• Proceedings of the Membrane Society of Korea Conference
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• 1994.04a
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• pp.34-35
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• 1994

Tube-in-orifice형태의 spinneret을 제작하여, polyethersulfone을 재질로 하는 capillary membrane을 건습식방사공정을 통해 제조하였다. 기공형성계는 PVP를, 용매는 NMP/DCM을, 내부응고제는 물과 NMP의 혼합물을, 외부응고제는 냉각수를 사용하였다. 내부응고제의 NMP농도에 따른 막의 형태와 microstructure를 연구하였다. 내부응고제가 약한 응고력을 가질 때 macrovoid가 없고, 내부의 활성층이 치밀한 막을 얻을 수 있었다. PES-NMP/DCM-PVP조성(25-44/11-20)의 용액으로, 40% NMP수용액을 내부응고제로 사용하여, 막을 제조하고 이를 모듈화하여, 한외여과실험을 한 결과, MWCO 8,000인 모듈이 얻어졌으며, 이 모듈의 Flux는 1기압에서 $1.44 \times 10^{-5}m/sec$이었다.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.06a
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• pp.207-207
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• 2011

본 논문은 공장 등에서 버려지는 중온온도영역($100{\sim}250^{\circ}C$)에서의 패열을 잠열축열 시스템에서 유용하게 사용을 목적으로 잠열축열재인 에리스리톨와 만니톨 그리고 이것들을 혼합한 혼합물에 대한 조사에 관한 것이다. 또한, 만니톨에 에리스리톨을 첨가하는 것에 의해 융해 응고온도가 조정의 가능성에 대해서도 조사한다. 이때 에리스리톨과 만니톨 그리고 이것들의 혼합물의 융점과 잠열량은 시차주사열량계(DSC)를 이용하여 측정되며, 시험관안에 상변화물질을 충전하여 융해 응고거동을 디지털 카메라를 이용하여 관찰 된다. DSC측정결과에서는 만니톨의 함유량이 50~60mass%에서는 3개의 융점, 70~90mass%에서는 2개의 융점을 나타내는 것을 확인할 수 있었다. 또한 시험관을 이용한 실험결과에서는 만니톨의 함유량에 따라서 각 각 다른 융해 응고거동이 일어나는 것을 확인할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.4
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• pp.440-451
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• 1998

An experimental study has been conducted to investigate solidification of NH$_{4}$CI-H$_{2}$0 mixtures inside a vertical rectangular enclosure. Solidification process is visualized by the shadowgraph method. Emphasis is placed on the effect of solidification parameters such as the aspect ratio, cooling wall temperature and initial composition. The aspect ratio shows a dominant effect on the number and developing time of the double diffusive layers which reveals the relative strength of solutal convection to thermal convection. Similar flow pattern is observed when the concentration difference between interdendritic liquid and the pure liquid which drives solutal convection is the same regardless of the different cooling wall temperature and initial concentration.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.1
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• pp.35-43
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• 1993

A numerical model for the solidification of binary mixture is proposed. Numerical model, which employs enthalpy method, is modified from Continuum model, that is, improved relation is proposed for the Enthalpy - Temperature - Concentration - Liquid Mass Fraction. One dimensional example was selected to verify the proposed model. The results show that the new relation can be applied successfully to the solidification or melting of binary mixture.

• Solar Energy
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• v.12 no.3
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• pp.107-115
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• 1992

An experiment was performed to study solidification of binary mixture with double-diffusive convection in the liquid. A rectangular enclosure was filled with ammonium chloridewater solution. The phase change and convection process were studied through shadowgraph. Becasuse of the double-diffusive convection, the temperature field and concentration filed were stratified very rapidly. Correlation between solidified mass fraction and the dimensionless numbers was found; solidified mass concentration can be expressed as a linear function of $(Ste{\cdot}Ra^{1/4})^{2-Ste}{\cdot}Fo^{1/2}$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.11
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• pp.3655-3665
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• 1996

An analytical solution is presented for the conduction-dominated solidification of a binary mixture in a semi-infinite medium. The present approach differs from that of other solution by these four characteristics. (1) Solid fraction is determined from the phase diagram, (2) thermophysical properties in mushy zone are weighted according to the local solid fraction, (3) non-equilibrium solidification can be simulated and (4) the cooling condition of under-eutectic temperature can be simulated. Up to now, almost all analyses are based on the assumption of constant properties in mushy zone and solid fraction linearly with temperature or length. The validation for these assumptions, however, shows that serious error is found except some special cases. The influence of microscopic model on the macroscopic temperature profile is very small and can be ignored. But the solid fraction and average solid concentration which directly influence the quality of materials are drastically changed by the microscopic models. An approximate solution using the method of weighted residuals is also introduced and shows good agreement with the analytical solution. All calculations are performed for NH$_{4}$Cl-H$_{2}$O and Al-Cu system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.2
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• pp.184-192
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• 1998

This paper deals with an extended analytical solution for the mixture solidification problem, in which temperature is inherently coupled with the solute transport due to the presence of volume contraction induced flow. A new exact solution to the energy equation accounting for the convection effect in the melt is successfully derived, which allows the present analysis to cover a high initial superheating. Difference in properties between the solid and liquid phases is rigorously incorporated into the model equations in the solid fraction weighted form. Taking advantage of linearized correction factors, a systematic and easy-to-implement algorithm for determining the solidus and liquidus positions is introduced, which proves not only to converge stably but also to be very efficient. For a specific case, the present results show excellent agreements with the existing solution. The effect of convection in the melt becomes appreciable with increasing the initial superheating. It is revealed that variable properties in the mushy region significantly affect the solidification behaviors. The present study is also capable of resolving the interaction between microsegregation and macrosegregation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.162-171
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• 1993

This paper deals with the anisotropy of the mushy region during solidification process of a binary mixture. A theoretical model which specifies a permeability tensor in terms of pricipal values is proposed. Also, the governing equations are modified into convenient forms for the numerical analysis with the existing algorithm. Some test computations are performed for soeidification of aqueous ammonium chloride solution contained in a square cavity. Results show that not only the present model is capable of resolving fundamental characteristics of the tranport phenomena, but also the anisotropy significantly affects the interdendritic flow structure, i.e., double-diffusive convection and macrosegregation patterns.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.2
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• pp.111-121
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• 1993

Double-diffusive convection during solidification process of the binary mixture was studied numerically. Enthalpy method and finite element method were implemented in the analysis. Calculation carried out for $R{\alpha}_T=10^3-10^4$ and $R{\alpha}_T=0-10^5$. The results show that the variation of thermal Rayleigh number changes the fields of velocity, temperature and concentration, but the variation of solutal Rayleigh number gives little effects on those. In conclusion, concentration gradient can be negligible compared with temperature gradient in macroscopic point of view, although concentration gradient plays a role in forming dendrite.

• Korean Chemical Engineering Research
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• v.47 no.2
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• pp.174-178
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• 2009

A mushy layer of dendritic crystals is often formed during solidification of a binary mixture. Natural convection in the mushy layer is analyzed by using the propagation theory we have developed. The critical Rayleigh numbers for the onset of convection are evaluated numerically using the self-similar stability equations based on Emms and Fowler's model. The present results approach those from quasi-static stability analysis in the limit of a large superheat or a small growth rate of the mushy layer.