Youn J. Kim

Unsteady MHD convective heat transfer past a semi-infinite vertical porous moving plate with variable suction

Abstract In this paper we study the unsteady two-dimensional laminar flow of a viscous incompressible electrically conducting fluid in the vicinity of a semi-infinite vertical porous moving plate in the presence of a transverse magnetic field. The plate moves with constant velocity in the direction of fluid flow, and the free stream velocity follows the exponentially increasing small perturbation law. A uniform magnetic field acts perpendicular to the porous surface which absorbs the fluid with a suction velocity varying with time. The effects of material parameters on the velocity and temperature fields across the boundary layer are investigated. Numerical results show that for a constant plate moving velocity with a given magnetic and permeability parameters, and Prandtl and Grashof numbers, the effect of increasing values of suction velocity parameter results in a slight increasing surface skin friction for lower values of plate moving velocity. It is also observed that for several values of Prandtl number, the surface heat transfer decreases by increasing the magnitude of suction velocity.

Transient mixed radiative convection flow of a micropolar fluid past a moving, semi-infinite vertical porous plate

Abstract The flow of viscous incompressible micropolar fluid past a semi-infinite vertical porous plate is investigated with the presence of thermal radiation field, taking into account the progressive wave type of disturbance in the free stream. The effects of flow parameters and thermophysical properties on the flow and temperature fields across the boundary layer are investigated. The Rosseland approximation is used to describe radiative heat transfer in the limit of optically thick fluids. Numerical results of velocity profile of micropolar fluids are compared with the corresponding flow problems for a Newtonian fluid. It is observed that, when the radiation parameter increases the velocity and temperature decrease in the boundary layer, whereas when Grashof number increases the velocity increases.

Unsteady MHD convection flow of polar fluids past a vertical moving porous plate in a porous medium

Abstract The objectives of the present study are to investigate the unsteady two-dimensional laminar flow of a viscous incompressible electrically conducting polar fluid via a porous medium past a semi-infinite vertical porous moving plate in the presence of a transverse magnetic field. The plate moves with a constant velocity in the longitudinal direction, and the free stream velocity follows an exponentially increasing or decreasing small perturbation law. A uniform magnetic field acts perpendicularly to the porous surface which absorbs the polar fluid with a suction velocity varying with time. The effects of material parameters on the velocity and temperature fields across the boundary layer are investigated. The method of solution can be applied for small perturbation approximation. Numerical results of velocity distribution of polar fluids are compared with the corresponding flow problems for a Newtonian fluid. For a constant plate moving velocity with the given magnetic and permeability parameters, and Prandtl and Grashof numbers, the effect of increasing values of suction velocity parameter results in an increasing surface skin friction. It is also observed that the surface skin friction decreases by increasing the plate moving velocity.

Magnetoconvection in a Square Enclosure with Sinusoidal Temperature Distributions on Both Side Walls

A computational study of convective flow and heat transfer in a cavity in the presence of uniform magnetic field is carried out. The side walls of the cavity have spatially varying sinusoidal temperature distributions. The horizontal walls are adiabatic. The governing equations are solved by the finite volume method. The results are discussed for different combinations of phase deviation, amplitude ratio, and Hartmann and Rayleigh numbers. It is observed that the heat transfer rate is increased with amplitude ratio. The heat transfer rate is increased first and then decreased on increasing the phase deviation. It is also found that the heat transfer rate is decreased with an increasing Hartmann number.

Numerical Study on Double Diffusive Mixed Convection with a Soret Effect in a Two-Sided Lid-Driven Cavity

In the present study, a numerical analysis is performed to understand the mixed convection flow, and heat and mass transfer with Soret effect in a two-sided lid-driven square cavity. The horizontal walls of the cavity are adiabatic and impermeable, while vertical walls are kept at constant but different temperatures and concentrations. The vertical walls move in a constant velocity. According to the direction of the movement of walls, three cases have been studied for different combinations of parameters involved in the study. The governing unsteady equations are solved numerically by the finite volume method with the SIMPLE algorithm. The results are presented graphically in the form of streamlines, isotherms, and velocity profiles. Heat and mass transfer rates are reduced if both walls are moving the in same direction, while heat and mass transfer rates are enhanced if the walls are moving in the opposite direction.

Analytical studies on MHD oscillatory flow of a micropolar fluid over a vertical porous plate

In recent years, the dynamics of micropolar fluids, originated from the theory of Eringen (J. Math. Mech., 16 (1964) 1), has been a popular area of research. As the fluids consist of randomly oriented molecules, and as each volume element of the fluid has translation as well as rotation, the analysis of physical problems in these fluids has revealed several interesting phenomena, which are not found in Newtonian fluid. In this study, we investigate the problem of the oscillatory two-dimensional laminar flow of a viscous incompressible electrically conducting micropolar fluid over a semi-infinite vertical moving porous plate in the presence of a transverse magnetic field. Here, it is assumed that the size of holes in the porous plate is much larger than a characteristic microscopic length scale of the micropolar fluid to simplify formulation of the boundary conditions. The effects of various flow parameters and thermophysical properties on the flow and temperature fields across the boundary layer are investigated. Especially, the effects of non-zero values of micro-gyration vector on the velocity and temperature fields across the boundary layer are studied, using the method of small perturbation approximation. Numerical results of velocity profiles of micropolar fluids are compared with the corresponding flow problems for a Newtonian fluid. The results also show that there exists completely oscillating behavior in the velocity distribution.

Effect of aspect ratio on convection in a porous enclosure with partially active thermal walls

The aim of the present numerical investigation is to understand the effect of aspect ratio and partially thermally active zones on convective flow and heat transfer in a rectangular porous enclosure. Five different heating and cooling zones are considered along the vertical walls while the remaining portions of the sidewalls and top and bottom of the enclosure are adiabatic. The Brinkman-Forchheimer extended Darcy model is used in the study. The governing equations are solved by the finite volume method with the SIMPLE algorithm. The computations are carried out for a wide range of parameters and the results are presented graphically. The results reveal that the location of heating and cooling zones has a significant influence on the flow pattern and the corresponding heat transfer in the enclosure. The rate of heat transfer approaches to a constant value for very low values of the Darcy number. The heat transfer rate is decreased on increasing the aspect ratio.

Study on the electrical properties of ITO films deposited by facing target sputter deposition

This study examined the mechanism for the change in the electrical properties (carrier concentration (n) and mobility (µ)) of tin-doped indium oxide (ITO) films deposited by magnetron sputtering in a confined facing magnetic field. The relationship between the carrier concentration and the mobility was significantly different from the results reported for ITO films deposited by other magnetron sputtering processes. The lowest resistivity obtained for ITO films deposited in a confined facing magnetic field at low substrate temperatures (approximately 120 ◦ C) was 4.26 × 10 −4 � cm at a power density of 3Wcm −2 . Crystalline ITO films were obtained at a low power density range from 3 to 5Wcm −2 due to the increase in the substrate temperature from 120 to 162 ◦ C. This contributed to the increased carrier concentration and decreased electrical resistivity. X-ray photoelectron spectroscopy revealed an increase in the concentration of the Sn 4+ states. This was attributed to the formation of a crystalline ITO film, which effectively enhanced the carrier concentration and reduced the carrier mobility.

The Falkner–Skan Wedge Flows of Power-Law Fluids Embedded in a Porous Medium

The non-Darcy flow characteristics of power-law non-Newtonian fluids past a wedge embedded in a porous medium have been studied. The governing equations are converted to a system of first-order ordinary differential equations by means of a local similarity transformation and have been solved numerically, for a number of parameter combinations of wedge angle parameter m, power-law index of the non-Newtonian fluids n, first-order resistance A and second-order resistance B, using a fourth-order Runge–Kutta integration scheme with the Newton–Raphson shooting method. Velocity and shear stress at the body surface are presented for a range of the above parameters. These results are also compared with the corresponding flow problems for a Newtonian fluid. Numerical results show that for the case of the constant wedge angle and material parameter A, the local skin friction coefficient is lower for a dilatant fluid as compared with the pseudo-plastic or Newtonian fluids.

Nano Manufacturing Using Fountain Pen Nano-Lithography with Active Membrane Pumping

In this paper, nano manufacturing using the FPN (Fountain Pen Nano-Lithography) with active membrane pumping is investigated. This FPN has integrated pumping chamber, micro channel, and high capacity reservoir for continuous ink feed. The most important aspect in this probe provided the control of fluid injection using active membrane pumping in chamber. The flow rates in channel by capillary force are theoretically analyzed with two different working fluids, DPD (diphenyldichlorosilane) and water, including the cantilever deflection and the control of mass flow rates by the deflection of membrane. The theoretical results are compared with numerical ones that calculated by commercial code, FLUENT.