• 멤브레인
• /
• 제23권3호
• /
• pp.237-244
• /
• 2013

수증기 투과는 용이하게 하면서 Dimethyl methylphosphonate (DMMP)에 대한 방호성능을 부여하는 선택투과성능을 가지도록 고안된 몇가지 복합막을 제조하였다. 선택투과막 재료는 폴리비닐알코올 고분자를 기반으로 염기성 작용기를 가지는 기능성 고분자를 포함하도록 하였다. 이들 재료를 사용하여 화생방호성능을 보유한 차세대 소재로서의 가능성을 확인하기 위하여 선택투과능을 평가하였다. 시험한 결과, 폴리비닐알코올/폴리에틸렌이민 소재가 우수한 수증기 투과성능($2,200{\sim}2,900g/m^2/day$) 및 DMMP 증기 방호성능($47g/m^2/day$)을 가지는 것을 확인하였다.

• 한국결정성장학회지
• /
• 제20권3호
• /
• pp.117-124
• /
• 2010

For Ar=5, Pr=1.18, Le=0.15, Pe=2.89, Cv=1.06, $P_B$=20 Torr, the effects of impurity $(N_2)$ on thermally and solutally buoyancy-driven convection ($Gr_t=3.46{\times}10^4$ and $Gr_s=6.02{\times}10^5$, respectively) are theoretically investigated for further understanding and insight into an essence of thermo-solutal convection occurring in the vapor phase during the physical vapor transport. For $10K{\leq}{\Delta}T{\leq}50K$, the crystal growth rates are intimately related and linearly proportional to a temperature difference between the source and crystal region which is a driving force for thermally buoyancy-driven convection. Moreover, both the dimensionless Peclet number (Pe) and dimensional maximum velocity magnitudes are directly and linearly proportional to ${\Delta}T$. The growth rate is second order-exponentially decayed for $2{\leq}Ar{\leq}5$. This is related to a finding that the effects of side walls tend to stabilize the thermo-solutal convection in the growth reactor. Finally, the growth rate is found to be first order exponentially decayed for $10{\leq}P_B{\leq}200$ Torr.

• 한국결정성장학회지
• /
• 제20권3호
• /
• pp.125-132
• /
• 2010

For typical governing dimensionless parameters of Ar = 5, Pr = 1.16, Le = 0.14, Pe = 3.57, Cv = 1.02, $Gr_s=2.65{\times}10^6$, the effects of thermo physical properties such as a molecular weight, a binary diffusivity coefficient, a partial pressure of component B on solutally buoyancy-driven convection (solutal Grashof number $Gr_s=2.65{\times}10^6$) are theoretically investigated for further understanding and insight into an essence of solutal convection occurring in the vapor phase during the physical vapor transport of a $Hg_2Cl_2-N_2$ system. The solutally buoyancy-driven convection is significantly affected by any significant disparity in the molecular weight of the crystal components and the impurity gas of nitrogen. The solutal convection in a vertical orientation is found to be more suppressed than a tenth reduction of gravitational accelerations in a horizontal orientation. For crystal growth parameters under consideration, the greater uniformity in the growth rate is obtained for either solutal convection mode in a vertical orientation or thermal convection mode in horizontal geometry. The growth rate is also found to be first order exponentially decayed for $10{\leq}P_B{\leq}200$ Torr.

• 한국결정성장학회지
• /
• 제18권6호
• /
• pp.225-231
• /
• 2008

For an aspect ratio (transport length-to-width) of 5, Pr=1.13, Le=1.91, Pe=4.3, Cv=1.01, $P_B=20\;Torr$, the effects of addition of inert gas Ne on thermally buoyancy-driven convection ($Gr=2.44{\times}10^3$) are numerically investigated for further understanding and insight into essence of transport phenomena in two dimensional horizontal enclosures. For $10K{\leq}{\Delta}T{\leq}50\;K$, the crystal growth rate increases from 10 K up to 20 K, and then is slowly decreased until ${\Delat}T=50\;K$, which is likely to be due to the effects of thermo-physical properties stronger than the temperature gradient corresponding to driving force for thermal convection. The dimensional maximum velocity gratitude reflecting the intensity of thermal convection is directly and linearly proportional to the temperature difference between the source and crystal regions. The rate is first order-exponentially decreased for $2{\leq}Ar{\leq}5$. This is related to the finding that the effects of side walls tend to stabilize convection in the growth reactor. In addition, the rate is first order exponentially decayed for $10{\leq}P_B{\leq}200\;Torr$.

• 한국결정성장학회지
• /
• 제16권5호
• /
• pp.203-209
• /
• 2006

For $P_B=50,\;{\Delta}T=10K$, Ar=5, Pr=2.36, Le=0.015, Pe=1.26, Cv=1.11, the intensity of solutal convection (solutal Grashof number $Grs=3.44x10^4$) is greater than that of thermal convection (thermal Grashof number $Grt=1.81x10^3$) by one order of magnitude, which is based on the solutally buoyancy-driven convection due to the disparity in the molecular weights of the component A($Hg_2Cl_2$) and B(He). With increasing the partial pressure of component B from 10 up to 200 Torr, the rate is decreased exponentially. The convective transport decreases with lower g level and is changed to the diffusive mode at 0.1 $g_0$. In other words, for regions in which the g level is 0.1 $g_0$ or less, the diffusion-driven convection results in a parabolic velocity profile and a recirculating cell is not likely to occur. Therefore a gravitational acceleration level of less than 0.1 $g_0$ can be adequate to ensure purely diffusive transport.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.73-78
• /
• 2003

The InP thin films grown by metalorganic chemical vapor deposition (MOCVD) are widely used to optoelectronic devices such as laser diodes, wave-guides and optical modulators. Effects of various parameters controlling film growth rate such as gas-phase reaction rate constant, surface reaction rate constant and mass diffusivity are numerically investigated. Results show that at the upstream region where film growth rate increases with the flow direction, diffusion including thermal diffusion plays an important role. At the downstream region where the growth rate decreases with flow direction, film deposition mechanism is revealed as a mass-transport limited. Mass transport characteristics are also studied using systematic analyses.

• 한국결정성장학회지
• /
• 제29권3호
• /
• pp.107-114
• /
• 2019

A computational analysis has been carried out to get a thorough and full understanding on the effects of convective process parameters on double-diffusive convection during the growth of mercurous bromide ($Hg_2Br_2$) crystals on earth and under ${\mu}g$ conditions. The dimensional maximum magnitude of velocity vector, ${\mid}U{\mid}_{max}$ decreases much drasticlly near Ar = 1, and, then since Ar = 2, decreases. The ${\mu}g$ conditions less than $10^{-2}g$ make the effect of double-diffusion convection much reduced so that adequate advective-diffusion mass transfer could be obtained.

• 한국결정성장학회지
• /
• 제19권1호
• /
• pp.39-47
• /
• 2009

The effects of thermo-solutal convection on mercurous chloride system of ${Hg_2}{Cl_2}$, and Ne during physical vapor transport are numerically investigated for further understanding and insight into essence of transport phenomena, For $10\;K{\le}{\Delta}T{\le}30\;K$, the growth rate slowly increases and, then is decreased gradually until ${\Delta}T$=50 K, The occurrence of this critical point near at ${\Delta}T$=30 K is likely to be due to the effects of thermo-physical properties stronger than the temperature gradient corresponding to driving force for thermal convection. For the range of $10\;Torr{\le}P_B{\le}300\;Torr$, the rate is second order-exponentially decayed with partial pressures of component B, $P_B$. For the range of $5{\le}M_B{\le}200$, the rate is second order-exponentially decayed with a function of molecular weight of component B, $M_B$. Like the case of a partial pressure of component B, the effects of a molecular weight arc: reflected through the binary diffusivity coefficients, which are intimately related with suppressing the convection flow inside the growth enclosure, i,e., transition from convection to diffusion-dominant flow mode as the molecular weight of B increases. The convective mode is near at a ground level, i,e., on earth (1 $g_0$), and the convection is switched to the diffusion mode for $0.1\;g_0{\le}g{\le}10^{-2}g_0$, whereas the diffusion region ranges from $10^{-2}g_0$ up to $10^{-5}g_0$.

• 한국결정성장학회지
• /
• 제19권4호
• /
• pp.172-183
• /
• 2009

For the effects of the nonlinear temperature profiles and reduced-gravity conditions we conduct a two-dimensional numerical modeling and simulations on the physical vapor transport processes of $Hg_2Cl_2-Xe$ system in the horizontal orientation position. Our results reveal that: (1) A decrease in aspect ratio from 5 to 2 leads to an increasingly nonuniform interfacial distribution and enhances the growth rate by one-order magnitude for normal gravity and linear wall temperature conditions. (2) Increasing the molecular weight of component B, Xenon results in a reduction in the effect of solutal convection. (3) The effect of aspect ratio affects the interfacial growth rates significantly under normal gravity condition rather than under reduced gravitational environments. (4) The transition from the convection-dominated regime to the diffusion-dominated regime ranges arises near at 0.1g$_0$ for operation conditions under consideration in this study.

• 한국결정성장학회지
• /
• 제31권3호
• /
• pp.127-136
• /
• 2021

This paper is dedicated to numerical simulation for diffusion-advective convection in a square cavity during physical vapor transport of Hg₂Br₂. Flow characteristics of the temperature difference between the source and crystal regions, 50℃ (300℃ → 250℃), partial pressures of component argon of 20 Torr and 100 Torr are investigated and presented as velocity vectors and streamlines, isotherms and iso-mass concentrations contours. Moreover, alterations of average Nusselt and average Sherwood numbers with (a) the source and crystal regions, (b) the pressures of component argon of 20 Torr and 100 Torr are analyzed and addressed in details. Both average Nusselt and average Sherwood numbers are seen to decrease with the increasing values of the partial pressures of component argon. Also, it is found that for the two different partial pressures of component argon, average Nusselt numbers at the source region are greater than at the crystal region, and inversely, average Sherwood numbers at the crystal region are greater than the source region by a factor of 3.