Showing papers on "Hartmann number published in 2014"

Effect of spatially variable magnetic field on ferrofluid flow and heat transfer considering constant heat flux boundary condition

Abstract: Ferrofluid flow and heat transfer in the presence of an external variable magnetic field is studied. The inner cylinder is maintained at uniform heat flux and the outer cylinder has constant temperature. The Control Volume based Finite Element Method (CVFEM) is applied to solve the governing equations. Combined magnetohydrodynamic and ferrohydrodynamic effects have been taken into account. The effects of magnetic number, Hartmann number, Rayleigh number and nanoparticle volume fraction on hydrothermal behavior have been examined. Results show that the Nusselt number is an increasing function of Magnetic number, Rayleigh number and nanoparticle volume fraction while it is a decreasing function of the Hartmann number. Also, it can be concluded that the enhancement in heat transfer decreases with an increase in the Rayleigh number and magnetic number but it increases with an increase in the Hartmann number.

Natural convection heat transfer in a cavity with sinusoidal wall filled with CuO–water nanofluid in presence of magnetic field

Abstract: Control volume based finite element method (CVFEM) is applied to investigate flow and heat transfer of CuO–water nanofluid in presence of magnetic field. The enclosure has a sinusoidal wall under constant heat flux. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo–Kleinstreuer–Li) correlation. In this model effect of Brownian motion on the effective thermal conductivity is considered. The numerical investigations are conducted at a fixed Prandtl number equal to 6.2. Various values of non-dimensional governing parameters such as volume fraction of nanoparticles (ϕ), Rayleigh number (Ra), dimensionless amplitude of the sinusoidal wall (a) and Hartmann number (Ha) are examined. Also a correlation of Nusselt number corresponding to active parameters is presented. The results show that Nusselt number is an increasing function of nanoparticles volume fraction, dimensionless amplitude of the sinusoidal wall and Rayleigh number while it is a decreasing function of Hartmann number.

Magnetic field effect on nanofluid flow and heat transfer using KKL model

Abstract: In this paper, MHD effect on natural convection heat transfer in an inclined L-shape enclosure filled with nanofluid is studied. The numerical investigation is carried out using the control volume based finite element method (CVFEM). The fluid in the enclosure is a water-based nanofluid containing Al2O3 nanoparticle. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo–Kleinstreuer–Li) correlation in which effect of Brownian motion on the effective thermal conductivity is considered. The heat transfer between cold and hot regions of the enclosure cannot be well understood by using isotherm patterns so heatline visualization technique is used to find the direction and intensity of heat transfer in a domain. Effect of Hartmann number, volume fraction of nanoparticle, Rayleigh number and inclination angle on streamline, isotherm and heatline are examined. The results show that Nusselt number increases with increase of Rayleigh number and volume fraction of nanoparticle while it decreases with augment of Hartmann number and inclination angle. Enhancement in heat transfer has reverse relationship with Hartmann number and Rayleigh number.

MHD free convection in an eccentric semi-annulus filled with nanofluid

Abstract: In this study magnetohydrodynamic effect on free convection of nanofluid in an eccentric semi-annulus filled is considered. The effective thermal conductivity and viscosity of nanofluid are calculated by the Maxwell–Garnetts (MG) and Brinkman models, respectively. Lattice Boltzmann method is applied to simulate this problem. This investigation compared with other works and found to be in excellent agreement. Effects of the Hartmann number, nanoparticle volume fraction, Rayleigh numbers and position of the inner circular cylinder on flow and heat transfer characteristics are examined. Also a correlation of Nusselt number corresponding to active parameters is presented. The results show that Nusselt number has direct relationship with nanoparticle volume fraction and Rayleigh number but it has inverse relationship with Hartmann number and position of inner cylinder at high Rayleigh number. Also it can be concluded that heat transfer enhancement increases with increase of Hartmann number and decreases with augment of Raleigh number.

MHD natural convection in a nanofluid filled inclined enclosure with sinusoidal wall using CVFEM

Abstract: Magnetohydrodynamic flow in a nanofluid filled inclined enclosure is investigated numerically using the Control Volume based Finite Element Method. The cold wall of cavity is assumed to mimic a sinusoidal profile with different dimensionless amplitude, and the fluid in the enclosure is a water-based nanofluid containing Cu nanoparticles. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell–Garnetts and Brinkman models, respectively. Numerical simulations were performed for different governing parameters namely the Hartmann number, Rayleigh number, nanoparticle volume fraction and inclination angle of enclosure. The results show that in presence of magnetic field, velocity field retarded, and hence, convection and Nusselt number decreases. At Ra = 103, maximum value of enhancement for low Hartmann number is obtained at γ = 0°, but for higher values of Hartmann number, maximum values of E occurs at γ = 90°. Also, it can be found that for all values of Hartmann number, at Ra = 104 and 105, maximum value of E is obtained at γ = 60° and γ = 0°, respectively.

Numerical study of MHD two-phase Couette flow analysis for fluid-particle suspension between moving parallel plates

Abstract: In this study, steady and unsteady magneto-hydrodynamic (MHD) Couette flows between two parallel infinite plates have been studied through numerical Differential Quadrature Method (DQM) and analytical Differential Transformation Method (DTM), respectively. Coupled equations by taking the viscosity effect of the two phases for fixed and moving plates have been introduced. The precious contribution of the present study is introducing new, fast and efficient numerical and analytical methods in a two-phase MHD Couette fluid flow. Results are compared with those previously obtained by using Finite Difference Method (FDM). The velocity profiles of two phases are presented and a parametric study of physical parameters involved in the problem is conducted. As an outcome, when magnetic source is fixed relative to the moving plate, by increasing the Hartmann number, velocity profiles for both phases increased, but when it is fixed relative to the fluid an inverse treatment is observed.

MHD mixed convection of nanofluid filled partially heated triangular enclosure with a rotating adiabatic cylinder

Abstract: MHD mixed convection of Cu–water nanofluid filled triangular enclosure with a rotating cylinder is investigated numerically. A partial heater is added on the left vertical wall of the cavity and the right inclined wall is kept at constant temperature. Other walls of the triangular cavity and cylinder surface are assumed to be adiabatic. The governing equations are solved using the finite element method. The effects of the Grashof number, Hartmann number, angular rotational speed of the cylinder and volume fraction of the nanoparticle on fluid flow and heat transfer are investigated numerically. The second law of thermodynamics is also applied to the flow and heat transfer corresponding to different combinations of parameters. It is observed that with increasing the Hartmann number the total entropy generation, local and averaged heat transfer decrease. Averaged Nusselt number increases with the Grashof number. Averaged heat transfer and total entropy generation increase with increase in the angular rotational speed of the cylinder. 50.4% and 37.4% of heat transfer enhancements are obtained for ω = 20 and ω = −20 compared to motionless cylinder ω = 0. Heat transfer and total entropy generation increase as the solid volume fraction of nanoparticle increases.

Numerical simulation of peristaltic flow of a Carreau nanofluid in an asymmetric channel

Abstract: In this article, we studied MHD peristaltic flow of a Carreau nanofluid in an asymmetric channel. The flow development is carried out in a wave frame of reference moving with velocity of the wave c 1 . The governing nonlinear partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations using similarity transformations and then tackled numerically using the fourth and fifth order Runge–Kutta–Fehlberg. Numerical results are obtained for dimensionless velocity, stream function, pressure rise, temperature and nanoparticle volume fraction. It is found that the pressure rise increases with increase in Hartmann Number and thermophoresis parameter.

Electromagnetohydrodynamic flow through a microparallel channel with corrugated walls

Abstract: In this paper a perturbation method is introduced to study the electromagnetohydrodynamic (EMHD) flow in a microparallel channel with slightly corrugated walls. The corrugations of the two walls are periodic sinusoidal waves of small amplitude either in phase or half-period out of phase, and the perturbation solutions of velocity and volume flow rate are obtained. Using numerical computation the effects of the corrugations on the flow are graphically analysed. The results show that the influence of corrugation on the flow decreases with Hartmann number. The phase difference of wall corrugations becomes unimportant when the wavenumber is greater than 3 or when the Hartmann number is greater than 4. With the increase in wavenumber, the decreasing effects of corrugations on the flow increase. When the wavenumber is smaller than the threshold wavenumber (it is a function of Hartmann number) and the wall corrugations are half-period out of phase, the corrugations can enhance the mean velocity of EMHD flow. However, the mean velocity is always decreased when the corrugations are in phase.

Investigation of Nanofluid Flow and Heat Transfer in Presence of Magnetic Field Using KKL Model

Abstract: In this paper, flow and heat transfer of a nanofluid in a square cavity with curve boundaries in presence of magnetic field is investigated numerically using lattice Boltzmann method. The base fluid in the enclosure is water containing Al2O3. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo–Kleinstreuer–Li) correlation. In this model effect of Brownian motion on the effective thermal conductivity is considered. This investigation when compared with other numerical methods was found to be in excellent agreement. The influence of the nanoparticle volume fraction, Rayleigh number and Hartmann number on flow and heat transfer is investigated. The results show that enhancement in heat transfer increases with increase of Hartmann number except for Ra = 104 in which Ha = 40 roles as a critical Hartmann number.

Metallic Nanoparticles Analysis for the Peristaltic Flow in an Asymmetric Channel With MHD

Abstract: The peristaltic flow of an incompressible viscous-fluid-containing metallic nanoparticles in an irregular conduit is analyzed. The metallic nanoparticles for the peristaltic flow are not explored so far. The governing equations are streamlined using “long wavelength and low Reynolds number approximation.” Exact solutions have been evaluated for velocity, pressure gradient, the solid volume fraction of the nanoparticles, and temperature profile. The effects of various flow parameters, i.e., Hartmann number, Eckert number, the solid volume fraction of the nanoparticles amplitude ratio, and Prandtl number are presented graphically.