Journal Of Applied Fluid Mechanics
Volume:8 Issue: 1, Nov-Dec 2015

An generalized advection dispersion model with time-fractional derivative is developed for analyzing underground injection of wastes. The governing equations for a cylindrically symmetrical system are cast in nondimensional form and then transformed and solved in Laplace space. With the help of Crump algorithm, the Laplace space solution is inverted. The effect of fractional derivative parameter to the particle movement process is discussed numerically, and it is pointed out that the role of fractional derivative parameter is to slow the particle motion when $0<\beta<1$.

An investigation of unsteady hydromagnetic natural convection heat and mass trans fer flow with Hall current of a viscous, incompressible, electrically conducting, heat absorbing and optically thin radiating fluid past an accelerated moving vertical plate through fluid saturated porous medium in a rotating environment is carried out when temperature of the plate has a temporarily ramped profile. The exact solutions of momentum, energy and concentration equations are obtained in closed form by Laplace transform technique. The expressions of skin friction, Nusselt number and Sherwood number are also derived. For both ramped temperature and isothermal plates, Hall current tends to accelerate primary and secondary fluid velocities whereas heat absorption and radiation have reverse effect on it. Rotation tends to retard primary fluid velocity whereas it has a reverse effect on secondary fluid velocity. Heat absorption and radiation have tendency to enhance rate of heat transfer at the plate.

The present study investigates entropy generation on a magnetohydrodynamic flow and heat transfer of a Maxwell fluid using a spectral relaxation method. The method is based on simple iteration schemes formed by reduction of the order of the momentum equation followed by a rearrangement of the resulting governing nonlinear equation systems which are then solved using spectral methods. The velocity and temperature profiles are obtained numerically and used to generate the entropy generation number. Entropy generation increased with the Reynolds number, the magnetic parameter and the dimensionless group parameter while decreased for higher Prandtl numbers. The effect of the flow parameters on the velocity and temperature of the flow were also investigated. The results were validated using the bvp4c where the spectral relaxation method was found to be accurate and rapidly convergent to the numerical results.

This paper describes a CFD study of the steam-reforming process (SRP) of methanol in a short pseudo-contact time reactor of fixed bed type, in axi-symmetric conditions. The SRP is important sake for hydrogen production, and the design /scale-up/control of the industrial processes in the future are supported by a reliable knowledge and prediction of the catalytic reaction. The difficulty of determining the reaction scheme and the associated constants is wellknown, due to the necessity of identifying the reaction kinetics in purely chemical regime, meaning with a perfect homogeneity and flow independence. Practically these ideal conditions, albeit assumed, are not fulfilled so that the intrinsic chemical kinetics is not reached. For the case of SRP, we have attempted here to validate the Peppley’s model by a numerical modelling reproducing exactly the local conditions in the experimental duct, accounting for gradients in the cross section. The numerical results show the same trends than the experimental one, but with a slight shift of 20% as a consequence of the reactor heterogeneity. This result seems acceptable to validate the use of the Peepley’s model for further studies in other types of complex flow reactors.

This paper deals with the dynamic analysis and simulation of Pipeline Inspection Gage (PIG) through the two and three dimensional gas pipelines. Continuity, momentum and the state equations are employed to achieve the gas flow parameters like density, velocity and pressure along the pipeline since the dynamic behavior of the pig depends on the flow field characteristics. Also, a differential equation which governs the dynamic behavior of the pig is derived. The pig is assumed to be a small rigid body with a bypass hole in its body. The variation of the diameter of the bypass port, which is controlled by a valve, is considered in this research. The path of the pig or geometry of the pipeline is assumed to be 2D and 3D curve. 2D and 3D simulations of the pig motion are performed individually using Rung- Kutta method and a case has been solved and discussed for each of them. The simulation results show that the derived equations are valid and effective for online estimating of the position, velocity and forces acting on the pig in gas pipelines at any time of the motion.

In the present note, we have considered the problem of the onset of convection in a couple-stress fluid with variable gravity to include the effects of suspended particles and vertical magnetic field through a porous medium. Following the normal mode method, dispersion relation is obtained in the presence of various parameters like porosity, permeability, suspended particle, couple-stress and magnetic field. For the case of stationary convection, it is found that the parameters like porosity, permeability and suspended particles have a destabilizing effect on the system whereas couple-stress and magnetic field have a stabilizing effect on the onset of convection. The dispersion relation is analyzed numerically and the results are also shown graphically. The necessary condition for the onset of instability and the sufficient condition for the non-existence of convection at the marginal state in the absence and presence of couple-stress parameter have also been obtained by using Rayleigh-Ritz and Cauchy-Schwartz inequality.

The purpose of present investigation is to analyse bouyancy-driven radiation-convection flow past a moving vertical plate with reference to an optically dense medium in the presence of mass concentration, using Rosseland approximation permeated by a magnetic field. The flow is considered to be gray in the presence of free convection, mass transfer and radiation. An exact solution of the governing equations is obtained by applying the Laplace transform method. Numerical results of velocity distributions, shear stress, temperature distribution and mass concentration are presented graphically to give physical insight into the flow pattern.

In this paper, an experimental investigation was conducted to analyze the effect of spacing between vertical plates of a parallelepipedic canal on the average thermal and dynamic fields of a thermal plume. To carry out this study, we placed at the laboratory a rectangular heat block at the entry of a vertical canal open at the ends. The internal walls of the plates are heated uniformly by Joule effect and by thermal radiation emitted by active source. The heating of walls creates a thermosiphon flow which interacts with the plume inside canal. Four dimensionless spacing between the plates 1.25 ≤ e* ≤ 30 are considered. It is found that the spacing is the most important geometrical parameter affecting the thermal and dynamical behavior of the flow. Using visualization by laser plan and hot wire probe, flow structure evolves in two zones for smallest and largest spacing while a supplementary zone near heat source is observed for an intermediate spacing. The variation of flow rate and energy transported by the fluid shows the existence of an optimum spacing where the propagation of plume flow is more accelerated.

An analysis has been carried out to investigate the influence of combined effects of MHD, suction and radiation on forced convection boundary layer flow of a nanofluid over an exponentially stretching sheet, embedded in a thermally stratified medium. The governing boundary layer equations of the problem are formulated and transformed into ordinary differential equations, using a similarity transformation. The resulting ordinary differential equations are solved numerically, by the shooting method. The effects of the governing parameters on the flow and heat transfer characteristics are studied and discussed in detail. Different types of nanoparticles, namely, Cu, Ag, Al2O3 and TiO2, with water as the base fluid, are studied. It is found that the effects of the radiation parameter, volume fraction and suction are same on the temperature profiles, in contrast to the effects of the thermal stratification. Comparisons with previously published works are performed in some special cases, and found to be in good agreement.

Hydrodynamics plays a major role in the design of an industrial liquid-solid circulating fluidized bed (LSCFB) system. Till date, research investigations have been carried out with tap water as a liquid phase in an LSCFB. But still there is a limited understanding regarding the circulation of particles in an LSCFB with viscous fluids. The aim of our study was to characterize the hydrodynamics in an LSCFB with varying viscosity. Experiments were conducted in a fluidized bed riser of 0.1 m diameter by 2.4 m height with different viscous liquids to study the effects of the operating parameters, namely, primary velocity, secondary velocity, and total velocity, on the hydrodynamic characteristics of the LSCFB with reference to its solid holdup, solid circulation rate, and particle velocity. Experiments were conducted using water and glycerol at different concentrations, and the solid particles (sand and resin) of different densities, but same diameter were used in the experiment. The results indicate that the solid holdup in the riser was axially uniform for viscous liquids, which increased with an increase in auxiliary velocity. The average solid holdup decreased with an increase in total velocity, and it increased with an increase in liquid viscosity as the critical transitional velocity decreased with an increase in viscosity. The solid circulation rate was found to be increased with increased total velocity, auxiliary velocity, and viscosity.

This report presents a study of the dynamics dispersion behaviors of inertial particle in solid-air two-phase flow within accelerated domains using both experimental and simulation approaches. In the simulation, a threedimensional model was proposed by means of the combined computational fluid dynamics and a discrete element method (CFD-DEM). The simulation model provides information regarding the particle distribution behaviors and the particle run-away rate from the calculation domain. In the experiment, particle image velocimetry (PIV) and laser tomography were used to measure the particle velocity and concentration distribution, respectively. The simulation results were than validated by the experimental measurement. And the influence mechanisms of acceleration on the particle flow behavior were discussed in detail. As results, acceleration of the calculation domain affects the particle motion and causes a relative dense particles distribution in the accelerated direction. The particle run-out rate under acceleration was initially the same, but subsequently lower than that of the condition without acceleration. This finding shows that the acceleration adversely affects the particle run-out rate.

In this paper, we propose a model designed to describe a strongly sheared compressible homogeneous turbulent flows. Such flows are far from equilibrium and are well represented by the A3 and A4 cases of the DNS of Sarkar. Speziale and Xu developed a relaxation model in incompressible turbulence able to take into account significant departures from equilibrium. In a previous paper, Radhia et al. proposed a relaxation model similar to that of Speziale and Xu. This model is based on an algebraic representation of the Reynolds stress tensor, much simpler than that of Speziale and Xu and it gave a good result for rapid axisymetric contraction. In this work, we propose to extend the Radhia et al’s. model to compressible homogenous turbulence. This model is based on the pressure-strain model of Launder et al., where we incorporate turbulent Mach number in order to take into account compressibility effects. To assess this model, two numerical simulations were performed which are similar to the cases A3 and A4 of the DNS of Sarkar.

In this study, slip-flow heat transfer in a laminar, steady state, two-dimensional incompressible flow between parallel plates micro-channel is investigated numerically. A new method based on perturbation expansion for modeling of slip micro-flows is presented. Navier-stokes equations are developed by using perturbation expansions of velocity, pressure and temperature fields. Different orders of equations depending on the magnitude of Knudsen number are obtained and each set of the equations are solved. The computations are performed for micro-channels with Constant Wall Heat Flux (CWHF) and Constant Wall Temperature (CWT) boundary conditions to obtain heat transfer characteristics of gaseous flow in slip regime. The effects of compressibility and viscous dissipation are neglected in this study. The numerical methodology is based on Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) method. The effects of Knudsen number and thermal creep flow on Nusselt number are numerically investigated.This study confirms that the perturbation method with different orders of Knudsen number can predict the velocity and temperature fields with good accuracy. The obtained solutions are compared with both available numerical and analytical results and good agreement is obtained.

Bladeless fan is a novel fan type that has no observable impeller, usually used for domestic applications. Numerical investigation of a Bladeless fan via Finite Volume Method was carried out in this study. The fan was placed in center of a 4×2×2m room and 473 Eppler airfoil profile was used as cross section of the fan. Performance and noise level of the fan by solving continuity and momentum equations as well as noise equations of Broadband Noise Source (BNS) and Ffowcs Williams and Hawkings (FW-H) in both steady state and unsteady conditions were studied. Flow increase ratio of the fan was captured. Furthermore, BNS method could find outlet slit of the air as the main source of the noise generation. In order to validation of aeroacousticcode results, a simulation of noise for NACA 0012 airfoil via FW-H method was compared to experimental results and good agreement was obtained.

This paper presents a specific experimental setup in which artificial vortices are successfully created and maintained under controlled conditions. The developed vortex simulation chamber is demonstrated to be crucial to the study of vortices and to improve the understanding of vortex nature and behaviour. Furthermore, the general simulation chamber characteristics, constructional details and working principle are elaborated in detail. Preliminary experimental results are also discussed. Specifically, the influence of the water vapour content on the pressure potential and the vortex stability has been analysed. The specific friction work in the vortex system has also been analysed; the novel specific vortex efficiency factor has been introduced. The gained research results and conclusions are important to understand the complex nature of vortex systems, which can be useful for both meteorological purposes and energy concepts research, where convective vortices are assumed to be used as heat engines.

The objective of this paper is to consider both effects of slip and convective heat boundary conditions on steady two-dimensional boundary layer flow of a nanofluid over a stretching sheet in the presence of blowing/suction simultaneously. Flow meets the Navier''s slip condition at the surface and Biot number is also used to consider the effects of convective heat transfer. The employed model for nanofluid includes two-component four-equation nonhomogeneous equilibrium model that incorporates the effects of nanoparticle migration owing to Brownian motion and thermophoresis. The basic partial boundary layer equations have been transformed into a two-point boundary value problem via similarity variables. Results for impermeable isothermal surface and also no-slip boundary condition were in best agreements with those existing in literatures. Effects of governing parameters such as Biot number (Bi), slip parameter (λ), thermophoresis (Nt), Prandtl number (Pr), Lewis number (Le), Brownian motion (Nb) and blowing/suction (S) on reduced Nusselt and Sherwood numbers are analyzed and discussed in details. The obtained results indicate that unlike heat transfer rate, concentration rate is very sensitive to all parameters among which Le, S and Pr are the most effective ones.

An investigation of the effects of Hall current and rotation on unsteady hydromagnetic natural convection flow with heat and mass transfer of an electrically conducting, viscous, incompressible and time dependent heat absorbing fluid past an impulsively moving vertical plate in a porous medium taking thermal and mass diffusions into account is carried out. Exact solution of the governing equations is obtained in closed form by Laplace Transform technique. Exact solution is also obtained in case of unit Prandtl number and unit Schmidt number. Expressions for skin friction due to primary and secondary flows and Nusselt number are derived for both ramped temperature and isothermal plates. Expression for Sherwood number is also derived. The numerical values of primary and secondary fluid velocities and species concentration are displayed graphically whereas that of skin friction and Nusselt number are presented in tabular form for various values of pertinent flow parameters.