Vertical Enclosure Research Articles

Numerical and theoretical study of natural convection in a nanofluid-filled vertical rectangular enclosure

The objective of the present research is to characterize the numerical and theoretical study of a non-stationary laminar natural convection in a vertical rectangular enclosure filled with a mixture of water and nanoparticles, and heated from the vertical sides. The governing equations have been discretized by the finite volume method. A numerical code was conceived and realized in this context to solve the obtained equations. A parametric study was conducted by considering the Rayleigh number, the type of nanofluid and the solid volume fraction. The results are in agreement with those obtained by others working in the same field.

Numerical Study of Natural Convection in Vertical Enclosures Utilizing Nanofluid

Enhancement of buoyancy-driven convection heat transfer within vertical cavities containing nanofluids subjected to different side wall temperatures and various aspect ratios is investigated. The computations are based on an iterative, finitevolume numerical procedure (SIMPLE) that incorporates the Boussinesq approximation to simulate the buoyancy term. With the base fluid being water, three different nanoparticles (Cu, TiO2, and Al2O3) are considered as the nanofluids. This study has been carried out for the pertinent parameters in the following ranges: the Rayleigh number, Raf = 105–107 and the volumetric fraction of nanoparticle between 0 and 5 percent. The results are presented for different length-to-height ratios varying from 0.1 to 1.0. The comparisons show that the mean Nusselt numbers and velocity magnitudes increase with volume fraction for the whole range of the Rayleigh numbers. The predictions show a noticeable heat transfer enhancement compared to pure fluid. It is also found that the heat transfer enhancement utilizing nanofluid is more pronounced at low aspect ratios than high aspect ratios. Moreover, the results depict that the addition of nanoparticles to the pure fluid has more effects at lower Rayleigh numbers.

Numerical modelling the unsteady process of closed rectangular area radiant heating in conjugate formulation with accounting energy distribution along horizontal and vertical enclosure structures

Mathematical modelling of unsteady convective-conductive heat exchange in premises, heated by infrared radiant heater is passed. Heat flux density from infrared radiant heater was calculated accounting energy distribution along horizontal and vertical building envelope. Comparison between zonal method and Lambert's law radiant energy distribution was done.

Natural Convection in a Vertical Rectangular Enclosure

Natural Convection in a Vertical Rectangular Enclosure

Heat transfer of Cu–water nanofluid in an enclosure with a heat sink and discrete heat source

Heat transfer inside horizontal and vertical enclosure filled with Cu–water nanofluid is studied. A heat sink with rectangular fins represents the base plate of the enclosure where it is heated by a discrete heat source at the bottom of the heat sink. The front face of the heat sink is kept at constant low temperature while the side walls are assumed adiabatic. The results are presented for the enclosure without and with a heat sink of one to seven fins. The ratio of enclosure height to enclosure width is 0.25 and the study is carried out at a fin length to enclosure height ratio of 0.25 and 0.5. The effect of the volume fraction and nanoparticle diameter of Cu nanoparticles is carried out for different spacings between the fins of the heat sink and different Rayleigh numbers. The numerical model is solved by a finite volume method. The results show that the average Nusselt number on the heat source increases with increase Rayleigh number and volume fraction of Cu nanoparticles and with decreasing diameter of Cu nanoparticles. At low Ra number (Ra=103), the average Nusselt number increases with increasing number of fins and increasing L/H. At high Raleigh number (Ra=106), an increase in the value of L/H has no great effect on the average Nusselt number. At high Rayleigh number (Ra=106) and low nanoparticle diameter and high volume fraction, the enclosure with a heat sink of one fin and L/H of 0.5 has the maximum average Nusselt number for horizontal and vertical enclosure.

Magnetoconvective Transport in a Vertical Lid-Driven Cavity Including a Heat Conducting Square Cylinder with Joule Heating

The hydromagnetic mixed convection flow and heat transfer in a vertical lid-driven square enclosure is numerically simulated following a finite volume approach based on the SIMPLEC algorithm. Both the top and bottom horizontal walls of the enclosure are insulated, and the left and right vertical walls are kept isothermal with different temperatures. The left vertical wall is translating in its own plane at a uniform speed, while all other walls are stationary. Two cases of translational lid motion, viz. vertically upward and downward, are considered. A uniform magnetic field is applied along the horizontal direction normal to the translating wall. A heat conducting horizontal solid square cylinder is placed centrally within the outer enclosure. Simulations are conducted for various controlling parameters, such as the Richardson number (1 ≤ Ri ≤ 10), Hartmann number (0 ≤ Ha ≤ 50), and Joule heating parameter (0 ≤ J ≤ 5), keeping the Reynolds number based on lid velocity fixed as Re = 100. The flow and thermal fields are analyzed through streamline and isotherm plots for various Ha, J, and Ri. Furthermore, the pertinent transport quantities such as the drag coefficient, Nusselt number, and bulk fluid temperature are also plotted to show the effects of Ha, J, and Ri on them.

The Effect of Alumina–Water Nanofluid on Natural Convection Heat Transfer Inside Vertical Circular Enclosures Heated from Above

Experimental investigation on natural convection heat transfer is carried out inside vertical circular enclosures filled with Al2O3–water nanofluid with different concentrations; 0.0%, 0.85% (0.21%), 1.98 (0.51%), and 2.95% (0.75%) by mass (volume). Two enclosures are used with 0.20 m inside diameter and with two different aspect ratios. The top surface of the enclosure is heated using a constant-heat-flux flexible foil heater while the bottom surface is subject to cooling using an ambient air stream. Various heat fluxes are used to generate heat transfer through the nanofluid. The average Nusselt number is obtained for each enclosure and correlated with the modified Rayleigh number using the concentration ratio as a parameter. A general correlation for the average Nusselt number with the modified Rayleigh number is obtained using the volume fraction and the aspect ratio as parameters to cover both enclosures. The results show that the Nusselt number for the alumina–water nanofluid is less than that of the base fluid. This means that using the alumina–water nanofluids adversely affects the heat transfer coefficient compared to using pure water. It is also found that the degree of deterioration depends on the concentration ratio as well as the aspect ratio of the enclosure.

Hydromagnetic Mixed Convective Transport in a Vertical Lid-Driven Cavity Including a Heat Conducting Rotating Circular Cylinder

Two-dimensional numerical simulation is performed for the hydromagnetic mixed convective transport in a vertical lid-driven square enclosure filled with an electrically conducting fluid in the presence of a heat conducting and rotating solid circular cylinder. Both the top and bottom horizontal walls of the enclosure are considered thermally insulated, and the left and right vertical walls are kept isothermal with different temperatures. The left wall is moving in the upward direction at a uniform speed, while all other walls are stationary. A uniform magnetic field is applied along the horizontal direction normal to the moving wall. A heat conducting circular cylinder is placed centrally within the outer enclosure. The cylinder is made to rotate in its own plane about its centroidal axis. Both the clockwise and counterclockwise rotations of the cylinder are considered. All solid walls are assumed electrically insulated. Simulations are performed for various controlling parameters, such as the Richardson number (1 ≤ Ri ≤ 10), Hartmann number (0 ≤ Ha ≤ 50), and dimensionless rotational speed (−5 ≤ Ω ≤ 5) keeping the Reynolds number based on lid velocity fixed as Re = 100. The flow and thermal fields are analyzed through streamline and isotherm plots for various Ha, Ω, and Ri. Furthermore, the pertinent transport quantities such as the drag coefficient, Nusselt number, and bulk fluid temperature are also computed to understand the effects of Ha, Ω, and Ri on them. It is observed that the heat transfer greatly depends on the rotational speed of the cylinder.

Natural Convection in Vertical I-Shaped Nanofluid-Filled Enclosures

Natural Convection in Vertical I-Shaped Nanofluid-Filled Enclosures

Numerical study of solidification of a nano-enhanced phase change material (NEPCM) in a thermal storage system

The effects of nanoparticle dispersion on solidification of a Cu-n-hexadecane nanofluid inside a vertical enclosure are investigated numerically for different temperatures of the left vertical wall. An enthalpy porosity technique is used to trace the solid-liquid interface. The resulting nanoparticle-enhanced phase change materials (NEPCMs) exhibit enhanced thermal conductivity in comparison to the base material. The effect of the wall temperature and nanoparticle volume fraction are studied in terms of the solid fraction and the shape of the solid-liquid phase front. It has been found that a lower wall temperature and a higher nanoparticle volume fraction result in a larger solid fraction. The increase in the heat release rate of the NEPCM shows its great potential for diverse thermal energy storage applications.

MHD Mixed Convection in a Lid-Driven Cavity Including a Heated Source

Numerical simulations are performed to understand the thermo-magneto-convective transport of fluid and heat in a vertical lid-driven square enclosure following a finite volume approach based on the SIMPLEC algorithm. The enclosure is filled with an electrically conducting fluid and having a heated source on the right vertical wall. Two different types of sources, such as a semicircular and a rectangular one, are considered. Both the top and bottom horizontal walls and the right vertical wall, except the source of the enclosure, are assumed insulated and the left vertical wall and the sources are kept isothermal with different temperatures. The left vertical wall is also translating in its own plane at a uniform speed, while all other walls are stationary. Two cases of translational lid motion, viz., vertically upward and downward are considered. A uniform magnetic field is applied along the horizontal direction normal to the translating wall. Shear forces due to lid motion, buoyancy forces as a result of differential heating, and magnetic forces within the electrically conducting fluid act simultaneously. Heat transfer due to forced flow, natural convection, and Joule dissipation are taken into account. Simulations are conducted for various controlling parameters, such as the Rayleigh number (103 ≤ Ra ≤ 105), Hartmann number (0 ≤ Ha ≤ 100), and Joule heating parameter (0 ≤ J ≤ 5), keeping the Reynolds number based on lid velocity fixed as Re = 100. The flow and thermal fields are analyzed through streamline and isotherm plots for various Ha and J. Furthermore, the pertinent transport quantities such as the drag coefficient, Nusselt number, and bulk fluid temperature are also plotted to show the effects of Ha, J, and Ra on them.

Three-dimensional PCM melting in a vertical cylindrical enclosure including the effects of tilting

Experiments have been conducted in order to generate detailed data associated with the outward melting of a PCM induced by a heated rod that is placed concentrically within a cylindrical enclosure. Heat transfer and melting effects in a base-case configuration consisting of a vertically-oriented enclosure are successfully simulated with an established two-dimensional numerical model, partially validating the experimental apparatus and procedure. Experimental measurements indicate that modest tilting of the test cell significantly affects measured local temperatures within the PCM, as well as the temporal evolution of the solid morphology as it melts. The modification is attributed to the establishment of three-dimensional flow within the molten PCM. The experimental data for the tilted enclosure cases might be used to validate three-dimensional models for PCM melting in geometrical configurations relevant to, for example, latent heat thermal energy storage systems.

CFD analysis of heat transfer within a bottom heated vertical concentric cylindrical enclosure

The CFD analysis of heat transfer within a bottom heated vertical concentric cylindrical enclosure is important with respect to the process in the chemical and process industries. The research work focuses on the CFD analysis of the enclosure with respect to the machines used for the segregation of chemicals in the chemical industries. The CFD simulations are performed to study the effects of inner cylinder material and outer cylinder geometric configurations on the heat transfer mechanism in the enclosure. The CFD simulations are conducted at a bottom disc temperature of 393 K and compared with the published results at a temperature of 433 K. This research study depicts the behavior of bottom heated vertical concentric cylindrical enclosure at different bottom disc temperatures. This study also investigates the heat transfer mechanism of the enclosure using different inner cylinder materials and different configurations of the outer cylinder. In such enclosures a uniform temperature is required for the segregation of chemicals. A more uniform temperature is observed in the enclosure by using aluminum inner cylinder of the bottom disc and using two different diameter outer cylinders as compared to the mild steel and stainless steel.

An experimental study on melting heat transfer of paraffin dispersed with Al2O3 nanoparticles in a vertical enclosure

Melting experiments in a vertical square enclosure are undertaken with a solid–liquid phase-change material (n-octadecane) dispersed with nanoparticles (Al2O3) as the nano-phase-change-material (nano-PCM). The enclosure has a cross-section dimension of 25 by 25mm and it was 60mm long. The vertical side walls were differentially heated isothermally while the remaining side walls were thermally insulated. The effect of dispersing nanoparticles in the base phase change material (PCM) on the melting heat transfer characteristics in the enclosure is examined for the relevant parameters in the following ranges: the mass particle fraction of nanoparticles, ωp=0, 5, 10wt.%; the Rayleigh number, Raf=1.71×106–5.67×107; the Stefan number, Stef=0.037–0.108; and the subcooling parameter, Sb=0.042–0.537. The surface-averaged heat transfer results obtained during the melting experiments indicate that natural convection heat transfer into the melted region of the enclosure tends to degrade markedly with increasing mass fraction of nanoparticles dispersed in the nano-PCM, when compared with that of the base PCM.

Numerical simulation of electrohydrodynamic effect on natural convection through a vertical enclosure channel

ABSTRACTAn externally applied electric field beside a plane layer of dielectric liquid can induce secondary flows. This phenomenon is called electrohydrodynamic (EHD) effect and can result in heat transfer enhancement. In this study the effect of EHD force on natural convection heat transfer coefficient of water through a vertical enclosure channel is investigated by numerical simulation, using Comsol Multiphysics software. Also, the interaction between EHD force, fluid flow field, pressure field and temperature field was investigated by computational fluid dynamics technique. Flow pattern, temperature distribution, back pressure and pressure due to suddenly expanded flow are substantially affected by applied electric field, especially at low Rayleigh numbers. The results show that by increasing the temperature difference up to 40 K and the applied voltage up to 100 V, the heat transfer coefficient is increased by more than 1000 kW/cm2 K for three different enclosure channel lengths. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Convectons and secondary snaking in three-dimensional natural doubly diffusive convection

Natural doubly diffusive convection in a three-dimensional vertical enclosure with square cross-section in the horizontal is studied. Convection is driven by imposed temperature and concentration differences between two opposite vertical walls. These are chosen such that a pure conduction state exists. No-flux boundary conditions are imposed on the remaining four walls, with no-slip boundary conditions on all six walls. Numerical continuation is used to compute branches of spatially localized convection. Such states are referred to as convectons. Two branches of three-dimensional convectons with full symmetry bifurcate simultaneously from the conduction state and undergo homoclinic snaking. Secondary bifurcations on the primary snaking branches generate secondary snaking branches of convectons with reduced symmetry. The results are complemented with direct numerical simulations of the three-dimensional equations.

Experimental and numerical study of buoyancy driven flow within a bottom heated vertical concentric cylindrical enclosure

The study of buoyancy driven flow within bottom-heated vertical concentric cylindrical enclosure was important with respect to the processes in chemical and nuclear industries. In this research paper, experimental and numerical study of the axial temperature gradient and the heat transfer mechanism within the enclosure were performed. The numerical simulations were validated by comparing the numerical results with experimentally measured axial temperature. The numerical results of the streamlines within the enclosure depicted the real picture of the buoyancy effects. Eighteen different experiments were performed by using inner cylinder of different materials and outer cylinder of different diameters within the bottom disc temperature range of 353 - 433 K. The CFD simulations were performed to study the buoyancy effects within the enclosure. At the bottom disc with temperature up to 393 K, the streamlines within the inner cylinder were almost the same for both con- figurations being independent of outer cylinder diameter, while at 433 K streamlines within the inner cylinders varied. With larger diameter outer cylinder configuration, the buoyancy effects in the outer annulus were stronger as compared to smaller one.

Entropy generation for unsteady natural convection and thermal radiation inside a porous enclosure

Entropy generation problem for unsteady natural convection and thermal radiation in a vertical porous enclosure, submitted to a uniform hot walls temperature and filled with a fluid saturated porous medium, has been performed. A time–space variations study is presented for fluid flow, heat transfer and radiative transfer irreversibilities, local entropy generation Sgen and modified Bejan number Bem. A sensitivity study shows that Bem increases, particularly near the boundaries, due to an increase in N or Br values and it decreases as τD or R values increase. For the cases of ε and ω, an inversion phenomenon is observed. Furthermore, Sgen and the total entropy generation Egen values rise when there is an increase in ε, τD, R or Br values. In opposition, Sgen and Egen values decrease with the increase of ω or N values.

Unsteady Double Diffusive Natural Convection in Porous Media-Application to CO2 Storage in Deep Saline Aquifer Reservoirs

Storage capacity of carbon dioxide (CO2) in deep saline aquifers is a challenging task. However, an assessment must be performed to determine whether there is sufficient capacity in a storage site for any CO2 sequestration project. We evaluated the CO2 storage capacity for a simplified reservoir system, which the layered potential storage formations are overlaid by sealing cap rock.In this paper, we aim to investigate numerically the storage of CO2 at supercritical conditions in deep saline aquifer reservoirs. Numerical simulations were carried out on non-deformable saturated porous material inside a vertical enclosure, assumed to be impermeable and isolated on three sides. The porous medium is considered to be homogeneous and isotropic with constant thermo-physical properties with the exception of the density of the fluid varying according to Boussinesq approximations.A dynamic model assuming that flow is two-dimensional and obeying to Darcy's law for motion has been used. We assume also that the thermal equilibrium assumption is valid. The set of the conservation equations along with the appropriate initial and boundary conditions have been resolved numerically by the classical finite volume method [1]. Spatio-temporal variations of different state variables such as pressure, velocity, temperature and concentration were numerically simulated and plotted versus different controlling parameters particularly, thermal and solutal Rayleigh numbers and Lewis number. Great attention was paid to examine the sensitivity of heat and mass transfer rates according to the reservoir form and the operating conditions.

The Solution to the Safety Factor of Vertical Shaft Enclosure with One-Side Elevation Angle Based on FLAC3D

The enclosure structure of the vertical shaft of subway engineering is generally vertical, and perpendicular to the plane. Due to the effects of the geological condition, the construction condition and the supporting method, the shaft reflects similar deformation characteristics to the enclosure structure of foundation pit. Generally, the enclosure structure deformation can be decomposed into three types, namely the forward rotation, reverse rotation and deflection. When the vertical shaft enclosure structure produces a forward rotation with a lesser degree, it can still be used for positive angle slope processing, which enables us to calculate the safety factor of one side with positive angle enclosure structure in the same way with the slope of foundation pit. Taking the shield-receiving shaft of Dalian Jiaotong university station, Dalian metro No.2, Section 201 as an example, it is the geological conditions and supporting structure that contribute to build the enclosure structure with one-side elevation angle. Based on the above method and taking the geological, construction and supporting conditions into account, FLAC3D is used to build the model, and carry out the solution on safety factor of the enclosure structure with positive angle. The results indicate that under the existing conditions, the enclosure structure safety factor for our example is more than 1.