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This study investigates fluid flow and natural convection heat transfer in a parallelogram-shaped cavity with a porous medium under non-uniform temperature condition. The bottom wall is heated with a non-uniform temperature, the side walls are cooled, and the upper wall is adiabatic. The governing equations, along with corresponding boundary conditions, are formulated in dimensionless stream function and vorticity using the extended Darcy model for the porous medium. The equations are solved by employing the finite difference method. The study presents outcomes for isotherms, streamlines, and Nusselt numbers across range of parameters, including the Rayleigh number (10 4 ≤ R a ≤ 10 8), Darcy number (10 − 1 ≤ D a ≤ 10 − 6), Prandtl numbers (P r = 0.71 , 1 , 7.1), fluid porosity (ϵ = 0.8) , and inclination angles (30 ∘ ≤ ϕ ≤ 90 ∘), about flow and heat transfer characteristics. The results indicate that an increase in Ra , Pr , and ϕ , along with a decrease in Da , leads to an enhancement in the strength of vortexes. It is observed that for constant R a ⁎ = R a D a , Rate of heat transfer increases with an increase in Ra and a decrease in Da. The maximum value observed is 10.15. Also rate of Heat transfer increases with the increase in angle and maximum rate of heat transfer is observed at ϕ = 90 ∘. [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]

This paper proposes a new correlation to evaluate the heat transfer coefficient between a vertical wall containing a phase change material (PCM) and air in a square enclosure. This correlation was determined in order to simulate the transient process during PCM discharge and its effect on the heat transfer inside the cavity without using complex CFD models. A 2D CFD model based on the resolution of Navier–Stokes and energy equations inside the air and the PCM was previously validated. It was used to generate numerical data in order to build the proposed heat transfer correlation. The new correlation is Nu = 0.186 · Ra 0.28 θ 0.271 Ste 0.022 valid for: 10 5 ≤ Ra ≤ 4.310 7 , 0.05 ≤ θ ≤ 1 and 0.05 ≤ ste ≤ 0.6 . The accuracy of the proposed correlation versus the correlations established without phase change is analysed through a simplified model considering only the PCM layer and replacing the air cavity by a flux condition with an appropriate heat transfer coefficient. The relative error being lower than 1%, the new correlation shows a better agreement with the CFD results than existing correlations. [ABSTRACT FROM AUTHOR]

Ground‐coupled heat exchangers (GCHE) have received significant attention over several decades as a result of increasing the world's energy demand and the need for reducing fossil fuels consumption. Prior studies have demonstrated the effectiveness of utilizing GCHE with refrigeration and heating systems. However, optimizing the performance of GCHE coupled with chillers for heat rejection, especially in extreme hot‐humid climates (where cooling towers are not very effective) is lacking in the literature. In this work, a ground borehole fitted with a coaxial‐tubes heat exchanger (BHE) is numerically simulated. Based on a wide range of data collected for the soil of Dubai, its real in situ thermophysical properties are characterized. The soil's upper layer thickness is relatively small and dry that operates in conduction mode, while the lower one is water‐saturated that works in coupled conduction‐advection mode. The study aims at optimizing the parameters advancing heat rejection into ground considering the actual properties of the soil of Dubai. The results indicate that the more feasible high‐density polyethylene pipes can perform as good as the steel ones. Also, a great finding based on the presented novel design is that insulating the inner pipe can increase the temperature duty by 55%. The proposed design of BHE is relatively inexpensive, more feasible and efficient, which is achieved for the first time based on a deep analysis of Dubai climate and soil. This makes the technology ready to be implemented for industrial applications in Dubai and other regions having a similar climate and soil nature. [ABSTRACT FROM AUTHOR]

Analyzing fluid dynamics and heat transfer holds significant importance in the design and enhancement of engineering systems. The current investigation utilizes the finite element method to explore natural convection and heat transfer intricacies within a novel cavity containing an inner circular cylinder under steady and laminar flow conditions. The principal aim of this study is to assess the impact of Rayleigh number (Ra), Bejan number (Be), and the presence of adiabatic, hot, and cold cylinders on heat transfer, entropy generation, and fluid flow. The range of Ra considered in this investigation spans from 103 to 106, while the Prandtl number for the air is fixed at 0.71. The findings illustrate that the presence of a cylinder leads to higher Be as Ra increase, compared to scenarios where no cylinder is present. This observation suggests that buoyancy forces dominate in the absence of a cylinder, resulting in significantly enhanced convective heat transfer efficiency. However, the presence of a heated cylinder within the tooth‐shaped cavity exerts a substantial influence on the overall thermal performance of the system. Notably, the average Nusselt Number (Nu) experiences a remarkable increase of 41.97% under the influence of a heated cylinder, when compared to situations where a cold cylinder is present. This elevated average Nu signifies improved heat transfer characteristics, ultimately resulting in an overall improvement in the thermal system's efficiency. [ABSTRACT FROM AUTHOR]

In this numerical study, a two-dimensional double-diffusive convective flow of a hybrid nanofluid in an inverted T-shaped porous media has been thoroughly investigated. The governing equations comprise the generalized Darcy-Forchheimer-Brinkman-based model along with the heat and mass transport equations. Furthermore, a penalty finite element approach has been employed for numerical simulation of the evolved mathematical model at the broad range of pertinent influencing parameters, including buoyancy ratio (N), Lewis number (Le), Darcy number (Da), and porosity value (ϵ) as a function of Rayleigh number (Ra). The results and discussion have been demonstrated through the results variations of streamlines, isotherms, isoconcentration, mean Nusselt (Num), and Sherwood number (Shm) at the considered range of flow parameters. The results show that the smaller Ra ≤ 10 5 values remain insignificant for convective heat and mass transport efficiency, whereas augmentation of Ra ≥ 10 5 reinforces these flows. Moreover, higher Ra values help in studying the real influence of other pertinent parameters. The increasing value of ϵ and Da strengthen the convection fluid, heat, and solute transfer intensity. In the case of Lewis number, a notable effect on improving the solute transport rate is more dominant than the heat transport rate. Similarly, the flow regime of fluid and solute, as well as heat and mass transfer rate, are significantly influenced by ranging values of buoyancy ratio ( − 4 ≤ N ≤ 4 ). The buoyancy-added flow (N > 1) improves the convective strength of heat and mass flow rate more effectively than the buoyancy-opposed flow (N < 1). Furthermore, the variation of Num and Shm justify the results interpreted in each flow parameter. [ABSTRACT FROM AUTHOR]

Natural convection heat transfer from periodically ribbed vertical surfaces is targeted for upscaling, incorporating the analysis of thermal conduction through the microscale ribs. Asymptotic homogenization theory is employed, considering the steady conjugate heat transfer problem, to formulate second-order accurate effective conditions for velocity and temperature at a fictitious plane surface, beyond which the macroscale behavior of the flow is computed. This allows to avoid the numerically expensive resolution of fields within and through the microstructured corrugations. For the streamwise velocity component, the no-slip boundary condition is corrected at first order (in terms of a small parameter ϵ , ratio of microscopic to macroscopic length scales) by the classical Navier-slip condition plus a buoyancy term, while the gradient of the normal stress appears at second order together with a temperature-gradient term. The temperature at the virtual boundary deviates from the uniform value at the baseplate; the thermal slip is described via a first-order temperature-gradient term with a coefficient depending on rib geometry and thermal conductivity. Different case studies are conducted on the case of transverse square ribs, varying the density of the pattern and the rib-to-fluid thermal conductivity ratio, to provide extensive validation of the model against full feature-resolving simulations. Beyond the validation phase, a better understanding of the effects of different parameters on the heat transfer performance is pursued. The presence of ribs is found to decrease the overall heat transfer rate from the surface, and this deterioration is only partially alleviated by raising the thermal conductivity of the ribs. Increasing the number of conducting ribs on the hot surface has a complex, non-monotonic effect on the heat transfer rate, unlike the case of adiabatic ribs where the average Nusselt number decays monotonically. The performance of low-thermal-conductivity elements (e.g. wooden ribs) may considerably differ from that of perfectly adiabatic ones. [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]

For combined sensible-latent heat storage system (CSLHS) (termed as the hybrid configuration), macro encapsulation can effectively solve the leakage problem of PCMs. However, due to the poor thermal conductivity of PCMs, the charging performance of the hybrid configuration slightly increases compared to the solid structure (with only sensible materials). Meanwhile, the natural convection in the PCMs zone could improve the charging performance. So, how to improve natural convection intensity is a key issue for the CSLHS by macro encapsulating. It is found that adding fins can significantly enhance natural convection and accelerate the melting of PCM. In this paper, we proposed the hybrid configuration with fins built-in by macro encapsulation, and analyzed its charging performance with different fin structural parameters in the PCM zone by CFD simulation. In the case, the sensible heat storage material is high-temperature concrete and the PCM is a low-melting-point mixed molten salt. We analyzed the effects of fin number, fin length and fin thickness on the charging performance of the hybrid configuration respectively. From the result, the charging performance increases with the fin number, but the increase rate gradually decreases. When the fin number is 6, the charging performance increases by 20.18% compared to the situation without fin. The charging performance increases gradually with the fin length. Compared with the hybrid configuration without fin, for each 10 mm increase in fin length, its charging performances increase by 4.09%, 5.26%, 7.02%, 8.77%, 11.70%, and 15.79%, respectively. Different from number and length of fins, the effect of thickness on the charging performance is very small. When the fin thickness increased from 1 mm to 4 mm, the charging performance only increased by 2.3%. It indicates that the main reason for the improving the charging performance is to increase the natural convection intensity by dividing the PCM zone through fins. These results show that the charging performance of the CSLHS with macro encapsulation can be improved by optimizing fin structural parameters. [ABSTRACT FROM AUTHOR]

AbstractNatural convection inside a cylindrical enclosure is important in many industrial applications. Laminar natural convective heat transfer in the annular space between heated semi-circular cylinder in a horizontal concentric cylindrical enclosure, which has relevance to cooling of electronic components, is studied in this work. Constant wall temperature (CWT) and constant wall heat flux (CWHF) boundary conditions are considered on the inner cylinder, whereas the outer cylindrical enclosure is maintained at a fixed lower temperature. The Finite Volume Method (FVM) is used for the computations. The effect of the Rayleigh number (Ra=102 to 105) and the angular orientation of the semi-circular cylinder on the convective heat transfer is investigated. The fluid flow, temperature profile, and heat flow are visualized via streamlines, isotherms, and heatlines. Further, the overall heat transfer is explained based on the local and average Nusselt number on the inner cylinder wall. The effect of the angular orientation of the inner cylinder is noticeable for Ra≥103. The angular orientation ϕ = 90° greatly enhances the heat transfer as compared to all other orientations for all Ra≥103 for both CWT and CWHF boundary conditions. The correlation between the average Nusselt and Rayleigh numbers for a particular orientation is proposed. [ABSTRACT FROM AUTHOR]

The thermal radiation and Fourier flux have drawn the attention of scientists and experts due to their extensive applications in the fields of medicine, manufacturing modern airplanes, water distillation, more efficient electronic devices, more efficient batteries, radiating treatment, and the textile industry. Through careful consideration of this, the mathematical investigation of natural convection and Fourier flux on the flow of energy and diffusion transmission of a body of cone and cylinder revolution, located in a saturated medium, has been described for the dual situations (flow over a cone and a cylinder). After then, the Runge–Kutta technique was used to explain the leading mechanism. Possessions of governing physical measures of local Nusselt and Sherwood numbers as well as velocity, thermal and diffusion figures are provided with support of tables and diagrams. It is motivating to declare that mass transfer rate is advanced in cone kind of revolution matched to cylinder kind of revolution with rising N R , N t , Q S . Also, the heat transmission rate is upper in cylinder revolution equated to cone revolution. [ABSTRACT FROM AUTHOR]

In the present study, natural convection heat transfer is investigated in a porous cavity filled with Cu/water nanofluid and equipped with horizontal fins. Optimization and sensitivity analysis of the fin's geometry, porous medium and nanofluid properties to maximize heat transfer rate is the aim of this work. To achieve this purpose, a design space is created by input parameters which include length, number of fins, distance between fins, porosity, Darcy number and volumetric fraction of the nanoparticles. Several tools have been used to implement optimization methods including the Taguchi method (TM) for design points generation, sensitivity analysis of design variables by using signal-to-noise ratio (SNR) and analysis of variance (ANOVA), response surface method (RSM) for interpolation and regression by using nonparametric regression, and genetic algorithm (GA) for finding optimum design point. The double multi-relaxation time lattice Boltzmann method (MRT-LBM) is used to analyze and simulate the flow field and heat transfer in each design point. The results show that the optimal configuration leads to an average Nusselt number of 5.56. This optimal configuration is at the length of fins L/2, the number of fins 2, the distance between fins L/12, porosity 0.8, Darcy number 0.1, and the volumetric fraction of the nanoparticles 0.02. By using the SNR results, the Darcy number and the number of fins have the most and the least effect in maximizing the average Nusselt number, respectively. The ANOVA results and global sensitivity analysis (GSA) findings further validated this conclusion. [ABSTRACT FROM AUTHOR]

AbstractThis numerical study aims to enhance the convective thermal and fluid flow characteristics in an inverted T-shaped porous enclosure saturated with a water-based special fluid. Moreover, a Darcy-extended Brinkman-Forchheimer-based mathematical model is numerically simulated with a penalty finite element approach to analyze the influence of aspect ratio and undulation effect on the developed mathematical model. Firstly, the various aspect ratios (Ar=0.25,0.50,and 0.75) of the mathematical model are numerically simulated at the varying range of Rayleigh number (Ra), which reveals that the increasing aspect ratios reinforce the convective heat and fluid flow phenomena. Moreover, it confirms the most pertinent aspect ratios (Ar = 0.50) that get superior results in reinforcing the convective flow among other aspect ratios. Furthermore, the optimal aspect ratio (Ar = 0.50) is further fixed to explore the parametric influences, including Rayleigh number (Ra=103−106), porosity value (ϵ=0.1−0.9), Darcy number (Da=10−5−10−2), and various undulation parameters such wave number (na=5,9,15) and amplitude of wavy surface (a=0,0.050,0.125,0.250). The results reveal that augmenting Ra, Da, and ϵ reinforces the convective thermal and fluid transport characteristics. Moreover, a combined effect of undulation factors (na,a) is also reported, indicating that decreasing na and increasing a magnitude strengthen the natural convection process. It is analyzed that the optimal combination of undulation parameters (na=5,a=0.25) results in a 16.15% in heat transfer enhancement. Additionally, maximum enhancements of 32.55%, 6.63%, and 41.47% in Num are reported while comparing between na = 5 and na = 15 for Ra, Da, and ϵ. Similarly, maximum enhancements of 17.87%, 16.10%, and 37.77% in Num are reported when comparing between a = 0.05 with a = 0.25 for Ra, Da, and ϵ. The research contributes valuable insights into improving thermal transport processes in real-world applications, especially in industrial solar power collectors, thermal exchangers, and heat storage industries that utilize the T-shaped configuration. [ABSTRACT FROM AUTHOR]

A deep collocation method (DCM) is proposed for studying the natural convection phenomenon in the porous media (NCPM). The buoyancy-driven convection analysis inside the porous media is a complex process governed by dynamical conservation laws. Furthermore, these conservation laws involve complex nonlinear governing equations, which are required special computational techniques in well-known numerical methods like finite element method (FEM), finite difference method (FDM), finite volume method (FVM), and others. Such numerical schemes often face computational limitations like mesh generation, dimensionality limitations, increased computation errors for complex domains, and challenges in modeling physics. This research employs an unsupervised deep learning (DL) approach to address and resolve the typical computational challenges encountered in traditional numerical methods when dealing with natural convection in complex porous enclosures. In contrast to mesh-based numerical methods, the computational procedure in the DL approach involves domain and boundary discretization, followed by the random sampling of collocation points throughout the entire physical domain and its boundaries. Furthermore, a loss function is defined based on the governing differential equations and boundary conditions, which are minimized at the collocation points to achieve the desired solution. A combination of gradient-based optimizers is deployed to obtain a better set of parameter values using the backpropagation algorithm. The entire setup of the feedforward neural network is trained to approximate the solution with acceptable accuracy. The study explores four configurations of porous enclosures for a nonlinear mathematical model of natural convection in porous media, with various combinations of Neumann and Dirichlet boundary conditions. Additionally, the results from the mesh-based FEM are chosen as reference data to validate the consistency and accuracy of the DCM results. In all cases, the DCM results exhibit excellent agreement with the FEM results. [ABSTRACT FROM AUTHOR]

In order to study the temperature change law of a nitrogen pre-cooling LNG unloading pipeline, a three-dimensional numerical simulation of an LNG pipeline with a bellow expansion bend was conducted using Fluent software (2020 R2). This simulation involved progressively controlling the nitrogen injection temperature and flow rate. The results show that increasing the nitrogen flow rate can improve the pre-cooling rate and reduce the top–bottom temperature difference of the pipeline, but there is an optimal value. Under the same nitrogen injection velocity conditions, it was found that smaller pipe diameters result in smaller temperature differences between the top and bottom of the pipeline. However, due to the reduced cooling capacity of the nitrogen injection, this leads to a decrease in the pre-cooling rate. The top–bottom temperature difference of the pipeline is mainly related to the strength of the natural convection in the pipeline. The stronger the natural convection, the greater the temperature difference between the top and bottom. Gr and Gr/Re2 reflect the relative magnitude of the natural convection intensity and forced convection intensity in the pipe. The larger the Gr and Gr/Re2, the stronger the natural convection. Therefore, Gr and Gr/Re2 are positively correlated with the top–bottom temperature difference, and the variation trend of the top–bottom temperature difference can be judged by the values of Gr and Gr/Re2. [ABSTRACT FROM AUTHOR]

The present work is deliberated to investigate the flow and thermal behavior of viscous fluid flow in permeable rhombic-shaped enclosure. Annular region lying below inner and outer rhombuses is the area of concentration during this study. Magnetic field is employed in horizontal direction to envision aspects of Lorentz field. Governing equations are developed in dimensional form of partial differential setup. Numerical experiments via finite element approach are capitalized to find solution. Grid convergence test is executed to show domain distribution along with decision about mesh level at which computations are to conducted. Streamlines and isothermal maps are sketched to show comprehensive change in associated flow fields against governing parameters. Kinetic energy and average heat flux coefficient are evaluated in comparative manner for magnetic and hydrodynamic situations. Through attained outcomes, it is concluded that kinetic energy and heat flux coefficient enhances reduction against Hartmann number. [ABSTRACT FROM AUTHOR]

In this study, a numerical investigation was conducted on the thermal analysis of transverse fluid flow in a gradient porous medium with exponential boundary conditions. By solving a two-dimensional system of dimensionless equations using the Newton–Raphson method and Galerkin finite element technique, the authors studied the effects of cross-diffusion on double-diffusive natural convection in shells. The simulation results for isoconcentrations, isotherms, and stream functions were analyzed for different flow parameters, and it was found that the mean Dufour and Soret numbers were more susceptible to cross-diffusion impacts. The researchers also found that altering the tilt angle of the trapezoidal enclosure can significantly impact flow circulation and temperature gradient, which has important implications for thermal energy control in different technical appliances. This study provides valuable insights into the thermal behavior of fluid flow in porous media, which can aid in the development of more efficient and effective thermal systems. [ABSTRACT FROM AUTHOR]

The lattice Boltzmann method is employed in the current study to simulate the heat transfer characteristics of sinusoidal-temperature-distributed heat sources at the bottom of a square cavity under various conditions, including different amplitudes, phase angles, initial positions, and angular velocities. Additionally, a machine learning-based model is developed to accurately predict the Nusselt number in such a sinusoidal temperature distribution of heat source at the bottom of a square cavity. The results indicate that (1) in the phase angle range from 0 to π, Nu basically shows a decreasing trend with an increase in phase angle. The decline in Nu at an accelerated rate is consistently observed when the phase angle reaches 4π/16. The corresponding Nu decreases as the amplitude increases at the same phase angle. (2) The initial position of the sinusoidal-temperature-distributed heat source Lc significantly impacts the convective heat transfer in the cavity. Moreover, the decline in Nu was further exacerbated when Lc reached 7/16. (3) The optimal overall heat transfer effect was achieved when the angular velocity of the non-uniform heat source reached π. As the angular velocity increases, the local Nu in the square cavity exhibits a gradual and oscillatory decline. Notably, it is observed that Nu at odd multiples of π surpasses that at even multiples of π. Furthermore, the current work integrates LBM with machine learning, enabling the development of a precise and efficient prediction model for simulating Nu under specific operational conditions. This research provides valuable insights into the application of machine learning in the field of heat transfer. [ABSTRACT FROM AUTHOR]

Highlights: What are the main findings? A comprehensive simulation model including particle flow and radiation transfer was developed for a CPC photocatalytic reactor. The ray tracing method was utilized to determine the radiation reaching the surface of the receiving tube, while the discrete ordinates method (DOM) was also employed to solve the radiative transfer equation (RTE), which shows the complete process of solar energy transfer. What is the implication of the main finding? Local volume radiative power absorption (LVRPA) and total radiative power absorption (TRPA) inside the receiving tube was obtained by this study, which is critical data for the photocatalytic reactor. Natural convection with intermittent disturbances is demonstrated to be effective operating mode for the CPC photocatalytic reactor. Compound parabolic concentrator (CPC) photocatalytic reactors are commonly used for photocatalytic water splitting in hydrogen production. This study aimed to gain a better understanding of the physical processes in CPC photocatalytic reactors and provide theoretical support for their design, optimization, and operation. The analysis involved the ray tracing approach, Euler–Euler two-fluid model, and discrete ordinates method (DOM) to study solar radiation transfer and particle flow in the reactor. The distribution of solar radiation on the receiving tube's surface after CPC concentration was obtained by conducting the ray tracing approach. This solar radiation distribution was then coupled into the Euler–Euler two-fluid model to solve for the natural convection flow field, the temperature field, and particle phase volume fraction distribution inside the receiving tube over a period of 120 s. Lastly, the discrete ordinates method (DOM) was used to analyze the transfer of radiation inside the receiving tube at different times, obtaining the distribution of local volume radiative power absorption (LVRPA) and the total radiative power absorption (TRPA) inside the tube. The results showed that the TRPA reached its maximum at 120 s, accounting for 66.61% of the incident solar UV radiation. According to the above results, it could be suggested that adopting an intermittent operation mode in CPC photocatalytic reactors is reasonable and efficient. [ABSTRACT FROM AUTHOR]

The present study presents a computational investigation into the thermal mixing along with entropy generation throughout the natural convection flow within an arbitrarily eccentric annulus. Salt water is filled inside the eccentric annulus, in which the outer and inner cylinders have T c and T h constant temperatures. The Boussinesq approximation is used to develop the governing equations for the natural convection flow, which are then solved on a structured quadrilateral mesh using the OpenFOAM software package (FOAM-Extend 4.0). The computational simulations are performed for Rayleigh numbers ( R a = 10 3 – 10 5 ), eccentricity ( ϵ = 0 , 0.4 , 0.8 ), angular positions ( φ = 0 ∘ , 45 ∘ , 90 ∘ ), and Prandtl number ( P r = 10 , salt water). The computational results are visualized in terms of streamlines, isotherms, and entropy generation caused by fluid friction and heat transfer. Additionally, a thorough examination of the variations in the average and local Nusselt numbers, circulation intensity with eccentricities, and angular positions is provided. The optimal state of heat transfer is shown to be influenced by the eccentricity, angular positions, uniform temperature sources, and Boussinesq state. Moreover, the rate of thermal mixing and the production of total entropy increase as R a increases. It is found that, compared to a concentric annulus, an eccentric annulus has a higher rate of thermal mixing and entropy generation. The findings show which configurations and types of eccentric annulus are ideal and could be used in any thermal processing activity where a salt fluid ( P r = 10 ) is involved. [ABSTRACT FROM AUTHOR]

The finned-tube sodium-to-air heat exchanger plays a crucial role in ensuring the safety of prototype Gen IV sodium-cooled fast reactors. It is designed to actively operate with power, but it is also important to consider its passive performance to ensure availability during power-out conditions. This study focused on addressing this limitation through a natural convection experiment using a dedicated facility, and the obtained results were compared with the safety analysis code MARS-LMR. The overall temperature difference was observed to be within an acceptable range of less than 5 %. While the code calculations aligned well with the experimental results at higher temperatures, they underestimated the experimental results at lower temperatures. These findings can serve as a basis for other codes employing different heat transfer correlations and for future reactor licensing purposes. [ABSTRACT FROM AUTHOR]

Convective heat transfer of nanofluids has been an active research topic in recent times. But the relative amount of research in natural convection of nanofluids is scarce in comparison with forced convection. In this study the effect of Fe3O4/water nanofluid on the natural convection behavior in a differentially heated cubic cavity of characteristic length 30 mm has been investigated. The nanofluids are synthesized using a two-step approach and their thermophysical properties like thermal conductivity and viscosity are measured in the temperature ranging from 20 to 60 ° C. The effect of nanoparticle volume fraction on heat transfer performance is studied with concentration ranging from 0–0.8% by volume. The cavity is made up of Poly-lactic acid (PLA) with two sides covered with copper plates. One of the copper plates is kept in contact with ambient atmosphere while variable heat flux using silica gel heater is applied on the other copper plate. All previous results have shown either monotonous deterioration or an increment followed by a continuous decrease in heat transfer coefficient and Nusselt number with increase in concentration. The results of this study have shown that for constant input heat flux the Nusselt number decreases monotonously. Further it is observed that for constant Rayleigh number there is an increase in Nusselt number with increase in concentration. [ABSTRACT FROM AUTHOR]

As the junction temperature of a light-emitting diode (LED) is inversely proportional to its lifespan and efficiency. This study investigates the thermal performance of heat sink-based model with a drop-shaped pin fin for LED cooling under natural convection, experimentally, and numerically. The study used three distinct drop form pin fin arrays with variable vertical fin spacing (Sv = 25, 50, and 75 mm), with the best array being used in subsequent studies with variations in drop-shaped pin fin size (diameter DD and apex length LD). The heat transfer coefficient and Nusselt number were obtained in the quantitative analysis of thermal performance. A numerical model with Boussinesq approximation for natural convection is used for this study and well-validated with experimental results. A qualitative investigation was also carried out utilizing numerical research to investigate velocity streamlines and their impacts on heat transfer enhancement in various configurations. An experimental test with conventional plate fin, circular pin fins were done for the verification of the test setup results and their results were compared with results calculated from the standard correlations presented in previous well-known literature. The maximum heat transfer coefficient was found to be 12.80 W/m2K for drop form pin fins with vertical fin spacing (Sv) equal to 75 mm, a diameter of 6 mm, and a length of 7.2 mm, and the corresponding Nusselt number was 94.85. Also, the maximum enhancement in Nusselt number was found to be (Nu/Nuplate fin) 3.11 corresponding to the conventional plate-fin heat sink. This comparison will help the industrialists determine innovative passive cooling technology for electronic devices such as LED street lights. [ABSTRACT FROM AUTHOR]

In this study, a mathematical model simulating the flow of ethylene glycol as a micropolar fluid supported by copper or graphene oxide nanoparticles around a cylinder affected by a magnetic field is established. A computational approximation is introduced for the solution of the governing mathematical model using the Keller-Box approximation. In addition, computations are executed with the aid of the MATLAB program to obtain numerical and graphical outcomes and validate and assess them. The graphical outcomes of the influential factors on the physical quantities related to energy transmission are analyzed and discussed. According to these outcomes, all physical groups are decreasing functions of the micropolar factor. With the exception of temperature, increasing the intensity of magnetic parameters has a negative impact on the studied physical groups. The fractional volume factor increases friction forces, the Nusselt number, and the temperature while decreasing velocity and angular velocity. [ABSTRACT FROM AUTHOR]

This study envisions the hydrothermal characteristics of a viscous fluid in a homogenously permeable hexagonal enclosure. Permeability aspects in the flow domain are described by employing the Brinkman-extended Darcy law. A corrugated hexagonal enclosure along with the placement of a star-shaped fin is taken into account. Heated rectangular blocks at horizontal extremities are installed and sliding sides of the enclosure are considered to be cold to provide convegtive potential to the flow. In addition, adjoining portions of the heated rectangular blocks are supposed to be adiabatic. The dimensionless governing .quations of the resultant problem are derived initially and then solved numerically by implementing the Galerkin finite element approach, and COMSOL is obliged. For this purpose, first, domain discretization is demonstrated in view of 2D elements by performing hybridized meshing. Then, the system of non-linear equations is resolved by a non-linear solver (PARADISO). The grid convergence test is performed to confirm the credibility of the carried out simulations by calculating the average Nusselt number at different refinement levels. A change in associated distributions against the involved physical parameters (Darcy number (Da), Rayleigh number (Ra), and Prandtl number (Pr)) for a wide range is revealed through graphs and tables. Quantities like kinetic energy and heat flux (local and average) are also evaluated through concerned parameters. The results clearly demonstrate that the Darcy number tends to reduce the heat transfer rate. In particular, it is depicted that by increasing the Rayleigh number (Ra), strengthening in the temperature potential arises in the system, thereby magnifying the heat transfer rate. Moreover, it is disclosed that by reducing the Darcy number, kinetic energy shows a decreasing trend. [ABSTRACT FROM AUTHOR]