Model Finds Applications Research Articles

Network Simulation of Laminar Convective Heat and Mass Transfer over a Vertical Slender Cylinder with Uniform Surface Heat and Mass Flux

The steady, laminar axisymmetric convective heat and mass transfer in boundary layer flow over a vertical thin cylindrical configuration in the presence of significant surface heat and mass flux is studied theoretically and numerically. The governing boundary-layer equations for momentum, energy and species conservation are transformed from a set of partial differential equations in a (x,r) coordinate system to a ([,K) system using a group of similarity transformations. The resulting equations are solved using the Network Simulation Method (NSM) for the buoyancy-assisted pure free convection and also the pure forced convection cases, wherein the effects of Schmidt number, Prandtl number and surface mass parameter on velocity, temperature and concentration distributions in the regime are presented graphically and discussed. For the buoyancy-assisted pure free convection case, nondimensional velocity (wf/wK) is found to increase with a rise in surface mass transfer (S) but decrease with increasing Prandtl number (Pr), particularly in the vicinity of the cylinder surface (small radial coordinate, K). Dimensionless temperature (T) decreases however with increasing S values from the cylinder surface into the free stream; with increasing Prandtl number, temperature is strongly reduced, with the most significant decrease at the cylinder surface. Dimensionless concentration (I) is decreased continuously throughout the boundary layer regime with an increase in S; conversely I is enhanced for all radial coordinate values with an increase in Prandtl number. For the pure forced convection case, velocity increases both with dimensionless axial coordinate ([) and dimensionless radial coordinate (K) but decays smoothly with increasing Prandtl number and increasing Schmidt number, from the cylinder surface to the edge of the boundary layer domain. The model finds applications in industrial metallurgical processes, thermal energy systems, polymer processing, etc.

Radiation and mass transfer effects on MHD free convection flow past a moving vertical cylinder in a porous medium

The interaction of free convection with thermal radiation of a viscous incompressible unsteady MHD flow past a moving vertical cylinder with heat and mass transfer in a porous medium is analyzed. The fluid is a gray, absorbing-emitting but non-scattering medium and the Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing equations are solved by using an implicit finite-difference scheme of Crank-Nicolson type. The effects of various physical parameters such as thermal Grashof number, mass Grashof number, magnetic parameter, radiation parameter and Schmidt number on the velocity, temperature, concentration, local as well as average skin-friction, Nusselt number and Sherwood number for various parameters are computed and represented graphically. It is found that at small values of radiation parameter , the velocity and temperature of the fluid increases sharply near the cylinder as the time increases. Also, an increase in the magnetic field leads to a decrease in the velocity and a rise in the temperature.As the permeability parameter increases,it is seen that the flow accelerates. This model finds applications in geophysics and engineering.DOI: 10.3329/jname.v7i1.2901

Radiation and Mass Transfer Effects on MHD Free Convective Dissipative Fluid in the Presence of Heat Source/Sink

Thermal radiation effects on MHD flow past an impulsively started vertical plate in the presence of heat source/sink is investigated, by taking into account the heat due to viscous dissipation. The governing boundary layer equations of the flow field are solved by an implicit finite difference method of Crank-Nichols on type. A parametric study is performed to illustrate the influence of radiation parameter, magnetic parameter, Grashof number, Prandtl number, Eckert number on the velocity, temperature and concentration profiles. Also, the local and average skin-friction, Nusselt number and Sherwood number are presented graphically. The numerical results reveal that the radiation induces a rise in both the velocity and temperature, and a decrease in the concentration. Also with an increase in the heat absorption/generation parameter the velocity increases whereas the temperature decreases. The model finds applications in solar energy collection systems, geophysics and astrophysics, aero space and also in the design of high temperature chemical process systems.

Non-linear transient hydromagnetic partially ionised dissipative Couette flow in a non-Darcian porous medium channel with Hall, ionslip and Joule heating effects

We study the transient magnetohydrodynamic (MHD) viscous laminar flow and heat transfer in a channel containing a Darcy-Forchheimer porous medium, under a constant pressure gradient with Hall current, ionslip, transpiration, viscous and Joule heating. The dimensionless momentum and heat conservation equations are solved using the Network Simulation Method (NSM). The effects of a number of thermophysical parameters on the transport phenomena are studied including Darcy number (Da), Forchheimer quadratic drag number (Fs), Hartmann number (Ha), Hall current parameter (βe), ionslip parameter (βi) and Eckert number (Ec). The model finds applications in geophysics and MHD energy generators.

Effects of thermophoresis on hydromagnetic mixed convection and mass transfer flow past a vertical permeable plate with variable suction and thermal radiation

The present paper deals with the effect of surface mass transfer on MHD mixed convection flow past a heated vertical flat permeable surface in the presence of thermophoresis, radiative heat flux and heat source/sink. Usual similarity transformations are introduced to obtain similarity solution, using regular perturbation technique. To observe physical insight and interesting aspects of the problem in the presence of thermophoresis, the non-dimensional velocity, temperature and concentration field are numerically studied and displayed graphically for pertinent parameters. It is observed that the thermophoresis has dominant effect on mass transfer mechanism in particle deposition process. The model finds applications in studying particulate deposition on turbine blades, removing small particles from gas streams and determining chemical vapor deposition rate in chemical industries.

EFFECTS OF HEAT SOURCE/SINK AND RADIATIVE HEAT TRANSFER ON HYDROMAGNETIC NATURAL CONVECTIVE FLOW THROUGH A VERTICAL CHANNEL

Effects of heat source and radiative heat transfer on unsteady hydromagnetic natural convective laminar flow of an incompressible homogeneous, electrical conducting, viscous fluid through a porous medium in a vertical channel consisting of semi-infinite parallel walls is studied. The fluid flows under the influence of uniform magnetic field applied normal to the flow. Using the Laplace transform technique, the solutions for velocity and temperature fields are obtained. Expressions for skin friction and rate of heat transfer are also derived. The effects of material parameters on temperature distribution, velocity field, skin friction, and rate of heat transfer are discussed for symmetrical cooling of the channel walls. The effects of material parameters on velocity are shown graphically, while those of skin friction and heat transfer rate are presented in tabular form and a corresponding discussion is made. The model finds applications in nuclear heat transfer processes, metallurgy, and energy systems.

Finite element study of nonlinear two-dimensional deoxygenated biomagnetic micropolar flow

In this paper, we consider the two-dimensional fully-developed steady, viscous hydrodynamic flow of a deoxygenated biomagnetic micropolar fluid, in an (X,Y) coordinate system. The momentum conservation equations with zero-pressure gradient are extended to incorporate the X- and Y-components of the biomagnetic body force term with appropriate boundary conditions. The equations are non-dimensionalized using a set of transformations. A finite element solution is obtained to the resulting non-dimensional model and the effects of biomagnetic number (NH), micropolar microinertia parameter (B) and micropolar viscosity ratio parameter (R) on the X- and Y-direction velocity profiles and micro-rotation (N) is studied in detail. Translational velocities (U,V) are seen to be reduced with an increase in micropolarity (R) and also biomagnetic effects (NH). Conversely the velocities are increased with a rise in microinertia parameter (B). Several special cases, e.g. Newtonian biomagnetic physiological flow, are also discussed. The model finds applications in blood flow in biomedical device technology (e.g. oxygenators), hemodynamics under strong external magnetic fields, magnetic drug carrier analysis, etc.

Radiation and mass transfer effects on MHD free convection flow past an impulsively started isothermal vertical plate with dissipation

This paper is focused on the study of effects of thermal radiation on the natural convective heat and mass transfer of a viscous, incompressible, gray absorbing-emitting fluid flowing past an impulsively started moving vertical plate with viscous dissipation. The governing boundary-layer equations are formulated in an (x, y, t) coordinate system with appropriate boundary conditions. The Rosseland diffusion approximation is used to analyze the radiative heat flux in the energy equation, which is appropriate for non-scattering media. The dimensionless governing equations are solved using an implicit finite-difference method of Crank-Nicolson type. The influence of Prandtl number, radiation-conduction parameter, thermal Grashof number, species Grashof number, Schmidt number, and Eckert number on the dimensionless velocity, temperature and concentration are studied. In addition the variation of the local and average skin-friction, Nusselt number, and Sherwood number for selected thermophysical parameters are computed and shown graphically. Increasing the Eckert number is seen to accelerate the flow. Thermal radiation reduces both velocity and temperature in the boundary layer. This model finds applications in solar energy collection systems, geophysics and astrophysics, aero space and also in the design of high temperature chemical process systems.

Network Numerical Simulation of Impulsively-Started Transient Radiation-Convection Heat and Mass Transfer in a Saturated Darcy-Forchheimer Porous Medium

We study the effects of thermal radiation and porous drag forces on the natural convection heat and mass transfer of a viscous, incompressible, gray, absorbingemmitting fluid flowing past an impulsively started moving vertical plate adjacent to a non-Darcian porous regime. The governing boundary-layer equations are formulated in an (X∗, Y∗, t∗) coordinate system with appropriate boundary conditions. The Rosseland diffusion approximation is employed to analyze the radiative heat flux and is appropriate for non-scattering media. The model is non-dimensionalized and solved with the network simulation model. We study the influence of Prandtl number, radiation-conduction parameter, thermal Grashof number, species Grashof number, Schmidt number, Darcy number and Forchheimer number on the dimensionless velocity, temperature and species function distributions. Additionally we compute the variation of the local skin friction, Nusselt number and Sherwood number for selected thermophysical parameters. Increasing Darcy number is seen to accelerate the flow; the converse is apparent for an increase in Forchheimer number. Thermal radiation is seen to reduce both velocity and temperature in the boundary layer. The interactive effects of second order porous drag and thermal radiation are also considered. The model finds applications in solar energy collection systems, porous combustors, transport in fires in porous media (forest fires) and also the design of high temperature chemical process systems.

NSM analysis of time-dependent nonlinear buoyancy-driven double-diffusive radiative convection flow in non-Darcy geological porous media

A network numerical simulator is developed and described to simulate the transient, nonlinear buoyancy-driven double diffusive heat and mass transfer of a viscous, incompressible, gray, absorbing–emitting fluid flowing past an impulsively started moving vertical plate adjacent to a non-Darcian geological porous regime. The governing boundary-layer equations are formulated in an (X *, Y *, t *) coordinate system with appropriate boundary conditions. An algebraic diffusion approximation is used to simplify the radiation heat transfer contribution. The non-dimensionalized transport equations are solved in an (X, Y, t) coordinate system using the network simulation model (NSM) and the computer code, Pspice. A detailed discussion of the network design is provided. The effects of Prandtl number, radiation–conduction parameter (Stark number), thermal Grashof number, species Grashof number, Schmidt number, Darcy number and Forchheimer number on the transient dimensionless velocities (U, V), non-dimensional temperature (T) and dimensionless concentration function (C) are illustrated graphically. Additionally, we have computed plots of U, V, T, C versus time and average Nusselt number and Sherwood number versus X, Y coordinate, for various thermophysical parameters. The model finds applications in geological contamination, geothermal energy systems and radioactive waste-repository near-field thermo-geofluid mechanics.

Computational modeling of biomagnetic micropolar blood flow and heat transfer in a two-dimensional non-Darcian porous medium

We study theoretically and computationally the incompressible, non-conducting, micropolar, biomagnetic (blood) flow and heat transfer through a two-dimensional square porous medium in an (x,y) coordinate system, bound by impermeable walls. The magnetic field acting on the fluid is generated by an electrical current flowing normal to the x–y plane, at a distance l beneath the base side of the square. The flow regime is affected by the magnetization B0 and a linear relation is used to define the relationship between magnetization and magnetic field intensity. The steady governing equations for x-direction translational (linear) momentum, y-direction translational (linear) momentum, angular momentum (micro-rotation) and energy (heat) conservation are presented. The energy equation incorporates a special term designating the thermal power per unit volume due to the magnetocaloric effect. The governing equations are non-dimensionalized into a dimensionless (ξ,η) coordinate system using a set of similarity transformations. The resulting two point boundary value problem is shown to be represented by five dependent non-dimensional variables, fξ (velocity), fη (velocity), g (micro-rotation), E (magnetic field intensity) and θ (temperature) with appropriate boundary conditions at the walls. The thermophysical parameters controlling the flow are the micropolar parameter (R), biomagnetic parameter (NH), Darcy number (Da), Forchheimer (Fs), magnetic field strength parameter (Mn), Eckert number (Ec) and Prandtl number (Pr). Numerical solutions are obtained using the finite element method and also the finite difference method for Ec=2.476×10−6 and Prandtl number Pr=20, which represent realistic biomagnetic hemodynamic and heat transfer scenarios. Temperatures are shown to be considerably increased with Mn values but depressed by a rise in biomagnetic parameter (NH) and also a rise in micropolarity (R). Translational velocity components are found to decrease substantially with micropolarity (R), a trend consistent with Newtonian blood flows. Micro-rotation values are shown to increase considerably with a rise in R values but are reduced with a rise in biomagnetic parameter (NH). Both translational velocities are boosted with a rise in Darcy number as is micro-rotation. Forchheimer number is also shown to decrease translational velocities but increase micro-rotation. Excellent agreement is demonstrated between both numerical solutions. The mathematical model finds applications in blood flow control devices, hemodynamics in porous biomaterials and also biomagnetic flows in highly perfused skeletal tissue.

Finite Element Solutions for Non-Newtonian Pulsatile Flow in a Non-Darcian Porous Medium Conduit

The present analysis is motivated by the need to elucidate with more accuracy and sophistication the hydrodynamics of non-Newtonian flow via a channel containing a porous material under pulsating pressure gradient. A one-dimensional transient rheological model for pulsating flow through a Darcy-Forcheimmer porous channel is used. A modified Casson non-Newtonian constitutive model is employed for the transport fluid with a drag force formulation for the porous body force effects. The model is transformed and solved using a finite element numerical technique. Rheological effects are examined using a β parameter which vanishes in the limit (Newtonian flow). Velocity profiles are plotted for studying the influence of Reynolds number, Darcy number, Forchheimer number and the β (non-Newtonian) parameter. The channel considered is rigid with a pulsatile pressure applied via an appropriate pressure gradient term. The model finds applications in industrial filtration systems, pumping of polymeric fluids etc.

Mathematical Modeling of Biomagnetic Flow in a Micropolar Fluid-Saturated Darcian Porous Medium

In this paper a mathematical model of the two-dimensional fully developed steady, viscous flow of a non-conducting biomagnetic micropolar fluid through a Darcian porous medium model of tissue is presented. The momentum conservation equations with zero pressure gradient are extended to incorporate the biomagnetic body force terms along the X and Y axes and also the Darcian linear drag in the X and Y directions, with appropriate boundary conditions. An angular momentum equation is also included for the spin of the microelements. The equations are non-dimensionalized using a set of transformations following Tzirtzilakis et al. (2004). A finite element solution is generated to the resulting non-dimensional model and the effects of biomagnetic number (NH), Darcy number (Da) and micropolar viscosity ratio parameter (R) on the X- and Y-direction velocity profiles is studied in detail. A number of special cases of the flow model are also discussed. The numerical solution is compared with a finite difference solution using central differencing and found to be in excellent agreement The model finds applications in biomedical device technology, blood transport in tumors, brain tissue and soft connective tissue zones as well as in fundamental hydrodynamics of ferrofluids in porous materials.

Dynamics of the quantum Duffing oscillator in the driving induced bistable regime

We investigate the non-linear response of an anharmonic monostable quantum mechanical resonator to strong external periodic driving. The driving thereby induces an effective bistability in which resonant tunneling can be identified. Within the framework of a Floquet analysis, an effective Floquet–Born–Markovian master equation with time-independent coefficients can be established which can be solved straightforwardly. Various effects including resonant tunneling and multi-photon transitions will be described. Our model finds applications in nano-electromechanical devices such as vibrating suspended nano-wires as well as in non-destructive read-out procedures for superconducting quantum bits involving the non-linear response of the read-out SQUID.

Multiparameter Perturbation Analysis of Unsteady Oscillatory Magnetoconvection in Porous Media with Heat Source Effects

Unsteady natural convection flow of a viscous, incompressible, electrically conducting fluid past an infinite vertical porous plate embedded within a saturated, highly porous medium under the influence of a uniform magnetic field, Eckert heating, and a heat-absorbing sink is studied. It is assumed that the suction velocity is subjected to small-amplitude oscillations in time about the steady nonzero mean suction velocity. Approximate solutions for the velocity and temperature field are obtained using the multiparameter perturbation technique. Expressions for skin friction and rate of heat transfer are also derived. Mean temperatures are boosted by both magnetic field and heat-source parameter, but are lowered by a rise in the Prandtl number, Grashof number, and permeability parameter (k). The effects of all parameters on velocity, temperature, skin friction, and heat transfer rate (Nusselt number) are graphically presented and tabulated, and are discussed in detail. The model finds applications in nuclear heat transfer processes, metallurgy, aerospace/aval propulsion, and energy systems.

Fuzzy control of arrivals to tandem queues with two stations

We consider two queues in tandem, each of which has its own input of arriving customers, which, in turn, may either be accepted or rejected. Suppose that the system receives a fixed reward for each accepted customer and pays a holding cost per customer per unit time in the system. The objective is to dynamically determine the optimal admission policies based on the state of the system so as to maximize the average profit (reward minus cost) over an infinite horizon. This model finds applications in flow control in communication systems, industrial job shops, and traffic-flow systems. In this paper, a novel approach is presented using fuzzy control. This approach explicitly finds the optimal policy, which up until now has defied analytical solutions.

Internal photoemission characteristics of metal–insulator–semiconductor structures at low electric fields in the insulator

This article completes the presentation of a model of photoelectric phenomena taking place in metal–insulator–semiconductor (MIS) structures at low electric fields, which was introduced in Ref. [H. M. Przewlocki, J. Appl. Phys. 78, 2550 (1995)]. A solution and analysis of model’s equations is given for the general case of nonzero net photoelectric current (J≠0) in the external circuit. This solution allows calculation of the photocurrent–voltage characteristics of MIS structures illuminated with ultraviolet radiation of different wavelengths λ. To verify these results, experimental characteristics were taken and are shown in comparison with the calculated ones. Excellent agreement between calculated and experimental characteristics, obtained for a wide range of different MIS structures, strongly supports the validity of the model. Limits of applicability of this model are illustrated and discussed. The model finds applications in developing new, highly precise, photoelectric measurement methods of MIS structures. Principles of three such methods are outlined. One of these methods has already been fully verified and has been successfully used in a number of investigations, while the other two, are currently being verified and optimized.