

Gas and Particle Flow in a Spray Roaster


Pages :
187196


Authors :
S. Johansson,
L. G. Westerberg,
T. S. Lundstrom,
In the steel industry, waste hydrochloric acid is produced through the process to pickle steel slabs for removal of corrosion. Regenerated hydrochloric acid is obtained by separating the chloride gas from the waste product through spray roasting.This process also produces a byproduct in the form of iron oxide which is sold to different industries. The present study is a continuation of a study arising from the need to better understand the dynamics inside the regeneration reactor, which in turn will improve possibilities to optimize the regeneration process, which to date has been manually adjusted by trial and error. In this study the velocity and temperature distribution inside the reactor is numerically modelled together with the droplet motion through the reactor. The main objective is to investigate the influence of a changed
spray nozzle position on the flow characteristics of the continuous and dispersed phase, and the relation between temperature and energy efficiency and the regeneration process. Numerical models of the type of flow present in the regeneration reactor are not represented to any major extent in the literature, making the present study relevant to the engineers and researchers active in the steel industry and the application in question.





Thermal Analysis of Superheater Platen Tubesin Boilers


Pages :
197208


Authors :
S. Falahatkar,
H. Ahmadikia,
Superheaters are among the most important components of boilers and have major importance due to this operation in
high temperatures and pressures. Turbines are sensitive to the fluctuation of superheaterstemperature;therefore even
the slightest fluctuation in the outlet vapor temperature from the superheaters does damage the turbine axis and fins.
Examining the potential damages of combustion in the boilers and components such as the superheaters can have a
vital contribution to the progression of the productivity of boiler, turbine and the power plant altogether it solutions
are to be fund to improve such systems. In this study, the focus is on the nearest tube set of superheaters to the
combustion chamber.These types of tubes are exposed to a wide range ofcombustion flames such that the most heat
transfer to them is radiation type.Here, the 320 MW boiler of Isfahan power plant (Iran), the combustion chamber, 16
burners and the platensuperheater tubes were remodeled by CFD technique. The fluid motion, the heat transfer and
combustion processes are analyzed. The twoequation turbulence model of kεis adopted to measure the eddy viscosity. The eddy dissipation model is used to calculate the combustion as well as the P1 radiation model to quantify the radiation. The overheated zones of superheater tubes and the combustion chamber are identified in order toimprove this problem by applying the radiation thermal shields and knees with porous crust which are introduced as the new techniques.





Viscous Potential Flow Analysis of Electrohydrodynamic RayleighTaylor Instability


Pages :
209216


Authors :
M. K. Awasthi,
D. Yadav,
G. S. Agrawal,
A linear analysis of RayleighTaylor instability in the presence of tangential electric field has been carried out using viscous potential flow theory. In viscous potential flow theory, viscosity is not zero but viscous term in the Navier Stokes equation is zero as vorticity is zero. Viscosity enters through normal stress balance and tangential stresses are not considered in viscous flow theory. A dispersion relation has been obtained and stability criterion has been given in the terms of critical value of electric field. It has been observed that tangential electric field influences stability of the system. A comparison between the results obtained by viscous potential analysis and inviscid potential flow has been made and found that viscosity reduces the growth of instability.





Computation of NonEquilibrium Chemically Reacting Hypersonic Flow from a Cartesian Mesh with Near Wall Viscous Resolution


Pages :
217226


Authors :
V. Ashok,
V. Adimurthy,
G. Joseph,
A hybrid solution methodology has been developed to solve chemically reacting laminar hypersonic flow in chemical
Nonequilibrium and thermal equilibrium, by a Cartesian mesh based hybrid solution methodology, which uses an unstructured prism layer solution near the wall and a Cartesian mesh solution away from the wall. The unstructured prism layer for near wall solution is obtained from the normal projection of wall panels of the Cartesian mesh and are stitched with the outer Cartesian mesh. The solver, developed based on this approach when compared with other chemically reacting CFD codes and limited experimental results show good comparison. This procedure has a good potential to handle nearwall resolution for chemically reacting flows with a Cartesian mesh for complex geometries
as well.





Empirical Modeling and Experimental Investigations on Isothermal AirWater TwoPhase Flow through Horizontal Circular Minichannel


Pages :
227237


Authors :
H. B. Mehta,
J. Banerjee,
The experimentally developed flow pattern maps for microscale channels reported by various researchers differ significantly. Also, no theoretical models effectively predict the flow regime transition boundaries in microscale channel. The present work proposes an empirical model for airwater twophase flow pattern transition boundaries for minichannel diameters between 2 to 5mm. Moreover, experiments are conducted with 2.5 mm diameter horizontal circular minichannel to develop a flow regime map. The proposed empirical model is found to provide good agreement with the experimental data. Comparisons are also shown with the work of Mandhane et al. (1974), Taitel and Dukler (1976), Barnea et al. (1983), Damianides and Westwater (1988), Coleman and Garimella (1999), Yang and Shieh (2001), Venkatesan et al. (2010).





Hydromagnetic Flow over an Inclined NonLinear Stretching Sheet with Variable Viscosity in the Presence of Thermal Radiation and Chemical Reaction


Pages :
239247


Authors :
G. C. Shit,
S. Majee,
An analysis has been made to investigate the effects of thermal radiation on the magnetohydrodynamic (MHD) flow and heat transfer over an inclined nonlinear stretching sheet. The surface velocity of the stretching sheet and the transverse magnetic field are assumed to vary as a power function of the distance from the origin. The effect of internal heat generation/absorption is taken into account. The fluid viscosity is assumed to vary as an inverse linear function of temperature. A generalized similarity transformation is used to reduce the governing partial differential equations to a system of nonlinear coupled ordinary differential equations, and is solved numerically by using a finite difference scheme. The numerical results concerned with the velocity, temperature and concentration distributions as well as the skinfriction coefficient and the Nusselt number for various values of the dimensionless parameters of interest are obtained. Some important findings reported in this paper reveal that the effect of thermal radiation and heat generation/absorption have significant role in controlling the rate of heat transfer in the boundary layer region.





Numerical Modeling of TwoPhase Hydromagnetic Flow and Heat Transfer in a ParticleSuspension through a nonDarcian Porous Channel


Pages :
249261


Authors :
S. Rawat,
R. Bhargava,
S. Kapoor,
O. A. Bég,
T. A. Bég,
R. Bansal,
A mathematical model is presented for the steady, twodimensional magnetoconvection heat transfer of a twophase, electricallyconducting, particlesuspension in a channel containing a nonDarcian porous medium intercalated between two parallel plates, in the presence of a transverse magnetic field. The channel walls are assumed to be isothermal but at different temperatures. The governing equations for the onedimensional steady flow are formulated following Marble (1970) and extended to include the influence of Darcian porous drag, Forcheimmer quadratic drag, buoyancy effects, Lorentz body force (hydromagnetic retardation force) and particlephase viscous stresses. Special boundary conditions for the particlephase wall conditions are implemented. The governing coupled, nonlinear differential equations are reduced from an (x,y) coordinate system to a onedimensional (y) coordinate system. A series of transformations is then employed to nondimensionalize the model in terms of a single independent variable, , yielding a quartet of coupled ordinary differential equations which are solved numerically using the finite element method, under appropriate transformed boundary conditions. The influence of for example Grashof free convection number (Gr), Hartmann hydromagnetic number (Ha), inverse Stokes number (Skm), Darcy number (Da), Forcheimmer number (Fs),particle loading parameter (PL), buoyancy parameter (B) on the fluidphase velocity and particlephase velocity are presented graphically. A number of special cases of the transformed model are also studied. The mathematical model finds applications in solar collector devices, electronic fabrication, jet nozzle flows, industrial materials processing transport phenomena, MHD energy generator systems etc.





Cell Model for Slow Viscous Flow past Spherical Particles with Surfactant Layer Coating


Pages :
263273


Authors :
S. Datta,
S. Raturi,
Creeping flow through a swarm of spherical particles, where each particle consists of a solid core covered by a liquid shell coated with monomolecular layer of surfactant layer, is studied using the cell model technique. The analytical solution of the problem for four models: Happel’s, Kuwabara’s, Kvashin’s and Cunningham’s (usually referred to as MehtaMorse’s) is derived. The drag force acting on each particle in the cell is evaluated for the four models. In limiting cases the drag force reduces to earlier analytical results. Results are discussed and presented in graphical forms.





Radiation and Inclined Magnetic Field Effects on Unsteady Hydromagnetic Free Convection Flow past an Impulsively Moving Vertical Plate in a Porous Medium


Pages :
275286


Authors :
N. Sandeep,
V. Sugunamma,
We analyse the effects of radiation and rotation on unsteady hydromagnetic free convection flow of a viscous incompressible electrically conducting fluid past an impulsively moving vertical plate in a porous medium by applying inclined magnetic field, Under Boussinesq approximation, assuming that the temperature of the plate has a temporarily ramped profile. An exact solution of the governing equations, in dimensionless form is obtained by Laplace transform technique. To compare the results obtained in this case with that of isothermal plate and exact solution of the governing equations are also obtained for isothermal plate and results are discussed graphically in both ramped temperature and isothermal cases.





A Modified Time Advancement Algorithm for Optimizing Channel Flow Analysis in Direct Numerical Simulation Method


Pages :
287297


Authors :
E. Rajabi,
M. R. Kavianpour,
In this research a direct numerical simulation (DNS) of turbulent flow is performed in a geometrically standard case like plane channel flow. Pseudo spectral (PS) method is used due to geometry specifications and very high accuracy achieved despite relatively few grid points. A variable timestepping algorithm is proposed which may reduce requirement of computational cost in simulation of such wallbounded flow. Channel flow analysis is performed with both constant and varied timestep for 128 × 65×128 grid points. The time advancement is carried out by implicit thirdorder backward differentiation scheme for linear terms and explicit forward Euler for nonlinear convection term. PS method is used in Cartesian coordinates with Chebychev polynomial expansion in normal direction for one nonperiodic boundary condition. Also Fourier series is employed in streamwise and spanwise directions for two periodic boundary conditions. The friction Reynolds number is about Reτ=175 based on a friction velocity and channel half width. Standard common rotational form was chosen for discritization of nonlinear convective term of NavierStocks equation. The comparison is made between turbulent quantities such as the turbulent statistics, Reynolds stress, wall shear velocity, standard deviation of (u) and total normalized energy of instantaneous velocities in both timediscretization methods. The results show that if final decision rests on economics, the proposed variable timestepping algorithm will be proper choice which satisfies the accuracy
and reduces the computational cost.





A Modeling Study of Boundary Layer Wind Flow over Tehran Region during a High Pollution Episode


Pages :
299313


Authors :
H. Malakooti,
A. A. Bidokhti,
The influence of a megacity on the atmospheric boundary layer wind field was examined in the complexterrain, semiarid Tehran region using the Pennsylvania State University/National Center for Atmospheric Research fifthgeneration Mesoscale Model (MM5) during a high pollution period. In addition, model sensitivity studies were conducted to evaluate the performance of the urban canopy and urban soil model "SM2U (3D)" parameterization on the wind field. The topographic flows and urban effects were found to play important roles in modulating the wind field, and the urbanized areas exerted important local effects on the boundary layer meteorology. An emission inventory of heat generation was developed and updated for 2005 in this work. By using a detailed methodology, we calculated spatial and temporal distributions of the anthropogenic heat flux (Qf) for Tehran during 2005. Wintertime Qf is found larger than summertime Qf, which reflects the importance of heating emissions from buildings and traffic during cold and warm periods respectively. Different urban parameterizations were used as a tool to investigate the modifications induced by the presence of an urban area in the area of interest. It is found that, for local meteorological simulations, the dragforce approach (DA) coupled with an urban soil model (SM2U) is preferable to the roughness approach (RA) coupled with a slab soil model. The comparisons indicated that the most important features of the wind field, in urban areas are well reproduced by the DASM2U configuration with the anthropogenic heat flux being taken into account. This modeling option showed that the suburban part of the city is dominated by topographic flows whereas the center and south of Tehran are more affected by urban heat island (UHI) forcing especially during the night in studied episodes.





Simulation of Viscous and Reactive Hypersonic Flows Behaviour in a Shock Tube Facility: TVD Schemes and Flux Limiters Application


Pages :
315328


Authors :
A. Boulahia,
S. Abboudi,
M. Belkhiri,
Work performed in this study concerns mainly the analysis and the wisely use of TVD type schemes (total variation diminishing) for numerical simulation of reactive flows, these schemes are first presented in scalar equation. Their extension to Euler equations for a reactive gas mixture is conducted through the approximate extended solver of Riemann problem. A comparative study of specific variants of TVD schemes has been made in the case of onedimensional unsteady flow for an inert and reactive gas mixture, which represents the classical instance of a shock tube. The purpose of this investigation is to highlight the general behaviour (order of accuracy) and performance of TVD schemes with various flux limiters for the simulation of reactive flows and in particular, to make possible the capture of the shock wave together with waves expansion for choosing the appropriate scheme to apply eventually in simulation of hypersonic viscous flow in chemical non equilibrium.





A Novel Aerodynamic Design Method for Centrifugal Compressor Impeller


Pages :
329344


Authors :
M. NiliAhmadabadi,
M. Durali,
A. Hajilouy,
This paper describes a new quasi3D design method for centrifugal compressor impeller. The method links up a novel inverse design algorithm, called BallSpine Algorithm (BSA), and a quasi3D analysis. Euler equation is solved on the impeller meridional plane. The unknown boundaries (hub and shroud) of numerical domain are iteratively modified by BSA until a target pressure distribution in flow passage is reached. To validate the quasi3D analysis code, existing compressor impeller is investigated experimentally. Comparison between the quasi3D analysis and the experimental results shows good agreement. Also, a full 3D NavierStokes code is used to analyze the existing and designed compressor numerically. The results show that the momentum decrease near the shroud wall in the existing compressor is removed by hubshroud modifications resulting an improvement in performance by 0.6 percent.





Airflow and AerosolDrug Delivery in a CT Scan based Human Respiratory Tract with Tumor using CFD


Pages :
345356


Authors :
V. K. Srivastav,
A. Kumar,
S. K. Shukla,
A. R. Paul,
A. D. Bhatt,
A. Jain,
This paper is focused on to study the effect of a tumor present in the respiratory tract (in trachea) on airflow pattern and aerosoldrug deposition. A realistic model of human respiratory tract was constructed from spiral computed tomography (CT) scan data and a bifocal tumor (Glomus tumor) was constructed in the tract. The inspiratory flow characteristics of the realistic human airway models (with and without tumor) was numerically solved using the realizable k turbulence model for airflow and Shear Stress Transport (SST) kω turbulence model for twophase flow. The velocity (contours and vector plots), wall shear stress and deposition efficiency of aerosol were obtained at different locations to the upstream and downstream region of the bifocal tumor in respiratory tract. The flow pattern shows that the maximum flow disturbance occurs around the tumor and at downstream of the flow. Magnitude and location of maximum wall shear stress in the presence of the tumor helps in identifying the extent and probable location of the wall injury during the normal and heavy breathing conditions. Deposition efficiency of aerosoldrug on tumor location will be useful for designing the efficient targeted drug delivery system.





Rotationally Symmetric Ferrofluid Flow and Heat Transfer in Porous Medium with Variable Viscosity and Viscous Dissipation


Pages :
357366


Authors :
P. Ram,
V. Kumar,
The analysis of three dimensional rotationally symmetric boundary layer flow of field dependent viscous ferrofluid saturating porous medium is performed. The fluid under consideration is electrically nonconducting incompressible magnetic fluid. The flow is generated due to the rotation of an infinite disk maintained at a uniform temperature. The momentum equations give rise to nonlinear coupled boundary value problem which is solved using Finite Difference and Newton methods. The numerical solutions for the governing nonlinear differential equations are obtained over the entire range of physical parameters. The effects of field dependent viscosity, permeability parameter, Prandtl number (Pr) and Eckert number (Ec) on various flow characteristics are discussed in detail and presented graphically. A special attention has been paid to study the effects of viscous dissipation on thermal boundary layer. Appreciable effects of these physical parameters are recorded on boundary layer displacement thickness, skin friction coefficients and rate of heat transfer.





Flow and Heat Transfer in a Newtonian Liquid with Temperature Dependent Properties over an Exponential Stretching Sheet


Pages :
367374


Authors :
P. G. Siddheshwar,
G. N. Sekhar,
A. S. Chethan,
The paper presents a study of a forced flow and heat transfer of an electrically conducting Newtonian fluid due to an exponentially stretching sheet. The governing coupled, nonlinear, partial differential equations are converted into coupled, nonlinear, ordinary differential equations by a similarity transformation and are solved numerically using shooting method. The influence of various parameters such as the Prandtl number, Chandrasekhar number, variable viscosity parameter, heat source (sink) parameter and suction/injection on velocity and temperature profiles are presented and discussed.





An Analytical Study on Boundary Layer Flow and Heat Transfer of Nanofluid Induced by a NonLinearly Stretching Sheet


Pages :
375384


Authors :
A. Malvandi,
F. Hedayati,
M. R. H. Nobari,
Steady twodimensional boundary layer flow of a nanofluid past a nonlinear stretching sheet is investigated analytically using the Homotopy Analysis Method (HAM). The employed model for nanofluid includes twocomponent fourequation nonhomogeneous equilibrium model that incorporates the effects of Brownian motion ( Nb ), thermophoresis ( Nt ) and Lewis number ( Le ) simultaneously. The basic partial boundary layer equations have been reduced to a twopoint boundary value problem via the similarity variables. Analytical results are in best agreements with those existing in the literatures. The outcomes signify the decreasing trend of heat transfer rate with thermophoresis, Brownian motion and Lewis number. However, concentration rate has a sensitive behavior with parameters, especially the Brownian motion and thermophoresis parameters. Also, the weak points of numerical methods in such problems have been mentioned and the efficiency of HAM, as an alternative approach, in solving these kinds of nonlinear coupled problems has been shown.





