졸업논문-박혜영.hwp

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1 Flow Field of Supersonic Silt Nozzle during Cold Spray Process

2 Flow Field of Supersonic Silt Nozzle during Cold Spray Process ii

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10 A cold spray process is an emerging technology that utilizes high velocity metallic particles for surface modification. Metallic powder particles are injected into a converging-diverging de Laval nozzle and accelerated to a high velocity by a supersonic gas flow. The gas velocity increases in the nozzle neck reaching a maximum at the nozzle exit. A cold spray process normally uses a circular nozzle, but a circular nozzle has a rather narrow spraying range though high gas velocity. To complement this fault, a slit nozzle was considered in this study. A slit nozzle is anticipated to reduce the coating process time because the nozzle has a wider coating width than a circular nozzle. However, the slit nozzle can reduce the coating efficiency because it does not allow as much gas or particle velocity as a circular nozzle. Improving the slit nozzle coating efficiency requires revising the nozzle size and shape, a numerical analysis of the nozzle s flow field and a comparison of the spraying properties of each nozzle. Analysis results show that comparing the spaying efficiency caused by nozzle configurations an improvement was shown at the expansion ratio of 7.5. When exploring the variances according to the nozzle shape, a greater performance was observed using square nozzle necks and a narrower slit nozzle shape at the exit plane. In addition, the slit nozzle showed greater performance in the particle velocity distribution than the circle nozzle. 7

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13 Powder supply Carrier gas Converge/diverge nozzle Powder Feeder Gas Heater Gas high pressure ( N 2 gas ) Process gas Super sonic region Numerical analysis region 3

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16 κ κ κ κ κ κ 6

17 κ υ κ υ υ ρ ρ ρ υ ρ ρκ ρ ρ κ ρ ρ 7

18 ρ ρρ 8

19 p T ρ a p+dp T+dT ρ +dρ a+da ρ ρ ρ ρ 9

20 γ 10

21 M 1 1 V 1 P 1 r 1 T 1 M 2 1 V 2 V 1 P 2 P 1 r 2 r 1 T 2 T 1 11

22 M 1 1 V 1 P 1 r 1 T 1 M 2 M 1 V 2 V 1 P 2 P 1 r 2 r 1 T 2 T 1 θ θ 12

23 Oblique shock Expansion fan M M 2 M 1 M 1 1 P 1 ρ 1 T 1. A θ P 2 P 1 ρ 2 ρ 1 T 2 T 1 P 1 ρ 1 T 1. A 1 θ 2 M 2 M 1 P 2 P 1 ρ 2 ρ 1 T 2 T 1 θ θ 13

24 ρ ρ ρρ A = 일정 p =p(x) ρ =ρ (x) T =T(x) A =A(x) p p(x) ρ ρ (x) T T(x) y x x z 14

25 ρ ρ ρ ρ 제어면 S u 1 p 1 T 1 A 1 제어체적 V u 2 p 2 T 2 A ρ ρ ρ ρ ρ 15

26 ρ ρ ρ ρ ρ 16

27 p 1 A 1 u 1 ρ 1 A 2 p 2 A 2 u 2 ρ 2 A 2 x Δ Δ Δ Δ Δ ρ ρ Δ Δ ρ ρ ρ 17

28 ρ ρ ρ ρ ρ ρ ρ ρ ρ ρ ρ ρ ρ ρ 18

29 ρ ρ 19

30 u 증가 M 1 (a) u 감소 u 증가 M 1 u 감소 (b) M=1 M=1 u증가 u감소 M 1 M 1 M 1 M 1 20

31 ρ ρ 21

32 ρ ρ V=0 T=T 0 p=p 0 V=a * ρ =ρ * p=p * T=T * M=1 V 0 ρ =ρ p =p ρ ρ γ 22

33 γ γ ρ ρ A 0= p 0, T 0, ρ 0 u 0=0 x A * M=1 u *=a * A(x) M(x) u(x) p b A e p e M e 23

34 ρ ρ ρ γ γ ρ ρ γ ρ γ γ γ ρ Ρ γ γ γ 24

35 γ γ γ γ 25

36 A R 2. T 0 m C p P 0 의증가 A * 초음속 아음속 0 p */p p/p 0 γ γ γ γ γ γ γ 26

37 γ γ γ γ m p m p du dt p = D ( U -U ) + m p p p b g -V Ñp p D p U ' U = U c + U c 27

38 V p Ñp 1 D p = rapcd U -U 2 2 pd A p p 4 p CD C D = 24 ( Re Re ) Re dm dt p = -pd p k c v pv Nu ln( 1 + B M ) d p 28

39 kv c pv Nu = 2( Re Pr ) F 1 F = ln(1 + B B M M ) B M Yvs - Y = 1- Y v vs Yvs Yv Y vs é æ P öw ù c = ê1 + ç -1 ú -1 ë è Pvs øwv û P Pvs Wc Wv 29

40 dt df dm p s p m pc p = m p L + H fg + a( Tg - Tp dt dt dt ) c p f s a Tg dtp m pc p = a - dt ( Tg Tp ) a = pk c Nu dp kc dtp m pc p = a - dt ( Tg Tp ) 30

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42 뉴턴유체에관하여주어진방향에대한운동량보존을지배하는미분 방정식을비슷한방법으로나타낼수있으나, 전단응력과수직응력이 고려되어야하며, 또 stokes 의점성법칙은 Fourier 의법칙에비하여 복잡하기때문에운동량방정식은에너지방정식에비하여식자체가복 잡하다. u 가 x 방향의속도일때이에관한운동량방정식은다음과같 다. (3-6) 여기서, 는점성계수, p 는압력, B x 는단위체적당 x 방향의체적, V x 는 외에추가되는점성항이다. 32

43 f t r ( rf ) + div( rvf ) = div( G gradf ) + S Γ f f Γ f f 33

44 f f f f f f f f f f 34

45 d d æ df ö (r uf) = ç G + S dx dx è dx ø ( r uf) ) æ df ö = ç G è dx ø æ df ö - ç G è dx ø e e - ( ruf w w e w + ò S dx ( r u) f - ( ru) f e P w W = G e ( f E -f P ) ( dx) e - G w ( f P -fw ) ( dx) w + S Dx 35

46 ap f P = aef E + awfw + b F º ru D º G d x ( d x) w ( dx) e w e x W P E Dx ap f P = åanbfnb + b 36

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50 Φ Φ 40

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55 ε Gas Particle Gas Type Nitrogen, Ideal gas(compressible flow) Initial pressure [MPa] 2.5 Initial temperature[k] 773 Turbulence model K-ε model Particle type Cu-Sn20wt% Initial temperature[k] 673 Density[ kg / m3 ] 8200 Diameter[ μm ] 12 Flow rate[g/sec]

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73 H. assadi, F. Gärtner, T. Stoltenhoff and H. Kreye, Acta Meterialia 51,4379(2003). 63

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75 2년간대학원생활을마무리지으며도움을받았던분들께감사의마음을전하고자합니다. 무지한저의가능성을보아연구할수있도록허락해주시고항상용기와격려를아끼지않으셨던지도교수님한정환교수님께가장큰감사를드립니다. 더좋은결과물과성과를올리지못하고졸업하게되어송구하오나사회에나가어떤일을하게되더라도교수님의가르침을항상명심하며연구자의자세로살겠습니다. 또한미흡한논문을심사해주신김목순교수님, 유병돈교수님그리고금속공학과모든교수님들께감사드립니다. 2년간연구실생활을하면서이제는가족들만큼정든재료공정연구실식구들, 방장종인오빠, 병덕오빠, 훈제오빠, 경수오빠, 의현오빠, 민규오빠그리고은정언니에게항상고맙고미안한마음을전하며합금방기현오빠, 도형오빠, 과사무실향숙언니, 김지예조교님및금속공학과원우회모든학생들에게도대단히감사드립니다. 인천올라와바쁘다는핑계로연락도제대로못해도만나면반겨줬던혜림, 고운, 유정, 승아, 은정, 소현, 혜민, 선미언니, 정목오빠, 창현오빠, 기열, 용준, 그리고이제는정말멋지게성공할내게는공기같은녀석인현주, 고맙고사랑한다. 제가어떤결정을내려도그의견과결정에동의해주시고지지해주신우리부모님, 정말감사합니다. 이제까진못난모습만보였지만미래에발전할제모습항상지켜봐주세요. 그리고하나밖에없는동생선영이, 좋은언니가되어네게모범이되도록노력할게. 마지막으로많이잘해주고챙겨주지도못하고미운짓만골라했는데도항상저를믿어준든든한남자친구변승용군에게미안하고고맙고또사랑한다고전합니다. 또한지금이논문을읽어주신분께아주조금이나마도움이되셨길바랍 니다. 65

저작자표시 - 비영리 - 변경금지 2.0 대한민국 이용자는아래의조건을따르는경우에한하여자유롭게 이저작물을복제, 배포, 전송, 전시, 공연및방송할수있습니다. 다음과같은조건을따라야합니다 : 저작자표시. 귀하는원저작자를표시하여야합니다. 비영리. 귀하는이저작물을영리목적으로이용할

저작자표시 - 비영리 - 변경금지 2.0 대한민국 이용자는아래의조건을따르는경우에한하여자유롭게 이저작물을복제, 배포, 전송, 전시, 공연및방송할수있습니다. 다음과같은조건을따라야합니다 : 저작자표시. 귀하는원저작자를표시하여야합니다. 비영리. 귀하는이저작물을영리목적으로이용할수없습니다. 변경금지. 귀하는이저작물을개작, 변형또는가공할수없습니다. 귀하는, 이저작물의재이용이나배포의경우,