• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.49-52
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• 2009

The response times of monopropellant thrusters at a pulse mode were investigated experimentally as design parameters and feed pressure conditions. Five different model thrusters as injection direction/uniformity, aspect ratio of reactor, volumes of manifold and chamber were designed. As a results, two parameters, aspect ratio and manifold volume, were directly related to response characteristics. Additionally, chugging instability at reaction chamber was observed when pressure drop across the catalyst bed was increased due to high aspect ratio or when low pressure was built at reaction chamber.

• Journal of Biomedical Engineering Research
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• v.20 no.5
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• pp.587-592
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• 1999

압력측정시스템은 입각기동안 동적압력분포를 성공적으로 측정할 수 있으나 하중수용기-중간입각기, 말기입각기-전유각기의 전환기들에 대해서는 운동분석시스템을 사용하지않고는 정확한 정의가 불가능하다. 따라서 저자들은 수평자유보행 시 압력중심의 이동을 이해하기 위해서 정상적인 발을 가진 20-30대 성인남자 78명을 대상으로 동작분석과발바닥 압력측정을 동시에 수행하였다. 결과로 하중반응기-중간입각기 전환시기의 발바닥 압력중심점은 후족부와 중족부의 경계선에서 앞쪽으로 1.9$\pm$1.5frame(32$\pm$24msec)에 위치하였으며 말기입각기-전유각기 전환시기에는 중족골두 최대 압력점의 앞쪽으로 2.3$\pm$2.0 frame(38$\pm$33msec)에 위치하였다. 정상수평보행에 있어서 최초접지 순간 압력중심은 전방으로 빠르게 이동하다가 바로 급속히 감소하여 하중반응기-중간입각기의 전환시기에는 작은 속도로 이동하였다. 압력중심의 이동속도는 그 후 다시 서서히 증가하다가 전체 보행주기의 25% 전후에서 서서히 감소하여 비교적 일정하다가 말기입각기-전유각기의 전환시점에서 다시 급격한 증가를 보였다. 족부질환과 보행특성을 판단하는데 있어서 압력중심의 이동궤적은 매우 유용한 인자가 될 것으로 기대된다. 본 연구를 통해서 압력측정시스템만으로는 정의할 수 없었던 두 전환기인 하중반응기-중간입각기, 말기입각기-전유각기를 결정할 수있게 되었다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.39.1-39.1
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• 2009

본 실험은 연성과 광 투명도가 뛰어난 아크릴 (PMMA) 과 폴리카보네이트 (Polycabonate) 기판의 축전 결합형 플라즈마 (CCP) 건식 식각 연구에 관한 것이다. 특히 식각 반응기 내부의 압력 변화에 따른 두 기판의 건식 식각 특성 분석에 초점을 맞추었다. 실험에 사용된 기판은 두께 1mm의 아크릴 (PMMA) 과 폴리카보네이트 (Polycabonate)를 $1.5\times1.5\;cm^2$로 절단하여 Photo-lithography 공정을 통하여 감광제 (Photo-resist)로 패턴하였다. 식각 반응기 내부에 패턴 된 아크릴(PMMA) 과 폴리카보네이트 (Polycabonate)를 넣은 후 반응기 내부 진공 상태로 만들었다. 그 후 5 sccm $O_2$ 가스를 유량조절기 (Mass flow controller)를 통하여 식각 반응기 내부로 유입하여 실험을 하였다. 이때 식각 공정 변수는 식각 반응기 내부 압력과 샘플 척 파워이다. 특성평가 항목은 식각 후 기판 (Substrate)의 식각율 (Etch rate), 식각 선택비 (Selectivity) 그리고 기판 표면 거칠기 (RMS roughness)이다. 실험 결과는 표면 단차 분석기(Surface profiler)를 이용하여 기판 (Substrate)의 표면을 분석 하였다. 또한 OES (Optical Emission Spectroscopy) 를 이용하여 식각 중 내부 플라즈마의 상태를 분석하였다. 본 실험 결과에 따르면 5 sccm $O_2$ 가스와 100 W 척 파워를 고정한 후 반응기 내부의 압력을 25 mTorr에서 180 mTorr까지 변화시켜 실험한 결과 40 mTorr의 반응기 내부 압력에서 실험 자료 중 가장 높은 식각율로 아크릴 (PMMA)은 $0.46\;{\mu}m/min$, 폴리카보네이트 (Polycabonate)는 $0.28\;{\mu}m/min$의 결과를 얻었다. 또한 이 자료를 바탕으로 5 sccm $O_2$ 가스와 반응기 내부 압력을 40 mTorr로 고정시키고 RIE 척 파워를 25 W에서 150 W로 증가시켰을 때 아크릴 (PMMA)의 식각율은 $0.15\;{\mu}m/min$에서 $0.72\;{\mu}m/min$까지 증가하였고, 폴리카보네이트 (Polycabonate) 의 식각율은 $0.1\;{\mu}m/min$에서 $0.36\;{\mu}m/min$까지 증가하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.117-120
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• 2011

The parameters which can affect the performance of small thruster were verified by experiments. The loss of catalyst through the port for pressure sensor was prevented by chamber wall mesh. There was no performance decrease due to chamber wall mesh, and stable supply of propellant is the key of stability of the thruster. However, sudden pressure drop in the chamber can decrease the performance instantly. Therefore, the sudden pressure drop should be eliminated as much as possible. The cross type distributor showed more stable performance than circular type, and structural strength is also stronger.

• Journal of the Korean Ceramic Society
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• v.41 no.9
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• pp.703-708
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• 2004

The variation of the reaction pressure and reaction product during the reaction was investigated according to the total mass of the reaction mixture at the optimum composition for the preparation of u-Si3N4 powder which had been confirmed in the former investigation; 'Preparation of $\alpha$-Si$_3$N$_4$ powder in reaction system containing molten salt by SHS - part 1. synthesizing of powder'. When the total mass of the reaction mixture was 100g, the minimum pressure for a complete reaction was 60atm in 5L reactor, whereas the reaction was incomplete in the case that the mass exceeded 200g because of pressure increase. Also, as the mass of the reaction mixture increased, the reactivity linearly decreased. Hence, the complete reaction was realized by decreasing an initial $N_2$ pressure, and thus obtained minimum initial pressure was recorded 20 atm for the initial mixture of 500g. The reason of the incomplete reaction with pressure Increase was found to be that NH$_4$Cl vapour which was suppressed by the gas pressure acted as a diluent.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.116-124
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• 2022

In this study, waste air containing ethanol and hydrogen sulfide, was treated by an integrated hybrid system composed of two alternatively-operating UV/photocatalytic reactor-process and biofilter processes of a biofilter system having two units with an improved design (R reactor) and a conventional biofilter (L reactor). Both a pressure drop (△p) per unit process of the integrated hybrid system and a microbe-population-distribution of each biofilter process were observed. The △p of the UV/photocatalytic reactor process turned out very negligible. The △p of the L reactor was observed to increase continuously to 4.0~5.0 mmH₂O (i.e., 5.0~6.25 mmH₂O/m). In case of R reactor, its △p showed the one below ca. 16~20% of the △p of the L reactor. Adopting such microbes-carrying biofilter media with high porosity as waste-tire crumb media, and the improved biofilter design, contributed to △p of this study, reduced by ca. 37~50% and 40~53%, respectively, from the reported △p of conventional biofilter packed with biofilter media of the mixture (50:50) of wood chip and wood bark. In addition, the △p of R reactor in this study, reduced by ca. 80% from the reported △p of conventional biofilter packed with biofilter media of the mixture (75:25) of scoria with high porosity and compost, was mainly attributed to adopting the improved biofilter design. On the other hand, in case of L reactor, the CFU counts in its lowest column was analyzed double as much as those in any other columns. However, in case of R reactor, its CFU counts were bigger by 50% than the one of L reactor and its microbes were evenly distributed at its higher and lower columns of R_dn reactor and R_up reactor. This phenomena was attributed to an even moisture distribution of 50~55% of R reactor at its higher and lower columns. Therefore, R reactor showed superb characteristics in terms of both △p and microbe-population-distribution, compared to L reactor.

• Proceedings of the KAIS Fall Conference
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• 2010.05b
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• pp.1237-1240
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• 2010

본 연구에서는 유동층반응기를 이용하여 왕겨의 탄화반응을 수행하였다. 탄화반응은 내경 40mm, 높이 1.8m의 유동층을 사용하였으며, 분산판은 다공성 스테인레스스틸을 사용하였다. 탄화반응은 질소를 이용하여 수행하였다. 왕겨 주입입자 크기는 직경 2.0mm, 0.715mm, 0.359mm, 0.194mm를 각각 사용하였으며, 유동층의 온도는 $400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, $700^{\circ}C$에서 탄화특성을 측정하였다. 또한 유동층의 매질로는 직경 1.0mm의 Co-Mo-Fe/$Al_2O_3$ 촉매를 사용하였으며, 탄화물은 유동층상부에 설치된 사이크론에 의하여 포집분리되었다. 탄화시 유동층 내부의 현상을 압력요동을 이용하여 해석하였으며, 압력신호로부터 평균압력, 압력요동의 표준편차, 주진동수, power spectrum density function을 계산하여 층내현상을 해석하였다. 층내온도, 유동화속도, 공급 입자크기에 따른 층내현상을 압력요동특성치를 이용하여 해석할 수 있었다.

• Korean Chemical Engineering Research
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• v.58 no.2
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• pp.307-312
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• 2020

Fluidized bed reactors operated in subatmospheric pressure has been focused because several industrial applications such as vacuum drying and plasma cvd requires reduced pressure fludization. However, the hydrodynamics of fluidized beds in subatmospheric pressure has not been extensively investigated. The pressure drop in the fluidized bed has been measured with variation of downstream pressures from 1.33 to 101.3 kPa in the shallow and deep fluidized beds under the sub-atmospheric pressures. The obtained minimum fluidization velocity of powders is a function of pressure due to the changes of gas density and mean free path. We can experimentally determine the critical Knudsen number and the critical pressure to define the slip regime significantly to influence the hydrodynamics of fluidized beds.

• Journal of the Korean Institute of Gas
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• v.8 no.3 s.24
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• pp.16-23
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• 2004

A membrane reactor concept, which combines the typical characteristics of chemical reaction with separation process, has been analyzed and simulated in this study. The advantages of the use of a membrane reactor include chemical equilibrium shift towards higher reactant conversion and purer product than the traditional reactors. A membrane reactor model which incorporates a catalytic reaction zone and a separation membrane is proposed. The water-gas shift reaction to produce hydrogen was chosen as a model reaction to be investigated. The membrane reactor is divided into smaller parts by number of n and each part (named cell), which contains both reaction and product separation function is modeled. One of the membrane outlet streams is connected to the next cell, which is repeated up to the last cell. The simulation results can be used for various purposes including decision of optimum operating condition and membrane reactor design.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.6
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• pp.381-387
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• 2017

Dehydrogenation from the hydrolysis of a sodium borohydride ($NaBH_4$) solution has been of interest owing to its high theoretical hydrogen storage capacity (10.8 wt.％) and potentially safe operation. An experimental study has been performed on the catalytic reaction rate and pressure drop of a $NaBH_4$ solution over both a single microchannel with a hydraulic diameter of $300{\mu}m$ and a staggered array of micro pin fins in the microchannel with hydraulic diameter of $50{\mu}m$. The catalytic reaction rates and pressure drops were obtained under Reynolds numbers from 1 to 60 and solution concentrations from 5 to 20 wt.％. Moreover, reacting flows were visualized using a high-speed camera with a macro zoom lens. As a result, both the amount of hydrogenation and pressure drop are 2.45 times and 1.5 times larger in a pin fin microchannel array than in a single microchannel, respectively.