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다공질 금속 Foam을 사용한 열교환기의 열전달계수에 관한 연구
鄭淳孝,吳英周 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.5
A foam-filled channel having constant wall temperature and allowing convective cooling was numerically analysed to obtain the overall heat transfer coefficient and the characteristic length as the function of foam density, cell spacing, foam thickness, fluid velocity and physical properties of foam and fluid. It is found that the numerically calculated overall heat transfer coefficient shows negative deviation from one calculated by analytical model assuming constant fluid temperature along direction of foam thickness. The deviation was strong at small foam density, small cell spacing, high fluid velocity and thick foam, where heat conduction capacity through solid ligaments was low compared with solid ligament-fluid heat transfer capacity and the fluid temperature variation along direction of foam thickness was remarkable. A general expression for the characteristic length, which was proportional to mass flow rate per unit foam width, and inversely proportional to the overall heat transfer coefficient could be obtained.
티타늄 탈산된 저탄소강에서 응고시 Ti_2O_3 비금속 개재물의 석출에 관한 속도론적 연구
鄭淳孝,李相潤,吳英周 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.1
The size distribution of Ti_2O_3 inclusion during solidification of low carbon steel has been calculated using reactive diffusion equations, which take account of the nucleation and growth of inclusion as well as solidification. The calculated results were compared to experimental observations. And the effect of various parameters such as cooling rate, chemical composition of steel, on the inclusion size distribution were studied.
IV족 천이금속 질화물과 bcc Fe간 계면 에너지의 제일원리 연구
정순효,정우상,변지영,Chung, Soon-Hyo,Jung, Woo-Sang,Byun, Ji-Young 한국재료학회 2006 한국재료학회지 Vol.16 No.8
The coherent interface energies and misfit strain energies of Fe/XN (X=Ti, Zr, Hf) systems were calculated by first principles method. The interface energies in Fe/TiN, Fe/ZrN and Fe/HfN systems were 0.343, 0.114, and 0.030 $J/m^2$, respectively. Influence of bond energy was estimated using the discrete lattice plane/nearest neighbor broken bond(DLP/NNBB) model. It was found that the dependence of interface energy on the type of nitride was closely related to changes of the bond energies between Fe, X and N atoms before and after formation of the Fe/XN interfaces. The misfit strain energies in Fe/TiN, Fe/ZrN, and Fe/HfN systems were 0.239, 1.229, and 0.955 eV per 16 atoms(Fe; 8 atoms and XN; 8 atoms). More misfit strain energy was generated as the difference of lattice parameters between the bulk Fe and the bulk XNs increased.
Rene 80 합금의 진공유도 용해정련에 관한 연구 (2) : 탈황 및 탄소함량의 거동 Desulfurization and Variation of Carbon Content
정순효,오영주 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.11
The vacuum refining of nickel base Rene´ 80 was studied by using a 2㎏ laboratory vacuum induction melting apparatus. It was possible to reduce the sulfur content of superalloy Rene´ 80 to below 2 ppm by strong induction stirring of melt and a use of calcia lined crucible. At initial carbon contents below 0.04%, the degree of decarburization after first refining and second refining were 77% and 57%, respectively. At initial carbon contents above 0.04%, the degree of decarburization decreased with increasing initial carbon content.
정순효,하헌필,변지영 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.8
A previously developed fixed grid finite volume method was used to investigate hydrogen removal process involving surface reaction, diffusion, β/α phase boundary movement and phase transformation that occurs during dehydrogenation of cylindrical β-titanium specimens. Effects of temperature, initial hydrogen content and radius of specimen on times for dehydrogenation were studied. It was found that dehydrogenaion occus through the following 4 steps: (1) lowering of hydrogen concentration at the surface of the β specimen to equilibrium value, (2) lowering of hydrogen concentration gradient to a value matching the surface reaction flux. (3) the (β/α phase transformation by inward movement of the β/α phase boundary and (4) further removal of hydrogen in the a phase specimen to final value. Time for hydrogen removal in the first step increases with increase of temperature and initial hydrogen content, due to the rapid increase of amount of hydrogen to be removed comparing with the increase of hydrogen removal rate. It increases with specimen radius. Time for hydrogen removal in 2nd step decreases with increase of temperature due to increase of hydrogen removal rate and decrease of amount of hydrogen to be removed, but it increases with specimen radius and initial hydrogen content. Time for hydrogen removal in 3rd step (β/α phase transformation) decreases with increase of temperature due to decrease of diffusion and reaction resistance and due to increase of partition coefficient, but it increases with specimen radius due to increase of diffusion and reaction resistance. It increases with initial hydrogen content. Time for hydrogen removal in 4th step decreases with increase of temperature due to decrease of diffusion and reaction resistance as well as equilibrium concentration, but it increases with specimen radius due to increase of diffusion and reaction resistance.
Rene 80 합금의 진공 유도 용해 정련에 관한 연구 (1) : 탈산 및 탈질소 Deoxidation and Denitriding
정순효,오영주 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.1
In this study, the vacuum refining trials of nickel base superalloy Rene 80 were done using 2kg laboratory vacuum induction melting apparatus. It was possible to lower the oxygen and nitrogen contents of superalloy Rene´ 80 to 4 ppm and 1 ppm, respectively, by low temperature vacuum refining after melt down (1500-1550℃) 1-3 mtorr), strong stirring of melt by induction, addition of alloying element with sequence of Ti after Al, low temperature vacuum refining after addition of alloying elements (1500-1550℃, 1-3 mtorr) and use of calcia lined crucible.