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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]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The behavior of non-Newtonian power-law nanofluids under free convection heat transfer conditions in a cooled square enclosure equipped with a heated fin is investigated numerically. In particular, the impact of nanofluids, composed of water and Al₂O₃ , TiO₂ , and Cu nanoparticles, on heat transfer enhancement is examined. The aim of this research is also to analyze the influence of different parameters, including the Rayleigh number (Ra = 104− 106), nanoparticle volume fraction (φ = 0% − 20%), non-Newtonian power-law indexes (n = 0.6 − 1.4), and fin dimensions (Ar = 0.3, 0.5, and 0.7). Streamlines and isotherms are used to depict flow and related heat transfer characteristics. Results indicate that thermal performance improves with increasing Rayleigh number, regardless of the nanoparticle type or nanofluid rheological behavior. This suggests that the buoyancy force has a significant impact on heat transfer, particularly near the heat source. The Nusselt number is more sensitive to variations in Cu nanoparticle volume fractions compared to Al₂O₃ and TiO₂. Moreover, the average Nusselt numbers for power-law nanofluids with n < 1 (n > 1) are greater (smaller) than for Newtonian fluids due to the decrease (increase) in viscosity with increasing (decreasing) shear rate, at the same values of Rayleigh number Ra owing to the amplification (attenuation) of the convective transfer. Notably, the most substantial enhancement is observed with Cu–water shear-thinning nanofluid, where the Nusselt number increases by 136% when changing from Newtonian to shear thinning behavior and by 154.9% when adding 16% nanoparticle volume fraction. Moreover, an even larger increase of 57% in the average Nusselt number is obtained on increasing the fin length from 0.3 to 0.7. Graphic Abstract [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]

Predicting the air flow pattern with proper accuracy and speed inside a building with natural ventilation is one of the important study topics of building design due to the economic importance of energy consumption. For this purpose, in this study, a chamber with certain dimensions and with natural connection has been investigated as a study sample to predict the air flow pattern and speed distribution with the help of regional models. Two air inlet and outlet valves were considered for natural air ventilation. After researching the previous models, the three-dimensional zone model coupled with heat transfer and air flow calculations (ZAER) was chosen as the basis for comparing the modeling results. In the following, after zoning, to improve the flow coefficient factor model, which is assumed to be a constant number, it was assumed to be variable and the results were recorded in different states. The behavior of the model has been checked in the flow coefficients between 0.3 and 1 in order to obtain the most optimal coefficient for the number of suitable cells. Comparing the results of the research with the results of other models and computational fluid dynamics (CFD) showed that the three-dimensional behavior of the flow shows better compatibility with the experimental researches. [ABSTRACT FROM AUTHOR]

Tea is an important industrial crop. It is the second most popular among all the drinks. The drying operation in the tea industry fulfills the aim of enzyme inactivation and reducing the moisture content to the desired level. The energy consumption in drying operation in the tea industry is mostly in the form of thermal energy. Drying consumes a greater amount of energy than other processes in tea industries. Thermal energy needs are met mainly through fossil fuels. Renewable energy sources such as bioenergy and solar energy are also being adopted but at the minute level. Further, addressing problems such as stewing and case hardening (arises due to improper drying conditions) during drying is necessary to avoid quality loss. In this study, mass transfer modeling of drying of crush tear curl (CTC) tea particles is conducted considering natural convection around the tea particle. A finite difference method with an explicit scheme is used to solve the equations for mass transfer modeling of drying. The effect of drying air temperatures on moisture content, moisture ratio, and drying rates are computed. Drying air temperatures such as 80, 90, and 100°C have not shown effective drying. However, drying at air temperatures of 110, 120, and 130°C are recommended for drying times of 1500 s, 1200 s–1500 s, and 1200 s, respectively. Additionally, the effect of the size of the particles is studied and the lower size of tea particles is recommended for better drying characteristics. The current drying model can be used for single tray/conveyor dryers and indirect natural convection single tray solar dryer. Practical applications: The present research work demonstrates the important information for the hot air drying of CTC tea particle in single tray dryer. The drying modeling results can be used to set the proper temperature level of drying air being sent inside the dryer to avoid the under and over‐drying of tea particle and achieve the desired level of moisture content in the tea particle. Thus, the present study helps in deciding drying conditions such as drying temperature, drying duration for CTC tea particle in single tray dryer, slow speed conveyor dryer, and also in indirect natural convection single tray solar dryer. [ABSTRACT FROM AUTHOR]

Copyright of Ordnance Industry Automation is the property of Editorial Board for Ordnance Industry Automation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Xi'an Jiaotong University is the property of Editorial Office of Journal of Xi'an Jiaotong University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

The multitube design in the shell-and-tube type latent heat thermal energy storage (LHTES) system has received intensive attention due to its promising benefits in enhancing heat storage efficiency. In this paper, single and multi-tube shell LHTES systems were experimentally investigated. First, this study experimentally compared the thermal characteristics between a multiple-tube heat exchanger (MTHX) and a single-tube heat exchanger (STHX). The STHX's geometrical parameters coincided with a virtual cylindrical domain in the MTHX, being similar to the single-tube model formulated by simplifying the numerical solution to investigate the MTHX. The experimental data was then used to validate the simplified numerical model commonly used in the literature that converted the multi-tube problem to a single-tube model by formulating a virtual cylindrical domain for each tube in the MTHX system. The results showed that there was a noticeable difference in the thermal characteristics between the actual STHX and the virtual cylindrical STHX domain in the MTHX system. The comparison indicated that the simplified numerical model could not accurately reflect the thermal performance of the MTHX system. An experimental study or three-dimensional numerical modelling was required for the thermal analysis of the multi-tube problems. Second, the effect of tube number in the MTHX was experimentally investigated. It was found that an increase in tube number boosted both charging and discharging rates without inhibiting the natural convection. The five-tube configuration decreased the total charging and discharging duration by 50% compared to the two-tube one. Finally, the effect of heat transfer fluid (HTF) operating parameters on the system performance was evaluated on the five-tube MTHX system. The results revealed that the adoption of higher HTF temperature considerably improved the charging performance. The charging time decreased by up to 41% with the HTF temperature increasing from 70 to 80 °C. Meanwhile, a variation in the HTF flow rate from 5 to 20 L/min showed a more pronounced influence on charging than on discharging due to the different dominant heat transfer mechanisms. [ABSTRACT FROM AUTHOR]

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

This study examines the simultaneous impact of temperature-dependent viscosity and Robin boundary conditions on velocity, focusing on analyzing the stability of buoyant parallel flow in a differentially heated vertical porous layer. The neutral stability condition and the instability thresholds are determined numerically for various values of governing parameters. The onset of instability of the base flow is accurately analyzed by introducing a non-negative parameter that measures the extent of departure of boundaries from impermeable to permeable. It is established that the base flow becomes unstable when this parameter exceeds a threshold value, which significantly depends on the variable viscosity parameter. This work demonstrates a clear bridge between impermeable and permeable boundaries in the context of a variable viscosity fluid. [ABSTRACT FROM AUTHOR]

The requirement for heat sinks to better reject excess thermal energy is ever increasing due to the recent improvements in output power capacity in the Information and Communications Technology (ICT) industry. Current ICT thermal management strategies rely on single phase heat transfer techniques which have attained their upper limit. The present work aims to demonstrate that two-phase thermal system strategies can decrease heat sink size. A comparison of the heat dissipation capacity of a natural convection heat sink with and without the thermal transport mechanism of vaporization are measured and discussed. A discussion relating to the mathematical analysis of the heat transfer mechanisms leads to quantified results showing the efficiency gains of a two phase micro-porous heat sink. It is shown that the presence of evaporation from the holes on the front surface of the radiator makes it possible to reduce its size by 37.6% compared to a radiator in which heat removal is carried out only by natural convection. [ABSTRACT FROM AUTHOR]

The phenomenon of natural convection is the subject of significant research interest due to its widespread occurrence in both natural and industrial contexts. This study focuses on investigating natural convection phenomena within triangular enclosures, specifically emphasizing a valley-shaped configuration. Our research comprehensively analyses unsteady, non-dimensional time-varying convection resulting from natural fluid flow within a valley-shaped cavity, where the inclined walls serve as hot surfaces and the top wall functions as a cold surface. We explore unsteady natural convection flows in this cavity, utilizing air as the operating fluid, considering a range of Rayleigh numbers from Ra = 100 to 108. Additionally, various non-dimensional times τ, spanning from 0 to 5000, are examined, with a fixed Prandtl number (Pr = 0.71) and aspect ratio (A = 0.5). Employing a two-dimensional framework for numerical analysis, our study focuses on identifying unstable flow mechanisms characterized by different non-dimensional times, including symmetric, asymmetric, and unsteady flow patterns. The numerical results reveal that natural convection flows remain steady in the symmetric state for Rayleigh values ranging from 100 to 7 × 103. Asymmetric flow occurs when the Ra surpasses 7 × 103. Under the asymmetric condition, flow arrives in an unsteady stage before stabilizing at the fully formed stage for 7 × 103 < Ra < 107. This study demonstrates that periodic unsteady flows shift into chaotic situations during the transitional stage before transferring to periodic behavior in the developed stage, but the chaotic flow remains predominant in the unsteady regime with larger Rayleigh numbers. Furthermore, we present an analysis of heat transfer within the cavity, discussing and quantifying its dependence on the Rayleigh number. [ABSTRACT FROM AUTHOR]

This work reports a numerical study on the effect of three nondimensionalization approaches that are commonly used to solve the classic problem of the 2‐D differentially heated cavity. The governing equations were discretized using orthogonal collocation with Legendre polynomials, and the resulting algebraic system was solved via Newton–Raphson method with LU factorization. The simulations were performed for Rayleigh numbers between 103 and 108, considering the Prandtl number equal to 0.71 and a geometric aspect ratio equal to 1, analyzing the convergence and the computation time on the flow lines, isotherms and the Nusselt number. The mesh size that provides independent results was 51 × 51. Approach II was the most suitable for the nondimensionalization of the differentially heated cavity problem. [ABSTRACT FROM AUTHOR]

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Abstract 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 ( $$10 \le Gr \le 10^{7}$$ 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.

The heat transfer by natural convection of a nanofluid, which is ethylene glycol−Al2O3 has been analyzed in an open cavity numerically using the multiple-relaxation-time - lattice Boltzmann method by the graphics processing unit high-performance parallel computing. The right side of the cavity is open, and different boundary conditions have been applied to all the walls. Besides, one adiabatic fin has been installed on each side of the enclosure’s top and bottom sides. Here, the Prandtl number is fixed at 16.6, and the Rayleigh number changes from 104−106 with the nanoparticle volume fraction from 0%−5% has been used for numerical simulations. Besides, in this work, the power-law index is an important parameter as well, and 0.7, 0.8, 1, 1.2, and 1.4 are the values of this parameter. Results are presented concerning both the average and local Nusselt numbers in the form of streamlines, isotherms, temperature distributions, velocity distributions, heat transfer rate, and entropy production. It is observed when increases, average Nusselt number increases 607.94%, and for this reason, the overall heat transfer rate rises because of buoyancy force. In addition, the average Nusselt number falls by 83.28% when the power-law index rises; as a result, the total heat transfer rate falls because fluid viscosity increases with the power-law index. It is also observed that for shear-thickening fluids, the temperature gradient is higher. On the contrary, the temperature started decreasing with the increase of the power-law index. Additionally, the local Nusselt number value rises as power-law index falls. Moreover, the heat transfer rate increases by 7.08% when volume fraction increases. The intensity of buoyancy force reduces with the increase of volume fraction. Besides, the overall entropy generation rises when the Rayleigh number and the volume fraction increase, but it decreases when the power-law index increases. So, when the Rayleigh number is 106, the power-law index is 0.7, and the volume fraction is 0.00 then the entropy generation is the highest. This current research has many applications for example heat exchangers, electronic cooling equipment, solar heating systems, aerospace applications, medical devices, and entropy generation-related systems.

The cellular automaton-lattice Boltzmann method-immersed moving boundary coupled model is established to study the microstructure evolution during the solidification process of 2009Al/SiCp. After several model benchmarks, the natural convection of liquid phase and its effect on particle settlement under different pulling velocities were studied firstly. The results showed that at higher pulling velocity, the particle decelerates downward before contacting with dendrite front due to intensified natural convection. At lower pulling velocity, the particle decelerates gradually until a change in direction and upward movement. As the particle approach the tip of the dendrite, the particle experiences a brief upward movement before contacting the dendritic front. Then the convection induced by particles has an impact on the distribution of solutes in the liquid phase. It has been observed that at lower pulling velocity, there is a significant difference in solute distribution at the solidification front. The primary reason for this phenomenon is the higher solute concentration near the solidification front at lower pulling velocity, rather than the higher liquid phase flowing rate. Finally, our model investigated the microstructure evolution process during the directional solidification process of 2009Al/SiCp at different pulling velocities. The results indicate a good agreement between the simulation results and experiment observations.