Numerical Simulation of Natural Convection Around an Obstacle Placed in an Enclosure Filled with Different Type of Nanofluid (original) (raw)
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In this research, the natural convection heat transfer from the horizontal circular cylinder in a vented enclosure filled with nanofluid is investigated numerically. Governing equations settling in the vorticitystream function formulation is inclusive in the numerical work, which transformed into fitted body coordinate system. The study covered the following ranges of Rayleigh number 10 4 Ra10 6 , nanofluid volume fraction 0 0.2, enclosure width 1.667 W/D 5, and opening size 0O/W1. The effect of Rayleigh number, nanofluid volume fraction, enclosure width, and opening size on the Nusselt number, flow patterns and isotherms were investigated. The result shows that the Nusselt number is proportional with Rayleigh number, opening size and volume fraction of nanofluid and inversely proportional with enclosure width. The isotherms and flow patterns display the temperature and flow behaviors with changing studied variables. The thickness of thermal boundary layer decreases with increasing Rayleigh number for each opening size, enclosure width and nanofluid volume fraction.
ScienceDirect, 2019
In this study, the mixed convection of nanofluid containing water as a base fluid and aluminum oxide as a nanoparticles in a lid-driven cavity including a hot elliptical centric cylinder is studied. The effects of a hot elliptical centric cylinder, cavity angle (α) and solid volume fraction (φ) of nanoparticles are investigated. The obtained results show that with increase of solid volume fraction and due to more condensation of nanofluid and more Brownian motion, the claustration phenomena occurred and resulting an increase of thermal conductivity and convection heat transfer coefficients (k, h) and heat transferred more from the higher temperature surface to the lower temperature wall. Also, heat transfer (q) and Nusselt number (Nu) increased due to the increase in the temperature difference (ΔT) between the hot cylinder and lower temperature surfaces at a constant cavity angle, solid volume fraction and Richardson number (Ri). By considering all diagrams, the highest value of nanofluid’s velocity was around the cap and right-side wall and the lowest velocity value was around the thermal cylinder and left side and down walls. The results show that the increase rate of the Nu from 0 to 45◦ in φ = 0.1% and 0.2% and base fluid is equal to 1.7, 0.8 and 0.3 respectively
International Journal of Numerical Methods for Heat & Fluid Flow, 2014
Purpose -The purpose of this paper is to study the effects of natural convection heat transfer in a cold outer circular enclosure containing a hot inner elliptic circular cylinder. The fluid in the enclosure is Cu-water nanofluid. The main emphasis is to find the numerical treatment for the said mathematical model. The effects of Rayleigh number, inclined angle of elliptic inner cylinder, effective of thermal conductivity and viscosity of nanofluid, volume fraction of nanoparticles on the flow and heat transfer characteristics have been examined. Design/methodology/approach -A very effective and higher order numerical scheme Control Volume-based Finite Element Method (CVFEM) is used to solve the resulting coupled equations. The numerical investigation is carried out for different governing parameters namely; the Rayleigh number, nanoparticle volume fraction and inclined angle of elliptic inner cylinder. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell-Garnetts (MG) and Brinkman models, respectively. Findings -The results reveal that Nusselt number increases with an increase of nanoparticle volume fraction, Rayleigh numbers and inclination angle. Also it can be found that increasing Rayleigh number leads to a decrease in heat transfer enhancement. For high Rayleigh number the minimum heat transfer enhancement ratio occurs at. Originality/value -To the best of the authors' knowledge, no such analysis is available in the literature which can describe the natural convection heat transfer in a nanofluid filled enclosure with elliptic inner cylinder by means of CVFEM.
Mixed Convection of Heat Transfer around Rotating Cylinders inside Enclosure Filled with Nano Fluid
International Research Journal of Innovations in Engineering and Technology, 2021
Mixed convection of heat transfer in 2D-square enclosure with an inner two rotating solid circular cylinder had been investigated numerically, the domain between the enclosure walls and cylinders is filled with (Cu-Water) nano fluid. For numerical computational, the dimensionless governing equations were modeled and formulated based on the Galerkin Finite Element Methods. All walls of the enclosure were insulated while the right cylinder was kept at constant hot temperature and the other left cylinder was kept at constant cold temperature. The current study examines the effect of the cylinders angular rotational speed between (0 and-10000), cylinders diameter (0.2, 0.3, and 0.4), Richardson number (0.1 and 10), and the volume fraction of the nano particle (0 to 0.6). The results have been shown in term of isotherm lines, stream function, average Nusselt number, and offered graphically. The results showed that the temperature gradient , intensity of flow and average Nusselt number increases with increase of angular rotational speed, the diameter, and the volume fraction of the nanoparticle whereas it decreases with an increase in Richardson number. The enhancement of the average Nusselt number increase with increase of rotating speed, concentration of nanoparticle and cylinder diameter with ratio of (75.17%), (3.37%) and (73.25%) respectively. While the average Nusselt number decreased with increase in Richardson number with ratio of (13.37%).
Journal of the Taiwan Institute of Chemical Engineers, 2018
Research on nanofluid for heat transfer enhancement of thermal systems has received great attention owing to the lack of energy sources. In this study, fluid flow and natural convection heat transfer of Al 2 O 3-Water or TiO 2-water nanofluid inside a U-shaped cavity consist of a hot obstacle has been investigated numerically by lattice Boltzmann method (LBM). In this paper, different parameters are investigated such as Rayleigh number, the solid volume fraction of the nanoparticles, the U-shaped cavity's aspect ratio and heating obstacle's height on the flow field and heat transfer in the enclosure. The results showed that the Rayleigh number (Ra), cavity aspect ratio (AR) and obstacle's height can be affected on isotherms, streamlines and local and average Nusselt number. The average Nusselt number of the obstacle sides increased by increasing the Ra number and solid volume fraction of nanoparticles (φ) regardless the AR. In addition, by increasing the AR , the average Nusselt number increased. At low Ra , the effect of nanoparticles on increment of heat transfer for narrow cavities was more than wide ones.
Acta Physica Polonica A, 2013
The phenomena of combined convection within a lid-driven square cavity subjected to variable properties of nanouid having a hot obstacle have been analyzed numerically. Finite volume method with SIMPLER algorithm is employed for solving the NavierStokes and energy balance equations. In this paper diameter of nanoparticles are uniform, constant and equal to 47 nm. Wide range of parameters such as Richardson number (0.01 < Ri < 100), solid volume fraction (0.00 < ϕ < 0.05), temperature of uid (300 < T < 340) and height of heated obstacle (0.1 < h < 0.3) have been used. Numerical results are presented in terms of streamlines, isotherms and average Nusselt numbers diagram. The comparisons show that the average Nusselt number decreases with increasing temperature of nanouid for the whole range of the Richardson numbers. Also heat transfer augments as the height of heat obstacle on the bottom wall increases.
Journal of Applied and Computational Mechanics, 2020
In this paper, laminar natural convection of copper/water nanofluid in an open-ended L-shaped cavity is investigated by Lattice Boltzmann Model (LBM). The results are compared by previous studies that are in good agreement. Influences of Rayleigh number (Ra = 10 3 , 10 4 , 10 5 , 10 6), cavity aspect ratio (AR = 0.2, 0.4, 0.6) and volume concentration of Cu nanoparticles (0 ≤ ≤ 0.1) on the momentum, thermal fields and heat transfer in the enclosure are studied. Also, the effect of changing the boundary conditions, on the heat transfer rate has been investigated. It is observed that maximum heat transfer enhancement by adding the nanoparticles for Ra = 10 6 with AR = 0.4 (32.76%) occurs. Results illustrate that increasing the cavity aspect ratio decreases heat transfer rate for Ra = 10 3 and Ra = 10 4. The least and most heat transfer rate for Ra = 10 5 occurs in enclosures by aspect ratios of 0.2 and 0.4 respectively, while it was observed at Ra = 10 6 for minimum and maximum rate of heat transfer the opposite behavior that at Ra = 10 5 occurs.
Heat transfer enhancement in engineering systems can be reached using nanofluids. Very often, technical devices are chambers with moving borders of a flat or a wavy shape having internal heat-conducting blocks. Therefore, the present study is devoted to study computationally the problem of time-dependent heat transfer of alumina-water nanoliquid within a differentially heated chamber with isothermal moving vertical walls and adiabatic horizontal ones under the impact of an inner solid cylinder. The upper wall of the chamber is assumed to have a wavy shape. Basic equations written in non-dimensional primitive variables using the two-component nonhomo-geneous equilibrium model for transport phenomena in nanofluids incorporating the effects of Brownian diffusion and thermophoresis with Corcione empirical correlations for the viscosity and thermal conductivity combined with heat conduction equation for the centered solid cylinder has been resolved by the Galerkin finite-element method. The influences of the dimensionless time (0 ≤ í µí¼ ≤ 120), Reynolds number (í µí±í µí± = 10 and 100), Richard-son number (0.01 ≤ Ri ≤ 100), constant moving parameter [(í µí¼ í µí± = 1 , í µí¼ í µí± = −1), (í µí¼ í µí± = 1 , í µí¼ í µí± = 1), (í µí¼ í µí± = −1 , í µí¼ í µí± = 1), (í µí¼ í µí± = −1 , í µí¼ í µí± = −1)], nanoparticle volume fraction (0 ≤ í µí¼ ≤ 0.04), number of undulations (0 ≤ N ≤ 4) and the dimen-sionless radius of solid cylinder (0.05 ≤ S ≤ 0.25) on the isolines of stream function, temperature and nanoparticles concentrations, as well as the local and average Nusselt numbers have been investigated. It has been found that a rise of the average Nusselt number at the hot wall depends on the moving parameter and the thermal transmission intensity diminishes with the undulations number and the inner solid cylinder diameter. At the same time, the wavy shape of the border, the characteristics of internal cylinder and the properties of nanofluid are very good control parameters for the heat transfer rate and the fluid flow rate.
Since in most industrial rotating equipment, increasing thermal efficiency and reduction of drag has always been subject of interest, in this paper, a 2-D numerical investigation on mixed convection heat transfer and drag coefficient in a lid-driven square cavity filled with Al 2 O 3 Nanofluid is done under the effect of an inner rotating cylinder. To analyze effective parameters on heat transfer and drag coefficient on movable wall, a sensitivity analysis is carried out utilizing the Response Surface Methodology. Simulations are performed for effective parameters of the Richardson number (0.1 ≤ Ri ≤ 10), dimensionless rotational speed (0 ≤ Ω ≤ 5), a/b ratios (0.5 ≤ S ≤ 1), and the Nanoparticle volume fraction (0.00 ≤ Ф ≤ 0.03) with a constant Grashof number of 10 4 . It is found that the mean Nusselt number enhances with Ri number and Ф and decreases with increasing of Ω and S. Additionally, increasing the Ri number and Ω increases the drag coefficient but it reduces as Ф and S increase. The sensitivity analysis results showed that to maximize the mean Nu number and minimize the drag coefficient simultaneously, the effective parameters must be Ω = 0, Ri = 0.13636, Ф = 0.03 and S = 0.5.
Review of Heat Transfer Analysis in Different Cavity Geometries with and without Nanofluids
Nanomaterials
Many strategies have been attempted for accomplishing the needed changes in the heat-transfer rate in closed cavities in recent years. Some strategies used include the addition of flexible or hard partitions to the cavities (to split them into various pieces), thickening the borders, providing fins to the cavities, or altering the forms or cavity angles. Each of these methods may be used to increase or decrease heat transmission. Many computational and experimental investigations of heat transport in various cavity shapes have been conducted. The majority of studies focused on improving the thermal efficiency of heat transmission in various cavity containers. This paper introduced a review of experimental, numerical, and analytical studies related to heat transfer analyses in different geometries, such as circular, cylindrical, hexagonal, and rectangular cavities. Results of the evaluated studies indicate that the fin design increased heat transmission and sped up the melting time o...