• 한국결정성장학회지
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• 제12권6호
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• pp.272-282
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• 2002

Mercurous bromide ($Hg_{2}0Br_{2}$) crystals hold promise for many acousto-optic and opto-electronic applications. This material is prepared in closed ampoules by the physical vapor transport (PVT) growth method. Due to the temperature gradient between the source and the growing crystal region, the buoyancy-driven convection may occur. The effects of thermal convection on the crystal growth rate was investigated in this study in a horizontal configuration for conditions ranging from typical laboratory conditions to conditions achievable only in a low gravity environment. The results showed that the growth rate increases linearly with Grashof number, and for 0.2 $\leq$ Ar (transport length-to-height, L/H)$\leq$1.0 sharply for Ar=5 and $\Delta$T=30 K. We have also shown that the magnitude of convection decreases with the Ar. For gravity levels of less than $10^{-2}$g the non-uniformity of interfacial distribution is negligible.

• 한국결정성장학회지
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• 제34권2호
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• pp.48-54
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• 2024

브로민화 수은(I)(Hg₂Br₂) 자체 확산 물리적 증착법 공정에서 자체 확산 전달현상 연구에서 얻어진 결론은 10^-3g₀ ≤ g ≤ 1g₀ 영역에서는 열 대류현상이 지배적이며, g = 10^-4g₀ 영역에서는 대류에서 확산영역으로 전이되는 영역이며, 10^-6g₀ ≤ g ≤ 10^-5g₀ 영역에서는 확산모드가 지배적이다. Hg₂Br₂의 총 몰플럭스는 중력가속도의 레벌(level)이 1/10 크기로 감소함에 따라 기하급수적으로 감소함을 나타내고 있다는 것이다. 10℃ ≤ ΔT ≤ 50℃의 온도차 범위에서는 온도차(ΔT)와 Hg₂Br₂의 총 몰플럭스에 대한 관계식은 선형적으로 직선적 비례관계성을 보여주고 있다.

• 한국결정성장학회지
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• 제14권2호
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• pp.50-57
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• 2004

Mercurous Bromide ($Hg_2Br_2$) crystals hold promise for many acousto-optic and opto-electronic applications. This material is prepared in closed ampoules by the physical vapor transport (PVT) growth method. We investigate the effects of solutal convection on the crystal growth rate in a horizontal configuration for diffusive-convection conditions and purely diffusion conditions achievable in a low gravity environment. Our results show that the growth rate is decreased by a factor of one-fourth with a ten reduction of gravitational acceleration near y = 2.0 cm. For 0.1 $g_O$ the growth rate pattern exhibits relatively flat which is intimately related to diffusion-dominated processes. The growth rate nonuniformity is regardless of aspect ratio across the interfacial positions from 0 to 1.5. Also, the effect of a factor of the ten reduction in the gravitational acceleration is same to both Ar = 5 and 2. The enlargement in the molecular weight of B from 50 to 500 by a factor 4 causes a decrease in the maximum growth rate by the same factor, indicative of the effect of solutal gradients.

• Korean Chemical Engineering Research
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• 제57권2호
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• pp.289-300
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• 2019

We have conducted a preliminary numerical analysis to understand the effects of double-diffusive convection on the molar flux at the crystal region during the growth of mercurous bromide ($Hg_2Br_2$) crystals in 1 g and microgravity (${\mu}g$) conditions. It was found that the total molar fluxes decay first-order exponentially with the aspect ratio (AR, transport length-to-width), $1{\leq}AR{\leq}10$. With increasing the aspect ratio of the horizontal enclosure from AR = 1 up to Ar = 10, the convection flow field shifts to the advective-diffusion mode and the flow structures become stable. Therefore, altering the aspect ratio of the enclosure allows one to control the effect of the double diffusive natural convection. Moreover, microgravity environments less than $10^{-2}g$ make the effect of double-diffusive natural convection much reduced so that the convection mode could be switched over the advective-diffusion mode.

• 한국결정성장학회지
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• 제29권3호
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• pp.107-114
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• 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
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• 제33권3호
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• pp.110-115
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• 2023

브로민화 수은(I)(Hg₂Br₂) 물리적 증착법 공정에서 구성요소 B의 분압, P_B를 40 Torr에서 200 Torr로 증가시켰을 때 1개의 셀(unicell)이 결정성장영역에서 기체상 공간의 중심으로 이동함을 보여주고 있다. P_B = 40 Torr에서는 경계층 흐름이 지배적이고, P_B = 200 Torr에서는 코어영역흐름(core region)을 보이고 있다. 고려되는 물리적 증착법 공정에서 P_B = 40 Torr와 P_B = 200 Torr에서 1개(single)의 셀(cell) 형태로 3차원의 유동의 흐름과 x, y 직교 중심축에 대하여 비대칭 유동흐름을 나타내고 있다. 소스와 결정 영역 사이의 임계 온도차는 약 30 K입니다. Hg₂Br₂의 총 몰 플럭스는 임계값에 도달할 때까지 온도차에 따라 증가한다. 임계 총 몰 플럭스에서 총 몰 플럭스는 갑자기 감소한다.

• 한국결정성장학회지
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• 제32권1호
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• pp.16-24
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• 2022

A computational study of combined thermal and solutal convection (double diffusive convection) in a sealed crystal growth reactor is presented, based on a two-dimensional numerical analysis of the nonlinear and strongly coupled partial differential equations and their associated boundary conditions. The average Nusselt numbers for the source regions are greater than those at the crystal regions for 9.73 × 10³ ≤ Gr_t ≤ 6.22 × 10⁵. The average Nusselt numbers for the source regions varies linearly and increases directly with the thermal Grashof number form 9.73 × 10³ ≤ Gr_t ≤ 6.22 × 10⁵ for aspect ratio, Ar (transport length-to-width) = 1 and 2. Additionally, the average Nusselt numbers for the crystal regions at Ar = 1 are much greater than those at Ar = 2. Also, the occurrence of one unicellular flow structure is caused by both the thermal and solutal convection, which is inherent during the physical vapor transport of Hg₂Br₂. When the aspect ratio of the enclosure increases, the fluid movement is hindered and results in the decrease of thermal buoyancy force.

• 한국결정성장학회지
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• 제14권4호
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• pp.160-168
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• 2004

We investigate the effects of solutal convection on the crystal growth rate in a horizontal configuration for diffusive-convection conditions and purely diffusion conditions achievable in a low gravity environment for a nonlinear thermal gradient. It is concluded that the solutally-driven convection due to the disparity in the molecular weights of the component A $(Hg_2Br_2)$ and B (CO) is stronger than thermally-driven convection for both the nonlinear and the linear thermal profiles, corresponding to $Gr_t= 8.5{\times}10^3,\; Gr_s = 1.05{\times}10^5$. For both solutal and thermal convection processes, the growth rates for the linear thermal profile (conducting walls) are greater than for the nonlinear case. With the temperature humps, there are found to be observed in undersaturation for diffusive-convection processes ranging from $D_{AB}$ = 0.087 to 0.87. For the vertical configurations, the diffusion mode is so much dominated that the growth rate and interfacial distribution is nearly regardless of the gravitational accelerations. Also, the diffusion mode is predominant over the convection for the gravity levels less than 0.1 $g_0$ for the horizontally oriented configuration.

• 한국결정성장학회지
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• 제33권4호
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• pp.145-152
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• 2023

2.31 × 10⁴ ≤ Gr_t ≤ 4.68 × 10⁴의 범위에서 온도 Grashof 수(Gr_t)의 변화에 대하여, 소스와 결정영역에서의 평균 Nusselt수를 나타내고 있다. 결정영역에서의 평균 Nusselt 수가 소스영역에서의 평균 Nusselt 수 보다 2배 이상 큰 것으로 나타나고 있다. 소스영역에서의 평균 Nusselt 수는 온도 Grashof 수(Gr_t)에 대하여, 증가하는 경향을 보여주고 있으며, 반면에 결정영역에서의 평균 Nusselt 수는 온도 Grashof 수(Gr_t)에 대하여, 감소하는 경향을 나타나고 있다. 3.28 × 10⁵ ≤ Gr_s ≤ 4.43 × 10⁵의 범위에서 농도 Grashof 수(Gr_s)의 변화에 대하여, 소스와 결정영역에서의 평균 Sherwood 수를 나타내고 있다. 소스영역과 결정영역에서의 평균 Sherwood 수는 농도 Grashof 수(Gr_s)가 증가함에 따라, 감소하는 경향을 보이고 있다. 결정영역에서의 평균 Sherwood 수는 소스영역에서의 평균 Sherwood 수보다 약 4배 정도 크다.