Showing papers on "Hartmann number published in 2019"

A numerical investigation of magneto-hydrodynamic natural convection of Cu–water nanofluid in a wavy cavity using CVFEM

Abstract: In this work, magneto-hydrodynamic natural convection of a nanofluid in a wavy cavity considering Brownian motion is studied numerically using the control volume finite element method. The effective viscosity and thermal conductivity of the nanofluid are defined by the correlation in which the impact of Brownian motion on the thermal conductivity is considered. The considered wavy cavity is heated from the left side and it cooled from the right side. Also, the top and bottom walls of the considered wavy cavity are assumed adiabatic. The impacts of various controlling parameters such as the Rayleigh number, wavy contraction ratio, Hartmann number and undulation number are examined on the contour maps of the streamlines and the isotherms. Further, the average and local Nusselt numbers are calculated and presented graphically and discussed. The findings narrate that the strength of the convective flow has a direct relationship with the Rayleigh number and also it has a reverse relationship with the wavy contraction ratio.

Natural Convection Analysis in a Cavity with an Inclined Elliptical Heater Subject to Shape Factor of Nanoparticles and Magnetic Field

Abstract: The objective of the present study is to peruse the natural convection in the cavity containing inclined elliptical heater under shape factor of nanoparticles and magnetic field. The control volume-based finite element method is used for solving conservation equations. Numerical results show very good grid independency and very good compromise with other works. The result shows the heat transfer grows via mounting nanofluid volume fraction. The increment of Ra number also leads the heat transfer to ascend. Heat transfer of nanofluid with three different shapes of nanoparticles is studied, and results show the platelet nanoparticle is better than the other ones. The influence of magnetic field on heat transfer is also investigated and discussed. The obtained outcomes represent that at a certain Rayleigh number, the average Nusselt number descends with the ascendant of Hartmann number. Finally, the new correlation is reported for calculating the Nu number in these geometries.

MHD natural convection of Cu–Al2O3 water hybrid nanofluids in a cavity equally divided into two parts by a vertical flexible partition membrane

Abstract: The aim of the present study is to investigate the effects of a hybrid nanofluid in a square cavity that is divided into two equal parts by a vertical flexible partition in the presence of a magnetic field. A numerical method called the Galerkin finite element method is utilized to solve the governing equations. The effects of different parameters, namely the Rayleigh number (106 ≤ Ra ≤ 108) and the Hartmann number (0.0 ≤ Ha ≤ 200) as well as the effects of nanoparticles concentration (0.0 ≤ φ ≤ 0.02) and magnetic field orientation (0 ≤ γ ≤ π), on the flow and heat transfer fields for the cases of pure fluid, nanofluid and hybrid nanofluid are investigated. The results indicate that the streamline patterns change remarkably and the convective heat transfer augments with increasing values of the Rayleigh number. Additionally, the maximum stress imposed on the flexible partition resulting from the interaction of the partition and pure fluid is more than those caused by the nanofluid and the hybrid nanofluid. Furthermore, the increase in the magnetic field strength decreases the fluid velocity in the cavity, which declines the fluid thermal mixing and heat transfer effects.

Numerical investigation for second law analysis of ferrofluid inside a porous semi annulus: An application of entropy generation and exergy loss

Abstract: Purpose The purpose of this paper is to present the entropy analysis of ferrofluid inside a porous space with magnetic force. Homogenous model with second law analysis is also taken into account. Design/methodology/approach Innovative model has been proposed and designed using control volume finite element method. Findings Experimental results demonstrate that Bejan number augments with augment of Rayleigh. As Hartmann number rises, exergy loss enhances. Exergy loss increases by increasing Hartmann number, whereas magnetic entropy generation reduces with the decrease of Ha. The proposed model can be used for combustion process and optimizing the performance of energy conversion system like gas turbine. Originality/value To the best of authors’ knowledge, this model is reported for the first time.

Unsteady magneto-hydrodynamics flow between two orthogonal moving porous plates

Abstract: An investigation has been performed to describe the unsteady MHD, laminar, incompressible and two-dimensional motion of viscous fluid between two orthogonal moving porous plates. The similarity transformation is adopted to amend the governing model into a non-linear problem of the ordinary differential equation. The homotopy analysis method (HAM) is then invoked to get the approximate solution. The influence of different substantial parameters such as wall permeable ratio, Reynold's number and Hartmann number are explained in detail. A further HAM's comparison is shown with an efficient numerical technique.

Effect of magnetic field on mixed convection and entropy generation of hybrid nanofluid in an inclined enclosure: Sensitivity analysis and optimization

Abstract: In this paper, a numerical study has been examined on the effect of the presence of a magnetic field on the rate of convective heat transfer and entropy generation of a hybrid nanofluid (water/Al2O3-CuO (50/50)) in a square diagonal cavity. The horizontal walls of the insulating cavity and fixed temperature source are set on the left and right vertical wall with cold temperature. The governing equations are solved by finite volume method using the SIMPLE algorithm. In this paper, the effect of the Richardson number, Hartman number, thermal source length on hybrid entropy generation and convective heat transfer rate has been examined. Using the Response Surface Methodology (RSM) method, a polynomial equation is obtained between the three parameters given for the Nusselt number, total entropy generation and Bejan number. Then the sensitivity of responses to factors is checked. Finally, depending on the importance of each of the responses, we use the optimal points where simultaneously the highest Nu number, the lowest entropy generation, and Bejan number occur. The results show that with increasing Richardson number, heat transfer rate is reduced, and this reduction is more pronounced in smaller Hartmann number. Also, total entropy generation increased with increasing Richardson number, but Bejan number reduced. With increasing the intensity of the magnetic field and reducing the length of the thermal source, the heat transfer rate also reduces. However, with increasing the intensity of the magnetic field, the total entropy generation and Bejan number increase. Also, with increasing the length of the thermal source, the total entropy generation and Bejan number increase.

Numerical investigation of MHD effects on nanofluid heat transfer in a baffled U-shaped enclosure using lattice Boltzmann method

Abstract: Lattice Boltzmann method (LBM) was carried out to investigate the effects of magnetic field and nanofluid on the natural convection heat transfer in a baffled U-shaped enclosure The combination of different specifications of the baffle, LBM, nanofluid and magnetic field is the main innovation in the present study In order to consider the effect of Brownian motion on the thermal conductivity, Koo–Kleinstreuer–Li model is used to define thermal conductivity and viscosity of nanofluid Effects of Rayleigh number, Hartmann number, nanoparticle volume fraction, height and position of the baffle on the fluid flow and heat transfer characteristics have been examined It was found that raising the Rayleigh number and nanoparticle solid volume fraction leads to increase the average Nusselt number irrespective of the position of the hot obstacle However, the heat transfer rate is suppressed by the magnetic field The heat transfer enhancement by introducing nanofluid decreases as increasing Rayleigh number, but it increases as increasing the Hartmann number Moreover, the maximum heat transfer rate was observed when the enclosure equipped with a baffle with (s, h) = (02, 03) or (04, 03)

LTNE modeling of Magneto-Ferro natural convection inside a porous enclosure exposed to nonuniform magnetic field

Abstract: Applying LTNE model, the natural convection of a porous enclosure, exposed to a nonuniform magnetic field, was numerically analyzed. At such conditions, the buoyancy, the Lorentz and magnetization forces are applied to the hybrid nanofluid. Utilizing the finite element technique, the set of governing equations pertinent to the present problem was discretized and solved. To validate the results of the current study, they are compared to previous studies and a good compromise is observed. The power ratio of the two magnetic sources γ r , the porosity coefficient, Rayleigh number, thermal conductivity proportion of hybrid nanofluid to that of the matrix material, local heat exchange between nanofluid and solid surface inside the pores, magnetization and Hartmann numbers on the flow and thermal indices have been perused. The results indicate that the Nusselt numbers of the two phases of porous material converge with increasing γ r ; whereas, these two thermal indices vary with reducing γ r . Also, the application of the local thermal equilibrium is justifiable when the Hartmann number and Lorentz forces acting on the hybrid nanofluid increase.

Magneto-hydrodynamic natural convection of CuO-water nanofluid in complex shaped enclosure considering various nanoparticle shapes

Abstract: The purpose of this study is to peruse natural convection in a CuO-water nanofluid-filled complex-shaped enclosure under the influence of a uniform magnetic field by using control volume finite element method.,Governing equations formulated in dimensionless stream function, vorticity and temperature variables using the single-phase nanofluid model with the Koo–Kleinstreuer–Li correlation for the effective dynamic viscosity and the effective thermal conductivity have been solved numerically by control volume finite element method.,Effects of various pertinent parameters such as Rayleigh number, Hartmann number, volume fraction of nanofluid and shape factor of nanoparticle on the convective heat transfer characteristics are analysed. It was observed that local and average heat transfer rates increase for higher value of Rayleigh number and lower value of Hartmann number. Among various nanoparticle shapes, platelets were found to be best in terms of heat transfer performance. The amount of average Nusselt number reductions was found to be different when nanofluids with different solid particle volume fractions were considered due to thermal and electrical conductivity enhancement of fluid with nanoparticle addition.,A comprehensive study of the natural convection in a CuO-water nanofluid-filled complex-shaped enclosure under the influence of a uniform magnetic field by using control volume finite element method is addressed.

Effect of replacing nanofluid instead of water on heat transfer in a channel with extended surfaces under a magnetic field

Abstract: Purpose The purpose of this study is to conduct a numerical analysis of flow and heat transfer of water–aluminum oxide nanofluid in a channel with extended surfaces in the presence of a constant magnetic field. The channel consists of two parallel plates and five obstacles of constant temperature on the lower wall of the channel. The upper wall and the inlet and outlet lengths of the lower wall are insulated. A uniform magnetic field of the magnitude B0 is located beneath the obstacles. The nanofluid enters the channel with a uniform velocity and temperature, and a fully developed flow leaves the channel. Design/methodology/approach The control volume-based finite difference and the SIMPLE algorithm were used for numerical solution. In addition to examining the effect of the Reynolds number, the effects of Hartman number, the volume fraction of nanoparticles, the height of obstacles, the length of obstacles and the distance between the obstacles were investigated. Findings According to the results, the heat transfer rate increases with an increasing Reynolds number. As the Hartmann number increases, the heat transfer rate increases. The heat transfer rate also increases with an increase in the volume fraction of nanoparticles. The mean Nusselt number is reduced by an increasing height of obstacles. An increase in the distance between the obstacles in the presence of a magnetic field does not have a significant impact on the heat transfer rate. However, the heat transfer rate increases in the absence of a magnetic field, as the distance between the obstacles increases. Originality/value This paper is original and unpublished and is not being considered for publication elsewhere.

MHD mixed convection in a nanofluid filled vertical lid-driven cavity having a flexible fin attached to its upper wall

Abstract: In this study, fluid flow and heat transfer in a vertical lid-driven CuO–water nanofluid filled square cavity with a flexible fin attached to its upper wall under the influence of an inclined magnetic field are numerically investigated. The left vertical wall of the cavity is colder than right vertical wall, and it moves in + y direction with constant speed. Horizontal walls of the cavity are insulated. The governing equations are solved with finite element method. The arbitrary Lagrangian–Eulerian method is used to describe the fluid motion within the cavity for the flexible fin in the fluid-structure interaction model. The influence of Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of the magnetic field (between 0 and 90%), nanoparticle volume fraction (between 0 and 0.05) and Young’s modulus of flexible fin (between 250 and 5000) on the flow and heat transfer were numerically studied. It is observed that the presence of the elastic fin affects the flow field and thermal characteristics of the cavity. The local and average heat transfer enhance as the Richardson number, solid volume fraction of the nanoparticle increase whereas deteriorate as the value of the Hartmann number and inclination angle of the magnetic field increases due to the dampening of the fluid motion with Lorentz forces. The addition of the nanoparticles is more effective along the lower part of the right vertical wall where the heat transfer process is effective. The average heat transfer increases by 28.96% for solid volume fraction of 0.05% compared to base fluid when the flexible fin is attached to the upper wall. The average heat transfer deteriorates by 10.10% for cavity with and without fin at Hartmann number of 50 compared to the case without magnetic field. The average heat transfer enhances as the Young’s modulus of the flexible fin decreases and the average Nusselt number increases by 13.24% for Young’s modulus of 250 compared to configuration for the cavity having the Young’s modulus of 5000.

Simulation of three dimensional MHD natural convection using double MRT Lattice Boltzmann method

Abstract: In this study, a three-dimensional mesoscopic simulation of magneto hydrodynamics (MHD) natural convection in a cubic cavity has been studied by new means of the Lattice Boltzmann method with double Multi-Relaxation-Time (MRT) model. In order to solve the momentum and energy equations, two different populations with various lattices have been used. This paper has been conducted for specific values of the Grashof number ( Gr = 2 × 1 0 3 _ 2 × 1 0 5 ) and Hartmann number (Ha=0–100), while the Prandtl number is fixed at Pr = 0 . 73 . The results are presented in the form of average and local Nusselt number and contours of temperature and velocity at different planes of the cavity. It was found that the double MRT-LBM method is an appropriate approach to solve the studied case. The present results also show that the increase of the Hartmann number causes the heat transfer to drop considerably. Also, the effect of Hartmann number increases by enhancing the Grashof number, as the reduction of average Nusselt number is 12% for Gr = 2 × 1 0 3 and 71% for Gr = 2 × 1 0 5 when Hartmann number increases from 0 to 100. In contrast with Hartmann number, increasing of Grashof number raises heat transfer rate and the average Nusselt number increases by more than three times by enhancing the Grashof number from 2 × 1 0 3 to 2 × 1 0 5 .