Average Nusselt Number Research Articles

Heat Transfer and Entropy Generation on Free Convection Airflow inside a T-shaped Cavity Considering Inner Obstacles

In this study, a numerical analysis of heat and entropy generation on free convection of airflow is performed inside a T-shaped cavity with and without circular obstacles. The T-shaped cavity is formed with two symmetrically isothermal rectangular blocks. A cold temperature is maintained on the cavity's upper wall. The adiabatic walls are connected to heated wall at constant temperature. It is assumed that the flow is laminar, 2-D, and steadily incompressible. The finite element analysis is employed for solving the governing equations. The calculated results are compared and validated with the other published works. The dimensionless velocity (streamlines) and temperature (isotherms) are calculated and illustrated for varying Rayleigh numbers. It is found that the average Nusselt number at the heated walls and entropy generation inside the cavity increase with the increment of Rayleigh numbers. Moreover, the thermal performance effects on natural convection flow are investigated with circular obstacles inside the enclosure. Five cases without and with circular obstacles regarding the boundary conditions are investigated. It is found that the thermal performance of the cavity can be improved by adding two circular obstacles with cool boundary conditions. It is evident that the innovative structure by adding two circular obstacles with cool boundary conditions gives higher average Nusselt number and entropy generation whereas lower Bejan numbers for varying Rayleigh numbers. The study is performed for and . Jagannath University Journal of Science, Volume 11, Number 1, June 2024, pp. 186−202

Comparative analysis of buoyancy-driven hydromagnetic flow and heat transfer in a partially heated square enclosure using Cu-Fe3O4 and MoS2-Fe3O4 nanofluids

Purpose This study aims to investigate entropy generation through natural convection and examine heat transfer properties within a partially heated and cooled enclosure influenced by an angled magnetic field. The enclosure, subjected to consistent heat production or absorption, contains a porous medium saturated with a hybrid nanofluid blend of Cu-Fe3O4 and MoS2-Fe3O4. Design/methodology/approach The temperature and velocity equations are converted to a dimensionless form using suitable non-dimensional quantities, adhering to the imposed constraints. To solve these transformed dimensionless equations, the finite-difference method, based on the MAC (Marker and Cell) technique, is used. Comprehensive numerical simulations address various control parameters, including nanoparticle volume fraction, Rayleigh number, heat source or sink, Darcy number, Hartmann number and slit position. The results are illustrated through streamlines, isotherms, average Nusselt numbers and entropy generation plots, offering a clear visualization of the impact of these parameters across different scenarios. Findings Results obtained show that the Cu-Fe3O4 hybrid nanofluid exhibits higher entropy generation than the MoS2-Fe3O4 hybrid nanofluid when comparing them at a Rayleigh number of 106 and a Darcy number of 10–1. The MoS2 hybrid nanofluid demonstrates a low permeability, as evidenced by an average Darcy number of 10–3, in comparison to the Cu hybrid nanofluid. The isothermal contours for a Rayleigh number of 104are positioned parallel to the vertical walls. Additionally, the quantity of each isotherm contour adjacent to the hot wall is being monitored. The Cu and MoS2 nanoparticles exhibit the highest average entropy generation at a Rayleigh number of 105 and a Darcy number of 10–1, respectively. When a uniform heat sink is present, the temperature gradient in the central part of the cavity decreases. In contrast, the absence of a heat source or sink leads to a more intense temperature distribution within the cavity. This differs significantly from the scenario where a uniform heat sink regulates the temperature. Originality/value The originality of this study is to examine the generation of entropy in natural convection within a partially heated and cooled enclosure that contains hybrid nanofluids. Partially heated corners are essential for optimizing heat transfer in a wide range of industrial applications. This enhancement is achieved by increasing the surface area, which improves convective heat transfer. These diverse applications encompass fields such as chemical engineering, mechanical engineering, surface research, energy production and heat recovery processes. Researchers have been working on improving the precision of heated and cold corners using various methods, such as numerical, experimental and analytical approaches. These efforts aim to enhance the broad utility of these corners further.

Multi-objective optimization towards cooling performance of teardrop section Kagome trusses array jet impingement composite cooling structure with cross-flow

Teardrop Section Kagome trusses array can be a spoiler for a new generation of advanced combustion chambers. In this study, multi-objective optimizations are applied to optimize a jet impingement composite cooling structure with cross-flow. Four structural parameters with five levels and three performance parameters are calculated in design of experiment and fitted by response surface methodology. The database is expanded by non-dominated sorting genetic algorithm-II, and then technique for order preference by similarity to an ideal solution is used to calculate the optimal structures under different operating conditions by different weights of the performance parameter. The conclusions are as follows: The minimal Equality of variances and fitting accuracy are 35.4371 and 93.6%. Diameter of the cross-section has the largest positive main effect on average Nusselt number and pressure loss coefficient, while angle between the rod and the horizontal plane has the largest positive effect on temperature uniformity coefficient. The interaction of trailing edge angle with angle between the front rod and the back rod in the horizontal plane is large. Case15 is chosen, where the weight ratio is 1:5:5, improvement of the corresponding optimized performance parameters of the simulation results with respect to the Origin of three performance parameters are 26.72%, −2.93%, 91.59% respectively. It provides a feasible reference for future advanced combustion chambers and accelerates their development process.

Machine Learning-Based Predictions of Flow and Heat Transfer Characteristics in a Lid-Driven Cavity with a Rotating Cylinder

Machine learning-based predictions of heat transfer characteristics in lid-driven cavities are transforming the field of computational fluid dynamics (CFD). Lid-driven cavities are a fundamental problem in fluid mechanics, characterized by the motion of a fluid inside a square cavity driven by the motion of one of its walls. The goal of this study was to develop multiple machine-learning regression models and highlight the discrepancies between the predicted and actual average Nusselt numbers. Additionally, the study utilized physics-informed neural networks (PINNs) to model the flow and thermal behavior at both low and high Reynolds numbers. The results were compared among actual data from computational fluid dynamics (CFD) simulations, PINN models trained with CFD data, and purely PINN models created without any prior data input. The findings of this study showed that the random forest model exhibited an exceptional stability in its predictions, consistently maintaining low errors even as the Reynolds number increased compared with other machine-learning regression models. Further, the results of this study in terms of flow and thermal behavior within the cavity were found to depend significantly on the PINN method. The data-driven PINN exhibited a much lower mean average errors at both Reynolds numbers, while the physics-based PINN showed lower physics loss.

Convection flow of NE-phase change material-water mixture in evacuated tube solar collector manifold: Numerical analysis of MHD double-diffusive convection and exothermic reaction

This study investigates the convection flow of nano-encapsulated phase change material (NEPCM)-water mixture in an evacuated tube solar collector manifold, focusing on the effects of magnetohydrodynamic (MHD) double-diffusive convection and exothermic reaction. Computational fluid dynamics simulations using the Galerkin finite element method were employed to analyze temperature and concentration distributions, fluid flow, melting zone of PCM nanocapsules, Nusselt number, Sherwood number, entropy generation, and thermal performance. The numerical analysis considers a range of dimensionless parameters, including Rayleigh number (Ra=103−105), Lewis number (Le=0.1−10), buoyancy ratio (Nz=1−5), nanoparticle concentration (ϕ=0.01−0.035), fusion temperature (ϴf=0.1−0.9), Stefan number (Ste=0.1−0.9), Hartmann number (Ha=0−50), magnetic field inclination angle (γ=0°−90°), and Frank-Kamenetskii number (FK=0−2.5). Results show that increasing Ra enhances the average Nusselt number (Nuav) by up to 156.1 % and the average Sherwood number (Shav) by up to 104.5 %, while increasing the total entropy generation by up to 13,155 %. Increasing FK reduces Nuav by up to 42.2 % but increases Shav by up to 13.1 %. The Lewis number and buoyancy ratio significantly influence the hydrothermal performance, with Nuav exhibiting non-monotonic behavior and Shav increasing by up to 240.9 % as Le increases. The nanoparticle concentration enhances Nuav by up to 49.7 %. Interestingly, the magnetic field effects are less pronounced than in previous studies, with Ha having a minor impact on Nuav and Shav. These findings have significant implications for the design and optimization of evacuated tube solar collectors and other thermal energy storage systems, potentially leading to improved efficiency and performance in real-world applications.

Heat transfer in a non-uniformly heated enclosure filled by NEPCM water nanofluid

Purpose This paper aims to focuses on by investigate the heat transmission and free convective flow of a suspension of nano encapsulated phase change materials (NEPCMs) within an enclosure. Particles of NEPCM have a core-shell structure, with phase change material (PCM) serving as the core. Design/methodology/approach The enclosure consists of a square chamber with an insulated wall on top and bottom and vertical walls that are differently heated. The governing equations are investigated using the finite element technique. A grid inspection and validation test are done to confirm the precision of the results. Findings The effects of fusion temperature (varying from 0.1 to 0.9), Stefan number (changing from 0.2 to 0.7), Rayleigh number (varying from 103 to 106) and volume fraction of NEPCM nanoparticles (changing from 0 to 0.05) on the streamlines, isotherms, heat capacity ratio and average Nusselt number are investigated using graphs and tables. From this investigation, it is found that using a NEPCM nano suspension results in a significant enhancement in heat transfer compared to pure fluid. This augmentation becomes more important for the low Stefan number, which is around 16.57% approximately at 0.2. Secondary recirculation is formed near the upper left corner as a result of non-uniform heating of the left vertical border. This eddy expands notably as the Rayleigh number rises. The study findings indicate that the NEPCM nanosuspension has the potential to act as a smart working fluid, significantly enhancing average Nusselt numbers in enclosed chambers. Research limitations/implications The NEPCM particle consists of a core (n-octadecane, a phase-change material) and a shell (PMMA, an encapsulation material). The host fluid water and the NEPCM particles are considered to form a dilute suspension. Practical implications Using NEPCMs in energy storage thermal systems show potential for improving heat transfer efficiency in several engineering applications. NEPCMs merge the beneficial characteristics of PCMs with the enhanced thermal conductivity of nanoparticles, providing a flexible alternative for effective thermal energy storage and control. Originality/value This paper aims to explore the free convective flow and heat transmission of NEPCM water-type nanofluid in a square chamber with an insulated top boundary, a uniformly heated bottom boundary, a cooled right boundary and a non-uniformly heated left boundary.

Magnetic field effects on double-diffusive mixed convection and entropy generation in a cam-shaped enclosure

This study investigates double-diffusive mixed convection and entropy generation under magnetic influence within a novel cam-shaped enclosure, with applications in automotive engineering. The unique geometry creates distinct flow patterns that enhance heat and mass transport. Using the Galerkin finite element method, we analyzed the effects of key parameters, including buoyancy ratio, Reynolds number, Hartmann number, magnetic field inclination angle on average Nusselt and Sherwood numbers, and total entropy generation. Results show that increasing the buoyancy ratio and Reynolds number enhances heat transfer, while the Hartmann number significantly impacts flow characteristics and entropy generation. The magnetic field inclination angle exhibits a non-linear effect on heat transfer and entropy production. These findings provide valuable insights for optimizing heat transfer systems in complex automotive geometries.

Numerical Investigation of Effect Partially Corrugated Heated Wall on Behaviour Natural Convection Heat Transfer in A Square Enclosure

For fluid flow and heat transfer with engineering industrial applications important methods called natural convection are used. The current numerical study focuses on the effect of changing the heating positions of the corrugated left wall on heat transfer by natural convection with laminar flow in a closed square two-dimensional cavity filled with air as a working fluid. The code of a commercial program (COMSOL Multiphysics 6.0) was used to solve the mathematical equations governing fluid flow represented by continuity, momentum, and conservation of thermal energy. The right wall is exposed to a cold temperature, the other walls are thermally insulated. The effect of partial heating of the left corrugated wall and the Rayleigh number on the process of heat transfer by free convection was studied. At different Rayleigh numbers, flow field patterns and temperature distribution lines appear. The average Nusselt number, the average air temperature, and the flow field are slightly affected by low Rayleigh numbers, while with high Rayleigh numbers, these parameters are significantly and noticeably affected and behave differently by changing the heating sites. Numerical results show negligible effects of wall heating sites at low Rayleigh numbers and significant effects at high Rayleigh numbers. Also, the Nusselt number increases progressively with increasing Rayleigh number, so the heat transfer process gets improved.

Effect of thermal radiation and inclined magnetic field on thermosolutal mixed convection in a partially active wavy trapezoidal enclosure filled with hybrid nanofluid

This work focuses on the examination of the magneto-thermosolutal convection in a lid-driven wavy trapezoidal enclosure in the presence of thermal radiation. The wavy cavity is filled with radiative Fe3O4-Cu-H2O hybrid nanoliquid. In this work, two cases are considered depending on the location of heat and concentration sources. A portion of the vertical walls are kept hot and in high concentration while the remaining parts are in adiabatic condition. The adiabatic flat upper lid is moving towards the right with equal speed. In addition, the lower wavy border is cold and low concentration. The governing Navier–Stokes equations are modeled to describe thermosolutal phenomena within the wavy enclosure. These equations are solved by reconstructing a recently developed compact scheme. Computed outcomes are presented in terms of streamlines, isotherms, iso-concentrations, average Nusselt and Sherwood numbers to evoke the thermosolutal phenomena for various physical parameters. Also, computing in-house code is validated with the published numerical and experimental and literatures. This investigation surveys the roles of several well-defined parameters such as Richardson number (Ri), Lewis number (Le), Buoyancy ratio number (N), Radiation parameter (Rd), Hartmann number (Ha), inclination of angle (γ), undulation of the wavy surface (d) and solid volume fraction (ϕhnp) of the hybrid nanofluid. An increase in the Lewis number (Le) enhances species diffusion within the system but diminishes thermal transport. This work reveal that a change in ϕhnp from 0% to 4%, heat transfer is upgraded up to 4.28% in Case I and 3.93% in Case II while mass transfer is declined by 2.24% in Case I and 1.60% in Case II. Results indicate that Case I performed better than Case II in the case of energy and solutal transfer. This work has many practical applications such as heat exchangers, electronic device cooling, food processing and porous industrial processes.

Numerical and experimental study on manifold-distributed jet microchannel with micro-pin-fins

Traditional parallel microchannels are inadequate for managing the thermal requirements of newer, large-area and high-heat-flux chips. This inadequacy arises from its high flow resistance and poor temperature uniformity. Therefore, A novel manifold microchannel heat sink combining manifold inlet/outlet structures, distributed array jets, and micro pin-fins is introduced. Numerical simulations and experimental methods were employed to investigate the flow and heat transfer performance of the heat sink. Experimental results show that, with an average heat flux density exceeding 330 W/cm2 and a total power of 2500 W, the average chip temperature remains below 70 °C, ensuring efficient heat dissipation. Secondary impingement occurs at sufficiently low jet chamber heights, resulting in an increase of 3 times in the average Nusselt number for a smooth base plate. For the micro-pin-finned surface, it is shown that the presence of micro-pin-fins is not necessarily conducive to heat transfer enhancement. A critical volume fraction of micro-pin-fins (critical fin-ratio) exists where the obstructive effect and enhancement effect balance each other out. This value is influenced by multiple parameters. Finally, a novel relationship for predicting the average Nusselt number of jet impingement was proposed, with an average absolute error of less than 15 %. This series of investigations addresses the existing gaps in research on manifold-distributed array jet heat sinks and provides a meticulous theoretical foundation for the design and optimization of heat sinks facing the high-power chips.

Analysis of the effects of inclination and configuration of the electroosmotic field on the cooling performance of a microchannel

The study investigates the effect of using electroosmotic pumps on the cooling of electrical devices in micro scales. The mutual effects of the microchannel inclination (ranging from 0° to 75°) and configuration of the electric field on the heat transfer have not been investigated. To this end, a numerical code based on the finite volume method (FVM) and Semi-Implicit Method for Pressure Linked Equations (SIMPLE) was developed in Fortran to model the two-dimensional flow dynamics and heat transfer. Two different arrangements were considered for the discrete heat sources and electroosmotic fields to examine their effects on fluid dynamics and heat transfer rate at Re=10. In addition, the effects of electrical parameters, which directly affect the flow dynamics, were also considered. Results indicate that decreasing the heat transfer rate at higher angles is because of the velocity mitigation, whereas an increase in the Grashof number causes a reverse effect. Altering the layout of heaters and electric field from the condition in which heat sources are facing each other (Arrangement 1) to the condition in which heat sources are not facing each other (Arrangement 2), leads to the formation of swirling flow, increased flow rate, and decreased average Nusselt number. The optimum configuration for maximum cooling performance is found in Arrangement 1 with the Grashof number of 0 and inclination angle of 0°, in which the highest average Nusselt number of 5.815 is achieved. Despite the reduction in cooling efficiency at higher angles, Arrangement 1 outperforms Arrangement 2.

Artificial intelligence and numerical study of the heat transfer and entropy generation analysis of NEPCM-MWCNTs-Water Hybrid Nanofluids inside a quadrilateral enclosure

In the present investigation, the primary objective is to assess the synergistic impact of a novel hybrid nanofluid composed of nano-enhanced phase change material, multi-walled carbon nanotubes, and water. The governing equations are transformed into dimensionless forms for a more generalized analysis. To solve the problem, the Galerkin finite element method is employed, offering a robust numerical approach. A dataset of 1000 records was created by numerically solving the model for various combinations of control parameters. Using the dataset, a neural network was trained to learn the relationship between control parameters and heat transfer rate. The evaluation outcomes are comprehensively illustrated through key parameters, including local and average Nusselt numbers, total entropy generation, contours, and streamlines in the range of 103<Rayleigh number<105, 0<nanotube concentration<0.025, 0<nano capsule concentration <0.025, and 0.1<non-dimensional fusion temperature <0.7. Remarkably, the results indicate a substantial improvement in the heat transfer rate of the suspension for a hybrid concentration of 5%, showcasing an impressive 13% enhancement in contrast to the water host fluid's performance. Notably, the observed rise in entropy generation is relatively moderate, only a 5% increase.

Hybrid Nanofluid Flow in Chamber Containing Heated and Concentrated Internal Source Under the Effectiveness of Applied Magnetic field

Extensive applications of buoyancy-induced flow owing to temperature and concentration gradients have been found exclusively in diversified industrial and technological processes, such as heat exchange systems, solar collectors, heat sinks, and power plants. Additionally, installation of internal sources in confined configurations is essential in operation performance of many devices relevant to transformers, radiators, air cooling engines, fuel cells, semiconductor instruments and so forth. Furthermore, in recent decades, hybridized nanoparticles have been added to different setups to increase their efficiency. Therefore, the premier motive of current work is to examine mass and heat transport mechanisms in water-based fluids encompassed in a corrugated rectangular chamber with the induction of copper (Cu) and alumina (Al2O3) in a hybrid manner. A horizontally oriented magnetic field is assumed, along with the adjustment of a uniformly heated and concentrated source. The thermal conductivity relation proposed by Maxwell is obliged to scrutinize the performance of hybridized nanoparticles in controlling heat exchange in the domain. In this study, a power-law viscosity model is manifested along with utilization of other conservation laws and model structuring in the form of dimensionless expressions is performed by accomplishsing variables. Finite element simulations are executed by utilizing COMSOL Multiphysics 6.0 to solve developed governing equations system. The quantities of interest, such as average heat and mass fluxex, along with presentation of percentage change versus sundry factors, through graphical and tabular display. From a thorough examination, it is inferred that magnetic field plays an effective significance in controlling the excessive thermosolutal gradients. In addition, inudction of hybridized nanoparticles will positively affect thermal exchange in the base liquid compared to the situation when nanoparticles are not added. It is also deduced that average Nusselt and Sherwood numbers decreased up to 3% and 2.4% respectively for hydromagnetic situation (Ha = 0) in comparison to hydrodynamic case (Ha ≠ 0). Decrement in coefficients representing thermosolutal exchange reach up to 55% and 66% approximately against increment in number of corrugations. Induction of hybrid nanoparticles resulted in an increase in the coefficients of thermal and solutal transfer up to 14% and 22%, respectively, compared to the scenario where the base fluid contained no particles. For shear thinning aspects of non-Newtonain liquid, Nusselt and Sherwood numbers exceeds in comparison to Newtonian case and contrary aspects are observed for shear thickening materials.

Heat Transfer Characteristics of Mixed Convection inside a Differentially Heated Square Cavity Containing an Oscillating Porous Cylinder

The current study presents mixed convective flow inside a square chamber holding a centrally placed and thermally conductive oscillating porous circular cylinder. The left boundary's temperature is kept larger than that of the right edge, and the horizontal edges are preserved at adiabatic settings. The circumferential speed of the cylinder is sinusoidal and oscillating in nature. The fluid region within the chamber is modeled employing 2D Navier-Stokes and heat energy equations. Furthermore, the fluid circulation and heat transmission within the porous cylinder are modeled using the Darcy-Brinkman-Forchheimer formulation. The leading equations are discretized utilizing the Galerkin finite element technique. The parametric study is undertaken considering three distinct diameters of the porous cylinder and three distinct oscillation frequencies. The instant Nusselt number is evaluated along the heated wall, which varies in an oscillatory pattern owing to the repeated contraction and enlargement of the thermal boundary layer. The Nusselt number is averaged over time once the value becomes statistically stationary. The study is conducted within a mixed convection region with Reynolds (Re = 100), Richardson (0.1 ≤ Ri ≤ 10), and Grashof (103 ≤ Gr ≤ 105) numbers. Upon thorough examination, it becomes clear that the system's thermal performance shows promising improvement with the largest cylinder diameter and the lowest oscillation frequency. Specifically, the average Nusselt number shows a maximum improvement of 21.50% at the largest cylinder diameter.

Mathematical theory and CFD solutions for internal convective cooling of gas turbine blades highlighting the effects of rotation

A quasi-one-dimensional mathematical theory is developed for determining the effects of rotation on the fluid flow and heat transfer in a cooling channel within a rotating gas turbine blade. The three-dimensional intricacies in the solutions of the same problem are captured through accurate computational fluid dynamic simulations. The derived analytical closed-form solutions predict the amount by which the relative total temperature of the coolant changes as a result of rotation. It is shown that such changes due to rotation are significant proportion of the change of coolant temperature due to heat transfer. The computed spatial evolutions of the primary velocity field, secondary velocity field and the force fields are presented as the coolant progresses from the inlet to the outlet so that the complexities and subtleties are exposed to a high degree of visualizability. Detailed considerations to various components of the centrifugal, Coriolis and pressure forces are given. The flow field is shown to depend strongly on whether the coolant moves in the spanwise outward or inward direction. The three-dimensionality of the flow field is reflected in complex circumferential variations of the blade temperature and the internal heat transfer coefficient. When the effects of the x–component of the Coriolis force interacts non-linearly with the effects of the z–component of the centrifugal force and a drastic x-gradient in fluid density due to a thin thermal boundary layer, then the primary velocity profile may exhibit great complexity, including flow separation. The present paper thus captures the strong, non-linear, two-way coupling between the fluid dynamics and heat transfer in the internal convective cooling occurring in a channel within a rotating gas turbine blade. Based on about 100 three-dimensional computational fluid dynamics simulations, new heat transfer correlations are developed for average Nusselt number for a rotating channel that will be of practical use.

Heat transfer enhancement and flow resistance reduction characteristics of non-uniform electrohydrodynamic conduction pumping in microchannels

In this study, the thermo-hydraulic performance of non-uniform electrohydrodynamic (EHD) conduction pumping in rectangular and straight microchannels was experimentally investigated. Electrodes are arranged in two ways: dimensions constant, spacing varies (Cases 1–3); both dimensions and spacing vary (Cases 4–6). The results show that EHD conduction pumping significantly enhances heat transfer performance, increasing the average Nusselt number (Nu) by 17.9 %-87 % compared to a smooth microchannel. As Re increases, the inertial force of the fluid dominates, diminishing EHD-induced vortices and limiting heat transfer enhancement. EHD conduction pumping enhances heat transfer by creating vortices that mimic solid pseudo-roughness microelements, increasing fluid disturbance and mixing near the wall. However, these vortices also impede the flow, resulting in a trade-off with increased pressure drop resistance. This paper innovatively adopts an arrangement of increasing electrode size (non-uniform), which effectively reduces the pressure drop resistance in the microchannel while maintaining the advantage of enhanced heat transfer. Cases 4, 5, and 6 exhibit significantly higher comprehensive heat transfer performance (η) than Case 0 (without electrodes), especially at low Re. While the inertial force at high Re suppresses vortex formation and heat transfer enhancement, η remains superior to Case 0. Notably, Case 5 maintains a minimum η of 1.18 even at Re = 1000. Furthermore, this paper proposes an equivalent slip drag reduction mechanism to elucidate the drag reduction effect of the increasing electrode size arrangement. Heat transfer augmentation and pressure drop reduction, as mentioned here in microchannels, are crucial for electronics cooling and microfluidic devices.

Numerical analysis of unsteady free convection of Al2O3 inside a tubular reactor under the influences of exothermic reaction, and inclined MHD as an application to chemical reactor

This paper delves into the numerical investigation of aluminum oxide–water nanofluid thermal and dynamic performances under the influences of magnetic field application and chemical reaction, utilizing the Finite Element Method within a circular enclosure containing three inner tubes, as an application to the heat exchanging phenomenon between the reactive shell of the cavity and the surface of the triple tubes. Various governing parameters were studied for their interaction on the nanofluid flow and heat transmission rate within the proposed geometry, including the Rayleigh parameter (103≤Ra≤105), Hartmann parameter (0≤Ha≤61), nanoparticles concentration (0≤∅≤6×10-2), magnetic rotational angle (0o≤γ≤90o), and Frank-Kamenetskii parameter (0≤Fk≤3). The results indicated that raising Ra from 103 to 105 results in expediting the nanofluid velocity by 10.62 % and 100 % respectively as well as raising the total heat transfer efficiency. The nanofluid speed was also increased by 28.57 % when Fk has to further increase to a value of 3. When there was no exothermic activity present, the rate of heat transmission was at its lowest, and it was greater when the Fk value was 3. Similarly, there were discernible impacts in various areas of the geometry as the Ha number intensified and the Nuavg decreased. Improvements in local and mean Nusselt parameters are observed when the concentration of nanoparticles is increased, suggesting better heat transfer, achieving an increase by 7 % in the average Nusselt number. This research emphasizes the importance of nanoparticle concentration in raising the medium’s rates of heat transmission, contributing to advancements in energy storage development.

Hybrid Nanoparticle-Enhanced Fluid Flow and Heat Transfer Behaviors in a Parabolic Cavity with a Heat Source

AbstractNatural convection of nanofluids holds considerable importance in both scientific research and engineering applications due to their exceptional heat transfer capabilities, which occur spontaneously without the need for additional energy input. In this paper, the natural convection of nanofluid inside a parabolic cavity containing a hot obstacle is studied numerically. The shape of the hot obstacle is selected as either circular or elliptical. Additionally, the effects of the Rayleigh number, nanoparticle volume fraction, and the position of the heat source are investigated. The computational fluid dynamics model was computed using COMSOL Multiphysics. It is observed that the average Nusselt number tends to increase with both the Rayleigh number and the volume fraction of nanoparticles in the fluid. When the heat source moves from the bottom region to the top area, the heat transfer performance of the heat source increases. When Ra ≤ 105, the cases with circular heat sources exhibit better heat transfer performance than those with elliptical heat sources. However, at Ra = 106, the average Nusselt number of the elliptical heat source is higher than that of the circular one.

Predicting MHD mixed convection in a semicircular cavity with hybrid nanofluids using AI

This study presents a numerical analysis of magnetohydrodynamic (MHD) mixed convection in a semicircular enclosure containing a rotating inner cylinder and filled with nanofluids and hybrid nanofluids. The investigation explores the effects of Al2O3-TiO2-SWCNT-water hybrid nanofluids with varying nanoparticle compositions, as well as Al2O3-water, TiO2-water, and SWCNT-water nanofluids. The analysis includes the development of an artificial neural network (ANN) model to predict outcomes, achieving 97.34 % accuracy in training and 97.41 % in testing for the average Nusselt number. The study examines the impact of Reynolds number (Re), Richardson number (Ri), Hartmann number (Ha), cylinder rotation speed (Ω), cylinder size, and nanoparticle volume fraction (φ) on heat transfer and fluid flow. Key findings include a 6.98 % increase in heat transfer for SWCNT-water nanofluid from Ri = 1 to Ri = 10, a reduction in heat transfer with higher Hartmann numbers, and a significant 21.12 % enhancement when cylinder speed increases to Ω = 10 compared to a stationary cylinder. Larger cylinder sizes also improve convective heat transfer, with a 66.14 % increase for SWCNT-water nanofluid. Additionally, higher concentrations of SWCNT and Al2O3 in hybrid nanofluids enhance heat transfer performance.

Investigating forced convection in porous media-filled cavities for designing supplementary passive cooling systems

This study aims to propose innovative passive cooling methods within the reservoir section of a closed-loop liquid cooling system. The techniques employed in this study include using a cold wall, a porous medium, varying inlet positions, and nozzles of different sizes and shapes. The effects of parameters associated with these techniques on outlet temperature reduction, pressure drop, and average Nusselt number (Nu¯) have been analyzed in detail. The reservoir section has been numerically modeled as a two-dimensional (2D) and a three-dimensional (3D) cavity. The numerical model implements mass, momentum, energy, and conservation equations for the Darcy model in the porous region. A fluid flow with Re=50 with a laminar generalized porous media modeling approach employing Brinkman’s and Forchheimer’s terms has been used. The optimized inlet position with respect to maximum cooling (55.60 K) and moderate pressure drop (2.30kPa) for the 2D cavity has been identified in this work for a given Darcy number and porosity. Results show that decreasing porosity improves convective heat transfer efficiency and increases pressure drop. Similarly, varying Darcy’s number affects heat transfer, with lower Da values resulting in reduced outlet temperature reduction and lower Nu¯, with higher pressure drop. A similar analysis was conducted for the 3D reservoir. The use of a converging nozzle can lead to an increase in cooling by 61.61% and 3.44% for the 2D and 3D reservoirs, respectively.