K.Mohan Laxmi, V.Ranjith Kumar, Y.V.Hanumantha Rao / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.518-522518 | P a g eModeling And Simulation of Gas Flow Velocity In CatalyticConverter With Porous*1K.Mohan Laxmi, 2V.Ranjith Kumar, 3Y.V.Hanumantha Rao1M.Tech Student, Mechanical Engineering Department, KL University, Vijayawada.2Assistant Professor, Mechanical Engineering Department, KL University, Vijayawada.3Professor, Head of The Department , Mechanical Engineering, KL University, Vijayawada.Abstract:Stringent emission regulations aroundthe world necessitate the use of high-efficiencycatalytic converters in vehicle exhaust systems.Experimental studies are more expensive thancomputational studies. Also using computationaltechniques allows one to obtain all the requireddata for the Catalytic Converter, some of whichcould not be measured. In the present work,Geometric modeling ceramic monolith substratewith square shaped channel type of Catalyticconverter and coated platinum and palladiumusing fluent software. In this software we areusing crate inlet-outlet flanges and housing ofthe catalytic converter. After design of modelingus done different parameters in Fluent Pre-process like Analysis Type, Domain Type etc.This project studies the differentporosity of porous medium how to affect to flowpressure field under the conditions of same inletvelocity and ceramic diameter by CFD method.Geometric model of the catalytic converter hasbeen establish and meshed by the pre-processingtool of FLUENT. The flow pressure simulationfilled contours and curve of center line staticpressure distribution of the ceramic porousmaterial show that in the case of otherconditions remain unchanged, the less theporosity of the ceramic porous material, thehigher the inlet pressure and the more thepressure loss of the porous material. The morePorosity of ceramic is beneficial to exhaustcatalytic converter.Key words: Catalytic Converter, Ceramicmaterial, CFX, FLUENT, Porous.I.INTRODUCTIONPorous material made with ceramic can beused into two way catalytic converter .The gasspeed distribution in the converter is an importantfactor in the catalytic ability and the effect ofcatalytic materials. The paper studies on thevariation of the gas flow pressure the converter bythe computational fluid dynamics methods. Thereare many CFD commercial software such asPHOENICS, CFX, STAR-CD, FIDIP andFLUENT etc. FLUENT software has a very widerange of applications flexible characteristics of thegrid, the strong capabilities of numerical solutioncomprehensive functionality. This article will studythe fluid dynamics of the catalytic converters usingthe FLUENT software.Air pollution and global warming is a major issuenowadays. For this reason, emission limits areintroduced around the world and continually beingmade stricter every year. The enforcement of thisregulation has led to the compulsory utilization ofcatalytic converter as an emission treatment to theexhaust gas of vehicles.1.1. HISTORYIn 1973, General Motors faced new airpollution regulations and needed a way to make itscars conform to the stricter standards. Robert C.Stempel, who at the time was a special assistant tothe GM president, was assigned to overseedevelopment of a technology capable of addressingthe problem. Under Stempels guidance, GM builton existing research to produce the first catalyticconverter for use in an automobile.Catalytic converters were first installed in vehiclesmade in 1975 in response to EPA regulationspassed two years earlier tightening auto emissionsand requiring a gradual decrease in the lead contentof all gasoline.Since the introduction of stringentemission regulations in the US in the 1970s, carmanufacturers have modified their exhaust systemsto incorporate catalytic converters for the removalof NOx, CO and hydro carbons. All new carsregistered throughout the European Union from 1stJanuary 1993 have to be fitted with catalyticconverters. Platinum, palladium and rhodium arethe main active components.A potential problem appears with therelease of platinum group metals (PGMs) from theconverters into the environment. There is nowconvincing evidence for the release of platinumgroup metals (PGMs) into the environment,possibly by abrasion of the auto catalyst. As aresult, PGMs are found to have increased in theenvironment. In recent study, we found that PGMshave increased in road dust since 1984 andparticularly 1991.
K.Mohan Laxmi, V.Ranjith Kumar, Y.V.Hanumantha Rao / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.518-522519 | P a g eII.PROBLEM DESCRIPTIONCatalytic converters are used on mostvehicles on the road today. They reduce harmfulemissions from internal combustion engines (suchas oxides of nitrogen, hydrocarbons, and carbonmonoxide) that are theresult of incompletecombustion. Most new catalytic converters are theceramic monolith substrate with square channelstype and are usually coated with platinum,rhodium, or palladium.Figure: 2.1. Mesh geometry of Catalytic ConverterIn this project Set up a porous zone for thesubstrate with appropriate resistances. Calculate asolution for gas ﬂow through the catalytic converterusing the pressure- based solver. Plot pressure andvelocity distribution on speciﬁed planes of thegeometry. Determine the pressure drop through thesubstrate and the degree of non-uniformity of ﬂowthrough cross sections of the geometry using X-Yplots and numerical reportsIII.PROBLEM FORMULATIONThe catalytic converter modeled here is shown inFigure. The nitrogen gas ﬂows in through the inletwith a uniform velocity of 22.6 m/s, passes througha ceramic monolith substrate with square shapedchannels, and then exits through the outlet.Figure:3: Geometry of Catalytic ConverterWhile the ﬂow in the inlet and outletsections is turbulent, the ﬂow through the substrateis laminar and is characterized by inertial andviscous loss coeﬃcients in the ﬂow (X) direction.The substrate is impermeable in other directions,which is modeled using loss coeﬃcients whosevalues are three orders of magnitude higher than inthe X direction.3.1.PARAMETERS: user mode: General Model Analysis Type: Steady State Domain Type: Multiple Domain Fluid Type: Nitrogen Gas Turbulence Model : K-Epsilon Heat Transfer: Thermal Energy Boundary Conditions: Inlet (Subsonic),outlet (Subsonic),Wall :No slip Domain Interface: Fluid-PorousIV.MODELLINGModeling of flows through a porousmedium requires a modified formulation of theNavier-Stokes equations, which reduces to theirclassical form and includes additional resistanceterms induced by the porous region.The incompressible Navier-Stokesequations in a given domain Ω and time interval(0,t) can be writtenas),0().( 2tXfonpuuutu · u = 0 on x(0,t)where u = u(x,t) denotes the velocity vector, p =p(x,t) the pressure field, ρ the constant density, µthe dynamic viscosity coefficient and f representsthe external body forces acting on the fluid (i.e.gravity).In the case of solids, small velocities canbe considered and (u·∇)u term is neglected.Therefore, assuming an incompressible flow(constant density) in a certain domain Ω andconsidering the mass conservation equation, alsocalled continuity equation, the Navier-Stokesequation can be written as follows:),0(2tXfonputu · u = 0 on x(0,t)The general form of the Navier-Stokesequation is valid for the flow inside pores of theporous medium but its solution cannot begeneralized to describe the flow in porous region.Therefore, the general form of Navier-Stokesequation must be modified to describe the flowthrough porous media. To this aim, Darcy’s law isused to describe the linear relation between thevelocity u and gradient of pressure p in the porousmedium. It defines the permeability resistance ofthe flow in a porous media:
K.Mohan Laxmi, V.Ranjith Kumar, Y.V.Hanumantha Rao / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.518-522520 | P a g e∇p= - µDu in Ωpx(0,t)Where Ωp is the porous domain, D the Darcys lawresistance matrix and u the velocity vector. In thecase of considering an homogeneous porous media,D is a diagonal matrix with coefficients 1/α, whereα is the permeability coefficient.The Reynolds number is defined as:Where U and L a characteristic velocity and acharacteristic length scale, respectively. In order tocharacterize the inertial effects, it is possible todefine the Reynolds number associated to thepores:Where δ is the characteristic pore size. WhereasDarcy law is reliable for values of Rep< 1,otherwise it is necessary to consider a more generalmodel which accounts also for the inertial effects,such as:∇p= - (µDu + ρCu|u|) in Ωpx(0,t)Where C the inertial resistance matrix.Considering a modified Navier-Stokesequation in the whole domain including the twosource terms associated to the resistance inducedby the porous medium (linear Darcy and inertialloss term), the momentum equations become:ρ - µ∇2u + ∇p- (µDu + ρCu|u|) = 0 in x(0,t)In the case of considering an homogeneous porousmedia, D is a diagonal matrix with coefficients1/α,where α is the permeability coefficient and C isalso a diagonal matrix. Therefore, a modifiedDarcys resistance matrix should be used in Tdyn,as followsρ - µ∇2u + ∇p= D*u in x(0,t)D* = D+ µρu|u|where I is the identity matrix. It should be notedthat in laminar flows through porous media, thepressure p is proportional to velocity u and C canbe considered zero (D*= D). Therefore, the Navier-Stokes momentum equations can be rewritten as:ρ - µ∇2u + ∇p= - µDu in Ωx(0,t)These momentum equations are resolvedby Tdyn in the case of solids, where (u·∇)u termvanishes due to small velocities. If (u·∇)u = 0 cantbe neglected in the modelization (i.e. highvelocities),then Tdyn should resolve the followingmomentum equations in a fluid instead of in asolid:ρ ( + (u · ∇)u) - µ∇2u + ∇p = - µDu in Ωx(0,t)In order to add the Darcys resistance matrix D*anappropriate function should be inserted in Tdyn.See the figure below and "Function syntax" in theHelp manual of Tdyn for more details aboutdefining functions4.1.Geometry And Boundary Conditions:The following Conditions concerns theanalysis of a gas flowing through a catalyticconverter. The main objective is to determine thepressure gradient and the velocity distributionthrough the porous media that fills the catalyticelement. This model is intended to exemplify theuse of Tdyn capabilities to solve problemsinvolving flow through porous media.The boundary conditions are applied as shown inthe figures below. First, a Wall/Body conditionwith a Y-Plus wall boundary type is applied to theexternal surface of the catalytic converter.Figure: 4.1. External Surface of the CatalyticConverterA Fix Velocity condition is further appliedto the inlet surface of the model (in blue in thefigure below) so that the velocity vector is fixedthere to the value v = (22.6, 0.0, 0.0) m/s. Finally, aPressure Field condition is used to fix the thedynamic pressure to zero at the outlet surface of thecontrol volume (in red in the figure below).Figure:4.2. Control Volumes of Catalytic Converter
K.Mohan Laxmi, V.Ranjith Kumar, Y.V.Hanumantha Rao / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.518-522521 | P a g e4.2. Materials:Two different materials are used in orderto simulate the gas flowing through the catalystconverter. Fluid flow properties, density andviscosity, are the same in both materials andcorrespond to those of nitrogen gas. The twomaterials only differ on the values of the Darcyslaw matrix. While the first one has a null matrix,the second one has assigned a Darcy matrixincorporating the resistance and inertial effects ofthe porous media. Hence, the first material isapplied to the inlet and outlet channel regions ofthecatalyst converter (in blue in the figure below),while the second one is applied to the intermediatevolume corresponding to the porous media (inyellow in the figure below).Figure: 4.3.Materials of the catalytic ConverterThe Darcys law matrix used to model the porousmedia is taken to be diagonal but anisotropic. Thecorresponding values of the viscous (D) and inertial(C) resistance terms are those in the table belowNote that the components of the Darcys matrix aregiven with respect to the global axis system (X, Y,Z) Note that the components of the Darcys matrixare given with respect to the global axis system (X,Y, Z) so that the geometry must be convenientlyoriented.V.RESULTS AND DISCUSSIONS5.1. Graphical Results:Graph: 5.1. Surface Monitor Plot of Mass Flow Ratewith Number of IterationsAfter running fluent software the values of massflow rate changes at different iteration we canobsever in the Garaph .The Graph changes atdifferent direction with respect to Mass Flowrates.After some iterations garph comes constantvalues (minor difference).Figure: 5.2. Plot of the Static Pressure on the porous-clLine SurfaceThe above Graph shown the Static Pressure on theporous-cl Line Surface the pressure drop across theporous substrate can be seen to be roughly 300 Pa.5.2. SIMULATION RESULTS:The Velocityflow of gases rapidly in the middlesection, where the ﬂuid velocity changes as itpasses through the porous substrate. The pressuredrop can be high, due to the inertial and viscousresistance of the porous media.The X-velocity component distribution ofthe fluid flow. In this picture, it becomes evidenthow the fluid decelerates rapidly when entering tothe porous region. It can also be observed how thefluid recirculates before entering the central regionof the catalyst (negative values of X-velocitycomponent in dark blue) due to the resistanceexherted by the porous mediaFigure: 5.2.1. Velocity Vectors on the y=0 PlaneThe ﬂow pattern shows that the ﬂow enters thecatalytic converter as a jet, with recirculation oneither side of the jet. As it passes through theporous substrate, it decelerates and straightens out,and exhibits a more uniform velocity distribution.