection in a differentially heated square chamber occupied by ionized propane and saturated permeable partition. The modified Navier–Stokes equations and temperature equations are used to describe fluid and porous domain flow and heat transport phenomena. To solve these equations, the Galerkin finite element technique is used. Parametric adjustments are made for various heat source and sink lengths, Rayleigh number, Hartman number, and Darcy number. The results are quantitatively described in terms of the mean Nusselt number along the heated wall as the Rayleigh number increases (104 ≤ Ra ≤ 106). Streamlines and isotherms are used to visualize qualitative insights on these parametric changes. A comparative study is also performed without the porous media. Conclusive data demonstrate that using a permeable partition over a solid partition improves the mean Nusselt value by 26.28% at Ra = 104 and to a highest value of 56.5% at Ra = 106. Notably, this work presents a sensitivity analysis based on response surface methodology, demonstrating subtle connections between magnetohydrodynamics, Rayleigh number, and porous material effects. These findings provide important perspectives for improving thermal control and energy efficiency in advanced magnetohydrodynamic systems. [ABSTRACT FROM AUTHOR]

AbstractThis article presents a numerical investigation and analysis of the cooling effectiveness of thermomagnetic transient natural convection in a long channel, equipped with four cylindrical heat-generating blocks. A non-Newtonian power-law ferrofluid was employed for the present investigation to achieve optimum cooling. The governing equations are the continuity equation, the momentum equation and the energy equation. The finite volume method was used to solve the resulting algebraic system. From an energy-saving point of view, this configuration can provide a good approximation for selecting effective physical and geometrical parameters to design a reliable thermal system. For this purpose, the study was carried out for various geometric and thermophysical parameters. Different values of thermal conductivity, power law index, Rayleigh number, Hartmann number and ferrofluid volume fraction, were considered. The results are illustrated in the form of streamlines, isotherms, average Nusselt and a spatio-temporal characterization of the mean ferrofluid velocity. From the results presented, we can conclude that the choice of non-Newtonian, pseudoplastic ferrofluid with a low thermal conductivity ratio subjected to a uniform magnetic field proves to be a crucial solution for efficient and stable cooling of heat-generating cylindrical blocks, which will have to be close to the cold walls of the channel. [ABSTRACT FROM AUTHOR]

Buoyancy-driven flow and heat transfer characteristics of the solid/hollow cylinders with concave shapes were numerically analyzed in a turbulent regime. The effects of Ra , L / D , and D th / D on heat dissipation have been studied in the range of 1010 to 1012, 2 to 10, and 0.2 to 0.9, respectively. It has been found that the Nu ¯ increases with Ra for solid/hollow cylinders. For a hollow cylinder, Nu ¯ in is always higher than Nu ¯ out except at D th / D = 0.2. The Nu ¯ in of a hollow cylinder increases up to D th / D = 0.6, irrespective of the Ra , and L / D ratios thereafter reduced drastically has been observed. Whereas, at a low D th / D , and high Ra (i.e., Ra ≥ 1011), Nu ¯ out of a hollow cylinder significantly decreases with D th / D . However, it shows a marginal decrement at a high length-to-diameter ratio. For solid and hollow cylinders, the thermo-fluid dynamics have been delineated through the temperature contours, streamline patterns, and vortex generation at the inner as well as outer wall of the hollow cylinder. This numerical study also proposes a correlation for the Nu ¯ of the solid/hollow cylinders to have an accuracy ± 6 % of relevant parameters. [ABSTRACT FROM AUTHOR]

AbstractThis investigation aims to scrutinize the flow and heat transfer characteristics of a hybrid nanofluid composed of Ag-MgO within an eccentric annular space, where the inner circular wall is held at a constant elevated temperature and the outer circular wall is uniformly cooled. Natural convection in such eccentric annular enclosures, with thermal radiation and the effects of heat generation/absorption taken into consideration, plays a vital role in various engineering applications, including solar collectors, nuclear reactors, thermal storage systems, and heat exchangers. The resolution of the fundamental governing equations was executed employing the Gauss-Seidel approach, with the inclusion of a sub-relaxation process, all within the framework of the finite volume method. The impact of the Rayleigh number, radiation number, volume fraction as well as heat generation/absorption coefficient on thermal transfer, flow, and temperature distributions were investigated. It was observed that for low Rayleigh numbers, radiation influences enhance flow stability and improve the conductive heat transfer mode. Conversely, at high Rayleigh numbers, radiation intensifies convective heat exchange. The growth of the Rayleigh number diminishes the impact of heat generation and reinforces the radiation heat transfer process, while heat absorption exhibits the opposite effect. From Nr = 1 onwards, the average Nusselt number values are no longer influenced by an increase in nanoparticle volumetric fraction, and they are solely linked to the radiation number. [ABSTRACT FROM AUTHOR]

This study focuses on how the porous medium affects the plume generated due to line heat source when an aligned magnetic field is present. For this study, the momentum equation of the flow model is modified for porous medium by including the porosity term. A mathematical model is developed as coupled partial differential equations in order to study the flow problem. Later, a numerical solution is found for the system of coupled partial differential equations that are transmuted in to ordinary differential equations. For this purpose, the numerical characteristics of the problem are derived employing a shooting approach in combination with the built-in MATLAB tool bvp4c. The graphical illustrations of missing and specified boundary conditions demonstrate the impacts of porosity parameter Ω, magnetic force parameter S, Prandtl number Pr and magnetic Prandtl number γ accompanied by a discussion of their corresponding physical implications. The novelty of this developed problem is proclaimed with justification by its emphasis on the principal characteristics of heat and fluid flow affected predominantly by the presence of a porous medium. The thorough examination of the porosity parameter Ω for missing conditions depicts that the temperature and velocity profiles enhance while current density drops for the increasing values of the porosity parameter Ω. Whereas, for specified conditions, the skin friction and magnetic flux enhance but heat transfer rate declines with increment in Ω. [ABSTRACT FROM AUTHOR]

AbstractIn this study, the two-dimensional, steady-state, and incompressible flow and thermal behaviors of a water-based nanoencapsulated phase-change material (NE-PCM) nanofluid within a closed chamber were investigated, considering the impact of buoyancy. A novel approach was introduced by implementing linearly varying temperature conditions along all chamber walls. The effective dynamic viscosity and thermal conductivity correlations, derived experimentally, were used to model the governing equations. These equations were then rendered dimensionless through suitable transformations and solved using the Galerkin finite-element method. Results showed that the phase change region’s width increased with higher Rayleigh numbers, scaled phase change bonds, NE-PCM volume fractions, and fusion temperatures between 0.1 and 0.5, but decreased with fusion temperatures between 0.6 and 0.9. The highest Nusselt number occurred along the bottom wall for a fusion temperature range of 0.4–0.5. For optimal thermal performance, a square chamber with linearly varying temperature walls and a fusion temperature of 0.5 is recommended. [ABSTRACT FROM AUTHOR]

The work numerically investigated laminar natural convection heat transfer from the single sphere with a constant heat flux surface in air over the wide range of Grashof number ( 10 ≤ G r ≤ 10 7 ). The more efficient and precise numerical method based on Bejan et al. was employed here, the accuracy of which has been confirmed through validation against a single sphere case. The heat transfer characteristics were systemically analyzed in terms of isothermal contours and streamlines around the sphere, dimensionless temperature and velocity profiles. Additionally, local Nusselt number as well as local pressure and friction drag coefficients were studied with different Grashof number. In comparison to the sphere with uniform heat flux surface, the heat transfer from the isothermal sphere was found to be enhanced attributable to a more robust buoyancy force and a steeper temperature gradient. Moreover, the average Nusselt number for the sphere with a constant heat flux between 60.4 and 98.6% of the isothermal sphere's value, this range being contingent upon the specific Grashof number. What's more, the proposed correlation addresses a notable void in the predictive understanding of heat transfer from the sphere with uniform heat flux, which is scenario prevalent in various engineering applications, particularly for the cooling of electrical and nuclear systems, and offer values for academic research. [ABSTRACT FROM AUTHOR]

In this paper, the entropy generation of natural convection Jeffrey fluid flow through an inclined porous channel is investigated by taking into account the impact of angled magnetic field, Soret parameter, thermal radiation, and Hall current. On the basis of simplified assumptions, the governing equations are transformed into dimensionless equations by using suitable transformations, and the spectral quasi-linearization method (SQLM) is used for the numerical solution. Graphs are utilized to address the effects of new thermophysical parameters. The calculations reveal that increasing the Soret parameter, inclination angle, Hall parameter, magnetic parameter, and Jeffrey fluid parameter induces an increase in entropy generation. Conversely, it decreases as the radiation parameter and channel angle of inclination increase. [ABSTRACT FROM AUTHOR]

Poor mass transport to or from vertical gas-evolving electrodes can adversely impact energy efficiency and product purity in the production of hydrogen, chlorine, and various metals. A proper description that combines natural convection with micromixing of growing, coalescing, and departing bubbles is presently lacking. This work develops a simple, physically sound analytical model that includes the influence of bubble size, flow regime, and bubble surface coverage. By comprehensively reviewing mass transfer measurements from the water electrolysis literature, we observe that the surface coverage of oxygen bubbles increases much more strongly with increasing current density than an often-used square root scaling predicts. Strong differences are observed in the degree of micromixing of hydrogen and oxygen bubbles in alkaline and acidic electrolytes. These varied results can all be explained by a combination of electrocapillarity, and coalescence induced by either a high surface coverage or Marangoni flows. [Display omitted] • A simple formula for adding micromixing and natural convection is derived. • A single micromixing parameter between 0 and 5 describes all literature data. • Micromixing is strongest for oxygen in alkaline and hydrogen in acidic electrolytes. • Marangoni forces are attractive in this case, causing coalescence and larger bubbles. • Bubble coverage increases with the square/square root of current for oxygen/hydrogen. [ABSTRACT FROM AUTHOR]

AbstractUtilizing response surface methodology, this work gives a thorough numerical evaluation of ferrofluid’s conjugate magnetohydrodynamic (MHD) natural convective flow within a porous annular chamber. The system is made up of an inner solid cylinder that generates heat and is subjected to an external magnetic field, which causes Joule heating effects. To explain the conservation equations for momentum and energy, the research uses a finite element method and systematically changes important parameters. By adjusting these factors, we may study how changes affect thermal performance, flow patterns, and the Nusselt number. The findings show a complex interplay between magnetohydrodynamics, Joule heating, and the effects of porous media, offering important clues for improving thermal management and energy efficiency in state-of-the-art MHD systems. Incorporating a response surface methodology (RSM) is a significant innovation in this work. Results reveal that the increment in the thermal conductivity of the solid wall upsurges the fluid velocity and the rate of convective heat transfer. There is a significant difference in the value of the local Nusselt number as the values of the thermal conductivity of the solid wall increase. Adding nanoparticles to the dusty fluid makes the flow stronger, but also improves heat transmission significantly. [ABSTRACT FROM AUTHOR]

Abstract\nHIGHLIGHTSThe single-phase approach, in which nanofluids are treated as pure fluids assuming that the solid and liquid phases are in local thermal and hydrodynamic equilibrium, has been used with good results to simulate forced convection flows. Conversely, its extension to natural convection has revealed to be more problematic, as the obtained numerical results are substantially different from the experimental data, mainly due to the effects of the slip motion occurring between the suspended nanoparticles and the base liquid, whose consequent nonuniform distribution of the solid phase concentration can significantly affect both heat and momentum transfer. In the present article, a two-phase model based on a double-diffusive approach is proposed to study the natural convection flows of water-based metal oxide nanofluids inside cylindrical and rectangular enclosures heated and cooled at their opposite sides with the scope to reproduce a number of experimental data-sets available in the literature. Given the assumption of local thermal equilibrium between nanoparticles and host liquid, and considering the Brownian and thermophoretic diffusion as responsible for causing significant relative velocity between the solid and liquid phases, the governing equations are solved by a control-volume numerical method implemented using the open-source platform OpenFOAM (Open Field Operation and Manipulation). It has been found that the nanoparticle diffusion gives the major contribution to the decrease of the heat transfer rate red usually observed experimentally in natural convection flows of nanofluids inside differentially-heated enclosures. This means that a two-phase model, in conjunction with proper correlations for the evaluation of the nanofluid effective physical properties, must be necessarily enforced to obtain reliable results for many engineering applications.A two-phase model has been tested and validated reproducing different sets of experimental data available in the literature for natural convection flows of nanofluids inside differentially-heated enclosures.A description of the nanoparticle diffusion is given with the scope to point out the two-phase behavior of nanofluids.Optimal values of both the nanoparticle volume fraction and average nanofluid temperature are found to be imposed to enhance the heat transfer rate.A two-phase model has been tested and validated reproducing different sets of experimental data available in the literature for natural convection flows of nanofluids inside differentially-heated enclosures.A description of the nanoparticle diffusion is given with the scope to point out the two-phase behavior of nanofluids.Optimal values of both the nanoparticle volume fraction and average nanofluid temperature are found to be imposed to enhance the heat transfer rate. [ABSTRACT FROM AUTHOR]

The integrity of a pressure vessel (PRV) is affected by the decay heat of the molten pool in the lower head, so it is very important to study the natural convection heat transmission in the lower head. Scholars from all over the world have carried out a lot of experimental studies and calculations to determine the convection mechanism and heat transmission characteristics of the molten pool. Most of them were based on the empirical formula of convective heat transmission on the wall of a hemispherical molten pool based on two-dimensional slice experiments and simulation calculations. In this study, FLUENT 2021R1 software was used to simulate the three-dimensional convective heat transmission process of the hemispherical molten pool, and the temperature, velocity and wall heat transmission coefficients of the flow field were analyzed. The results were in good agreement with experimental data from UCLA (University of California, Los Angeles). Through research on the heat transmission of the lower head, the results showed that in the region where the wall angle was θ between approximately 72 and 90 degrees, heat transmission coefficients had larger fluctuations, and a more reasonable empirical relation was proposed. Comparing between the simulation results of CFD and the two-dimensional empirical formula, it was found that the latter one was smaller under the same θ angle condition. Finally, the convection phenomena of different external temperatures were simulated, and the main factors affecting the flow field by temperature were analyzed. [ABSTRACT FROM AUTHOR]

The present work investigates the combined effect of varying gravity and heat flux direction with respect to gravity on the melting dynamics of Phase Change Material. Similar conditions are relevant to applications in space, at different space infrastructures, such as orbiting satellites, as well as various extraterrestrial surface assets, landers, and rovers. The numerical simulations are performed to study the melting dynamics of a paraffin-based phase change material with Prandtl number Pr ≈ 71 and Stefan number Ste ≈ 0.33 inside a differentially heated square enclosure. The mathematical model employs a control volume-based enthalpy porosity approach to simulate the melting process inside enclosure. The direction of the incoming heat flux relative to the gravity vector is defined in terms of an orientation angle, which is varying circularly with a step of 45°, whereas the gravity level is ranging from the terrestrial surface value g to 0.2 g to analyze the melting process over a wide range of Rayleigh number 100 ≤ Ra ≤ 107. The study provides a detailed insight into the attributes of heat transfer, flow dynamics, and energy storage, along with a quantitative analysis of the transition between various melting regimes and temporal fluctuations in the performance parameters. The findings demonstrate that the mutual orientation between the directions of incoming heat flux and gravity, as well as the value of the latter, significantly affect features of the convective motion in the liquid phase, as well as the entire thermally driven heat transfer within the domain. In particular, for the oppositely directed gravity and heat flux, the melted fluid closely resembles Rayleigh-Bénard convection with the presence of multicellular flow structures, while at other orientation angles, except for a co-directed gravity and heat flux case, a circular convective motion of the melted fluid takes place. The results of numerical simulations reveal declining melting rates as the mutual orientation of gravity and heat flux changes from opposite to co-directed and vice versa. The low gravity conditions delay the onset of convection-driven melting, reducing the melting rate significantly. • Effect of heat flux direction and varied gravity on PCM melting dynamics is studied. • Paraffin-based PCM (Pr ≈ 71, Ste ≈ 0.33) filled inside square enclosure is investigated. • Study considers orientation angle range (0 ° to 315 °) and gravity level (0.2g to g). • A detailed analysis of thermal, flow, and energy storage attributes is presented. • Results reveal details useful for designing thermal control for space applications. [ABSTRACT FROM AUTHOR]

The key attention of this work is on the impact of suction/injection on the free convective flow of a viscous fluid passing between two infinite, parallel, vertical and porous plates with non‐Fourier effects. The analysis focuses on a porous channel with boundaries featuring a steady–periodic temperature regime. The governing equations, representing velocity(momentum) and temperature(energy) fields, are well‐stated in dimensional form. Employing a separation technique, the momentum and energy equations are separated into steady and periodic components. On solving, the resulting second‐order ordinary differential equations derived, revealed the expressions for velocity and temperature in dimensionless form. However, the study investigates the influence of various flow parameters used in this work, including suction/injection (s) $(s)$, heat source/sink (H) $(H)$, Strouhal number (St) $({St})$, Prandtl number (Pr) $(Pr)$, and dimensionless relaxation time (γ) $(\gamma)$, on the velocity and temperature distributions. Also not left out is the rate of heat transfer on the flow performance and the skin‐friction coefficient on the plates. The findings are visualized using MATLAB‐generated graphs. An interesting observation found during the course of investigation in that the introduction of suction/injection enhances the flow velocity and fluid temperature within the channel, and they are both seen as declining functions of the Strouhal number, which measures the frequency of periodic heating on the plates. Furthermore, when the suction/injection parameter(s) is being relaxed, this study demonstrates a strong agreement with the findings of Ajibade and Mukhtar. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate fluid‐structure interaction (FSI) within conjugate natural convection. An oscillating fin, featuring a heat source placed at different locations, is examined using the Arbitrary Lagrangian–Eulerian formulation. The Galerkin finite element method is utilized to solve nonlinear dimensionless equations. Verification of grid independence is conducted and the model undergoes validation. Simulation outcomes for three fin positions (left, center, and right) and three heat source locations (bottom, middle, and top) are presented, illustrating streamlines, isotherms, and the average Nusselt number. The governing equations and boundary conditions are addressed using the finite element method. Temperature profiles in four scenarios are analyzed, along with horizontal velocities at different levels (0, D/2, D from the bottom wall). Dimensionless time (10−5 ≤ t ≤ 3), Ra = 106, Kr = 10, E = 1011 are used as parameters. The impact of the heat source position on vibratory motion is evaluated through Nusselt number variation, affecting heat exchange in different cases. The results show that heat transfer is minimal for a source location at the center of the fin (c). These findings also offer insights into FSI applications in economics and industry, guiding practical design considerations. Additionally, coupling the vibratory motion of the heat source with the flexible oscillating fin at the same frequency enhances understanding of the system. [ABSTRACT FROM AUTHOR]

Natural convection in enclosures is a phenomenon significantly affected by the geometry of the physical domain, however, comparing different formats is challenging because features such as the characteristic length varies with the geometry. This study proposes examining natural convection in 3D convex regular polyhedra, also known as Platonic solids, using the number of faces as a parameter. Differentially heated enclosures were analyzed to investigate the effect of shape on fluid flow and energy distribution. By comparing the different solids, it was found that the dodecahedron and the icosahedron exhibit very similar behaviors and tend to be the more efficient shapes for improving convection heat transfer. In contrast, the tetrahedron is much less efficient due to its structure, which does not favor the presence of a single convective cell. In general, increasing the number of faces, which leads to a more spherical shape and eliminates sharp corners, tends to enhance fluid recirculation and increase the average Nusselt number. For example, the icosahedron showed a 12% increase in the Nusselt number compared to the commonly studied hexahedron for Ra = 106. On the other hand, the tetrahedron demonstrated a 50% decrease in the Nusselt number relative to the cube, making it the least efficient shape among those evaluated. [ABSTRACT FROM AUTHOR]

The present article deals with the influence of the local thermal nonequilibrium (LTNE) state on natural convection in an enclosure filled with nanofluid-saturated porous medium. The flow is induced due to the maintenance of constant heat flux on the vertical walls and insulation of horizontal walls. The Darcy model has been adopted to describe the flow governing equations. These equations are solved numerically by using the alternate direction implicit method and analytically by applying parallel flow assumptions valid for large aspect ratios. Boundary layer analysis is performed to report the boundary layer thickness (δ x ∼ 2 1 / 2 (k nf / k f) 1 / 10 (R a T) − 1 / 5) as well as the heat transfer rate of nanofluid ( N u nf ∼ (k nf / k f) − 1 / 5 R a T 2 / 5). The combined effect of LTNE state parameters (interface heat transfer coefficient (H), porosity scaled thermal conductivity ratio (γ)) and volume fraction of nanoparticle ( ϕ ) is addressed on the flow dynamics and heat transfer mechanism. Rigorous analysis, indicates that the average heat transfer rate of nanofluid and solid porous matrix are increasing function of H and γ, however, the role of γ is accelerated for a relatively high value of H. For increasing the value of γ from 1 to 10, the enhancement in the heat transfer rate of nanofluid is reported to be up to 27% at 10% volume fraction of nanoparticles. The average Nusselt number of nanofluid, as well as solid phase, are reduced when the value of ϕ is increased under the LTNE circumstances. Furthermore, the flow structure is controlled by unicellular structure with rotating anticlockwise direction in the entire study. For the very small value of H the temperature distribution in the solid porous matrix is mainly by conduction mode and distribution is linear, however, for a relatively high value of H the distribution in the same is controlled by both conduction as well as convection, and it will be more pronounced for the higher value of γ. [ABSTRACT FROM AUTHOR]

The investigation of entropic variations in the thermal transport mechanism produced by buoyantly driven temperature gradients has attracted significant attention because of excellent physical significance. Therefore, the prime consent to manipulate the current investigation is to explore the impact of change in the aspect ratio of the trapezoidal cavity in the optimization of the entropy phenomenon. After attaining motivation from its practical essence different entropies including thermal, viscous, and local are estimated. Additionally, global quantities such as average Bejan and Nusselt numbers calculated along with total entropy are measured against flow concerning parameters (aspect ratio (AR), Rayleigh number (Ra) and irreversibility ratio (ϕ )). Numerical experiments are performed by implementing a finite element approach using open-source software renowned as COMSOL Multiphysics. Before the accomplishment of the outcomes, confirmation of the numerical technique is assured by establishing grid sensitivity testing. Comparison of results between present and previous studies is also demonstrated. A wide range of involved sundry parameters varying from 10 - 4 ≤ ϕ ≤ 10 - 2 , 10 2 ≤ Ra ≤ 10 5 and 0.25 ≤ AR ≤ 0.75 are accounted. It is concluded that by escalating the aspect ratio from 0.50 to 0.75, the magnitude of the local entropy enhances from 3370 to 3424. It is revealed that the highest value of viscous entropy that is, 45, is achieved at Ra = 105 and by keeping the aspect ratio of enclosure equal to 0.75, whereas, the thermal entropy approaches 2 for the same situation of parameters. The magnitude of the average Bejan number reaches unity at AR = 0.5 and Ra = 105, whereas for low and high aspect ratios it depicts a magnitude less than 1 for the same Rayleigh number. [ABSTRACT FROM AUTHOR]

Alumina nanoparticles have been accumulating attention in recent years because of their unique physical characteristics and broad range of engineering and industrial applications. Scientists are paying close attention to analyzing the flow and heat transfer features of alumina-based nanofluids filled within a cavity due to their wide range of applications, such as heat exchangers, fuel cells, room ventilation, and cooling electronic systems. Motivated by the applications, the current study numerically analyzes the natural convective flow and heat transfer features of A l 2 O 3 - H 2 O and A l 2 O 3 / C 2 H 6 O 2 - H 2 O nanofluids in a rectangular porous cavity under the presence of thermal radiation and heat generation/absorption by using the non-Fourier heat flux model. The system of equations is numerically solved by utilizing the Marker and Cell technique. The comparative fluid flow and heat transfer features are performed by using different shapes of A l 2 O 3 nanoparticles (spherical, brick, cylindrical, platelet, and blade) dispersed in two different kinds of base fluids ( H 2 O and C 2 H 6 O 2 - H 2 O ). The flow domain is filled with an isotropic porous medium. Several pertinent parameters are considered in this investigation, such as the Darcy number, Rayleigh number, heat source/sink, radiation parameter, and nanoparticle volume fractions, which are analyzed in terms of streamlines, isotherms, and local and average Nusselt numbers. According to the findings, the average Nusselt number increases by augmenting the nanoparticle volume concentration and the heat source/sink parameters, while it decreases by improving the radiation influence. Thermal performance within the cavity is affected by varying radiation influences. By increasing the spherical-shaped A l 2 O 3 nanoparticle concentration from 0 to 5% in H 2 O and C 2 H 6 O 2 - H 2 O base fluids, the average heat transfer rate is augmented by 27.37% and 27.62%, respectively. The blade-shaped nanoparticles produce a better heat transfer rate than other-shaped nanoparticles. Finally, it was concluded that A l 2 O 3 - H 2 O nanofluid delivers better fluid flow and temperature distribution than A l 2 O 3 / C 2 H 6 O 2 - H 2 O nanofluid. [ABSTRACT FROM AUTHOR]

In this manuscript, an attempt is made to investigate the natural convection process in hybrid nanofluid (Al2O3–Cu/water) contained in an isosceles triangular porous conduit with heated side/congruent walls by considering the performance of various thermal conditions. The bottom side of the enclosure is kept isothermally cooled, whereas uniformly and non-uniformly thermal boundary conditions are applied on congruent/side walls. Thermophysical properties of water and nanoparticles are used to model the problem with the help of continuity, momentum, and energy equations. Appropriate combination of variables is used to make the transport equations dimensionless. The obtained partial differential equations (PDEs) have been solved numerically by using Galerkin-based finite element method (GFEM). Trends of Darcy number Da (10 - 5 ≤ Da ≤ 10 - 3) , Rayleigh number Ra (10 3 ≤ Ra ≤ 10 6) , and solid volume fractions ϕ 1 , ϕ 2 (0.00 ≤ ϕ 1 , ϕ 2 ≤ 0.06) on streamlines, local Nusselt number, and isotherms have been presented in pictorial form. Bifurcation analysis is also described to make the contribution more versatile. Finally, results obtained from present simulation are matched for limited version (i.e., ϕ 1 = ϕ 2 = 0.0 ) in order to ensure the accuracy of the GFEM and modeling procedure of the mathematical model. [ABSTRACT FROM AUTHOR]

This work focuses on the study of natural convection in a flat porous microchannel with asymmetric heating. The novelty of the work lies in the fact that for the first time the method of discrete symmetries was used to analyze the complete system of Navier–Stokes and energy equations in a two-dimensional approximation. Analytical solutions for velocity and temperature profiles have been derived based on symmetry analysis, taking into account boundary conditions such as slip and temperature jump at the channel walls. The effect of Grashof, Knudsen, Darcy, and Prandtl numbers on the flow characteristics in the microchannel and heat transfer coefficients was elucidated. At high Grashof numbers, an ascending flow near the hot wall and a descending flow near the cold wall arise. Increasing the Knudsen number leads to an increase in the velocity, temperature jump at the walls and a decrease in heat transfer coefficients. As the Darcy number increases, velocities amplify in both ascending and descending flows. The temperature jump at the hot wall grows up, while it remains unchanged at the cold wall. In the same time, the heat transfer coefficient at the hot wall decreases. [ABSTRACT FROM AUTHOR]

AbstractThe design of enclosures is crucial in thermal engineering applications and technologies, encompassing areas such as electronics, heat transfer devices, power reactors, heating systems, solar panels, and nuclear power plants. Thermal efficiency in microchannels is optimized and improved by using triangular enclosures with varying aspect ratios. Specifically, the purpose of these triangular enclosures with cool cylinders is to reduce energy loss in nanoscale thermal sinks and thermal exchange devices. The current study aims to explore the thermal radiation effects on magnetohydrodynamic MHD Casson fluid flow within a wavy triangular cavity that includes an embedded cold inverted triangle. The inner inverted triangle is kept at a lower temperature, while the wavy bottom wall of the outer triangular cavity acts as an isothermal heat source at a higher temperature. The numerical solution for this mathematical model is obtained using the open-source finite element software COMSOL. In this study, the wavy triangular enclosure is analyzed for key parameters such as Casson parameter β, Hartmann number Ha, Rayleigh number Ra, numbers of undulation N, radiation Rd and inclination γ. The study presents the local distribution of streamlines, velocity profiles, isothermals, and entropy production, along with the Nuavg. The results reveal the rate of heat transport and total entropy production raise with the increasing number of undulations N and the Casson parameter β, while they decrease with increasing Hartmann number Ha. The number Nuavg rises with the increasing radiation parameter Rd and Rayleigh number Ra. The maximum stream function is observed at an inclination angle of 60°. [ABSTRACT FROM AUTHOR]

Natural convection in a square porous cavity with a partial magnetic field is investigated in this work. The magnetic field enters a part of the left wall horizontally. The horizontal walls of the cavity are thermally insulated. The wave vertical wall on the right side is at a low temperature, while the left wall is at a high temperature. The Brinkman-Forchheimer-extended Darcy equation of motion is utilized in the construction of the fluid flow model for the porous media. The Finite Element Method (FEM) was used to solve the problem's governing equations, and the current study was validated by comparing it to earlier research. On streamlines, isotherms, and Nusselt numbers, changes in the partial magnetic field length, Hartmann number, Rayleigh number, Darcy number, and number of wall waves have been examined. This paper will show that the magnetic field negatively impacts heat transmission. This suggests that the magnetic field can control heat transfer and fluid movement. Additionally, it was shown that heat transfer improved when the number of wall waves increased. [ABSTRACT FROM AUTHOR]

The allocation of energy through buoyancy, along with the generation of irreversibility, has been examined in a porous, air-filled, quadrantal-shaped enclosure at different inclinations. The contour has a continuous heat source at the lowest wall, while the left and curved walls remain at colder temperature. The results are presented using vortex patterns and non-dimensional temperature distributions, Nusselt number along the hot leading lowermost wall, and the generation of entropy inside the cavity. Adjusting the Rayleigh number (Ra), Darcy number (Da), and inclination angle (φ ) to values between 103 and 106, 10−4 to 10−1, and 15–60°, respectively, allows for the explanations to be prepared. The analysis has revealed that altering these parameters causes noteworthy alterations in the flow dynamics and entropy generation. The prime design for thermal applications is initiated to be a contour with an inclination of 30° attributable to restrained magnitudes of average heat allocation and less establishment of irreversibility. [ABSTRACT FROM AUTHOR]

Hybrid nanofluids have shown promise as advanced novel heat transfer fluids by effective utilization of properties of its sub-constituents. This study explores the synergistic effect of silver-doped titania nanoparticles in ethylene glycol, focusing on thermal conductivity and viscosity improvements. A two-step synthesis method is employed to create the hybrid nanofluids, followed by comprehensive measurements of their thermal properties. Results demonstrate an impressive 18.9% increase in effective thermal conductivity compared to the base fluid. Furthermore, the viscosity of the hybrid nanofluids shows a concentration-dependent increase and a temperature-dependent decrease. Buoyancy-driven convective heat transfer experiments are conducted to evaluate the heat transfer performance of the hybrid nanofluids. A cubic cavity filled with the nanofluids allows for the assessment of Nusselt number and heat transfer coefficient values. Significant enhancements are observed compared to the base fluid, with maximum increases of approximately 16.8% for the Nusselt number and 26.87% for the heat transfer coefficient. However, these enhancements reach their peak at an optimal concentration before diminishing. Correlations are developed to predict the Nusselt number for natural convection within the cavity based on the experimental data. Additionally, an artificial neural network (ANN) model is employed for prediction and is found to outperform the correlations in accurately estimating the Nusselt number. These findings contribute to the understanding and advancement of hybrid nanofluids for efficient heat transfer applications. [ABSTRACT FROM AUTHOR]

The objective of this study is to create a simulation of a cavity containing high-heat rack server computing equipment. The aim is to explore various numbers of openings (two and four apertures) and rack layouts (shelf spacing of 30 and 60 mm and shelf height spacing of 35 and 17 mm) in order to minimize indoor temperature and achieve optimal heat dissipation. The numerical results are evaluated against the experimental data through the utilization of the least squares approach to determine unknown physical quantities. Next, a turbulence model that is appropriate is chosen using root mean square error analysis. The zero-equation model was selected for scenarios involving four ventilation openings, whereas the RNG k-ε model was good for scenarios involving two openings. Then, the resulting temperature and flow fields are assessed thereafter. Results revealed that expanding the distance between two racks has a minimal impact on the temperature of the rack surface and the convection coefficients. Thus, this research suggested using a shelf arrangement with a 30 mm shelf spacing to mitigate the occurrence of localized eddy currents at the upper part of the cavity, potentially diminishing the efficiency of ventilation. The presence of openings at the bottom of the cavity led to a 42% improvement in convection heat transfer coefficients, compared to cases without such apertures. Hence, it was recommended to incorporate apertures at the lower part of the cavity to facilitate the intake of cold air. Furthermore, reducing the shelf height spacing resulted in an increase in temperature of around 2 K on the surface of the rack. Nevertheless, it was deemed suitable for optimizing space utilization. [ABSTRACT FROM AUTHOR]

AbstractIn the present investigation, a numerical investigation of the flow and heat transfer characteristics inside an L-shaped enclosure with a flexible fin and an elastic wall has been carried out using the finite element method. The Fluid-Structure Interaction model is used to capture the interaction between the fluid and the solid structure. The free end of the flexible fin is exposed to sinusoidal vertical force and the upper wall of the enclosure is considered to be elastic and a sinusoidal force is applied on this elastic wall. The obtained results showed that the fluid flow through the enclosure is entirely influenced by the periodic oscillation of the flexible fin and elastic wall. Besides, the Nusselt number over the horizontal and vertical hot walls of the L-shaped enclosure is strongly affected by the amplitude and frequency of the applied sinusoidal forces on the flexible fin and elastic wall. The heat transfer over the vertical hot wall is enhanced considerably with an increase in the amplitude and frequency of the applied sinusoidal forces. Moreover, the Nusselt number over the hot vertical wall is increased with the decrease of the elastic modulus value of the elastic wall. The results also show that the combination of the flexible fin and elastic wall has contributed to the extra enhancement of the Nusselt number over the hot vertical wall of the L-shaped enclosure. [ABSTRACT FROM AUTHOR]

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

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]

The concept behind this article is an extensive analysis of the most recent findings about free convection thermal flow in an enclosure or cavity, as well as the methods employed to enhance heat transfer (HT). There are different heat transfer enhancers such as (a) nanofluids, (b) porous media, (c) large particle suspensions, (d) phase-change devices, (e) flexible seals, (g) fins and microfins, and (h) ultra high thermal conductivity composite materials. The majority of heat transfer enhancement techniques that use porous media, fins, and nanofluids are reviewed in the literature. In this review, both experiments and theoretical studies on different cavities are highlighted through investigating the subsequent parameters: impacts of the configuration of the cavities, effect of the type of nanoparticles, significance of cavities in nanofluids, effects of the cavities' tilt angle, wave amplitude, the magnetic field's (MF) influence in cavities, and cooler and heater impacts. Through a review of the literature, it was found that the use of nanofluid in all forms of cavities increases its thermal performance. The most used cavity is square, which has many applications. The results obtained from previous studies can be used to improve the design and heat refinement of the geometry applied in diverse energy systems. Additionally, as the Hartmann number rises, there is a rising tendency observed in the average Nusselt number. Furthermore, as the concentration of nanofluid particles and Rayleigh numbers rise, so does the rate of heat transfer. The heat transfer within the cavity is improved by the hybrid nanoparticles. The amount of the augmentation would, however, decrease as the concentration of nanoparticles increased. The lowest volume fraction of nanoparticles, Ø = 0.2 vol.%, showed the greatest increase. Also, the inner wave affects the flow pattern when the wave amplitude rises but the flow strength stays constant. The most important findings showed that the heterogeneous porous medium transfers heat more effectively than the homogeneous porous medium in different enclosures. [ABSTRACT FROM AUTHOR]

The creation of heat is inextricably tied to the functioning of vehicle headlights, which presents a substantial problem for dependable and long-term operations. The concomitant rise in heat generation has grown to be a significant problem as the luminous effectiveness of light-emitting diode (LED) headlights continues to improve. Heat sinks have been commonly employed to remove surplus heat from the LED chips and other parts of the lighting system to solve this problem. This research investigates the impact of different heat sink fin architectures on the thermal performance of LED headlights by subjecting numerical models to varying LED powers ranging from 6 to 12 W across four fin models. Outcomes reveal that the diverse thermal characteristics resulting from variations in the number of fins in the heat sink lead to enhanced thermal dissipation of up to 73.6%. Furthermore, these heat sinks are subjected to vibrational testing under the ISO 16750 standard, assessing vibrational characteristics in three distinct scenarios: Passenger Car Engine, Passenger Car Sprung Masses, and Passenger Car Unsprung Masses. Through analysis, it reveals that the vibrational characteristics of the heat sinks align with established standards, reinforcing their reliability and suitability for automotive applications. [ABSTRACT FROM AUTHOR]

The experiments with a LiFePO4 battery pack operating at room temperature and with various charge and discharge rates to analyze its durability are described in this study. At a temperature of 23°C with natural convection, the thermal performance of a cylindrical (LFP) battery is experimentally studied. In this study, the battery is fully charged. After reaching 14.6 V, the battery is charged at a current of 4.8 A for 10 min to allow for stabilization. The battery is then depleted at 4.8 A until its voltage hits 10.5 V, followed by an additional 10‐min resting time. The processes reached their highest and lowest temperatures, respectively, were 29°C and 22°C. The battery is charged for a total of 46.877 Ampere‐hours (Ah) during the course of the 10‐h operation at a constant current of 4.8 A. Similar to this, a 10‐h discharge operation is carried out with a constant current of 4.8 A, yielding a discharge of 47.207 Ah. The processes reached their highest and lowest temperatures, respectively, were 36°C and 24°C. Another possibility is to charge the battery at a steady 24 A until the voltage reaches 14.6 V, then let it rest for 10 min, a further 10‐min rest period is added after it is discharged at 24 A until its voltage hits 10.5 V. After 5 h of charging at 24 A, the capacity is 46.958 Ah, and after 5 h and 47.51 min of discharging at 24 A, the capacity is 47 Ah. The processes reached their highest and lowest temperatures, respectively, were 49°C and 33°C. [ABSTRACT FROM AUTHOR]

The buoyant airflow along a vertical isothermal wall, under conditions close to transitional, is studied. The schlieren technique and miniature thermocouples are employed for qualitative (flow unsteadiness) and quantitative (heat transfer coefficient and local air temperature) observations. For the smooth surface, the phenomena are found to be sensitive to the enclosure configuration surrounding the plate. Roughening the heated surface with staggered rib segments of proper dimensions leads to increased heat transfer, ascribed to the onset of unsteadiness close to the segments’ edges, together with a better redistribution of the flow thanks to a favorable hydrodynamic interaction between fluid and protrusions. [ABSTRACT FROM AUTHOR]

AbstractIn this article, the influence of the local thermal non-equilibrium (LTNE) state on free convection in a square cavity filled with fluid-saturated porous medium is investigated numerically. The steady-state flow is induced due to sinusoidal heat distributed on the side walls of the cavity and insulated of the horizontal walls. The coupled flow governing equations are solved numerically by using the finite volume method (FVM) consisting of the SIMPLER (Semi-Implicit Method for Pressure Linked Equation Revised) Algorithm. The numerical simulations of temperature and stream-function contours are carried out for the non-Darcy model. The developed code is validated with existing numerical and present computed results for the case of a square enclosure associated with non-uniform heat source. Then, the present numerical results are analyzed over a range of physical parameters, like periodicity parameter (N≥1), interface heat transfer coefficient (10−2≤H≤102), porosity scaled thermal conductivity ratio (10−2≤γ≤102), with a fixed Rayleigh number (Ra=106), Darcy number (Da=10−4), Prandtl number (Pr = 0.71), and porosity (ε=0.8). To study the impacts of these key parameters on the fluid flow behavior and isotherm patterns of fluid as well as solid phase in the porous-square enclosure. From present numerical experiments that the structure of flow is controlled by multicellular structure with rotating clockwise and anticlockwise directions in the entire results. The flow dynamics are highly affected by the periodicity parameter (N) under LTNE circumstances. The characteristics of the local Nusselt number have the point of inflection and the maximum magnitude of it increases with N. The significant effect of H is found on the heat transfer rate of fluid phase but it is negligible on the heat transfer rate of solid phase. However, the influence of γ is found reverse in nature on the heat transfer rate of fluid as well as solid phase when as compared to the effect of H. [ABSTRACT FROM AUTHOR]

The phenomenon of natural convection in rectangular cavities of different aspect ratios is considered. The water is considered a base fluid associated with copper nanoparticles. The flow is induced only due to buoyancy force that arises by heating the right side of the cavity. The left side is set cold while the other walls are assumed to be at zero flux temperature. The governing equations of the present communication are simulated by the finite difference method. This study explores the impacts of Rayleigh number (Ra), Prandtl number (Pr), nanoparticles volume fraction (ϕ), and aspect ratio (A). Different combinations of these parameters are investigated. Compared to other parameters, Rayleigh number (10 4 < Ra < 1 0 8 ), aspect ratio (1 ≤ A ≤ 3), and volume fraction of nanoparticles (0. 0 1 ≤ ϕ ≤ 0. 1), A is found more effective on the flow field and isotherms. Regression curves are determined for the mean Nusselt number (Nuavg) as a function of Ra for different cases. It is found that Nuavg more precisely fits the exponential function. Also, it is found that Nuavg decreases as the values of A increase. But, ϕ , shows the opposite behavior. It is noticed that when the A of the cavity grows, so does the mean heat transfer Nu. With rising Ra, the local heat transfer NuL decreases and the heat transfer rises. In the case of the square cavity, the regression coefficient for Nuavg is found to be 0.3673 and 0.2514 for an exponential function. [ABSTRACT FROM AUTHOR]

The transition from steady-state flow to periodic oscillatory flow for the natural convection by Hopf bifurcation is investigated in a three-dimensional (3D) cavity. The spectral collocation method (SCM) in combination with the artificial compressibility method (ACM), which is developed by ourselves as a numerical method SCM-ACM with high accuracy, is employed to solve the governing equations directly instead of linear stability analysis method that is commonly used for the research on flow instability. The results show that the amplitude decays exponentially with time and the decay rate is linear with the Grashof number (Gr). The critical Grashof number for steady-oscillatory transition is obtained as Gr cr = 3.423 × 106. The dimensionless angular frequency ω cr = 0.24 is also determined by Fourier analysis. In this work, we also examine the heat-momentum interactions within the boundary layers, visualize the periodic oscillations of temperature and velocity amplitudes, and analyze the origin of instability from multiple angles. The results show that large oscillations of velocity and temperature are observed near the isothermal walls. The oscillation is enhanced by the increase of thermal boundary layer thickness and flow velocity at both ends of isothermal walls. The maximum velocity and temperature amplitudes appear at the lower left and upper right corners of the mid-plane (Z = 0.5), where are the origin of instability, and the spanwise walls are almost independent of oscillations. The oscillatory flow of natural convection in three-dimensional cavity originates from the continuously increasing buoyancy force, and its transition occurs by Hopf bifurcation. Moreover, the temperature amplitude exhibits a wavy distribution on the mid-plane (X = 0.5) and strongly depends on the depth Z. These results provide benchmark data for future numerical studies and engineering application. • The high-precision SCM-ACM developed by authors is employed to directly solve the governing equations. • The critical Grashof number for the steady-oscillatory transition of natural convection is predicted. • The evolution pattern of velocity, amplitude and frequency is analyzed. [ABSTRACT FROM AUTHOR]

The use of nanofluids for convectional heat transfer has become a spry area of research in recent years with the aim of improving heat transfer efficiency. Hybrid nanofluids have attracted significant attention and are advancing research and industrial applications since they involve employing more than one type of nanoparticle(s) in a base fluid. They enhance heat transfer by combining the chemical and physical properties of several nanoparticles concurrently and providing the properties in a homogeneous state. However, few experimental studies have focused on natural convective heat transfer using hybrid nanofluids. In this study, the natural convection of alumina – multiwalled carbon nanotube/water hybrid nanofluids formulated using a two-step method at a percentage weight ratio of 10:90 Al2O3: MWCNT at various nanoparticles volume concentrations of 0.00, 0.05, 0.10, 0.15, and 0.20 vol% was studied inside a square cavity (AR = 1) with two vertical walls which are isothermal, aimed at the Rayleigh number (Ra) range of 2.81 × 108 to 8.58 × 108. The average Nusselt number (Nuav), heat transfer coefficient (hav), heat transfer (Qav), and Rayleigh number (Ra) were considered at varying temperature gradients of 20°C – 50°C. Al2O3-MWCNT/water hybrid nanofluid with 0.10 vol% volume concentration was discovered to have the maximum value for hav,Qav, and Nuav. However, it was also observed that a further increase in the hybrid nanoparticles' volume concentration led to their deterioration at various temperature gradients. The maximum enhancements of 44%, 49%, and 42% were noted for hav,Qav, and Nuav, respectively, at ∆T = 50 °C, in comparison with the base fluid. Al2O3-MWCNT/water hybrid nanofluids application in a square cavity demonstrated enhanced natural convection. This present study concluded that hybrid nanofluids as heat transfer fluid significantly improved heat transfer performance compared to the base fluid. [ABSTRACT FROM AUTHOR]

The application of a new sedimentation similarity parameter, containing an electrochemical number, is considered. Generalization of the results of experimental studies in various media under conditions of natural convection was carried out. New dimensionless equations of heat exchange have been derived. A new method has been developed for calculating the emission of heat during local formation of deposits on the heat exchange surface. [ABSTRACT FROM AUTHOR]