Journal Of Applied Fluid Mechanics
Volume:7 Issue: 2, Mar-Apr 2014

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 by-product 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.

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 two-equation turbulence model of k-εis adopted to measure the eddy viscosity. The eddy dissipation model is used to calculate the combustion as well as the P-1 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.

A linear analysis of Rayleigh-Taylor 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.

A hybrid solution methodology has been developed to solve chemically reacting laminar hypersonic flow in chemical Non-equilibrium 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 near-wall resolution for chemically reacting flows with a Cartesian mesh for complex geometries as well.

The experimentally developed flow pattern maps for micro-scale channels reported by various researchers differ significantly. Also, no theoretical models effectively predict the flow regime transition boundaries in micro-scale channel. The present work proposes an empirical model for air-water two-phase 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).

An analysis has been made to investigate the effects of thermal radiation on the magnetohydrodynamic (MHD) flow and heat transfer over an inclined non-linear 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 non-linear 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 skin-friction 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.

A mathematical model is presented for the steady, two-dimensional magneto-convection heat transfer of a two-phase, electrically-conducting, particle-suspension in a channel containing a non-Darcian 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 one-dimensional 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 particle-phase viscous stresses. Special boundary conditions for the particle-phase wall conditions are implemented. The governing coupled, non-linear differential equations are reduced from an (x,y) coordinate system to a one-dimensional (y) coordinate system. A series of transformations is then employed to non-dimensionalize 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 fluid-phase velocity and particle-phase 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.

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 Mehta-Morse’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.

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.

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 time-stepping algorithm is proposed which may reduce requirement of computational cost in simulation of such wall-bounded flow. Channel flow analysis is performed with both constant and varied time-step for 128 × 65×128 grid points. The time advancement is carried out by implicit third-order 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 non-periodic boundary condition. Also Fourier series is employed in stream-wise and span-wise 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 Navier-Stocks 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 time-discretization methods. The results show that if final decision rests on economics, the proposed variable time-stepping algorithm will be proper choice which satisfies the accuracy and reduces the computational cost.

The influence of a mega-city on the atmospheric boundary layer wind field was examined in the complex-terrain, semi-arid Tehran region using the Pennsylvania State University/National Center for Atmospheric Research fifth-generation 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 «SM2-U (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 drag-force approach (DA) coupled with an urban soil model (SM2-U) 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 DA-SM2-U 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.

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 one-dimensional 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.

This paper describes a new quasi-3D design method for centrifugal compressor impeller. The method links up a novel inverse design algorithm, called Ball-Spine Algorithm (BSA), and a quasi-3D 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 quasi-3D analysis code, existing compressor impeller is investigated experimentally. Comparison between the quasi-3D analysis and the experimental results shows good agreement. Also, a full 3D Navier-Stokes 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 hub-shroud modifications resulting an improvement in performance by 0.6 percent.

This paper is focused on to study the effect of a tumor present in the respiratory tract (in trachea) on airflow pattern and aerosol-drug 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) k-ω turbulence model for two-phase 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 aerosol-drug on tumor location will be useful for designing the efficient targeted drug delivery system.

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.

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, non-linear, partial differential equations are converted into coupled, non-linear, 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.

Steady two-dimensional 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 four-equation non-homogeneous 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 two-point 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.