Numerical Study Of Natural Convection Research Articles

A numerical study of natural convection through a vertical heated channel with a confined circular cylinder

This study examines thermal flow structures and heat transfer through a vertical heated channel with an adiabatic circular cylinder symmetrically positioned between lateral walls. A two-dimensional numerical simulation is conducted covering a range of parameters including Rayleigh numbers Ra = 8.9 × 106–8.9 × 108, cylinder positions relative to the channel height h = 0–0.50, and blockage ratios (the ratio of cylinder diameter to channel width) β = 0.25–0.75. Three distinct flow regimes are observed at different Rayleigh numbers and blockage ratios, including steady symmetric, unsteady periodic, and unsteady asymmetric flow regimes. The steady symmetric and unsteady periodic flows are observed at all blockage ratios, while the unsteady asymmetric flow is only observed at the highest blockage ratio of β = 0.75 for Rayleigh numbers above 8.9 × 107. It is found that the presence of the cylinder significantly enhances mixing and turbulence in the channel, which in turn enhances heat transfer through the channel. A 64.3% enhancement of heat transfer is achieved at β = 0.50 and h = 0.05 for Ra = 8.9 × 108.

Numerical study of natural convection in an inclined cavity filled with Al2O3/Cu-H2O nanofluids

The lattice Boltzmann method (LBM) was implemented in the present research to assess a numerical investigation of the heat transfer caused by natural convection in a nanofluid-filled inclined square cavity with a sinusoidal distribution of temperatures on a heated chip in the left wall. It has its foundation in the lattice-BGK (Bhatnagar-Gross-Krook) model and the single-relaxation-time approach of the D2Q9 scheme. A discussion is held concerning the impact of different physical variables on thermal transfer efficiency. The purpose of this study is to examine the impacts of four essential parameters: the Rayleigh number, length of the heated chip, volume concentration of the nanofluids, and tilt angle. These variations encompassed ranges of 103 to 106, H/4 to H, 0% to 6%, and 0° to 315°, respectively. The results indicate that an increase in the Rayleigh number leads to a noteworthy improvement in heat transfer, driven by an accelerated fluid flow induced by buoyancy forces. The tilt angle, interacting with the hot wall’s position, becomes a crucial factor, significantly influencing heat transfer in specific orientations. The length of the heating chip impacts fluid flow, demonstrating a marked enhancement in heat transfer within the cavity. Importantly, the use of nanoparticles, particularly in the Cu/H2O nanofluid, exhibits a substantial increase in thermal transmission as the nanoparticle volumetric fraction rises. These findings extend beyond heat transfer mechanisms, carrying significant implications for the scientific and technological realms. The validation findings are in good accord with the available research, the results of experiments, and the numerical data.

Numerical simulation of natural convection heat transfer in a cavity with finned surface under linear temperature profile

This paper is dedicated to a numerical study of natural convection through a cavity with finned surface where its base temperature is variable with linear profile. An approach based on modelling of internal fluid flow around a finned surface in laminar and at steady state conditions is used. Thermal and hydrodynamic aspects of the fluid flow were analyzed through the numerical resolution of equations of fluid dynamics. For this purpose, we have developed a computer code (in Fortran 90) based on the finite volume method. The studied model consists of a rectangular cavity where vertical walls are thermally insulated, the horizontal ones are maintained at different temperatures: cold and constant temperature on the upper wall and hot temperature with linear profile on the lower wall. The Rayleigh number used is in the range of 103 to 106 and the Prandtl number is fixed at 0.71. The plotted results are related to temperature distribution, streamlines, velocity fields as well as the mean Nusselt number.

Numerical study of natural convection in an annulus

In this paper, 2-D laminar free convection thermal transmission has been investigated numerically. Double concentric rectangular enclosures with discrete heaters were studied using COMSOL Multiphysics 6.0 software package. Heat flux was applied using specific number of heaters as well as changing the number and distances of the heaters in each case. Heaters were installed on the left vertical wall of the enclosure the opposite wall was kept at constant temperature. The horizontal walls were considered adiabatic. Air was taken as working fluid and all the features of air were considered constant except the change in density due to buoyancy forces that are driving the fluid. Finite volumes method was chosen for solving the governing equations in the dimensionless formula. The effect of Rayleigh number on Nusselt number was analyzed using the resultant isothermal contours. We attained the results for different values of Rayleigh number. A large enhancement in thermal transmission was achieved in the attained results, it was found that the amount of thermal energy transmitted will increase by increasing the value of Ra.

Natural Convection in Trapezoidal Cavity containing Hybrid Nanofluid

In this paper, a numerical study of natural convection in a trapezoidal cavity with left heated wall, right cold wall and filled with Cu – Al2 O3 and water hybrid nanofluid. The remaining walls of the cavity are kept at adiabatic. An enhancement in heat transfer is observed with the increase of three different parameters. Based upon the numerical predictions, the effect of Rayleigh number, inclination of the slopping wall, solid volume fraction of nanoparticles on flow and patterns as well tested. We found that acute slopping wall, high Rayleigh number and Cu – Al2 O3 nanoparticles with high concentration are effective to enhance the rate of heat transfer. We also developed a new correlation for the average Nusselt number as a function of the angle, effective thermal conductivity and viscosity as well as Rayleigh number.

Numerical study of natural convection of fluid with temperature-dependent viscosity inside a porous cube under non-uniform heating using local thermal non-equilibrium approach

Numerical study of natural convection of fluid with temperature-dependent viscosity inside a porous cube under non-uniform heating using local thermal non-equilibrium approach

Numerical Study of Natural Convective Heat Transfer in an Air Filled Square Cavity Heated from Below and Symmetrically Cooled from the Sides with a Partition in the Hot Wall

A two-dimensional numerical study of laminar natural convection in a square enclosure filled with air with a wall partially heated on the bottom is presented. The heat source is located on the lower wall with different heated widths varied from 20 to 80%(ε = 0.2–0.8) of the total width of the lower wall and different heights h = H/4 and H/2 of the partition. The effect of the partition height on the main system dynamics is investigated through solution of the two-dimensional Navier–Stokes equations and the energy equation by means of a finite volume method based on the SIMPLE algorithm. The influence of the Rayleigh number (Ra = 103 to 106) and the hot wall length is also examined. It is shown that the average Nusselt number grows when ε increases and when h decreases. For a given value of ε and h, the average Nusselt number increases as Ra increases. It is concluded that the partition height causes a decrease in the average Nusselt number.

Three-dimensional simulation of conjugate heat transfer using the hybrid lattice Boltzmann-finite difference method

This paper presents a three-dimensional numerical study of natural convection and conduction thermal phenomena using MRT-lattice Boltzmann and finite difference approaches. Conduction is examined using a simple conjugate heat transfer technique, which is predicated on the assumption of continuity of heat flux and temperature at the solid/fluid interfaces, instead of utilizing the conventional method based on the solution of the conduction equation. Several parameters such as Rayleigh number and thermal conductivity related to common construction materials are also investigated to explore their effects on the evolution of heat transfer. The obtained results show that augmentation of the Rayleigh number increases the quality of heat transfer by around 35–293% for various values of thermal conductivity ratio (solid/fluid). While the increase in thermal conductivity ratio enhances the heat transfer rate by about 212–685%, where the maximum rate of heat exchange is still the same for the thermal conductivity ratio ≥1000. Entropy generation is also examined in this paper to evaluate the efficiency of our studied system. The performed investigations indicate that the rate of entropy generation due to heat transfer, friction, and total entropy generation varies significantly with increasing Rayleigh number and thermal conductivity of the solid.

Numerical Analysis of Natural Convection in a Concentric Trapezoidal Enclosure Filled with a Porous Medium

Numerical study of natural convection around a heated trapezoidal block of different sizes located centrically in a larger trapezium has been investigated. The annulus between the trapeziums is filled with porous media. The sides of the inner trapezium are heated to a fixed temperature (T_h), and the slanted walls of the outer trapezium are adiabatic while its upper and lower walls are heated to temperatures of 〖T_c+(T_h-T_c)sin〗⁡(πx⁄L) and 〖T_h+(T_h-T_c)sin〗⁡(πx⁄L) respectively. The finite element numerical approach was used to solve the relevant dimensionless equations. Results are gotten for salient parameters including; modified Rayleigh number (10≤Ra_m≤ 1000), Darcy number (10^(-5)≤Da≤ 10^(-2)), and area ratio (1/5≤AR≤ 1/3). The results of this study are shown as isothermal contours, stream functions, and average Nusselt number. The results show that increasing Ra_m improves heat transfer; however, the response of thermal characteristics to AR increment depends on the range of Darcy number considered. Results from this study find application in ingot treatments and microchannel cooling among others.

An Experimental and Numerical Analysis of Natural Convection in Open Square Enclosure

Experimental and numerical study of natural convection of air in a partially open square enclosure with two internal heat sources, located at the respective centers of the bottom wall and the right vertical wall, are performed. The left vertical wall, made up of an aluminum plate, has a partial opening that occupies 12.8%, 25%, and 50% of the wall. The effect of opening sizes and Rayleigh numbers on natural convective heat transfer is evaluated. The temperature distribution and the average Nusselt numbers at various Rayleigh numbers are obtained experimentally using the Mach-Zehnder interferometer. These results are compared with the temperature distribution obtained from a numerical simulation performed using ANSYS Fluent 2020 and a maximum deviation of below 8% is obtained with respect to the average Nusselt number. The fringe patterns are found to be highly clustered at higher Rayleigh numbers and larger opening sizes. The average Nusselt number is observed to be higher at higher Rayleigh number and larger opening. The primary circulating cell is stronger for 50% opening which leads to higher heat transfer.

Heat Transfer By Natural Convection from a Heated Square Inner Cylinder to Its Elliptical Outer Enclosure Utilizing Nanofluids

In this paper a numerical study of natural convection of stationary laminar heat transfers in a horizontal ring between a heated square inner cylinder and a cold elliptical outer cylinder is presented. A Cu-water nanofluid flows through this annular space. Different values of the Rayleigh number and volume fraction of nanoparticles are studied. The system of equations governing the problem was solved numerically by the fluent calculation code based on the finite volume method and on the Boussinesq approximation. The interior and exterior surfaces are kept at constant temperature. The study is carried out for Rayleigh numbers ranging from <i>103</i> to <i>105</i>. We have studied the effects of different Rayleigh numbers and volume fraction of nanoparticles on natural convection. The results are presented as isotherms, isocurrents, and local and mean Nusselt numbers. The aim of this study is to study the influence of the thermal Rayleigh number and volume fraction of nanoparticles on the heat transfer rate.

Numerical study of natural convection of nanofluid in a rectangular closed enclosure (RCE) affected by hot and cold flow in a two-layer microchannel

Numerical study of natural convection of nanofluid in a rectangular closed enclosure (RCE) affected by hot and cold flow in a two-layer microchannel

The emergence of pressure self-oscillations in the flow of heat carriers and the development of mechanisms for reducing the amplitude of these oscillations

Self-oscillations of pressure arising in the elements of power equipment with an internal heat supply can, in some cases, impair the operation of this equipment. At high amplitudes of self-oscillations, conditions for its damage can be created. Thermoacoustic self-oscillations are a consequence of flow instability. A well-known example of processes accompanied by the generation of thermoacoustic self-oscillations is vibration combustion, which is observed in rocket engines, in air heaters for blast furnaces, etc. In order to determine the characteristics of pressure self-oscillations, numerical studies of natural convection in a vertical channel with internal local heat release are carried out. Heat release from internal sources occurs in a limited section of the channel, which is closer to the inlet cross section of the channel. At the outlet cross section of the channel, there is a system of coaxial cylindrical bodies that constitute additional local hydraulic resistance to air flow. The characteristics of the air flow in the channel, which are accompanied by self-oscillations of velocity and pressure, are determined from the numerical solution of the system of equations of dynamics and heat transfer for a compressible medium, taking into account the dependence of the thermophysical properties of air on temperature. Based on the results of this solution, the velocity, pressure and temperature fields in the flow are determined. It is shown that changes in flow velocity and pressure with time have the character of oscillations with variable amplitude. Velocity oscillations at the channel outlet are in antiphase with velocity oscillations at the channel inlet. The amplitudes and frequencies of these oscillations are found. The measures were determined to reduce the amplitude of pressure fluctuations in the flow. Among them - the dispersal of sources of internal heat release and a decrease in local hydraulic resistance. These measures can be applied to reduce the negative impact of self-oscillations on power equipment.

Numerical study of natural convection in an annulus between two concentric cylinders provided with metal foam fins

Natural convection in an annular space provided with metal foam fins attached to the inner cylinder is studied numerically. The metal foam fins made of copper were inserted in different axial sections with three fins in each section. The temperature of the inner cylinder is kept constant while the annular outer surface is adiabatic. The thickness effect of the inner pipe wall was considered. Naiver Stokes equation with Boussinesq approximation is used for the fluid regime while Brinkman-Forchheimer Darcy model is used for metal foam. In addition, the local thermal non-equilibrium condition in the energy equation of the porous media is presumed. The effect of Rayleigh number and number of foam fins in the axial direction, on fluid flow and heat transfer characteristics, were examined. The current model was valid with the available published results and good agreement is noticed. Results showed that as the Rayleigh number increases the dominated of convection mode increases and average Nusselt increases. It was found that at Rayleigh of 106 Nusselt reached its higher value which is 4.6 for the case of adding seven axial metal foams. A comparison between adding foam fins and copper fins was established for a range of Rayleigh numbers between 104 and 106. It showed a good enhancement in Nusselt number and the greatest enhancement percentage was 45.9% at Rayleigh equal 106 for the case of using seven sections of foam fins.

Numerical Study of Natural Convection of Power Law Fluid in a Square Cavity Fitted with a Uniformly Heated T-Fin

Flow of a liquid in an enclosure with heat transfer has drawn special focus of researchers due to the abundant thermal engineering applications. So, the aim of present communication is to explore thermal characteristics of natural convective power-law liquid flow in a square enclosure rooted with a T-shaped fin. The formulation of the problem is executed in the form of partial differential expressions by incorporating the rheological relation of the power-law fluid. The lower wall of the enclosure along with the fin is uniformly heated and vertical walls are prescribed with cold temperature. For effective heat transfer within the cavity the upper boundary is considered thermally insulated. A finite element based commercial software known as COMSOL is used for simulations and discretization of differential equations and is executed incorporating a weak formulation. Domain discretization is performed by dividing it into triangular and rectangular elements at different refinement levels. A grid independence test is accomplished for quantities of engineering interest like local and average Nusselt numbers to attain accuracy and validity in results. Variation in the momentum and thermal distributions against pertinent parameters is analyzed through stream lines and isothermal contour plots. Measurement of the heat flux coefficient along with the calculation of kinetic energy against involved parameters is displayed through graphs and tables. After the comprehensive overview of attained results it is deduced that kinetic energy elevates against the upsurging magnitude of the Rayleigh number, whereas contrary behavior is encapsulated versus power-law index n. Elevation in the Nusselt number for the shear thinning case i.e., n=0.5 adheres as compared to Newtonian i.e., n=1 and shear thickening cases i.e., n=1.5. It is perceived that by the upsurging power-law index viscosity augmentations and circulation zones increases. Heat is transferred quickly against Rayleigh number (Ra) due to production of temperature difference in flow domain.

Experimental and numerical study of natural convection in 3D double horizontal annulus

Presented paper is focused on numerical simulation of turboprop engine cooling in the section of a gas turbine. The method of heat transfer motor cooling by natural convection and radiation is described. The heat transfer in gas turbine section is represented on a simplified double annular geometry. Numerical data were compared with data that was gained from measuring on an experimental stand. The surface temperatures of the tubes were measured on the experiment stand during the cooling of the engine model. Numerical and experimental results reach a good agreement and will be further applied to the study of temperature-dependent deformation of aircraft engine parts, which have a significant effect on the safety and flawless operation of the aircraft engine.

Numerical Study of Natural Convection in an Inclined Porous Cavity

Two-dimensional transient laminar natural convection in a square cavity containing a porous medium and inclined at an angle of 30∘ is investigated numerically. The vertical walls are differentially heated, and the horizontal walls are adiabatic. The effect of Rayleigh number on heat transfer and on the road to chaos is analyzed. The natural heat transfer and the Darcy Brinkman equations are solved by using a finite volume method and a Tri Diagonal Matrix Algorithm (TDMA). The results are obtained for a porosity equal to 0.45, a Darcy number and a Prandtl respectively equal to 10−3 and 0.71; they are analyzed in terms of streamlines, isotherms, phase portrait, attractors, and spectra amplitude as a function of the Rayleigh number. It is found that, as Rayleigh number increases, the natural convection changes from a steady state to a time-periodic state and finally to a chaotic condition.

Numerical study of natural-convection from horizontal cylinder at eccentric positions with change in aspect ratio of a cooled square enclosure

Numerical study of natural-convection from horizontal cylinder at eccentric positions with change in aspect ratio of a cooled square enclosure

Numerical Study of Natural Convection of Biological Nanofluid Flow Prepared from Tea Leaves under the Effect of Magnetic Field

The heat transfer of a biological nanofluid (N/F) in a rectangular cavity with two hot triangular blades is examined in this work. The properties used for nanoparticles (N/Ps) are derived from a N/P prepared naturally from tea leaves. Silver N/Ps are distributed in a 50–50 water/ethylene glycol solution. The cavity’s bottom wall is extremely hot, while the upper wall is extremely cold. The side walls are insulated, and the enclosure is surrounded by a horizontal magnetic field (M/F). The equations are solved using the control volume technique and the SIMPLE algorithm. Finally, the Nu is determined by changing the dimensions of the blade, the Rayleigh number (Ra), and the Hartmann number (Ha). Finally, a correlation is expressed for the Nu in the range of parameter changes. The results demonstrate that an increment in the Ra from 103 to 105 enhances the Nu more than 2.5 times in the absence of an M/F. An enhancement in the strength of the M/F, especially at the Ra of 105, leads to a dramatic reduction in the Nu. An increase in the height of the triangular blade intensifies the amount of Nu in weak and strong convection. The enlargement of the base of the triangular blade first enhances and then decreases as the Nu. The addition of 5% silver biological N/Ps to the fluid enhances the Nu by 13.7% in the absence of an M/F for high Ras.

Numerical study of natural convection of nanofluids in an inclined flat bottom flask using finite-volume approach.

In this work, we study numerically the natural convection of nanofluids (NF) in an inclined flat bottom flask; it is one of laboratory flasks used in organic chemistry synthesis. The main reason of this study is to enhance the thermal properties of the reaction medium inside the flat bottom flask and to ameliorate the rate of chemical reactions using nanofluids. The flat bottom wall is maintained at a constant high temperature Th. While the top, left and right walls of the cavity are maintained at a low temperature TL. The NF comprises Cu and Al2O3 nanoparticles (NP) suspended in pure water. The governing equations are solved numerically using the finite-volume approach and formulated using the Boussinesq approximation. In this simulation we examined the effects of the NP volume fraction (φ) from 0% to 5%, the Rayleigh number from 103 to 106, the various inclination angles of enclosure (γ=0°,5°,10°, 15°) and the NF type (Cu and Al2O3) on the flow streamlines, isotherm distribution and Nusselt number. The obtained results show that the addition of Cu and Al2O3 NP increases the mean Nusselt number which enhances the heat transfer in the flat bottom flask and causes significant changes in the flow pattern. In addition, the mean Nusselt number is increase with increasing the Rayleigh number and the volume fraction and the best results have obtained from the Cu nanofluide. Also, as the inclination angle increases the mean Nusselt number decreases and the highest value of Nusselt number was obtained for a vertical enclosure (γ=0°). The obtained streamlines are mostly symmetric and their values are generally increase by increasing the Rayleigh number and volume fractions of NPs. Besides, the obtained isotherms are generally follow the geometry of the flat bottom flask.