• 대한기계학회논문집
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• 제13권4호
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• pp.618-624
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• 1989

본 연구의 목적은 낮은 포화 압력하에서의 초음파에 의한 미세포 포움 구조 획득의 가능성을 평가하기 위한 것으로, 이 초음파 가공을 고분자 포움의 연속적인 압출 가공에 적용하기 위한 기초 연구를 이론적 및 실험적으로 수행함에 있다.따라서 미세포구조의 획득이 본 연구의 목적은 아니며 초음파를 이용한 열가소성 수지내의 핵생성 거동에 대한 고찰을 하고자 한다.

• 대한기계학회논문집B
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• 제22권6호
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• pp.813-822
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• 1998

The microexplosion of a slurry droplet was considered to be caused by the shell formation and the following pressure build-up in the shell which would be promoted by the suppression of evaporation, subsequent superheating and heterogeneous nucleation of liquid carrier. To closely investigate the pressure build-up and the heterogeneous nucleation, a numerical model was introduced by considering the internal temperature distributions with the shell formation, suppression of evaporation and pressure build-up inside. The microexplosion time was estimated by postulating the limit of superheat for heterogeneous nucleation. The simulation yielded a reasonably good agreement with experimental results for Al/n-heptane slurry droplets under various solid loadings.

• Nuclear Engineering and Technology
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• 제38권2호
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• pp.175-184
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• 2006

Boiling and flashing are driven by the same physics for nucleation, bubble growth, departure etc. An adequate model of boiling has to describe the flashing too. The subject of this paper is to prove this uniqueness of the elementary physics driving the both processes.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1885-1890
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• 2008

3-D heterogeneous nucleation was simulated by classical molecular dynamics (MD), where the Lennard-Jones (LJ) gas and solid cluster-seed molecules have argon and aluminum properties, respectively. There are three shapes of cluster-seeds, cube, rod, and sphere, and three classes of masses and the simulation took place under nine supersaturation ratios, making a total of 81 calculations. Results show that the dimension of the cluster-seed highly affects the rates of cluster development. In order to analyze heterogeneous nucleation above and below the critical supersaturation ratio, growth rate and liquefaction rate were separately defined to supplement the investigation. Design of experiments (DOE) was used for analysis which displayed that the shape and mass of the cluster-seed are prominent for the growth rate, while the supersaturation ratio is most significant followed by the mass for liquefaction rate. The significance of the supersaturation ratio for overall liquefaction suggests that thermal diffusion is more dominant than mass interactions for this system.

• Applied Microscopy
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• 제43권3호
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• pp.122-126
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• 2013

The heterogeneous nucleation of the ${\Theta}^{\prime}$ phase on nanoscale precipitates has been investigated using a combination of three-dimensional atom probe tomography and high-resolution transmission electron microscopy. Two types of ${\Theta}^{\prime}$ phases were observed, namely small (~2 nm thick) cylindrical precipitates and larger (~100 nm) globular precipitates and both appear to be heterogeneously nucleated on the nanoscale precipitates. The composition and crystal structure of precipitates were directly analyzed by combination of two advanced characterization techniques.

• 한국입자에어로졸학회지
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• 제5권4호
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• pp.171-178
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• 2009

$PM_{2.5}$ is one of critical air pollutants due to its high absorbability of heavy metallic fumes, PAH and bacillary micro organisms. Such a fine particulate matter is often formed through various nucleation processes including condensation. This study attempts to find the nucleation behaviors of $PM_{2.5}$ arisen from coal power stations using a classical heterogeneous Fletcher's theory. The numerical simulation by C-language could approximate the nucleation process of $PM_{2.5}$ from water vapor, of which approach revealed the required energy for embryo formation and embryo size and nucleation rate. As a result of the calculation, it was found that wetting agents could affect the particle nucleation in vapor condensation. In particular, critical contact angle relates closely with the vapor saturation. Particle condensation could be reduced by lowering the angles. The wetting agents aid to decrease the contact angle and surface tensions, thereby may contribute to save the formation energy.

• Fibers and Polymers
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• 제4권3호
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• pp.102-106
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• 2003

Crystallization behaviour of blends of different MFI isotactic polypropylenes (PP), and blends of PP with carbon nanofibre have been investigated by DSC and polarizing optical microscope. Both higher MFI PP component and the carbon nanofibre in the blend influence the nucleation activity of the melt during non-isothermal crystallization. In presence of carbon nanofibre, the sherulitic growth rate is highly disturbed. The calculation of nucleation activity indicates that carbon nanofibres act as active substrate for heterogeneous nucleation.

• 한국세라믹학회지
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• 제38권11호
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• pp.1030-1036
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• 2001

공침법을 이용하여 수산화아파타이트[HAP]-콜라겐[COL] 나노복합재료를 제조하였다. HAP 결정과 COL 분자 사이의 화학결합형성을 확산반사법 FT-IR 및 투과전자현미경(TEM) 관찰로부터 확인하였다. 제조 시에 첨가되는 콜라겐 단백질의 농도가 높으면 미세한 아파타이트 나노결정의 콜라겐 복합체가 만들어지고 첨가되는 단백질의 농도가 낮으면 아파타이트 결정이 비교적 크게 발달하였다. FT-IR과 전자선 회절(electron diffraction)로부터 콜라겐 매체에 발달된 아파타이트 결정입자 들은 콜라겐 분자의 c 축을 따라 정렬하는 것임을 알 수 있었다. 칼슘이온 농도와 인산이온 농도를 일정하게 유지하는 수용액 계에 용해되어 있는 콜라겐 단백질의 농도는 아파타이트 결정의 발달을 위한 불균질 핵생성 위치를 제공하는 중요한 역할을 하고 있다. 콜라겐의 농도가 높으면 칼슘이온(Ca$^{2+}$)에 대한 핵생성을 위한 활성화 위치를 많이 제공하게 되며, 이는 핵생성 위치에 대한 칼슘이온 농도가 상대적으로 낮아지는 것에 대응하게 된다.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
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• pp.241-246
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• 1996

An analytical model to calculate rate of vapor generation due to heterogeneous wall nucleation in flashing flow is developed. In the present model, an important parameter of the vapor generation term, i.e. nucleation site density is calculated by integrating its probability distribution function with respect to active cavity radius. The limits of integration are minimum and maximum active cavity radii, and these are formulated using an active cavity model for nucleate boiling. This formulation, therefore. can statistically account for the effect of surface specific thermo-physical and geometric conditions on the vapor generation rate and flashing inception. For verifying the adequacy of the present model, steady state two-fluid and the bubble transport equations are solved with applicable constitutive equations. The applicable region of the bubble transport equation is also extended to churn-turbulent flow regime to predict interfacial area concentration at high void fraction. Predicted results in terms of axial pressure and void fraction profiles along the channels are compared with experimental data of Super Moby Dick and BNL Reasonable agreements have been achieved and this shows the applicability of the present model to flashing flow analysis.

• 대한기계학회논문집B
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• 제21권12호
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• pp.1576-1585
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• 1997

The microexplosive combustion of a slurry droplet was investigated experimentally. The microexplosion has been approximately considered to be caused by pressure build-up in the shell and to be promoted by heterogeneous nucleation of liquid carrier, which is due to the suppression of evaporation and subsequent superheating of liquid carrier. To closely investigate the pressure build-up and the heterogeneous nucleation, the experiments were conducted in an electric combustor, of which temperature was controllable (400 K-900 K). And the effects of two aligned droplets on the interactive combustion and microexplosion were found in a hot post region of a flat flame burner. Transient internal temperature distributions for slurry droplets were measured. And the shell formation and the microexplosion of suspended A1/JP-8 and Al/n-heptane slurry droplets were examined with various surfactant concentrations (0.5-5 wt%) and solid loadings (10-50 wt.%). The microexplosion time of binary array of droplets was found to be less than that of the isolated droplet due to radiative interaction between droplets.