A CFD Study of Sensitive Parameters Effect on the Combustion in a High Velocity Oxygen-Fuel Thermal Spray Gun

Transcription

1 World Academy of Scence, Engneerng and Technology Internatonal Journal of Mechancal and Mechatroncs Engneerng A CFD Study of Senstve Parameters Effect on the Combuston n a Hgh Velocty Oxygen-Fuel Thermal Spray Gun S. Hossanpour, and A. R. Bnesh Internatonal Scence Index, Mechancal and Mechatroncs Engneerng waset.org/publcaton/15134 Abstract Hgh-velocty oxygen fuel (HVOF) thermal sprayng uses a combuston process to heat the gas flow and coatng materal. A computatonal flud dynamcs (CFD) model has been developed to predct gas dynamc behavor n a HVOF thermal spray gun n whch premxed oxygen and propane are burnt n a combuston chamber lnked to a parallel-sded nozzle. The CFD analyss s appled to nvestgate axsymmetrc, steady-state, turbulent, compressble, chemcally reactng, subsonc and supersonc flow nsde and outsde the gun. The gas velocty, temperature, pressure and Mach number dstrbutons are presented for varous locatons nsde and outsde the gun. The calculated results show that the most senstve parameters affectng the process are fuel-to-oxygen gas rato and total gas flow rate. Gas dynamc behavor along the centerlne of the gun depends on both total gas flow rate and fuel-to-oxygen gas rato. The numercal smulatons show that the axal gas velocty and Mach number dstrbuton depend on both flow rate and rato; the hghest velocty s acheved at the hgher flow rate and most fuel-rch rato. In addton, the results reported n ths paper llustrate that the numercal smulaton can be one of the most powerful and benefcal tools for the HVOF system desgn, optmzaton and performance analyss. Keywords HVOF, CFD, gas dynamcs, thermal spray, combuston. I. INTRODUCTION HE hgh-velocty oxygen fuel (HVOF) thermal spray s a T partculate deposton process n whch mcro-sze partcles of metals, alloys or cermets are propelled and heated n a sonc/supersonc combustng gas stream and are deposted on a substrate at hgh speeds to form a thn layer of lamellar coatng. The coatngs prepared by HVOF thermal spray process have been wdely used n the automotve, aerospace and chemcal ndustres. The HVOF systems employ varous knds of gun nozzle contours, such as convergent-barrel,[1,] convergent-dvergent (or Laval nozzle),[3] convergentmultstage dvergent,[4] and convergent-dvergent-barrel.[5,6] The HVOF gun systems wthout any nozzle are also n use.[3].in ths study convergent-dvergent-barrel system was S. Hossenpour s wth the Mechancal Engneerng Department, Sahand Unversty of Technology, Tabrz, Iran (correspondng author to provde phone: ; fax: ; e-mal: hossanpour@sut.ac.r). A. R. Bnesh s wth the Mechancal Engneerng Department, Sahand Unversty of Technology, Tabrz, Iran (e-mal: alreza.bnesh@yahoo.com). smulated. In ths system durng a HVOF thermal sprayng as shown n Fg. 1, premxed fuel and oxygen streams are nected nto combuston chambers and energy generated by the combuston process s transformed nto a hot hgh-pressure gas. Fg. 1 Schematc of the HVOF thermal spray gun geometry In order to mprove the operaton of the HVOF thermal spray process, much expermental work has been done n the last decade to study the effect of operatng parameters ncludng gun type, fuel type, feedstock type and sze, combuston pressure, fuel/oxygen rato and spray dstance on the partcle temperature, velocty, meltng rato, oxdant content and the resultng coatng mcrostructure, porosty, hardness, wear abrason and corroson resstance [7-1]. Many parametrc studes have been performed on process controllng parameters and coatng qualty wthout a detaled understandng of the physcal and chemcal processes nvolved, especally n the presence of entraned partcles. HVOF sprayng nvolves an ntrcate nterplay between flud flow, heat transfer, turbulence, chemcal reactons, dffuson of mult-component gases, and varous gas-partcle nteractons at elevated temperatures. A detaled understandng of these processes s essental for the HVOF process to reach ts full potental. Several prevous CFD smulatons have nvestgated gas and partcle flows n HVOF thermal spray guns. Power et al.[13] and Smth et al.[14] modeled a Metco Damond Jet gun (Sulzer Metco, Westbury, NY) usng a steady-state axsymmetrc analyss. In the Damond Jet system, premxed oxygen (O) and propylene (C3H6) are nected nto an ar-cooled nozzle. They modeled the nternal flow and external flow separately wth a fnte-rate chemstry model n the nternal flow and equlbrum chemstry results as boundary condtons for the external flow. Oberkampf and Talpallkar[15,16] also developed a model of a smlar gun geometry, agan usng an axsymmetrc, steadystate analyss. In ther work, there was full couplng between the nteror and exteror flow felds, and an approxmate Internatonal Scholarly and Scentfc Research & Innovaton (5)

2 World Academy of Scence, Engneerng and Technology Internatonal Journal of Mechancal and Mechatroncs Engneerng Internatonal Scence Index, Mechancal and Mechatroncs Engneerng waset.org/publcaton/15134 equlbrum chemstry model was used to treat the combuston of C3H6. Chang and Moore [17] studed the transent flow and temperature dstrbuton n a lqud-fueled HVOF gun. In ths gun, oxygen and kerosene are nected nto the combuston chamber and gaseous products are accelerated through a convergng-dvergng throat and along a barrel. They assumed complete combuston of the fuel, allowed for chemcal reactons of the gaseous products n the flow through the throat and barrel, but dd not smulate the free et external to the gun. A steady-state soluton was found to develop n 3 less than 10 s, and, n ths system, Mach numbers greater than one were calculated to develop nsde the barrel because of the convergng- dvergng desgn of the throat of the burner. Because of the nherent complexty of the process, a fundamental understandng of the physcochemcal phenomena nvolved n the HVOF thermal spray process generally requres comprehensve numercal models ncludng computatonal flud dynamc (CFD) models [18-]. In ths paper a computatonal flud dynamc (CFD) model s developed to predct gas dynamc behavor n a hgh-velocty oxygen-fuel (HVOF) thermal spray gun n whch premxed oxygen and propane are burnt n a combuston chamber lnked to a parallel-sded nozzle. The CFD analyss s appled to nvestgate axsymmetrc, steady-state, turbulent, compressble, chemcally reactng, subsonc and supersonc flow wthn the gun. Results descrbes the general gas dynamc features of HVOF sprayng and then gves a detaled dscusson of the numercal predctons of a computatonal flud dynamc (CFD) analyss. The gas velocty, temperature, pressure and Mach number dstrbutons are presented for varous locatons nsde the convergent-dvergent-barrel system. The specfc obectves of the paper are to dentfy the approprate governng equatons for the Problem, usng a computer code to create a computatonal grd and solve the governng equatons on the computatonal doman, compare the predctons of the numercal smulaton and make suggestons for the better performance of the devce. II. COMPUTATIONAL MODEL A. Model Geometry and the Mesh The studed HVOF gun s represented schematcally n Fg. 1. Fuel and oxygen are nected axally nto the combuston chamber, where the fuel burns and the combuston products are accelerated down through the convergent dvergent nozzle and the long parallel-szed barrel. The gun s protected by coolng water to avod over-heatng. Powder partcles are nected nto the barrel through a tappng angle by a carrer gas n the front of the barrel, ths desgn can effectvely reduce the overheatng of powder partcles. The study s focused on the combuston process and subsequent gas flow pattern, whle partcle dynamcs and gas partcle nteracton are not ncluded. Wth a well desgned nozzle confguraton, the maxmum gas velocty can be up to 000 m/s, wth a Mach number around at the ext of the nozzle. The computatonal doman used n the present smulaton s shown n Fg.. A convergent-dvergent nozzle s desgned to generate a supersonc et. Because the gun geometry s symmetrcal about ts axs, a two-dmensonal (-D) axsymmetrc grd s used to smulate the gas phase flow behavor. The computatonal grd of ths axs-symmetrc flow ncludes the gun and external free et regon as llustrated n Fgs. 3 and 4. The grd s fner n the regons where large gradents of flow propertes exst, and gradually changes to become coarser n the regons where small gradents of flow propertes are expected. Ths fne mesh sze wll be able to provde good spatal resoluton for the dstrbuton of most varables wthn the combuston chamber, convergent dvergent nozzle, barrel and external doman. Fg. Computatonal doman Fg. 3 Grd structure wthn the combuston chamber and convergent dvergent nozzle part Fg. 4 Grd structure wthn the External doman B. Governng Equatons A computer code s used to perform numercal smulatons of the flud flow n HVOF system by solvng the conservaton equatons of mass, momentum, energy and speces. A standard, two-equaton, realzable k turbulence model s employed for the turbulent flow feld. Contnuty Equaton: ρ + t Momentum Equaton: ( ρu ) = 0 (1) p τ ( ρ u ) + ( ρuu ) = + () t Where p the statc pressure and the stress tensor are τ s gven by: u u τ μ = + μδ dvv (3) x x 3 Internatonal Scholarly and Scentfc Research & Innovaton (5) 008 6

3 World Academy of Scence, Engneerng and Technology Internatonal Journal of Mechancal and Mechatroncs Engneerng Internatonal Scence Index, Mechancal and Mechatroncs Engneerng waset.org/publcaton/15134 Where μ are the molecular vscosty and the second term on the rght hand sde s the effect of volume dlaton. Energy Equaton: T E u E p ( ρ ) + ( ( ρ + )) = keff h J u + ( τ ) eff + Sh t x (4) Where k eff s the effectve conductvty and J s the dffuson flux of speces. The frst three terms on the rght-hand sde of Equaton represent energy transfer due to conducton, speces dffuson, and vscous dsspaton, respectvely. S h ncludes the heat of chemcal reacton, and any other volumetrc heat sources we have defned. In equaton (4), P E = h + ρ u Where sensble enthalpyh s defned for deal gases as Where h = m h m s the mass fracton of speces and h T T ref = c dt (5) (6) (7) p, Where Tref s K. Speces Conservaton Equaton: When we choose to solve conservaton equatons for chemcal speces, we predcts the local mass fracton of each speces, m, through the soluton of a convecton-dffuson equaton for the th speces. Ths conservaton equaton takes the followng general form: p t ( ρm ) + ( ρum ) = J + R + S, Where R s the net rate of producton of speces by chemcal reacton and S s the rate of creaton by addton from the dspersed phase. An equaton of ths form wll be solved for N 1speces where N s the total number of flud phase chemcal speces present n the system. Snce the mass fracton of the speces must sum to unty, the N th mass fracton s determned as one mnus the sum of the N 1solved mass fractons. To mnmze numercal error, the N th speces should be selected as that speces wth the overall largest mass fracton, such as N when the oxdzer s (8) ar. J, s the dffuson flux of speces, whch arses due to concentraton gradents. We use the dlute approxmaton, under whch the dffuson flux can be wrtten as Here D, m J = D m ρ (9),, m s the dffuson coeffcent for speces n the mxture. The reacton rates that appear as source terms n Equaton (8) are computed by eddy dsspaton model. The reacton rates are assumed to be controlled by the turbulence nstead of the calculaton of Arrhenus chemcal knetcs. The net rate of producton for speces due to reacton r, s gven by the smaller of the two expressons below: YR R =, r, rmw, Aρ mn k R υ R, rm R, r = υ (10) N w, R P P υ, rm w, ABρ (11) k υ, rm w, Where YP s the mass fracton of any product speces P and YR s the mass fracton of a partcular reactant R and A,B are emprcal constants equal to 4.0 and 0.5. A wde varety of flow problems can be calculated by usng the standard k model based on the presumpton that an analogy between the acton of vscous stresses and Reynolds stresses on the mean flow exsts. Although t s usually acceptably accurate for smple flows, naccuraces could rse from the turbulent-vscosty hypothess and from the equaton of turbulence dsspaton rate for complex flows. Improvement has been made to the standard k model; a recent development s the realzable k model. The transport equatons for the realzable k model are: Turbulent knetc transport equaton: t + G ( ρk) + ( ρku ) k + G b ρ Y M = + S k Y μt k μ + σ k Rate of dsspaton of energy from the turbulent flow: (1) Internatonal Scholarly and Scentfc Research & Innovaton (5)

4 World Academy of Scence, Engneerng and Technology Internatonal Journal of Mechancal and Mechatroncs Engneerng Internatonal Scence Index, Mechancal and Mechatroncs Engneerng waset.org/publcaton/15134 t ( ρ ) + ( ρu ) + ρc S 1 ρc = + C k + ν Where the turbulent vscosty s μ ρc k μt μ + σ 1 The coeffcent of dynamc vscosty s C μ C k G b + S (13) t = (14) μ 1 = (15) A0 + As ( ku / ) In comparson wth the standard k model, the realzable k model contans a new formulaton of the turbulent vscosty where the dynamc vscosty coeffcent s no longer constant. C. Boundary Condtons A fxed composton (a stochometrc mxture) of oxygen propane s specfed at the fuel nlet of combuston chamber. The nlet temperature of fuel mxture s consdered to be unform at 300 K. A fxed, unform mass flow kg/s s specfed at the nlet. Ax-symmetrc boundary condtons are appled along the central axs of the combuston chamber. The nteror surfaces of the gun are protected by the coolng water and defned as no-slp wall wth a constant temperature of 360Kwhch s the measured temperature for the outflow water. The gas exhausts from the gun to ar, where external pressure boundary s appled to the ambent temperature of 300K and atmospherc pressure of Pa. III. NUMERICAL MODEL The numercal method used n ths study s a segregated soluton algorthm wth a fnte volume-based technque. The segregated soluton s chosen, due to the advantage over the alternatve method of strong couplng between the veloctes and pressure. Ths can help to avod convergence problems and oscllatons n pressure and velocty felds. Ths technque conssts of an ntegraton of the governng equatons of mass, momentum, speces, energy and turbulence on the ndvdual cells wthn the computatonal doman to construct algebrac equatons for each unknown dependent varable. The pressure and velocty are coupled usng the SIMPLE (sem-mplct method for pressure lnked equatons) algorthm whch uses a guess-and-correct procedure for the calculaton of pressure on the staggered grd arrangement. It s more economcal and stable compared to the other algorthms. The second order upwnd scheme s employed for the dscretzaton of the model equatons as t s always bounded and provdes stablty for the pressure-correcton equaton. The CFD smulaton convergence s udged upon the resduals of all governng equatons. Ths "scaled resdual s defned as where R φ = p anbφnb + b p a pφ p cells nb p p cells a φ φ p s a general varable at a cell p, cm 3 (16) a p s the center coeffcent, anb are the nfluence coeffcents for the neghborng cells, and b s the contrbuton of the constant part of the source term. The results reported n ths paper are 4 acheved when the resduals are smaller than IV. RESULTS A number of numercal smulatons have been performed to study the gas dynamc behavor n a hgh-velocty oxygen-fuel (HVOF) thermal spray gun n whch premxed oxygen and propane are burnt n a combuston chamber lnked to a parallel-sded nozzle. The flow transton from subsonc to supersonc condtons through the convergent dvergent nozzle s vvdly shown by the Mach number plot n Fg. 5. The subsonc flow s accelerated n the convergent regon, the flow reaches sonc state at the throat and further accelerated to supersonc condton n the dvergent regon. On enterng the barrel, the supersonc flow further expands through a seres of shock waves and becomes stablzed. In ths HVOF gun system, key process varables are total gas flow rate, and oxygen-to-fuel gas rato. Two dfferent total gas flow rates were consdered, namely, 1 and 18 g/s, and, at each of these flows, two fuel-to oxygen ratos, namely, 0.5, 0.75, were nvestgated. In consderng dfferences among smulatons, for the range of gas flows and ratos examned, results wll be plotted as centerlne flow feld varable versus axal dstance. Fg. 6 shows the centerlne Mach numbers plotted aganst axal dstance. The overall trend s that the Mach number ncreases sharply as t converges nto the nozzle but ncreases only margnally wthn the parallel-sded regon. A maxmum velocty s acheved at the hgher total flow (1 g/s) and the hgher fuel-to-oxygen rato (0.3). Conversely, the lower flow (18 g/s) and most oxygen-rch rato (0.5) gve the lowest velocty. Also, the three profles for a 1 g/s flow rate le above those for the 18 g/s total flow rate. Fg. 7 shows the varaton of centerlne gas pressure wth axal dstance. The pressure remans hgh wthn the combuston chamber, decreases sharply n the convergent dvergent nozzle and reaches near atmospherc level n the barrel. It needs to pont out that the shocks encountered n the front part of the convergent dvergent nozzle are not desrable whch gves rse to energy loss when the thermal energy s converted to knetc energy n the gas phase. It s possble to desgn a nozzle wth perfect expanson at a partcular pressure rato, however, that wll mpose a lmtaton on the operatng condton of the nozzle. The combuston chamber dmensons shown n these plot fgures are normalzed by the correspondng barrel dameter (D).. The hgher total flow rate Internatonal Scholarly and Scentfc Research & Innovaton (5)

5 World Academy of Scence, Engneerng and Technology Internatonal Journal of Mechancal and Mechatroncs Engneerng Internatonal Scence Index, Mechancal and Mechatroncs Engneerng waset.org/publcaton/15134 generates sgnfcantly hgher gas pressures as would be expected, whereas the effect of gas rato s rather lmted. Fg. 8 shows Contours of gas Mach number outsde the HVOF gun and wave structure n supersonc under expanded et. Because the pressure at the ext of the barrel s lower than the ambent pressure, the et s over-expanded and adusts to the ambent pressure by a seres of shock damonds. Ths pattern of expanson and compresson waves s repeated untl mxng wth the surroundng atmosphere whch eventually dsspates the supersonc et. Fg. 9 shows the Calculated streamlnes of the gas phase outsde the HVOF gun. As a result, the gas flows parallel to the substrate near the substrate. Ths phenomenon s very mportant snce the partcles mght move radally due to the drag force n the radal drecton. To further demonstrate ths behavor, we provde the evoluton of the axal velocty and radal velocty of the gas n several dfferent locatons n the external flow feld, as shown n Fg. 10. These locatons are based on the dstance from the ext of the HVOF torch. It s clearly seen that the axal velocty n the centerlne decays along the axal drecton, and the et propagates outwards n the radal drecton. Close to the substrate, the axal velocty profle s close to zero whle the radal velocty ncreases far away from the centerlne. V. SUMMARY AND CONCLUSION Ths paper descrbes the gas dynamcs features that exst nsde and outsde a hgh-velocty oxygen-fuel (HVOF) thermal spray gun n whch premxed oxygen and propane are burnt n a combuston chamber lnked to a parallel-sded nozzle. Numercal results from the computatonal flud dynamcs modelng are gven and dscussed. The gas velocty, temperature, pressure, and Mach number dstrbutons are presented for varous locatons nsde and outsde the HVOF system. The two-dmensonal numercal smulatons show large varatons n gas velocty and temperature both nsde and outsde the torch due to flow features such as mxng layers, shock waves, and expanson waves. Insde the gun, premxed oxygen and propane burn n the combuston chamber and the hot gas s accelerated along the parallel-sded nozzle. Although the maxmum gas temperature reaches 3300 K close to the annular flame front, the centerlne temperature only reaches a value of 3000 K. The gas velocty at the end of the nozzle s, 500 m/s wth a Mach number of.3. In the free et regon, the calculatons predct the exstence of shock damonds. In addton, the results reported n ths paper llustrate that the numercal smulaton can be one of the most powerful and benefcal tools for the HVOF system desgn, optmzaton and performance analyss. The results ndcate that the most senstve parameters that affect the behavor of the system both total gas flow rate and fuel-tooxygen gas rato. The axal gas velocty depends on both flow rate and rato; the hghest velocty s acheved at the hgher flow rate and most fuel-rch rato. REFERENCES [1] Davd L. Mason and Krs Rao: n Thermal Spray Coatngs New Materals, Processes and Applcatons, F.N. Longo, ed., Amercan Socety for Metals, Metals Park, OH, 1984, pp [] K.A. Kowasky, D.R. Marantz, M.F. Smth, and W.L. Oberkampf: n Thermal Spray Research and Applcatons, T.F. Berneck, ed., ASM Internatonal, Materals Park, OH, 1990, pp [3] Product Catalogue Damond Jet, Sulzer Metco (US) Inc., New York, NY, [4] Product Catalogue Carbde Jet System (CJS), OZU-Mashnenbau GmbH, Castrop-Rauxel, Germany, [5] M.L. Thope and H.J. Rcher: n Thermal Spray: Internatonal Advances n Coatng Technology, C.C. Bernt, ed., ASM Internatonal, Materals Park, OH, 199, pp [6] G.R. Heath and R.J. Dumola: n Thermal Spray: Meetng the Challenges of the 1st Century, C. Coddet, ed., ASM Internatonal, Materals Park, OH, 1998, pp [7] de Vllers Lovelock, H.L., Rchter, P.W., Benson, J.M., Young, P.M. Parameter study of HP/HVOF deposted WC-Co coatngs. Journal of Thermal Spray Technology 7, 1998, [8] Gl, L., Staa, M.H. Influence of HVOF parameters on the corroson resstance of NWCrBS coatngs. Thn Sold Flms, 00, 40 41, [9] Hanson, T.C., Settles, G.S. Partcle temperature and velocty effects on the porosty and oxdaton of an HVOF corroson-control coatng. Journal of Thermal Spray Technology 1, 003, [10] Khor, K.A., L, H., Cheang, P.,. Sgnfcance of melt-fracton n HVOF sprayed hydroxyapatte partcles splats and coatngs. Bomaterals 5, 004, [11] Marple, B.R., Voyer, J., Bsson, J.F., Moreau, C. Thermal sprayng of nanostructured cermet coatngs. Journal of Materals Processng Technology 117, 001, [1] Zhao, L., Maurer, M., Fscher, F., Lugscheder, E. Study of HVOF sprayng of WC CoCr usng on-lne partcle montorng. Surface & Coatngs Technology 185, 004, [13] G.D. Power, E.B. Smth, T.J. Barber, and L.M. Chapetta: Analyss of a Combuston (HVOF) Spray Deposton Gun, UTRC Report No. 91-8, UTRC, East Hartford, CT, Mar [14] E.B. Smth, G.D. Power, T.J. Barber, and L.M. Chapetta: n Applcaton of Computatonal Flud Dynamcs to the HVOF Thermal Spray Gun,Thermal Spray: Internatonal Advances n Coatngs Technology,C.C. Berndt, ed., ASM Internatonal, Materals Park, OH, 199, pp [15] W.L. Oberkampf and M. Talpallkar: J. Thermal Spray Technol., 1996, vol. 5 (1), pp [16] W.L. Oberkampf and M. Talpallkar: J. Thermal Spray Technol., 1996, vol. 5 (1), pp [17] C.H. Chang and R.L. Moore: J. Thermal Spray Technol., 1995, vol. 4 (4), pp [18] Kamns, S., Gu, S. Numercal modelng of propane combuston n a hgh velocty oxygen-fuel thermal spray gun. Chemcal Engneerng and Processng 45, 006, [19] Dolatabad, A., Mostaghm, J., Pershn, V. Effect of a cylndrcal shroud on partcle condtons n hgh velocty oxy-fuel spray process. Journal of Materals Processng Technology 137, 003, [0] L, M., Chrstofdes, P.D.. Mult-scale modelng and analyss of HVOF thermal spray process. Chemcal Engneerng Scence 60, 005, [1] Gu, S., Eastwck, C.N., Smmons, K.A., McCartney, D.G. Computatonal flud dynamc modelng of gas flow characterstcs n a hgh-velocty oxy-fuel thermal spray system. Journal of Thermal Spray Technology 10, 001, [] Mngheng L, Panagots D. Chrstofdes, Computatonal study of partcle n-flght behavor n the HVOF thermal spray process, Chemcal Engneerng Scence 61,006, Internatonal Scholarly and Scentfc Research & Innovaton (5)

6 World Academy of Scence, Engneerng and Technology Internatonal Journal of Mechancal and Mechatroncs Engneerng Internatonal Scence Index, Mechancal and Mechatroncs Engneerng waset.org/publcaton/15134 Fg. 5 Predcted March number contours n the convergent dvergent nozzle and barrel Fg. 6 Varaton of Mach number wth dstance along the centerlne (symmetry axs) of the computatonal doman Internatonal Scholarly and Scentfc Research & Innovaton (5)

7 World Academy of Scence, Engneerng and Technology Internatonal Journal of Mechancal and Mechatroncs Engneerng Internatonal Scence Index, Mechancal and Mechatroncs Engneerng waset.org/publcaton/15134 Fg. 7 Varaton of pressure wth dstance along the centerlne (symmetry axs) of the computatonal doman Fg. 8 Contours of gas Mach number outsde the HVOF gun and wave structure n supersonc under expanded et Fg. 9 Calculated streamlnes of the gas phase outsde the HVOF gun Internatonal Scholarly and Scentfc Research & Innovaton (5)

8 World Academy of Scence, Engneerng and Technology Internatonal Journal of Mechancal and Mechatroncs Engneerng Internatonal Scence Index, Mechancal and Mechatroncs Engneerng waset.org/publcaton/15134 Fg. 10 Axal gas velocty along the radal drecton at dfferent axal locatons outsde the HVOF gun Internatonal Scholarly and Scentfc Research & Innovaton (5)