Numerical Analysis Of Natural Convection Research Articles

Numerical analysis of natural convection in a porous circular bend

The study of natural convection in porous circular bends is pivotal due to its applications in various cooling system designs. This paper focuses on a circular bend with a heated inner wall and a colder outer wall, employing the finite difference method to solve the governing equations. The research encompasses Rayleigh numbers ranging from 20 to 750 and an aspect ratio (defined as R=R2−R1R1) from 1.0 to 2.0. The findings highlight that variations in Rayleigh numbers and the circle’s radius significantly enhance heat transfer rates via convection, underscoring their critical roles in influencing flow and heat transfer within this configuration. It is also observed that theNuAvg on the heated wall increase with the increase in R. It is observed that for R = 0.75, NuAvg is 8.8 and for R = 1.5, NuAvg is increase to 9.7.

An experimental and numerical analysis of natural convection in a partially open cuboid enclosure with a cylindrical obstacle

Natural convection in partially open enclosures has been area of intensive research in the past. However, a dearth of experimental or numerical studies has been found on the effect of cylindrical obstacle size on natural convection in such an enclosure. To address this gap, this study employs real-time experimental analysis using a non-invasive technique (Mach-Zehnder interferometry), that provides temperature distribution of flowing fluid in the investigating domain. The experiments are conducted in a partially open cuboid enclosure with an internal heat source on the bottom wall and a centrally placed cylindrical obstacle. The partial opening occupies 50% of the height of the left vertical wall. The study investigates the effect of obstacle diameter and Rayleigh number on natural convection through experimentation and numerical simulations using ANSYS Fluent 2020. An air velocity transducer is used to measure velocity at the opening. The interferograms obtained from the experiment are used to characterize the natural convection and compared with the results obtained from the numerical investigation. Fringes intensify at higher Rayleigh number, and the temperature gradient near the heat source increases with increase in obstacle diameter. The average Nusselt number and average exit velocity of flowing fluid increase with increase in obstacle diameter and Rayleigh number. For Rayleigh numbers in the range of 107 to 108, a threefold increase in the obstacle diameter results in an average increment in Nusselt number by 22% and an increment in the average exit velocity by 25%.

A Comprehensive Numerical Analysis of Natural Convection in Nanofluids within Various Enclosure Geometries: A Review

A Comprehensive Numerical Analysis of Natural Convection in Nanofluids within Various Enclosure Geometries: A Review

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.

Thermogravitational convection of power‐law nanofluid in a cavity with a heat‐generated section on the bottom wall

Optimization of cooling systems for electronic devices is one of the crucial challenges in the modern engineering world. Inclusion of nanosized particles to working heat transfer liquids can enhance the heat removal from the heated elements in electronics. Taking into account these data, the present research is devoted to numerical analysis of natural convection in a cavity filled with a non‐Newtonian nanosuspension under an influence of a heat‐generating wall section. The paper contains the simulation outcomes for two different cases, namely, a heat‐generating wall section with constant heat flux and a heat‐generating wall section with constant temperature. The considered phenomenon has been described using the single‐phase nanofluid model where the base liquid is a pseudoplastic fluid. The rheological parameters of the host liquid including the coefficient of flow density and an indicator of fluid behavior are the empirical data of MWCNT nanofluids. The non‐Newtonian nature of the nanoliquid has been described by the Ostwald‐de‐Waele power law. Detailed analysis has been carried out for different governing parameters including the Rayleigh number, the volume fraction of nanoparticles, and the size of the heater using the non‐primitive dimensionless variables and the finite difference method. Obtained results illustrate different temperature patterns for various boundary conditions. Moreover, in the case of heat‐generating element, the average Nusselt number is greater than for the isothermal heater. It should be noted that the considered nanofluid model reflects the energy transference degradation with a growth of the nanoparticles concentration.

Numerical Analysis of Natural Convection Driven Flow of a Non-Newtonian Power-Law Fluid in a Trapezoidal Enclosure with a U-Shaped Constructal

Placement of fins in enclosures has promising utilization in advanced technological processes due to their role as heat reducing/generating elements such as in conventional furnaces, economizers, gas turbines, heat exchangers, superconductive heaters and so forth. The advancement in technologies in power engineering and microelectronics requires the development of effective cooling systems. This evolution involves the utilization of fins of significantly variable geometries enclosed in cavities to increase the heat elimination from heat-generating mechanisms. Since fins are considered to play an effective role in the escalation of heat transmission, the current study is conducted to examine the transfer of heat in cavities embedding fins, as well as the effect of a range of several parameters upon the transmission of energy. The following research is supplemented with the interpretation of the thermo-physical aspects of a power-law liquid enclosed in a trapezoidal cavity embedding a U-shaped fin. The Boussinesq approximation is utilized to generate the mathematical attributes of factors describing natural convection, which are then used in the momentum equation. Furthermore, the Fourier law is applied to formulate the streaming heat inside the fluid flow region. The formulated system describing the problem is non-dimensionalized using similarity transformations. The geometry of the problem comprises a trapezoidal cavity with a non-uniformly heated U-shaped fin introduced at the center of the base of the enclosure. The boundaries of the cavity are at no-slip conditions. Non-uniform heating is provided at the walls (l1 and l2), curves (c1,c2 and c3) and surfaces (s1 and s2) of the fin; the upper wall is insulated whereas the base and sidewalls of the enclosure are kept cold. The solution of the non-dimensionalized equations is procured by the Galerkin finite element procedure. To acquire information regarding the change in displacement w.r.t time and temperature, supplementary quadratic interpolating functions are also observed. An amalgam meshing is constructed to elaborate the triangular and quadrilateral elements of the trapezoidal domain. Observation of significant variation in the flow configurations for a specified range of parameters is taken into consideration i.e., 0.5≤n≤1.5 and 104≤Ra≤106. Furthermore, flow structures in the form of velocity profiles, streamlines, and temperature contours are interpreted for the parameters taken into account. It is deduced from the study that ascending magnitude of (Ra) elevates level of kinetic energy and magnitude of heat flux; however, a contrary configuration is encapsulated for the power-law index. Navier–Stokes equations constituting the phenomenon are written with the help of non-dimensionalized stream function, temperature profiles, and vortices, and the solutions are acquired using the finite element method. Furthermore, the attained outcomes are accessible through velocity and temperature profiles. It is worth highlighting the fact that the following analysis enumerates the pseudo-plastic, viscous and dilatant behavior of the fluid for different values of (n). This study highlights that the momentum profile and the heat transportation increase by increasing (Ra) and decline as the viscosity of the fluid increases. Overall, it can be seen from the current study that heat transportation increases with the insertion of a fin in the cavity. The current communication signifies the phenomenon of a power-law fluid flow filling a trapezoidal cavity enclosing a U-shaped fin. Previously, researchers have studied such phenomena mostly in Newtonian fluids, hence the present effort presents novelty regarding consideration of a power-law liquid in a trapezoidal enclosure by the placement of a U-shaped fin.

Structure of turbulent natural convection in a heated rapidly rotating inter-disk cavity with near-axis heat sinks

The paper presents the results of implicit LES numerical analysis of natural convection developing in a rapidly rotating inter-disk cavity with the width-to-radius aspect ratio equal to 0.13. The convection under study is developed under conditions of a prescribed temperature distribution over the disk surfaces and heat removing action of two near-axis volume sinks of a proper intensity. The thermal conditions are defined on the base of experimental data available in the literature for the prototype case of mixed-convection flow in a cavity heated from the side of the disk surfaces with axial throughflow of cooling air. The computations were carried out for the Ekman layer equal to 0.28· 10−4, if evaluated with the cavity width. Using the closed-cavity model with near-axis heat sinks, principal features of the flow structure and heat transfer, revealed previously for the prototype case of mixed convection have been reproduced successfully, including formation of a pair of global cyclonic/anticyclone vortices and a cold flow core of nearly constant temperature. It is shown also that each near-disk shear layer can be subdivided into a relatively thin highly gradient “internal” Ekman-type layer and a much thicker “outer” layer, which thickness is of the same order as the thermal layer thickness. For the case considered, groups of elongated regular structures occur within the outer layer that can be detected by analyzing the low-speed fluid motion in the axial direction. Further studies are needed to reveal physical reasons of occurring these structures.

Numerical analysis of free convection from a spinning cone with variable wall temperature and pressure work effect using MD-BSQLM

Abstract The problem of the numerical analysis of natural convection from a spinning cone with variable wall temperature, viscous dissipation and pressure work effect is studied. The numerical method used is based on the spectral analysis. The method used to solve the system of partial differential equations is the multi-domain bivariate spectral quasi-linearization method (MD-BSQLM). The numerical method is compared with other methods in the literature, and the results show that the MD-BSQLM is robust and accurate. The method is also stable for large parameters. The numerical errors do not deteriorate with increasing iterations for different values of all parameters. The numerical error size is of the order of 1 0 − 10 1{0}^{-10} . With the increase in the suction parameter ξ \xi , fluid velocity, spin velocity and temperature profiles decrease.

Analysis of nanofluid based natural convection in a square cavity applying corner heating and cooling

The present investigation aims at the numerical analysis of natural convection in a square cavity. The cavity is filled with nanofluid using water as the base fluid and Al2O3 as nanoparticles. The investigation is carried out in a square cavity with corner heating and cooling. The numerical simulations are performed using a finite volume method. The average Nusselt number is calculated for a wide range of Rayleigh number from 104 to 106 keeping solid volume fraction of nanoparticle fixed at 0.04. The details of flow and heat transfer for various cases are analyzed using the contour of streamlines and isotherms.

Transient air natural convection in asymmetrically heated vertical channels

A numerical analysis of natural convection in air in a vertical channel asymmetrically heated at uniform heat flux is carried out in this work. One channel wall is heated whereas the other one is adiabatic, and the problem is transient, two-dimensional and laminar. Constant and variable property models are considered. For both models, numerical solution is obtained by means the commercial CFD code Fluent. An extended computational domain is considered in order to simulate the far field conditions and it consists of the channel geometry with an upstream reservoir and a downstream reservoir. Simulations are achieved for Rayleigh number, Ra, values in the range 102–106 and results are showed as temperature profiles along the heated wall as a function of time, stream function and temperature fields. The present analysis allows to improve the knowledge of the effects related to the variable properties on the inlet and outlet zone and consequently inside the channel by numerical investigation during the development of fluid dynamic and thermal fields which are strongly linked. The results give quantitative information on the errors due to the use of constant properties model with respect to the variable properties model in natural convection in asymmetrical heated vertical channels.

Numerical analysis of natural convection of alumina–water nanofluid in H-shaped enclosure with a V-shaped baffle

Numerical analysis of the free convection heat transfer in an H-shaped cavity loaded with alumina–water nanofluid is performed in this work. The entire bottom wall of the H-shaped enclosure and the top rib are at the hot temperature, the two sidewalls are at the lower temperature, and the others are insulated. This study aims to elucidate the influences of different variables on the heat transfer of nanofluid, namely the Rayleigh number (Ra = 104–106), nanoparticle volume fraction percentage (ϕ = 0–2%), aspect ratio (AR = 0.2–0.4), installation of baffle, location of baffle in the cavity, and the types of baffle boundary condition. To model the buoyancy force, the Boussinesq approximation is employed. The characteristics of flow and thermal transmission are presented in streamlines and isotherms. The results show that the heat transmission is improved by Rayleigh number enhancement and nanoparticle volume fraction due to the enhanced temperature gradient and the nanofluid thermal characteristics. In addition, the baffle installation at the bottom rib under a non-adiabatic boundary condition improve the heat transfer because the bottom wall has a larger mean temperature than the top wall.

Transient Numerical Analysis of Natural Convection in Partially Open Cavities Filled with Water near the Density Inversion Point

A transient numerical analysis of natural convection of near-freezing water in a cavity with lateral openings and internal heat sources is carried out to investigate the influence of the heat dissipation rate in the flow configuration. The heat sources were positioned to create buoyancy-opposing and buoyancy-assisted conditions simultaneously and the top and bottom walls are kept at 0◦C. The non-linear dependence of the physical properties with temperature is considered in the governing equations. Based on the heat dissipation rate, six different regimes were observed and classified through a qualitative analysis of the temporal evolution of the velocity and temperature fields. The characteristics of heat transfer for each regime are analyzed to define the most important mechanisms of heat removal. In the upper layer (heated from below), the buoyancy forces eventually overcome the viscous forces and unsteady thermal plumes are formed, in-creasing the heat removal through the openings, while the heat transfer with the top wall is not significant. In the lower layer, the development of wave-like instabilities leads to oscillatory regimes for intermediate heat dissipation rates, while for high dissipation rates a steady convective regime is observed. This behavior increases the heat transfer with the bottom wall, making it much more significant when compared with the upper layer.

Numerical Analysis of Natural Convection of Suspension with Phase Change of Dispersoid in a Rectangular Vessel with Vertical Heating/Cooling Walls

Numerical Analysis of Natural Convection of Suspension with Phase Change of Dispersoid in a Rectangular Vessel with Vertical Heating/Cooling Walls

Numerical analysis of natural convection between a heated cube and its spherical enclosure

Three-dimensional numerical simulations were conducted for the natural convection phenomena which occurs between an inner hot body and its outer enclosure. The physical model considered here is that a body of cubical shape is located at the center of an isothermal cooled spherical enclosure. Therefore, the fluid flow inside the enclosure results from the temperature difference between the cooled spherical enclosure and the heated cube. The governing equations are solved using a second-order accurate finite volume approach on a staggered grid system and multi-grid acceleration. Three different fluids, an air (Pr = 0.71), a water (Pr = 6.2) and the other a dielectric liquid (Pr = 25) are employed encompassing descriptive Rayleigh numbers Ra that range three orders of magnitude from 104 to 107. The conducted benchmark study leads to excellent accordance with previous findings. Detailed three-dimensional flow and thermal structures in the enclosure were analyzed using the distribution of iso-contours of temperature, iso-surfaces of the standard velocity vector and streamtraces for different Rayleigh numbers. The variation of the local and the surface-averaged Nusselt numbers at the inner hot cube wall are also presented to exhibit the overall heat transfer characteristics inside the enclosure. At the end, monomial correlations are presented for the quantification of the heat transfer that emanates from the heated cube and the spherical enclosure in harmony with the various Rayleigh number. It was found that the thermal and flow fields eventually reach steady state for Rayleigh numbers ranging from 104 to 107. Results indicate also that the heat transfer is increasing significantly by increasing Rayleigh numbers and optimal heat transfer rate is obtained for high Rayleigh number set to 107.

Numerical analysis of natural convection in a differentially heated packed bed with non-uniform wall temperature

We report numerical simulations of natural convection and conjugate heat transfer in a differentially heated cubical cavity packed with relatively large hydrogel beads (d/L=0.2) in a Simple Cubic Packing configuration. We study the influence of a spatially non-uniform, sinusoidally varying, wall temperature on the local flow and heat transfer, for a solid-to-fluid conductivity ratio of 1, a fluid Prandtl number of 5.4, and fluid Rayleigh numbers between 105 and 107. We present local and overall flow and heat transfer results for both sphere packed and water-only filled cavities, when subjected to variations of the wall temperature at various combinations of the amplitude and characteristic phase angle of the imposed wall temperature variations. It is found that imposing a sinusoidal spatial variation in the wall temperature may significantly alter the local flow and heat transfer, and consequently the overall heat transfer. At identical average temperature difference, applying a spatial variation in wall temperature at well-chosen phase angle can lead to significant heat transfer enhancement when compared to applying uniform wall temperatures. However, this is achieved at the cost of increased entropy generation.

Numerical Analysis of Natural Convection with Thermal Radiation in a Partially Heated 3D Cavity

In this study, the finite volume and the discrete ordinate methods are used to study the phenomenon of radiation and natural convection in a cubical cavity for both transparent and participating media. The cavity is heated by six identical isothermal elements placed on one of its vertical walls. Three possible arrangements named cases I, II, and III of the six elements are studied. In case I, the number of these elements increases with the height of the cavity: one, two then three elements (1 × 2 × 3). Case III is the opposite with 3, 2, and then 1 elements passing from the bottom to the top of the hot wall. Case II corresponds to the uniform arrangement 2 × 2 × 2. The simulation results are obtained for different values of the Rayleigh number in the range of $$ 10^{3} \le {\text{Ra}} \le 10^{7} $$, the common emissivity of the walls (0 ≤ e ≤ 1) and the optical thickness of the fluid (0 ≤ τ ≤ 103). The thickness of the cavity varies from 2 cm to 12 cm, and the horizontal and vertical distances separating the six isothermal elements are in the range of $$ 0.25 \le {\text{D}}_{\text{H}} \le 0.75 $$ and $$ 0.208 \lesssim {\text{D}}_{\text{V}} \le 0.375 $$, respectively. The number of Prandtl and the cold wall temperature are fixed at $$ { \Pr } = 0.71 $$ and $$ {\text{T}}_{\text{C}} = 293\,{\text{K}} $$. The obtained results show that the case II leads to the largest global heat transfer and the radiation contribution becomes negligible if τ is too high.

Numerical Analysis of Natural Convection inside Spray Coating Room on Temperature Distributions

Numerical Analysis of Natural Convection inside Spray Coating Room on Temperature Distributions

Numerical analysis of natural convection with conjugate heat transfer in coarse-grained porous media

We report numerical simulations of fluid natural convection with conjugate heat transfer in a bottom-heated, top-cooled cubical cavity packed with relatively large (d/L=0.2) solid spheres in a Body Centred Tetragonal (BCT) configuration. We study largely varying solid-to-fluid thermal conductivity ratios between 0.3 and 198, for a fluid Prandtl number of 5.4 and fluid Rayleigh numbers between 1.16 × 106 and 1.16 × 108 and compare global heat transfer results from our present simulations to our previously published experimental results. The interplay between convection suppression due to the solid packing, and conductive heat transfer in the packing leads to three different regimes, each with a distinct impact of the solid packing on the flow and heat transfer. At low Rayleigh numbers ≈ 106, all packings suppress convective flow. Compared to fluid only Rayleigh–Bénard convection, heat transfer is therefore reduced in low conductivity packings, whereas for high conductivity packings it is increased due to significant conductive heat transfer. At intermediate Rayleigh numbers ≈ 107, low conductivity packings no longer suppress convection, whereas flow is still suppressed in high conductivity packings due to the thermal stratification imposed on the fluid by the solid. Consequently, heat transfer is lower compared to fluid only Rayleigh–Bénard convection, even in high conductivity packings. With a further increase of Rayleigh number ≳ 108, convection starts to be the dominant heat transfer mechanism in all packings, and convective heat transfer is close to that for fluid only Rayleigh–Bénard convection. The contribution of solid conduction in high conductivity packings causes the overall heat transfer to be above that for Rayleigh–Bénard convection.

MHD natural convection in a square porous cavity filled with a water-based magnetic fluid in the presence of geothermal viscosity

PurposeThe purpose of this paper is a numerical analysis of natural convection in a square porous cavity filled with a water-based magnetic fluid of geothermal viscosity under the effect of inclined uniform magnetic field.Design/methodology/approachThe domain of interest includes the square porous cavity filled with a water-based magnetic fluid (W40). Horizontal walls are supposed to be adiabatic, while right vertical wall is kept at constant low temperature and left vertical wall is kept at constant high temperature. An inclined uniform magnetic field affects the fluid flow and heat transfer inside the cavity. The viscosity of the working fluid is proportional to the linearly decreasing function of depth (vertical coordinate) and inversely proportional to the linear function of temperature. It is assumed in the analysis that the flow is laminar. The fluid is Newtonian and the Boussinesq approximation is valid. The governing equations have been discretized using the finite difference method with the uniform grid. Simulations have been carried out for different values of the Rayleigh number, Hartmann number, Darcy number, magnetic field inclination angle and viscosity variation parameters.FindingsIt has been revealed that an increase in the viscosity parameters leads to the heat transfer enhancement and convective flow intensification. At the same time, this intensification is more essential for high values of the Rayleigh number.Originality/valueThe originality of this work is to analyze MHD natural convection in a square porous cavity filled with a water-based magnetic fluid of geothermal viscosity. The results would benefit scientists and engineers to become familiar with the analysis of convective heat and mass transfer in nanofluids, and the way to predict the properties of nanofluid convective flow in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors and electronics.