Convective Flow Research Articles

Fractional numerical analysis of γ-Al2O3 nanofluid flows with effective Prandtl number for enhanced heat transfer

Abstract Nanoparticles have gained recognition for significantly improving convective heat transfer efficiency near boundary layer flows. The characteristics of both momentum and thermal boundary layers are significantly influenced by the Prandtl number, which holds a crucial role. In this vein, the current study conducted a detailed computational analysis of the mixed convection flow of $\gamma$Al$_2$O$_3$-H$_2$O and $\gamma$Al$_2$O$_3$-C$_2$H$_6$O$_2$ nanofluids over a stretching surface. This research integrates an effective Prandtl number, utilizing viscosity and thermal conductivity models based on empirical findings. Additionally, a unique double-fractional constitutive model is debuted to accurately evaluate the effective Prandtl number’s function in the boundary layer. The equations were solved using a numerical technique that combined the finite-difference method with the L$_1$ algorithm. This investigation presents numerical findings related to the velocity, temperature distributions, wall shear stress coefficient, and heat transfer coefficient, contrasting scenarios with and without the effective Prandtl number. The research shows that integrating nanoparticles into the base fluids reduces the temperature of the nanofluid with an effective Prandtl number while enhancing the heat transfer rate irrespective of its presence. Nonetheless, the introduction of a fractional parameter reduced the heat transfer efficiency within the system. Notably, the $\gamma$Al$_2$O$_3$-C$_2$H$_6$O$_2$ nanofluid demonstrates superior heat transfer enhancement capabilities compared to its $\gamma$Al$_2$O$_3$-H$_2$O counterpart but also exacerbates the drag coefficient more significantly. Many practical applications of this study include electronics cooling, industrial process heat exchangers, and rotating and stationary gas turbines in power plants, and efficient heat exchangers in aircraft.

Structural Color Enhancement through Synchronizing Natural Convection and Marangoni Flow in Pendant Drops.

Structural color, renowned for its enduring vibrancy, has been extensively developed and applied in the fields of display and anticounterfeiting. However, its limitations in brightness and saturation hinder further application in these areas. Herein, we propose a pendant evaporation self-assembly method to address these challenges simultaneously. By leveraging natural convection and Marangoni flow synchronization, the self-assembly process enhances the dynamics and duration of colloidal nanoparticles, thereby enhancing the orderliness of colloidal photonic crystals. On average, this technique boosts the brightness of structural color by 20% and its saturation by 35%. Moreover, pendant evaporation self-assembly is simple and convenient to operate, making it suitable for industrial production. We anticipate that its adoption will remarkably advance the industrialization of structural color, facilitating its engineering applications across various fields, such as display technology and anticounterfeiting identification.

Heat absorption effect of magneto-natural convection flow in vertical concentric annuli with influence of radial and induced magnetic field

This paper aims to study the natural convective magneto-hydrodynamic flow of fluid through vertical concentric annuli with iso-flux heating under the conditions of constant internal heat absorption and an induced magnetic field. By solving the set of dimensionless coupled governing equations, we were able to obtain exact expressions for the temperature field, velocity field, and induced magnetic field. We also managed to derive the formulas for skin friction, mass flux, and induced current density. We also examined the effects of non-dimensional parameters on skin friction and mass flux. For easy comprehension and interpretation, the results are provided graphically and in tabular form. The heat absorption parameter, the induced current density, the induced magnetic field, and velocity exhibit a negative trend as the Hartmann number (Ha) value increases. The induced magnetic field has the effect of raising both the induced current density and velocity profile. It is found that, when a fluid absorbs heat, the heat absorption parameter experiences reverse flow. For the heat-absorbing fluids, the radii ratio has the effect of increasing velocity, induced magnetic field, and induced current density. The numerical values of skin friction and mass flux at cylindrical walls increase (decrease) with increasing heat absorption parameter and generally it has decreasing tendency with increasing Hartmann number

Unlocking high-efficiency lithium-ion batteries: Sucrose-derived carbon coating on nickel-rich single crystal Li[Ni₀.₈Co₀.₁Mn₀.₁]O₂ cathodes

This study introduces a novel approach to enhancing the electrochemical properties of nickel-rich single crystal NCM811 (Li[Ni0.8Co0.1Mn0.1]O2) cathodes through carbon surface coating. Utilizing low-cost sucrose as a precursor, we applied a carbon-doped shell-like structure to the sNCM811 surface via convective flow treatment, optimized for temperature and coating density. This carbon surface layer significantly improved the delithiation kinetics, enabling rapid and stable electrochemical reactions. Notably, it mitigated electrical isolation, suppressed irreversible phase transitions, and reduced electrolyte-related side reactions within the sNCM811 during repeated charge-discharge cycles. Cathodes with a 7 wt.% sucrose coating demonstrated a high discharge capacity of 218 mAh g−1 at 0.1C/0.1C charge/discharge rates, with impressive capacity retention of 89 % after 100 cycles at 1C/1C charging/discharging. This represents a performance enhancement of 16 % and an improvement in cycle stability of 5.6 % over bare sNCM811. Furthermore, even at high charging/discharging rates of 5C/5C, the coated cathodes maintained a notable capacity of 125 mAh g−1, effectively mitigating structural degradation under high-output conditions. These findings suggest that carbon-coated sNCM811 is a promising solution for addressing degradation issues in high-capacity, high-output nickel-rich cathodes, potentially revolutionizing lithium-ion battery systems in demanding applications.

Comparison of unsteady MHD flow of second grade fluid by two fractional derivatives

A study is conducted on the unsteady motion of a free convective flow of second grade fluid, energy transfer, and Darcy’s law over an oscillatory smooth vertical plate. The study compares two different approaches in developing a fractional model: the Caputo-Fabrizio operator with nonsingular kernel and the constant proportional Caputo fractional operator with Fourier’s and Fick’s laws. By applying the Laplace method and transforming the provided set of equations into nondimensional form, we obtained semi-analytical results and presented these results through graphical analysis. The study examines how different flow parameters, including the fractional parameters, affect the velocity, mass, and heat profiles of the physical system. The results suggest that the physical model using constant proportional Caputo derivative leads to higher temperature, stronger concentration, and increased velocity compared to the Caputo-Fabrizio model. This highlights the importance of selecting an appropriate fractional model when studying complex physical systems. It is also depicted from the whole analysis that field variables with novel hybrid fractional derivative constant proportional Caputo exhibits a more effective and declining tendency than Caputo-Fabrizio.

Magnetohydrodynamic convection in a heat-generating ferrofluid within a corrugated cavity containing a rotating cylinder

This study introduces a novel approach by combining magnetohydrodynamic flow with Joule heating effects to investigate the conjugate mixed convective flow of ferrofluid in a non-homogenously warmed wavy-walled squared-shaped chamber with a spinning cylindrical object positioned at the center of the chamber. The current study seeks to maximize heat transmission effectiveness by scrutinizing optimum system attributes and conducting entropy production analysis. Numerical solutions are achieved by employing the Galerkin finite element weighted residual approach to solve the two-dimensional Navier–Stokes and heat energy equations representing the mathematical model. The parametric alterations encompass Grashof (103 ≤ Gr ≤ 106), Reynolds (31.62 ≤ Re ≤ 1000), and Hartmann (5.623 ≤ Ha ≤ 31.623) numbers, volumetric heat generation coefficient (0 ≤ Δ ≤ 10), thermal conductivity ratio (K = 20.07, 95.14), corrugation frequency (6.5 ≤ f ≤ 8.5), dimensionless corrugation amplitude (0.02 ≤ A ≤ 0.04), and dimensionless cylinder diameter (0.3 ≤ D ≤ 0.5). The study assesses the thermal characteristics of a heat source and the entropy generated within the computational domain while considering varying corrugation frequency and amplitude, cylinder diameter, thermal conductivity, strength of magnetism, and heat generation. The findings are quantitatively showcased through the Nusselt number of the hot wall, mean fluid temperature, overall entropy production, and thermal performance criterion (TPC) across the domain. After extensive analysis, it is evident that minimum cylinder diameter (= 0.3), corrugation frequency (= 6.5), and amplitude (= 0.02) while the maximum thermal conductivity ratio (= 95.14) ensure optimal system performance. Surprisingly, incorporating interior heat production diminishes thermal performance significantly while increasing TPC. Understanding the impacts of the magnetic field, Joule heating, and interior heat production on convective flow offers key perceptions into temperature variation, heat transport, velocity profile, and irreversible energy loss in numerous engineering applications.

The intruder motion in a cubic granular container

The Brazil nut effect is a key issue impeding the uniform distribution of particles in a mixed granular system. Extensive research was conducted on this segregation phenomenon in the 1990s and 2000s to identify the mechanisms and influencing factors involved. However, due to limitations in experimental techniques, the scope and effectiveness of research have been restricted. In this study, the Hall-effect magnetic sensing technique was utilized to track the motion of a single magnetic sphere (referred to as the intruder) within a cubic granular bed. This tracking method allowed for the measurement of the intruder's equilibrium positions as well as its trajectories. In a vibration-fluidized cubic granular container, an interesting phenomenon was observed: the intruder displayed a unique periodic helical oscillatory motion near the corner of the cubic container, with the oscillation amplitude gradually attenuating until stabilizing at its equilibrium position. A discrete element method simulation was carried out, revealing that the granular convection flow ascends from the center and descends near the container walls, with a faster flow rate at the four corners. An equation of motion was established accordingly for an intruder in such a convective granular flow, providing a comprehensive explanation for the observed intruder behavior. As a result of this comprehensive approach, we have uncovered the unique phenomenon of different mechanisms collectively driving the periodic spiral oscillation of the intruder before it eventually rested in its equilibrium position, a phenomenon whose mechanism has not previously been investigated in the literature.

Eulerian–Lagrangian hybrid solvers in external aerodynamics: Modeling and analysis of airfoil stall

Hybrid computational solvers that integrate Eulerian and Lagrangian methods are emerging as powerful tools in computational fluid dynamics, particularly for external aerodynamics. These solvers rely on the strengths of both approaches: Eulerian methods efficiently handle boundary layers, while Lagrangian methods excel in reducing numerical diffusion in flow convection. Building on our prior development of a two-dimensional hybrid solver that combines OpenFOAM with vortex particle method, this paper extends its application to the complex phenomena of airfoil stall at low Reynolds numbers. Specifically, we examine both static and dynamic stall conditions of a National Advisory Committee for Aeronautics (NACA) airfoil series 0012 (NACA0012) across a wide range of attack angles and oscillation frequencies, comparing our results with established data. The findings demonstrate the accuracy of hybrid Eulerian–Lagrangian solvers in replicating known stall behaviors, underscoring their potential for advanced aerodynamic studies. This work not only confirms the capability of hybrid solvers in accurately modeling challenging flows but also paves the way for their increased involvement in the field of external aerodynamics.

Investigation of the characteristics of optically dense gray mixed convection fluid flow along a cantilever shape

The goal of the work under consideration is to inspect the steady buoyancy driven flow for a viscous and density independent fluid along a cantilever shape, by considering the optically dense gray fluid. This study examines the characteristics of buoyancy driven convective heat and fluid flow adjacent to the cantilever shape. The governing equations constituting the aforementioned problem are converted into ordinary differential equations by utilizing the stream function formulation. The shooting technique BVP4C along with the MATLAB program is then used to obtain the numerical solutions. The impact of dimensionless cantilever shape parameter n, Prandtl number Pr, Richardson parameter λ, and thermal radiation parameter F on the velocity and temperature profile of the cantilever shape is demonstrated graphically. The tables provide the results for the skin friction and rate of heat transfer coefficient due to the impact of a number of evolving parameters.

The role of adding carbon nanoparticles to free convective boundary layer viscoelastic fluid flow past a vertical porous cone surface: application in wastewater treatment

The role of adding carbon nanoparticles to free convective boundary layer viscoelastic fluid flow past a vertical porous cone surface: application in wastewater treatment

Plume‐Driven Subduction Termination in 3‐D Mantle Convection Models

AbstractThe effect of mantle plumes is secondary to that of subducting slabs for modern plate tectonics when considering plate driving forces. However, the impact of plumes on tectonics and planetary surface evolution may nonetheless have been significant. We use numerical mantle convection models in a 3‐D spherical chunk geometry with damage rheology to study some of the dynamics of plume‐slab interactions. Substantiating our earlier 2‐D results, we observe a range of interaction scenarios, and that the plume‐driven subduction terminations we had identified earlier persist in more realistic convective flow. We analyze the dynamics of plume affected subduction, including in terms of their geometry, frequency, and the overall effect of plumes on surface dynamics as a function of the fraction of internal to bottom heating. Some versions of such plume‐slab interplay may be relevant for geologic events, for example, for the inferred ∼183 Ma Karoo large igneous province formation and associated slab disruption. More recent examples may include the impingement of the Afar plume underneath Africa leading to disruption of the Hellenic slab, and the current complex structure imaged for the subduction of the Nazca plate under South America. Our results imply that plumes may play a significant role not just in kick‐starting plate tectonics, but also in major modifications of slab‐driven plate motions, including for the present‐day mantle.

The Spatial Variation of Large‐ and Meso‐Scale Plasma Flow Vorticity Statistics in the High‐Latitude Ionosphere and Implications for Ionospheric Plasma Flow Models

AbstractThe ability to understand and model ionospheric plasma flow on all spatial scales has important implications for operational space weather models. This study exploits a recently developed method to statistically separate large‐scale and meso‐scale contributions to probability density functions (PDFs) of ionospheric flow vorticity measured by the Super Dual Auroral Radar Network (SuperDARN). The SuperDARN vorticity data are first sub‐divided depending on the Interplanetary Magnetic Field (IMF) direction, and the separation method is applied to PDFs of vorticity compiled in spatial regions of size 1° of geomagnetic latitude by 1 hr of magnetic local time, covering much of the high‐latitude ionosphere in the northern hemisphere. The resulting PDFs are fit by model functions using maximum likelihood estimation (MLE) and the spatial variations of the MLE estimators for both the large‐scale and meso‐scale components are presented. The spatial variations of the large‐scale vorticity estimators are ordered by the average ionospheric convection flow, which is highly dependent on the IMF direction. The spatial variations of the meso‐scale vorticity estimators appear independent of the senses of vorticity and IMF direction, but have a different character in the polar cap, the cusp, the auroral region, and the sub‐auroral region. The paper concludes by discussing the sources of the vorticity components in the different regions, and the consequences for the fidelity of ionospheric plasma flow models.

Multi-physics study on double-diffusion convective flow in an inverted T-shaped porous enclosure: ANN-based parametric estimation

This study explored the multi-physics effects (chemical reaction, magnetic field, etc.) on double-diffusion natural convection within an inverted T-shaped porous enclosure saturated with hybrid nanofluid. A penalty FEM is employed for numerical simulation, whereas an ANN-based approach was proposed for efficient parameter estimation. Results show a significant reduction in computational cost using the ANN method. Streamlines, isotherms, and heat/mass transfer rates are analyzed for various flow parameters, which reveals that the higher buoyancy forces enhance convection while stronger magnetic fields suppress it. The influence of other flow parameters is complex and depends on specific parameter values.

Unsteady wake and heat transfer characteristics of three tandem circular cylinders in forced and mixed convection flows

In natural convection (high Richardson number Ri), a high Prandtl number (Pr) leads to thinner thermal boundary layers, enlarging the thermal gradient and hence the enhancement of buoyancy effect. In forced convection (low Ri), a high Pr introduces thicker velocity boundary layers. In mixed convection scenarios, where both forced and natural convection are significant, the interaction between Pr and Ri determines the resultant flow pattern and heat transfer characteristic. Three tandem circular cylinders with an identical spacing ratio of 4.0 in both forced and mixed convection flows were numerically investigated by using finite element method. The computations were carried out in the range of Pr = 5–50 and Ri = 0–2 at a low Reynolds number of Re = 150. The results of the squared strain rate and the vorticity shed light on the enstrophy transfer process. Thermal plume structures in the far wake originate from the upper dispersed vortices due to the high superimposed buoyancy at low Pr, while they are suppressed at high Pr. The increase in Pr plays a role as the flow stabilization, while the growth of Ri plays the reverse role. The time-averaged velocity, pressure coefficient, and temperature become more asymmetrical at high Ri. The Nusselt number of the upstream cylinder is approximately equal to the empirical result without the consideration of thermal buoyancy. Due to the thermal buoyancy, the migration of shear layers along the cylinder surface leads to the frequency alteration and harmonic frequency in the drag, lift, and Nusselt coefficients.

Impact of free-stream orientation and thermal buoyancy on aerodynamic and heat transfer characteristics in mixed convective flow past an elliptical cylinder

Impact of free-stream orientation and thermal buoyancy on aerodynamic and heat transfer characteristics in mixed convective flow past an elliptical cylinder

Toward submicron inkjet-printed ZnO microdots with suppressed coffee-ring effect via controlled drying conditions for potential solar cell applications

The high-resolution, inkjet-printed zinc oxide (ZnO) microdot arrays with suppressed coffee-ring effect was demonstrated by investigating the correlation between drying and solidification processes. The internal microfluidic behavior of an ejected droplet and the associated drying process is geometry-dependent, which can be controlled by the temperature and surface energy of the substrate. During evaporation, droplets in contact with a wettable surface exhibit a dominant outward convective flow, resulting in a pronounced coffee-ring effect. In contrast, for droplets with minimal contact area on a substrate with low surface energy, the surface energy gradient along the relatively long thermal conducting path length reinforces the Marangoni flow, which retards the pinning of the contact line, resulting in tiny microdots with suppressed coffee-ring effect. The controlled ZnO microdots exhibit a diameter of approximately 3 μm with a thickness of 50 nm, which is one of the smallest microstructures produced by the inkjet printing method. Additionally, the integration of the ZnO microdot arrays into organic solar cells aimed to alter the light path length, leading to enhanced internal absorption. The P3HT:PCBM, PTB7-Th:PCBM, and PM6:Y6 devices with ZnO microdot arrays exhibit higher power conversion efficiencies of 3.54%, 9.04%, and 15.61% compared to reference devices of 3.38%, 8.85%, and 15.25% respectively.

Investigating the convective flow of ternary hybrid nanofluids and single nanofluids around a stretched cylinder: Parameter analysis and performance enhancement

Within this research, we examined the convective flow of a blend of ternary hybrid nanofluids and single nanofluids with a stagnation point caused by a stretched cylinder. The purpose of this study is to investigate the effect of using a ternary hybrid nanofluid instead of a single nanofluid. Water is used as the base fluid in this investigation. The single nanofluid is made of copper and the ternary hybrid nanofluid is made of Molybdenum disulfide, copper, and silver. The impact of the curvature parameter, nanoparticle volume fraction, mixed convection parameter, velocity ratio, shape factor, conjugate number and Eckert number parameters on temperature and velocity profiles has been investigated. Differential equations with partial derivatives were transformed to equations of ordinary differential type. The ODEs were then solved using the RK5th method. The ternary hybrid nanofluid has greater advantages than the single nanofluid and enhances the velocity and temperature compared to the single nanofluid, according to this study. Furthermore, the results showed that when curvature parameter, volume fraction and shape factor improved, so did the velocity and temperature profile. The results showed that moving from a single nanofluid to a ternary hybrid nanofluid at shape factor equal to 16.2 (Lamina) boosts the velocity by 20 %. Also, in Eckert number equal to 0.45, and substituting the ternary hybrid nanofluid boosts the temperature tenfold.

Numerical study of Marangoni convective hybrid-nanofluids flow over a permeable stretching surface

This paper is discussing nanofluid flow with effect of radiation along a stretching sheet in a porous means. Also, magnetic field is applied uniformly. The hybrid nanofluid is blend of base fluid kerosine oil and suspending particles of Copper Aluminum Oxide (Cu − Al2O3). The Marangoni boundary condition is considered. The flow considered is mathematically modeled with suitable boundary conditions in partial differential equations. Similarity transformations applied and followed numerical computations with Runge–Kutta method of order 4th aided by shooting approach. The graphs for different flow control parameters plotted and analytical study carried with illustration of temperature and velocity fields. Heat transfer rate for hybrid-nanofluid falls with increasing Mass transfer, Wall parameter (fw)and Prandtl Number (Pr), and the reversed effect for same is seen for higher Radiation parameter values (R). The current study's relevance has numerous applications in the key fields of materials processing, industrial thermal control, and heat transfer optimization in energy-efficient systems.

피동형 촉매 수소재결합기 상단부 형상에 따른 자연대류 특성 수치 해석

피동형 촉매 수소재결합기 상단부 형상에 따른 자연대류 특성 수치 해석

Natural Convection Flow in a Thermally Stratified Fluid Through an Asymmetrically Heated and Cooled Vertical Channel with Anisotropic Porous Material

Natural Convection Flow in a Thermally Stratified Fluid Through an Asymmetrically Heated and Cooled Vertical Channel with Anisotropic Porous Material