Horizontal Enclosure Research Articles

Rayleigh–Bénard Convection in a Gas-Saturated Porous Medium at Low Darcy Numbers

Abstract Natural convection heat transfer is measured in a horizontal enclosure filled with a gas-saturated porous medium composed of glass spheres. The height-to-pore scale ratio (H/d) is in the range of 25–150, yielding a low Darcy number (5.87×10−8≤Da≤1.94×10−6), which satisfies the porous medium assumption more rigorously. The maximum values attained for the modified Rayleigh numbers (Ra* up to 6150) and fluid Rayleigh numbers (Raf up to 2.5×1011) at these low Darcy numbers enable access to both the Darcy and Forchheimer flow regimes. The heat transfer relationship just beyond the onset of convection is in good accordance with theory and previous experiments, varying linearly with the modified Rayleigh number. For higher modified Rayleigh numbers, the data diverge as a function of the Darcy number, depending on both Da and the modified Rayleigh number. Transition points between the Darcy and Forchheimer regimes are estimated. At the highest fluid Rayleigh numbers, the data with the largest pore scales show some evidence of moving toward a regime similar to that of Rayleigh–Bénard convection, where boundary layer and plume length scales are small enough that the details of the porous medium cease to matter. It is argued that even in this regime, the boundary layer length scales are not diminished enough to make the contribution of Brinkman drag significant.

Parametric studies of mixed convective fluid flow around cylinders of different cross‐sections

AbstractA numerical study of mixed convective heat transfer in a lid‐driven square enclosure containing a hot elliptic cylinder is conducted. The impacts of the Grashof number , Reynolds number , cylinder tilt angle , and aspect ratio have been examined for a fluid of of 0.71. The horizontal enclosure walls are insulated, while its vertical walls are restricted to a nonvarying temperature Tc, whereas a sinusoidal temperature of is imposed on the wall of the elliptical cylinder. The governing equations are solved using COMSOL Multiphysics 5.6 software. The fluid dynamic and the heat transport profiles between the enclosure and the elliptical cylinder walls are represented by the stream function, isothermal contours, and average Nusselt number. Results established that for all the considered aspect ratios, the thermal heating range of is predominantly a conduction mechanism. The critical position of the ellipse where the inclination effect becomes insignificant is determined by the Grashof number and aspect ratio when the Re = 100. The strength of vortices and cell numbers are significantly influenced by the aspect ratio, particularly when the . When , the average heat transfer from the cylinder remains the same regardless of the cylinder's orientation. The impact of cylinder orientation on heat transfer from the cylinder wall is minimal for . For AR values of , increasing the inclination angle does not result in improved heat transfer. The influence of the increasing inclination angle on the right wall diminishes as the angle increases, except when the Grashof number is greater than 105, where the rate of heat transfer is enhanced for inclination angles beyond 45°.

Study of heat transfer and the nanofluid flow inside a rectangular enclosure with five rectangular baffles in the middle affected by a magnetic field

This article simulates free and forced convection (FCN) in a two-dimensional rectangular enclosure. In the center of the cage are five rectangular heat sources with high temperatures. The two side walls are insulated, and the top (moving) and bottom walls are maintained at a low temperature. In the presence of a magnetic field (MFD) along the length of the enclosure, which is saturated with copper/water nanofluid, the enclosure is affected. The study examines the impact of the Richardson number (Ri) ranging from 0.1 to 100 and Hartmann number (Ha) changing from 0 to 40 on average Nusselt number (NUA). Lattice Boltzmann method (LBM) and FORTRAN software are employed for numerical simulations. The results of this study demonstrate that an increment in the Ha enhances the Nusselt number (Nu) at the Ri of 0.1. At other Ri, enhancing the Ha reduces the NUA. The maximum NUA is 6.89 for the Ha of 40 and the Ri of 0.1. The enhancement in the Ri and the reduction of FCN strength reduce the NUA. The horizontal enclosure has the maximum Nu, which is equal to 3.10, and the vertical enclosure has the minimum NUA.

RETRACTED: Utilization of machine learning and neural networks to optimize the enclosure angle, magnetic field, and radiation parameter for mixed convection of hybrid nanofluid flow next to assess environmental impact

This paper examines the mixed convective heat transfer (HTR) of nanofluid (NFD) flow in a rectangular enclosure with the upper moving wall numerically. The lower wall has a high temperature and a number of semi-circular obstacles with the same temperature are installed on it. The upper moving wall has a low temperature and the other two walls are insulated. The enclosure can change from horizontal to vertical. Radiation HTR is considered in the enclosure and there is a magnetic field (MGF) that can change the angle from horizontal to vertical affecting the NFD. This study is carried out for different angles of the enclosure and MGF from horizontal to vertical for radiation parameters (RDP) of 0 to 3 and a constant MGF with Hartmann number of 20 and Richardson number of 10. The aim is to estimate the Nusselt number (Nu), entropy generation (ETG), and Bejan number (Be). The SIMPLE algorithm is utilized using FORTRAN software, and optimization is done using artificial intelligence to find the maximum and minimum output values. The results demonstrate that the maximum value of Nu and Bes corresponds to the MGF angle and enclosure angle of 90°. The minimum value of the Nu and the maximum amount of ETG corresponds to the horizontal MGF and horizontal enclosure when the RDP is 1.5. An increment in the RDP enhances the amount of Nu. The maximum amount of ETG, i.e. 12.87, corresponds to the enclosure with an angle of 45° for the horizontal MGF and the absence of RDP. corresponds to the enclosure with an angle of 45° for the horizontal MGF and the absence of RDP. It was also found that most environmental impacts, and hence values for different environmental factors, arise from the production of nanoparticles; thus, it is a significant contributor to environmental impacts.

Sensitivity analysis of design parameters for melting process of lauric acid in the vertically and horizontally oriented rectangular thermal storage units

Widespread commercialization of PCM-based latent heat storage systems is limited by the low melting and solidification rates during the phase transition process. In this study, fins are used to enhance the phase change process. A parametric study is conducted to understand the effect of fins on the thermal performance of vertically- and horizontally-oriented rectangular storage tanks. Throughout simulations, the fin volume, and thereby the mass of PCM in the tank, were kept constant. It was observed that the horizontal enclosures can take advantage of the development of strong natural convection flow until near the end of the melting process, whereas with vertical counterparts the strength of the convection currents was diminished during the shrinkage stage. The results suggest that longer and thinner fins are more beneficial for enhancing the melting rate than shorter and thicker fins. It was concluded that for horizontal enclosures with fin lengths of 25 and 35 mm, increasing the number of fins does not necessarily shorten the melting time. The maximum melting time reduction compared to the 3-fin vertical enclosure with a fin length of 25 mm (chosen as our benchmark case) was 75.1% when nine 45-mm-long fins are used in a horizontal enclosure.

Magnetoconvection around an elliptic cylinder placed in a lid‐driven square enclosure subjected to internal heat generation or absorption

AbstractThe impacts of MHD and heat generation/absorption on lid‐driven convective fluid flow occasioned by a lid‐driven square enclosure housing an elliptic cylinder have been investigated numerically. The elliptic cylinder and the horizontal enclosure boundaries were insulated and the left vertical lid‐driven wall was experienced at a fixed hot temperature, and the right wall was exposed to a fixed cold temperature. COMSOL Multiphysics 5.6 software was used to resolve the nondimensional equations governing flow physics. A set of parameters, such as Hartmann number (), Reynolds number (), Grashof number (), heat generation‐absorption parameter (), and elliptical cylinder aspect ratio (AR) () have been investigated. The current study discovered that for low Reynolds number, the adiabatic cylinder AR of 2.0 provided the optimum heat transfer enhancement for the model investigated, also the impact of cylinder size diminishes beyond Gr = 104. But for high Reynolds (Re = 1000), the size of the cylinder with AR = 3.0 offered the highest heat transfer augmentation. The clockwise flow circulation reduces because of an increase in AR, which hinders the flow circulation. In addition, heat absorption supports heat transfer augmentation while heat generation can suppress heat transfer improvement.

The experimental investigation of pipes system array inside the pressurized cylindrical container in various orientations

The experimental investigation of natural convection analysis in pressurized containers has been successfully addressed fusing four identical circular rectangle pipes. The pressurized tank of 0.3 m diameter and 0.45 m height within 0.43 m height and 0.025 m side length interior square pipes are used to obtain the present investigation. Various parameters are used such as gauge pressure (0.5-1 bar), pipes Ra configurations and enclosure orientations. The results are Nusselt number for cold and hot sides. Both sides has reverse response, the parametric analysis shows the ordinary behavior according to gravity and pressure forces interaction. The optimum conditions is observed when horizontal enclosure of top pipe in one bar is applied where the heat transfer improvement is 24 % approximately.

The effect of the baffle length on the natural convection in an enclosure filled with different nanofluids

This paper presents a numerical investigation of the natural convection in an inclined rectangular enclosure with a baffle filled with Cu/water and then with Al2O3/water nanofluids using the finite difference method for tracking the thermal behavior within it versus the baffle length. The horizontal enclosure walls are assumed to be adiabatic, while the vertical ones are supposed to be a differentially heated. A thin horizontal baffle was attached to its left sidewall and is assumed to be cold. The flow and thermal fields are computed, respectively, for various values of Rayleigh number (103 ≤ Ra ≤ 105), inclination angle (0° ≤ $$\emptyset$$ ≤ 60°), baffle length (0.25 ≤ Lb ≤ 0.5), solid volume fraction (0.02 ≤ $$\phi$$ ≤ 0.06), and aspect ratio (1 ≤ AR ≤ 2). It was found that as the Rayleigh number, solid volume fraction, baffle length, and aspect ratio increase, an enhancement in the intensity of fluid flow in the enclosure was observed. In comparison, it reduces when the inclination angle increases. Moreover, it was found that the local Nusselt number (Nuc) enhances with the rise in Rayleigh number and the solid volume fraction. In contrast, it reduces with the increase in the aspect ratio and the inclination angle.

Entropy generation and natural convection flow of a suspension containing nano-encapsulated phase change particles in a semi-annular cavity

Abstract The natural phase change convection of a new type of hybrid nanofluids, suspensions of Nano-Encapsulated Phase Change Materials (NEPCM), was addressed in a semi-annular inclined enclosure. The nanoparticles consist of a polymer shell and a nonadecane shell, in which the nonadecane core can change phase at its melting temperature and absorb/release a significant quantity of latent heat. The NEPCM-suspension circulates in the enclosure due to the natural convection, and the NEPCM particles contribute to heat transfer by phase change. The equations governing the movement and heat transfer of the suspension and nanoparticles were inserted in the form of partial differential equations. The finite element method was used to numerically solve the equations. Then, the entropy generation of NEPCM suspension in the attendance of the phase change was examined. The influence of the fusion temperature and volume fraction of nanoparticles, Stefan number, Rayleigh number, and inclination angle of enclosure on the thermal behavior and entropy generation of the suspension was explored. The results showed that the contribution of phase change core of nanoparticles was significant, and the heat transfer was enhanced by the presence of NEPCM particles. The fusion temperature of particles controls the Bejan number (entropy generation) behavior of the NEPCM suspension. There is an optimum phase change temperature for nanoparticles, which results in maximum heat transfer. For a horizontal enclosure, the optimum fusion temperature is the average temperature of the active walls. This optimum phase change temperature is a function of the tilting angle of the enclosure.

INTEGRATED INFLUENCES OF INCLINATION, NANOFLUIDS, AND FINS ON MELTING INSIDE A HORIZONTAL ENCLOSURE WITH CROSS SECTION OF MAJOR CIRCLE SECTOR

Combined effects of inclination with respect to gravity, Cu nanoparticles, and stainless steel partial fins on constrained ice melting with natural convection inside a horizontal enclosure with cross section of major circle sector are examined. Two-dimensional temperature-based lattice Boltzmann method (TLBM) in single-phase framework is applied to treat the solid-liquid phase change process in the presence of nanofluids. Pertinent variables such as transient liquid fraction, average Nusselt number on hot surfaces, average temperature of PCM, and maximum velocity in molten PCM are investigated. It is found that influences of nanofluids and partial internal fins on thermal performance of the horizontal enclosure and interface morphology are related to inclination angle despite the negative effects of increment of viscosity, weakening of natural convection flow, and decrease of storage capacity.

Numerical investigation on the effect of four constant temperature pipes on natural cooling of electronic heat sink by nanofluids: A multifunctional optimization

In the present study, natural-convective heat transfer along with the effects of radiation of aluminum/water nano-fluid between two blades of a heat sink, which is under the impact of a uniform magnetic-field, is studied numerically. The space between two blades of the heat sink is considered as a two-dimensional square enclosure. In the square cavity, there are four pipes with constant temperature Th with a circular cross section. The RSM method is used to optimize the geometric parameters of the pipes. The results show that the heat transfer rate from the pipes and the irreversibility generation augment and the Bejan number reduces by augmenting the Rayleigh number. The heat transfer intensified 7% and 16% by doubling of the aspect ratio of the pipes at the Rayleigh number of 103 and 106, respectively. As the distance between constant-temperature pipes intensified, Nusselt number augments. As the horizontal enclosure rotates 90°, i.e., it becomes a vertical enclosure, the heat transfer decreases by 22% and total irreversibility decreases by 21%. The optimum physical conditions of the pipes are is in the diameter of 0.15 and 0.25 of distance from each other to have maximum heat transfer and the minimum irreversibility generation.

Experimental investigation on very-high-Rayleigh-number thermal convection in tilted rectangular enclosures

High Rayleigh number thermal convection in tilted rectangular enclosures of different aspect ratios (1,3,6, and 10) and angles of inclination (0°,30°,60°,90°,120°, and 150°) is experimentally studied for 1.85×106⩽Ra⩽1.04×1011 employing compressed gases. For a fixed Rayleigh number, aspect ratio is found to have a discernible effect on Nusselt number for all the cases, except for the horizontal enclosure case (0°), and this decreasing effect becomes stronger as the angle of inclination increases. Nusselt number is observed to monotonously decrease as the angle of inclination is increased, for any given Rayleigh number. A new set of correlations for Nusselt number, valid for the investigated range of studied variables, is proposed. An Racosθ scaling is also found to work reasonably well for angles of inclination less than 60°.

Numerical simulation of turbulent natural convection of nanofluid with thermal radiation inside a tall enclosure under the influence of magnetohydrodynamic

AbstractIn the present study, the natural convective heat transfer in the turbulent flow of water/CuO nanofluid with volumetric radiation and magnetic field inside a tall enclosure has been numerically investigated. The thermophysical properties of nanofluid have been considered variable with temperature and the effects of Brownian motion of nanoparticles have been considered. The main objective of this work is an investigation of the effect of using water/CuO nanofluid and presence of magnetic field on turbulent natural convection in three types of enclosures (vertical, inclined, and horizontal) by considering the volumetric radiation. The governing equations on turbulent flow domain under the influence of the magnetic field and by considering the combination of volumetric radiation and natural convection have been solved by a coupled algorithm. For validating the present research, a comparison has been carried out with the laminar natural convection flow under the influence of the magnetic field and radiation effects and also, the natural turbulent convection flow of previous studies and a proper coincidence has been achieved. The results indicated that by increasing volume fraction and Hartmann number the average Nusselt number enhances and reduces, respectively. By adding 1% CuO nanoparticles to the base fluid, heat transfer improves from 10.59% to 17.05%. However, by increasing the volume fraction from 1% to 4%, heat transfer improves from 1.35% to 4.90%. By increasing Hartmann number from 0 to 600, heat transfer reduces from 9.29% to 22.07%. Also, the results show that the ratio of deviation angle of the enclosure to the horizontal surface has considerable effects on heat transfer performance. Therefore, in similar conditions, the inclined enclosure with a deviation angle of 45° compared to the vertical and horizontal enclosure has better thermal performance.

Optimization of Convective Heat Transfer from Two Heating Generators into Horizontal Enclosure Including A Discrete Obstacle: A Lattice Boltzmann Comprehensive Investigation

Optimization of Convective Heat Transfer from Two Heating Generators into Horizontal Enclosure Including A Discrete Obstacle: A Lattice Boltzmann Comprehensive Investigation

A Gas-Kinetic BGK Scheme for Natural Convection in a Rotating Annulus

In this paper, a gas-kinetic Bhatnagar–Gross–Krook (BGK) scheme is developed for simulating natural convection in a rotating annulus, which arises in many scientific and engineering fields. Different from most existing methods for the solution of the incompressible Navier–Stokes (N–S) equations with the Boussinesq approximation, compressible full N–S equations with allowable density variation are concerned. An appropriate BGK model is constructed for the macroscopic equations defined in a rotating frame of reference. In particular, in order to account for the source (non-inertial) effects in the BGK model, a microscopic source term is introduced into the modified Boltzmann equation. By using the finite volume method and assuming the flow is smooth, the time-dependent distribution function is simply obtained, from which the fluxes at the cell interface can be evaluated. For validation, a closed rotating annulus with differentially heated cylindrical walls is studied. A conventional N–S solver with the preconditioner is used for comparison. The numerical results show that the present method can accurately predict the variation of the Nusselt number with the Rayleigh number, but no preconditioning is required due to its delicate dissipation property. The computed instantaneous streamlines and temperature contours are also investigated, and it is verified that the Rayleigh–Bénard convection in a rotating annulus is very similar to that in a classical stationary horizontal enclosure.

Experimental investigation of melting behaviour of phase change material in finned rectangular enclosures under different inclination angles

The deployment of phase change materials (PCMs) in practical applications is in large part limited by the low thermal conductivity of the available PCMs. Hence, in this study, enhancement in the melting rate of PCM by addition of fins in rectangular enclosures was experimentally investigated under different inclination angles. The melting process of lauric acid in side-heated enclosures with different numbers of fins was evaluated for inclination angles of 90° (vertical), 45° and 0° (horizontal). In order to visualize the melting process, the enclosure was fabricated from transparent acrylic material except one side made of an aluminum plate to heat the enclosure isothermally. Solid-liquid interface positions and temperature history of the PCM were recorded and applied to calculate the liquid fractions and heat transfer rates. The evolution of the interface in the inclined enclosures revealed that the development of vortical flow structures in the liquid PCM by decreasing the inclination angle significantly improves the melting rate. It was found that for both finned and unfinned enclosures the melting rate increases by reducing the inclination angle. Heat transfer enhancements obtained by the 0-fin horizontal and 3-fin vertical enclosures compared to the 0-fin vertical enclosure were 115% and 56%, respectively. This thermal behavior proposes that simply inclining the enclosure can be more effective to enhance the melting rate than adding fins to the vertical enclosure. Among the different cases studied, the 3-fin horizontal enclosure showed the maximum heat transfer rate and consequently the minimum melting time. The present investigation can contribute to a better understanding of PCM melting in the inclined finned enclosures and provide much-needed benchmark data for the future numerical simulations.

Numerical simulation of natural convection in a horizontal enclosure: Part I. On the effect of adiabatic obstacle in middle

In this study, an effect of a three-dimensional obstacle of natural convection in a horizontal enclosure was discussed. Geometry which was taken into account was horizontal enclosure with unit aspect ratio and length of π along spanwise direction. The enclosure was heated from the bottom wall, and then was cooled down from above. An obstacle was located in the middle of the enclosure to examine its effect. A three-dimensional solution was obtained using Chebyshev spectral multi-domain methodology for different Rayleigh number at which the thermal behavior was evolved from a steady state to a chaotic pattern. As the geometry was elongated in conjunction with periodic boundary conditions to allow lateral freedom for the convection cells, longitudinal geometry along spanwise direction was discretized through a Fourier series expansion with a uniform mesh configuration. An adiabatic obstacle played a different role in determining the thermal behavior: No-slip condition of the surface of the obstacle disturbed the overall plume behavior in terms of the momentum transfer, whereas the adiabatic boundary condition did not influence significantly in terms of energy transfer. At a low Rayleigh number, thermal behavior in three-dimensional enclosure showed steady invariant solution along spanwise direction which is identical to two-dimensional result. With increasing buoyant force, spanwise invariance of longitudinal roll cell was collapsed and three-dimensional mode was obtained following flow regime transition. After undergoing periodically oscillatory phase, a chaotic flow transition occurred. At a high Rayleigh number, three-dimensional thermal plume oscillates freely in elongated geometry and consequently yields higher heat transfer rate. In addition, the thermal flow field was captured by visualizing the three-dimensional vortical structure. The chaotic three-dimensional flow behavior was quantitatively examined by obtaining the turbulent statistics.

The Weight Loss Effect of Heated Inner Cylinder by Free Convection in Horizontal Cylindrical Enclosure

The work presents results of numerical simulations of natural convection in cavity formed by the surfaces of two horizontal coaxial cylinders. The temperature of the outer cylinder is constant. The area between the cylinders is filled with an ideal incompressible fluid. The inner cylinder is set as the heater. The solution of the equations of thermal convection in a two-dimensional approximation performed by the software package ANSYS Fluent with finite volume method. The study compares the results of numerical simulation with several well-known theoretical and experimental results. The nature of interaction of the inner cylinder with a convection current created in the gap was observed. It was shown that the flux appeared around a heated cylinder affects the weight of the heat source and causes an additional lift force from the surrounding fluid. The various Rayleigh numbers (from 1.0 ⋅ 103 to 1.5 ⋅ 106) and fluid with different Prandtl number (from 0.5 to 1.0 ⋅ 105) are considered.

On the three-dimensional effect for natural convection in horizontal enclosure with an adiabatic body: Review from the 2D results and visualization of 3D flow structure

In this study, effect of three-dimensionality of natural convection in horizontal enclosure was discussed. Geometry which was taken into account was horizontal enclosure with radially unit aspect ratio and π of longitudinal direction. The enclosure was heated from the bottom wall, and then was cooled down from above. In addition, obstacle was located in middle of the enclosure to examine an effect of the existence of it. A two-dimensional solution was obtained using Chebyshev spectral multi-domain methodology for different Rayleigh number at which the thermal behavior was evolved from steady state to chaotic pattern. As the geometry was elongated in conjunction with periodic boundary conditions to allow lateral freedom for the convection cells, longitudinal direction was discretized through a Fourier serious expansion with a uniform mesh configuration. Prior to investigate thermal behavior of fluid layer in three-dimensional simulation, two-dimensional results were reviewed with respect to spatial resolution. Whereas coarse resolution provoked thermal instability at intermediate Rayleigh number to have subharmonic solution, fine spatial resolution yielded stably steady convection mode. Thermal behavior in three-dimensional enclosure at low Rayleigh number showed two-dimensional pattern invariant to longitudinal direction. As increasing of buoyant force, longitudinal invariance was collapsed and onset of three-dimensional thermal plume occurred. At high Rayleigh number, three-dimensional thermal plume oscillates freely in elongated geometry and consequently yields higher heat transfer rate. In addition, thermal flow field was captured by visualizing the three-dimensional vortical structure. The chaotic three-dimensional flow behavior was quantitatively examined by obtaining turbulent statistics and compared with those from two-dimensional simulation.

Natural convective heat transfer within nanofluid-filled hemispherical horizontal enclosure

This survey deals with some steady-state natural convection taking place in a hemispherical enclosure filled with nanofluid consisting of water based metallic nanoparticles, with volumetric fraction ranging between 0% (pure water) and 20%. The hot active wall of the cavity is its horizontal disk subjected to a wide range of constant heat fluxes. The 3D numerical approach is done by means of the finite volume method based on a mixture model. Temperature and velocity distributions are presented for some typical cases and the heat transfer is quantified by means of the Nusselt number versus Rayleigh number. A comparison done between the results with the water and the nanofluid clearly confirms enhancement of the convective heat transfer with the nanoparticles.