Effect of a Magnetic Field on Mixed Convection of a Nanofluid in a Square Cavity (original) (raw)
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Thermal Science, 2016
In this paper, a new approach is used for numerical analysis of the sole effects of nanoparticles volume fraction of Cu-water nanofluid on laminar mixed and natural convection heat transfer in a 2-D cavity. Horizontal walls are insulated and fixed, and vertical walls are maintained at constant temperature. Vertical walls are considered for both fixed and moving conditions. Some researchers have studied flow and heat transfer of nanofluid in a lid-driven cavity, keeping fixed both Richardson and Grashof numbers. They found that by the increase of nanoparticles volume fraction, Nusselt number increases, then from this result they concluded the total heat transfer increases from the walls. It is shown that total heat transfer obtained from the Nusselt number by the mentioned approach results from not only the nanoparticles volume fraction increase but also temperature difference and walls velocity increases. Thus, this approach is not appropriate to study the sole effects of nanoparticles volume fractions on the mixed convection heat transfer. Using the new approach, it is shown that in order to have specific heat transfer rate from the walls, base fluid (water) needs less power for moving the wall than Cu-nanofluid. Therefore, the usage of Cu-water nanofluid is not recommended to increase mixed convection heat transfer in a lid-driven cavity. Moreover, using this new approach, it is shown that the increase of nanoparticles volume fraction reduces natural convection heat transfer, which is contradictory to the previous studies. Thus, its usage is not recommended for this case as well.
Emerald Publishing Limited, 2020
Purpose-The purpose of this paper is to investigate the mixed convection of a two-phase water-aluminum oxide nanofluid in a cavity under a uniform magnetic field. Design/methodology/approach-The upper wall of the cavity is cold and the lower wall is warm. The effects of different values of Richardson number, Hartmann number, cavitation length and solid nanoparticles concentration on the flow and temperature field and heat transfer rate were evaluated. In this paper, the heat flux was assumed to be constant of 10 (W/m 2) and the Reynolds number was assumed to be constant of 300 and the Hartmann number and the volume fraction of solid nanoparticles varied from 0 to 60 and 0 to 0.06, respectively. The Richardson number was considered to be 0.1, 1 and 5. Aspect ratios were 1, 1.5 and 2. Findings-Comparison of the results of this paper with the results of the numerical and experimental studies of other researchers showed a good correlation. The results were presented in the form of velocity and temperature profiles, stream and isotherm lines and Nusselt numbers. The results showed that by increasing the Hartmann number, the heat transfer rate decreases. An increase from 0 to 20 in Hartmann number results in a 20 per cent decrease in Nusselt numbers, and by increasing the Hartmann number from 20 to 40, a 16 per cent decrease is observed in Nusselt number. Accordingly, it is inferred that by increasing the Hartmann number, the reduction in the Nusselt number is decreased. As the Richardson number increased, the heat transfer rate and, consequently, the Nusselt number increased. Therefore, an increase in the Richardson number results in an increase of the Nusselt number, that is, an increase in Richardson number from 0.1 to 1 and from 1 to 5 results in 37 and 47 per cent increase in Nusselt number, respectively. Originality/value-Even though there have been numerous investigations conducted on convection in cavities under various configurations and boundary conditions, relatively few studies are conducted for the case of nanofluid mixed convection in square lid-driven cavity under the effect of magnetic field using two-phase model. Nomenclature C p = specific heat, J/kg K; k = thermal conductivity, W/mK; L = length, m; H = height, m; Nu x = local Nusselt number; Water/alumina nanofluid mixed convection 2781 Nu m = average Nusselt number; P = pressure, Pa; Pr = Prandtl number; q 00 = heat flux (W/m 2); x, y = Cartesian coordinates, m; X, Y = dimensionless coordinates; u, v = velocity components in x, y directions, m/s; U, V = dimensionless velocity components; T = temperature, K; Ha = Hartmann number; Ra = Rayleigh number; and g = gravitational acceleration, m/s 2. Greek symbols s = electrical conductivity, mS/cm; m = dynamic viscosity, Ns/m 2 ; r = density, kg/m 3 ; a = thermal diffusivity, m 2 /s; # = kinematic viscosity, m 2 /s; w = volume fraction; H = dimensionless temperature; b = thermal expansion coefficient, 1/K; and c = stream function. Subscripts h = hot wall; c = cold wall; f = fluid (pure water); m = nanofluid; and p = nanoparticle.
Procedia Engineering, 2014
The existing work is focused on the numerical modelling of mixed convection of Cu-water nanofluid in a square enclosure filled with non-darcian fluid saturated porous medium. The enclosure object has cooled vertical walls and insulated horizontal walls. Finite volume method has been employed to solve the generalised Darcy-Brinkmann Forchheimer extended momentum and energy equations. The parametric study has been taken out for wide ranges of Richardson number, Darcy number and solid volume fraction. The performance of nanofluid is tested inside an enclosure by using solid volume fraction and compared with respect to base fluid (water). A fair degree of precision can be found between the present and previously published work. The results are presented in the form of streamlines, isotherms, average nusselt number and velocity graphs; it clearly explained the influence of flow governing parameters on heat transfer rate and fluid flow within the enclosure.
MATEC Web of Conferences, 2020
The present work is dedicated to the three-dimensional numerical study of mixed convection heat transfer, taking place within a ventilated cavity (of shape L) crossed by Cu-water nanofluid. The enclosure is subjected to the action of a magnetic field. The ventilation is assured by two openings of the same size. The cold flow enters by an opening practiced at the top of the left wall, and exits by another opening practiced at the bottom of the right vertical wall. All the cavity walls are maintained at the same temperature, superior to that of the entering flow, except the side walls which are considered as adiabatic. The control parameters are: the Reynolds number and the Hartmann number as well as the nanoparticles volume fraction.
Journal of Computational and Theoretical Nanoscience, 2013
This paper examines the thermal and flow fields characteristics of laminar steady mixed convection flow in a rectangular inclined lid-driven cavity filled with water-based nanofluids numerically using finite difference method. Whilst a uniform heat source is located on a part of the left inclined sidewall of the cavity, the right inclined sidewall is considered adiabatic together with the remain parts of the left inclined sidewall. The top and bottom walls are maintained at a relatively low temperature and the top wall moves from left to right with uniform lid-driven velocity. The fluid inside the cavity is a water based nanofluid containing different types of solid spherical nanoparticles: Cu, Ag, Al203, and Ti02• Based on the numerical simulation, the effects of the dominant parameters such as Richardson number, cavity inclination angle, solid volume fraction, heat source effect and type of nanoparticles are examined. The numerical results are obtained for inclination angles ranging from 0° to 90°, for Reynolds numbers varying from 1 to 100 and for the solid volume fractions varying from 0% to 20%. Comparisons with previously published numerical works on mixed convection in a nanofluid filled cavity are performed and good agreements between the results are observed. It is found that the local Nusselt number is seen to decrease as the inclination angle and solid volume fraction increase. Also, the results of the present study indicate that the presence of nanoparticles in the fluid is found to alter the structure of the fluid flow. Moreover, it is observed that the shape of the circulation vortex is sensitive to the inclination angle and addition of nanofluids.
Journal of Thermal Analysis and Calorimetry, 2020
The emergence of nanofluids as high-performance thermal transport media has drawn great research attention in the field of heat transfer. Owning to the huge importance of natural convection applications in environmental, agricultural, manufacturing, electronics, aviation, power plants, and industrial processes, heat transfer and flow characteristics of these special fluids in various cavities have been extensively researched. This review paper has paid serious attention to the benefits of controlling the natural convection heat transfer and flow performance of nanofluids in square cavities using magnetic field sources in addition to the aspect ratio, porous media, cavity and magnetic field inclination, hybrid nanofluids, etc. The influence of several variables such as heat distribution methods, thermal and concentration boundary conditions, governing parameters, magnetic field types, numerical schemes, thermophysical correlation types, nanofluid types, slip conditions, Brownian motion, and thermophoresis on the magnetohydrodynamic (MHD) natural convection behaviours of nanofluids in square cavities has been reviewed. The paper focused on the application of numerical and experimental methods to hydromagnetic behaviours of nanofluids in square-shaped enclosures. The concept of bioconvection, bio-nanofluid (green nanofluid), ionic nanofluid, and hybrid nanofluid has also been reviewed in relation to natural convection for the first time. Special cases of MHD natural convection in cavities involving micropolar and hybrid nanofluids are also presented herein. Convective heat transfer in square cavities has been demonstrated to be altered due to the presence of magnetic fields.
IOS Press, 2020
Optimization of the cooling processes by fluids in many industries such as power generation, transportation, machining, and electronics is very important. Heat transfer equipment to achieve higher efficiency, need to downsizing of the equipment, and increase the heat transfer rate per unit of surface. The aim of this paper is to investigate the effect of MHD mixed convection flow of Cu-water nanofluid in a trapezoidal lid-driven cavity with different tilt angles in a range of 0°to 60°. The cavity consists of the non-uniformly heated bottom wall, insulated top wall, and isothermal sidewalls. The governing equations of the flow by using the finite volume method and the SIMPLE algorithm have been numerically solved. The studies for the wide range of Richardson number (Ri) from 0.01 to 10, volume fraction of nanoparticles from 0.1% to 4% and Hartman number (Ha) from 0 to 40 in the steady-state have been done. Result in the form of streamline, vorticity and temperature contours for three geometry, local Nusselt number graphs for non-uniformly heated bottom surface and velocity profile on the vertical centerline of the cavity in different geometry have been investigated. The results show that the average Nusselt number on the non-uniformly heated bottom wall is dependent on dimensionless parameters and tilt angles. Also, applying a magnetic field, reduce the velocity profile changes, and using nanoparticles will cause increasing the Nusselt number.
Numerical Simulation of Mixed Convection of Nanofluids in a Ventilated Square Cavity
AIP Publishing, 2012
This article presents a numerical investigation of mixed convection flows in a discretely heated rectangular cavity having two inlet and outlet ports. Two different kinds of nanofluids, namely Al2O3-water and Cu-water are considered as working fluids. A flash mounted constant heat flux heat source is attached to the horizontal bottom wall of the cavity while the other walls are considered to be adiabatic. The transport equations for Newtonian fluid have been solved numerically, using finite volume method and employing the SIMPLER algorithm. The effects of relevant parameters such as inflow Reynolds number (50≤Re≤1000), Richardson number(0.1≤Ri≤10), type of nanofluid, solid volume fraction of the nanoparticles, and the location of the heat source on cooling performance of the ventilated cavity have been studied. Data and results are presented in the form of streamlines, isotherms, average Nusselt number values, and temperature distributions. The results show a significant enhancement in thermal specifications of the flow when nanofluid is used instead of pure fluid. Also Cu-water nanofluid exhibits elevated thermal perfomance in comparison with Al2O3-water nanofluid.
Journal of Thermal Analysis and Calorimetry, 2019
The lattice Boltzmann method is utilized to investigate the mixed convection of a CuO/water nanofluid by magnetic field's effect in a lid-driven U-shaped enclosure filled with a baffle. The bottom wall's temperature is high. The Koo-Kleinstreuer-Li model, which considering the Brownian motion of nanoparticles, is adopted to obtain the thermophysical properties of the nanofluid. How the Hartmann number (Ha), Richardson number (Ri), Reynolds number (Re), and nanoparticle concentration (ϕ) affect streamlines, isotherms, and average Nusselt number (Nu ave) is also examined. The results reveal that, at Re = 100 and for a large Ri, the nanofluid strategy degrades the Nu. The favorable effect of increasing the Re on the average Nu and adverse trends of the increment in the Ha on the heat transfer are the main highlights in this study. In addition, the increase in the Re more strongly affects the heat transfer rate at higher Ri.
Numerical simulation of water/alumina nanofluid mixed convection in square lid-driven cavity
International Journal of Numerical Methods for Heat & Fluid Flow, 2019
Purpose-The purpose of this paper is to investigate the mixed convection of a two-phase water-aluminum oxide nanofluid in a cavity under a uniform magnetic field. Design/methodology/approach-The upper wall of the cavity is cold and the lower wall is warm. The effects of different values of Richardson number, Hartmann number, cavitation length and solid nanoparticles concentration on the flow and temperature field and heat transfer rate were evaluated. In this paper, the heat flux was assumed to be constant of 10 (W/m 2) and the Reynolds number was assumed to be constant of 300 and the Hartmann number and the volume fraction of solid nanoparticles varied from 0 to 60 and 0 to 0.06, respectively. The Richardson number was considered to be 0.1, 1 and 5. Aspect ratios were 1, 1.5 and 2. Findings-Comparison of the results of this paper with the results of the numerical and experimental studies of other researchers showed a good correlation. The results were presented in the form of velocity and temperature profiles, stream and isotherm lines and Nusselt numbers. The results showed that by increasing the Hartmann number, the heat transfer rate decreases. An increase from 0 to 20 in Hartmann number results in a 20 per cent decrease in Nusselt numbers, and by increasing the Hartmann number from 20 to 40, a 16 per cent decrease is observed in Nusselt number. Accordingly, it is inferred that by increasing the Hartmann number, the reduction in the Nusselt number is decreased. As the Richardson number increased, the heat transfer rate and, consequently, the Nusselt number increased. Therefore, an increase in the Richardson number results in an increase of the Nusselt number, that is, an increase in Richardson number from 0.1 to 1 and from 1 to 5 results in 37 and 47 per cent increase in Nusselt number, respectively. Originality/value-Even though there have been numerous investigations conducted on convection in cavities under various configurations and boundary conditions, relatively few studies are conducted for the case of nanofluid mixed convection in square lid-driven cavity under the effect of magnetic field using twophase model.