• Membrane and Water Treatment
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• 제9권6호
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• pp.435-445
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• 2018

In this work, desalination experiments were performed on vacuum membrane distillation (VMD). Process parameters such as feed flow rate, vacuum degree on permeate side, feed bulk temperature and feed salt concentration were optimized using sensitivity analysis and Taguchi method. The optimum values of process parameters were found to be 2 lpm of feed flow rate, $60^{\circ}C$ of feed bulk temperature, 5.5 kPa of permeate-side pressure and 5000 ppm of salt concentration. The permeate flux at these conditions was obtained as $26.6kg/m^2{\cdot}hr$. The rejection of salt in permeate was found to be 99.7%. The percent contribution of various process parameters using ANOVA results indicated that the most important parameter is feed bulk temperature with its contribution of 95%. The ANOVA results indicate that the percent contribution of permeate pressure gets increased to 5.384% in the range of 2 to 7 kPa as compared to 0.045% in the range of 5.5 to 7 kPa.

• 한국염색가공학회지
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• 제20권3호
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• pp.1-7
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• 2008

Three kinds of 135D/108F ITY were produced from raw yam 85D/72F + SDY 50D/36F with. interlacing pressure $1.5kg/cm^2$, $2.5kg/cm^2$, $3.5kg/cm^2$ respectively. 72 kinds of sized yams were manufactured from three ITYs by altering sizing speed, sizing temperature and sizing tension. The mechanical characteristics of 72 kinds of plain fabrics which were woven using the sized yam as a warp were analyzed after scouring. The initial modulus of scoured fabric responded sensitively to the sizing speed in high tension. The WT of scoured fabric recorded the. highest1n the conditions of sizing tension 30g, and air pressure $2.5kg/cm^2$ in interlacing treatment. When sizing temperature was high, the WT value appeared low, but when sizing speed was high, the WT value was much affected by air pressure in interlacing raw yam. The MIU value of fabric according to sizing tension variations increased up to sizing tension 40g, but decreased above it. The bulk density decreased up to sizing tension 30-40g, but increased above it. In addition, the bulk density decreased as sizing temperature increased.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1998년도 PROCEEDINGS OF THE 14TH KACG TECHNICAL MEETING AND THE 5TH KOREA-JAPAN EMGS (ELECTRONIC MATERIALS GROWTH SYMPOSIUM)
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• pp.149-156
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• 1998

In this work, aiming at improvement of growth processes for the bulk GaAs single crystals, efforts have been made first in investigate thermodynamic properties of the Ga and As system and second to suggest that bulk GaAs crystals could be grown in principle with the single temperature zone only by determining the excess arsenic charge as a function of growth conditions. During crystal growth, this will be evaporized inside the growth chamber to induce the required inner pressure, instead of aesenic vapor pressure in the double temperature zone method, so as to be in equilibrium with the method, growth experiments have been prepared and carried out for dopes and undoped GaAs crystals with the newly built Bridgman system which was designed according to this principle. To compare the results to those of the double temperature zone method, the same numbers of GaAs crystals have been grown with both processes and all of them were characterized in single crystallinity, lattice defects and electrical properties. Especially, the relationship between growth conditions and crystal quality was discussed from the viewpoint of growth peculiarities with this method.

• Transactions on Electrical and Electronic Materials
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• 제10권3호
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• pp.75-79
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• 2009

An intrinsic silicon thin film passivation layer is deposited by the microwave remote-plasma enhanced chemical vapor deposition at temperature of $175^{\circ}C$ and various gas ratios for solar cell applications. The good quality amorphous silicon films were formed at silane $(SiH_4)$ gas flow rates above 15 seem. The highest effective carrier lifetime was obtained at the $SiH_4$, flow rate of 20 seem and the value was about 3 times higher compared with the bulk lifetime of 5.6 ${\mu}s$ at a fixed injection level of ${\Delta}n\;=\;5{\times}10^{14}\;cm^{-3}$. An annealing treatment was performed and the carrier life times were increased approximately 5 times compared with the bulk lifetime. The optimal annealing temperature and time were obtained at 250 $^{\circ}C$ and 60 sec respectively. This indicates that the combination of the deposition of an amorphous thin film at a low temperature and the annealing treatment contributes to the excellent surface and bulk passivation.

• 한국초전도ㆍ저온공학회논문지
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• 제9권1호
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• pp.37-42
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• 2007

We are developing a 22.9 kV/25 MVA superconducting fault current limiting(SFCL) system for a power distribution network. A Bi-2212 bulk SFCL element, which has the merits of large current capacity and high allowable electric field during fault of the power network, was selected as a candidate for our SFCL system. In this work, we experimentally investigated important characteristics of the 190 kVA Bi-2212 SFCL element in its application to the power grid e.g. DC voltage-current characteristic, AC loss, current limiting characteristic during fault, and so on. Some experimental data related to thermal and electromagnetic behaviors were also compared with the calculated ones based on numerical method. The results show that the total AC loss at rated current of the 22.9 kV/25 MVA SFCL system, consisting of one hundred thirty five 190 kVA SFCL elements, becomes likely 763 W, which is excessively large for commercialization. Numerically calculated temperature of the SFCL element in some sections is in good agreement with the measured one during fault. Local temperature distribution in the190 kVA SFCL element is greatly influenced by non-uniform critical current along the Bi-2212 bulk SFCL element, even if its non-uniformity becomes a few percentages.

• 한국자기학회지
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• 제5권6호
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• pp.937-946
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• 1995

본 연구에서는 NiCuZn Ferrite 제조공정의 제어를 위하여 제조공정 변수에 따른 NiCuZn Ferrite의 물성 및 자기적특성의 변화를 검토하여, 겉보기밀도(bulk density)와 초기투자율의 관계를 명확하게 하는 것을 목적으로 하였다. $700^{\circ}C$에서 3시간 하소 한 NiCuZn Ferrite를 약 60시간 볼밀링하여 약 $0.5\mu\textrm{m}$ 입자크기로 분쇄한 후 분무 건조하여 과립화하였다. 본 연구에서는 (1)NiCuZn Ferrite 과립의 크기와 성형압력 변화와 (2)일정한 성형조건에서 소성온도의 변화에 따른 성형체 및 소성체의 물성측정, 그리고 자기적 특성을 검토하였다. NiCuZn Ferrite의 green density는 과립의 크기보다는 성형압력에 더 의존하였으며, 과립의 크기가 $150\mu\textrm{m}$ 이하 일 때 성형압력이 증가 함에 따라 green density는 $2.484\;g/cm^{3}$에서 $3.002\;g/cm^{3}$로 크게 증가하 였다. NiCuZn Ferrite의 bulk density는 소성온도에 의하여 거의 직선적으로 $3.470\;g/cm^{3}$에서 $4.754\;g/cm^{3}$로 증가하였다. 성형압력 변화 및 소성온도 변화에 따른 NiCuZn Ferrite 초기투자율과 겉보기밀도 관계를 비교 검토한 결과, NiCuZn Ferrite의 초기투자율($\mu_{i}$)과 겉보기밀도($\rho$)의 관계를 $\mu_{i}=a+b_{\rho}+c_{\rho}^2$와 같이 실험식으로 표현할 수 있었다.

• 한국재료학회지
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• 제3권1호
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• pp.3-6
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• 1993

Gd박막의 강자성-상자성 상전이 온도(Tc)이동을 조사했다. 강자성-상자성 상전이 온도에서 전기저항이 변화되는 변곡점을 관측하여 Tc를 결졍하였는데, 두께가 6600$\AA$인 Gd박막의 상전이 온도는 bulk상태의 Gd의 전이온도보다 4$\pm$0.$3^{\circ}C$정도 아래로 이동됨을 알았다. 이것은 강자성 Gd박막의 Tc이동에 대한 최초의 측정이며, 실험과 finite-sime scaling이론을 비교 분석했다.

• Membrane and Water Treatment
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• 제2권3호
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• pp.159-173
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• 2011

The air gap membrane distillation (AGMD) process was applied for water desalination. The main objective of the present work was to study the heat and mass transfer mechanism of the process. The experiments were performed on a flat sheet module using aqueous NaCl solutions as a feed. The membrane employed was hydrophobic PTFE of pore size 0.22 ${\mu}m$. A mathematical model is proposed to evaluate the membrane mass transfer coefficient, thermal boundary layers' heat transfer coefficients, membrane / liquid interface temperatures and the temperature polarization coefficients. The mass transfer model was validated by the experimentally and fitted well with the combined Knudsen and molecular diffusion mechanism. The mass transfer coefficient increased with an increase in feed bulk temperature. The experimental parameters such as, feed temperature, 313 to 333 K, feed velocity, 0.8 to 1.8 m/s (turbulent flow region) were analyzed. The permeation fluxes increased with feed temperature and velocity. The effect of feed bulk temperature on the boundary layers' heat transfer coefficients was shown and fairly discussed. The temperature polarization coefficient increased with feed velocity and decreased with temperature. The values obtained were 0.56 to 0.82, indicating the effective heat transfer of the system. The fouling was observed during the 90 h experimental run in the application of natural ground water and seawater. The time dependent fouling resistance can be added in the total transport resistance.

• Progress in Superconductivity
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• 제8권1호
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• pp.122-126
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• 2006

This paper presents experimental and numerical investigation on heat generation of a bulk HTS for application to a 100 kWh Superconductor Flywheel Energy Storage System(SFES) bearing. An experimental device is manufactured to reproduce varying magnetic field conditions that a bulk HTS may experience during the operation of the 100 kWh SFES. The bulk HTS is directly cooled by a cryocooler while the heat is generated by the eddy currents created by varying magnetic fields induced by a coil. In order to design the cryocooling system for the 100 kWh SFES project, a preliminary experiment to investigate the actual cooling load variation under AC magnetic field has been carried out. In the experiment, two different copper holders were designed and tested. Several temperature sensors were installed on each component of the assembly and the temperatures were measured for several operating conditions of the 100 kWh SFES. The experimental investigation on the thermal response of the bulk HTS and its holder is considered to be a valuable step fur the successful materialization of a large-scale SFES.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 추계학술대회 논문집
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• pp.356-359
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• 1997

The Effects of different melting temperature and holding time in the melting temperature on J$\sub$c/ of YBa$_2$Cu$_3$O$\sub$x/ based superconducting bulk using MPMG process were investigated. the value of critical current density was the largest at l120$^{\circ}C$, the melting temperature which is appointed to the mid point of (Y$_2$BaCuO$\sub$5/ + Liquid)region. With the melting temperature in which the value of J$\sub$c/ is the largest, J$\sub$c/ was again measured to see whether the holding time at this proper melting temperature has the effect on the critical characteristics. From the result above it was concluded that the melting temperature and holding time were important to improve the J$\sub$c/ and the formation of the Y$_2$BaCuO$\sub$5/. In this paper, the melting temperature obtained was l120$^{\circ}C$ and propel holding time could be obtained as 20 minute and the more holding time was not effective in the J$\sub$c/ improvement as well as the formation of Y$_2$BaCuO$\sub$5/.