• Applied Chemistry for Engineering
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• v.19 no.3
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• pp.295-298
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• 2008

In the reactor for the american standard test method (ASTM) D5757-95 with swirl injection nozzles, the attrition characteristics of sand was investigated. The change of particle size distribution and weight of fine particles were compared to identify the effect of swirl injection nozzle on attrition. The fine particles due to particle attrition increased with increasing gas velocities. The weight of fine particles due to jet attrition was changed with angle of swirl injection nozzle. The fine particles decreased with decreasing the angle of swirl injection nozzle. Also, the change of particle size distribution increased with increasing the number of swirl injection nozzles at the same flow rate.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.816-821
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• 1997

The hydrodynamics and the liquid flow characteristics were investigated in an internal circulation airlift reactor with a single nozzle as a gas distributor. In an air-water system, the gas holdup in the individual flow zone and the impulse-response curve of tracer were measured at various gas velocities and reactor heights. Experimental results showed that for the higher gas velocity(>about 8 cm/s), the flow behavior of bubbles in the riser was turbulent flow due to strong bubble coalescences and the axial height of dispersion zone of large bubbles having uniform sizes in the downcomer was decreased with increasing gas velocity. And mean gas holdups in the individual flow zone and the reactor were increased with increasing gas velocities and were decreased with increasing heights of the top section of the reactor and it was decreased with increasing the height of the top section and gas velocity. Flow characteristics of liquid in the riser and the downcomer was tend to access to plug flow and the overall flow behavior of liquid was mainly varied with the size of the top section which it was assumed to be perfect mixing zone. In these conditions, liquid circulation velocities were increased with increasing gas velocities and they were higher than those by using other gas distributors.

• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.459-464
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• 2009

Gas-liquid mass transfer characteristics were investigated in pressurized three-phase slurry bubble columns with variation of column diameter. Effects of gas velocity, operating pressure, liquid viscosity, solid content in the slurry phase and column diameter on the gas-liquid volumetric mass transfer coefficient($k_La$) were determined. The effects of operating variables on the mass transfer coefficient tended to change with variation of column diameter. The mass transfer coefficient increased with increasing gas velocity or operating pressure but decreased with increasing column diameter, liquid viscosity or solid concentration in the slurry phase. The increase trend of $k_La$ value with increasing gas velocity and the decrease trend of $k_La$ value with increasing liquid viscosity, tended to decrease gradually with increasing column diameter. However, the effects of operating pressure and solid concentration in the slurry phase on the $k_La$ value did not change considerably with variation of column diameter. The values of $k_La$ were well correlated with operating variables with in this experimental conditions as $k_La=0.02D^{-0.26}U_G^{0.28}P^{0.43}{\mu}_L^{-0.04}S_c^{-0.35}$.

• Journal of the Korean Chemical Society
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• v.43 no.5
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• pp.564-577
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• 1999

The purpose of this study is to help an improvement of conceptional learning about the properties of gas based on molecular kinetics for secondary school students and to help an improvement of teaching method for reducing misconceptions regarding the molecular kinetics in gas phase for teachers. The subjects of this study were l00 students of 9th grade and 150 students of 11th grade students. The results showed that students had various misconceptions about the properties of gas. The major misconceptions are as follows. First, the energy is released due to the collision of the molecules, and also the direction of action of pressure is related to the direction of gravity. Second, as molecule is heated, the size of molecule is increased, and the molecule is more active because the number of moIecules is increased. Third, the pressure is reduced because of decreasing the temperature at the higher altitude and the pressure of gas molecuIes is inversely proportional to the collision number of gas molecules. Forth, the numbers of molecules of two different molecules in two same containers differ because the size of molecules differ each other. The results suggest that these problems ought to be addressed in chemistry textbooks and in the classroom teaching of chemistry. If teachers are more aware of students' misconceptions they wilI be better able to remove them.

• Membrane Journal
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• v.12 no.2
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• pp.107-119
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• 2002

Carbon-silica ($C-SiO_2$) membranes can be easily prepared by the pyrolysis of two-phase copolymers containing an aromatic imide block and a siloxane block and remarkably high permselectivities of $He/N_2, O_2/N_2,$ and $CO_2/N_2$. The pyrolysis of the imide-siloxane block copolymers was carried out at different final temperatures, $600^{\circ}C, 800^{\circ}C,$ and $1000^{\circ}C$ under an inert atmosphere, and is the first reported case of the precursors being used for the preparation of carbon membrane. The polymeric precursors were synthesized in a wide range of siloxane content and different final morphology, and the pyrolozed membranes were tested with a high vacuum time-lag method at $25^{\circ}C$ and 76cmHg of feed pressure. In experiments with He, $CO_2, O_2 \;and \;N_2$, the membranes were found to have good $O_2/N_2$ selectivity up to 32.2 and $O_2$ permeability on the order of $10-8/cm^2(STP)cm/cm^2seccmHg.$.

• Journal of the Korean Electrochemical Society
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• v.10 no.4
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• pp.306-310
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• 2007

Characteristics of GDL (Gas Diffusion Layer) mainly determine the gas diffusion and water removal in a cell, thereby changing the performance and affecting durability of PEFC. To optimize the water management and understand the two phase flow in a GDL, it is important to study the behaviors of GDL micro structure under the real operating condition. In the clamped condition of cell, the GDL beneath the rib is more compressed than beneath the channel. Many researches on physical, electrochemical, mechanical behaviors of gas diffusion layer has been conducted. However, changes in surface properties under clamped condition have rarely studied. In present study, the morphology of broken connections of carbon fibers and detachment of PTFE coatings on the fibers were shown from the microscopic observations. In addition, changes in wetting properties of GDL by compression were investigated by using XPS and liquid uptake methods. The hydrophobic characteristics of GDL surface beneath the rib of the flow field plate are changed due to the deformation of micro structure.

• Applied Chemistry for Engineering
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• v.21 no.2
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• pp.205-210
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• 2010

In this study, a brass electrode gas discharge tube (GDT) was prepared to investigate its discharge characterization, which affects surge protection efficiency and lifetime of GDT. Discharge characterization of GDT using a brass electrode was investigated by changing applied voltage gradient and nitrogen gas pressure inside the GDT. As applied voltage gradient in GDT increased, electrical breakdown voltage and threshold energy largely increased and electrical breakdown time delay decreased. It was found that electrical breakdown voltage, electrical breakdown time delay, and threshold energy were largely decreased with decreasing the nitrogen gas pressure in GDT. As a result, electrical breakdown voltage, electrical breakdown time delay, threshold energy needed to be decreased to increase surge protection efficiency and lifetime. It was also found that the nitrogen gas pressure of GDT influenced strongly the performances as well as life span of it.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.71.1-71.1
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• 2010

고분자 전해질 연료전지(PEMFC) 내의 기체확산층(GDL)은 셀 내의 물 관리에 중요한 역할을 수행한다. 일반적으로 다공성 기제(GDBL) 위에 미세기공층(MPL)을 코팅한 2층 구조의 기체확산층이 사용되는데, 이 미세기공층은 카본파우더와 테프론의 혼합물로 이루어져 있으며 촉매층에서 발생한 물을 셀 밖으로 빠르게 배출하는 역할을 수행한다. 본 연구에서는 다양한 기공분포를 갖는 미세기공층을 제조하여 고분자 전해질 연료전지 성능에 미치는 영향을 분석하였다. 미세기공층 슬러리내에 암모늄염 계열의 기공형성제를 혼합하여 다공성 기제 위에 코팅한 후 다양한 온도조건에서 건조함에 따라 기공분포가 다른 미세기공층을 제조하였다. 이렇게 제조된 미세기공층의 물성은 수은기공도계, FE-SEM, 자체적으로 제조한 기체투과도 측정 장치를 사용하여 측정하였으며, 단위 전지 성능 측정은 두 개의 가습조건(RH100%, RH50%)에서 실시하였다. 기공분포 측정결과 건조온도가 높은 미세기공층은 건조온도가 낮은 미세기공층에 비해 직경이 1,000 - 20,000 nm 인 대공극(macropore)의 수가 많지만, 직경이 100 nm 이하의 미세공 (micropore)의 수가 적은 것을 확인하였다. 전지성능 측정 결과 고가습 조건 (RH100%)에서는 미세공 (micropore)이 발달한 미세기공층을 포함한 기체확산층을 사용한 경우 가장 우수한 성능을 보여고, 저가습 조건 (RH50%)에서는 대공극 (macropore)이 발달한 미세기공층을 포함한 기체확산층을 사용한 경우 가장 우수한 성능을 나타내었다. 이는 물배출에 유리한 미세공 (micropore)의 성질과 원료 기체의 이동에 유리한 대공극(macropore)의 성질에 의한 것으로 판단된다. 따라서 셀 운전 가습조건에 따라 최적화된 기공구조를 갖는 미세기공층을 사용함으로써 셀 운전 성능을 향상 시킬 수 있을 것으로 예상된다.

• Korean Journal of Agricultural and Forest Meteorology
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• v.9 no.3
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• pp.170-178
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• 2007

Rapid increases in the concentrations of greenhouse gases and many other chemically important trace gases have occurred over the last several centuries. For understanding the roles of these important gases in global change, it is essential to identify their sources and sinks, to characterize biogenic gas fluxes between the biosphere and atmosphere, and to understand the processes that control them. In this paper, enclosure-based measurements are described in a practical manner for field experiments. Theoretical reviews of mass balance equation in the enclosure and sensitivity of the flow-through dynamic flux chamber technique are presented; specifically for the case of NO flux measurements from soil surface. The physical system and theory behind the flow-through dynamic flux chamber method are examined. New calculation flux formula was introduced by considering NO chemical loss on chamber wall and uncertainties of the NO flux calculation were discussed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6412-6418
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• 2014

This paper performed a numerical study of an air-liquid ejector. An ejector is a fluid-transportation device that spouts high-pressure fluid from driving pipes using the kinetic energy of the spouted fluid and increases the pressure through the exchange of momentum with the surrounding gases of the lower pressure. The air-liquid ejector was investigated through steady three-dimensional multiphase CFD analysis using commercial software ANSYS-CFX 14.0. Water as the primary fluid is driven through the driving nozzle and air is ejected as the second gas instead of ozone in real applications. The difference in performance according to the shape of the diffuser of the ejector was examined. The results provide deep insight into the influence of various factors on the performance of the air-liquid ejector. The proposed numerical model will be very helpful for further design optimization of the air-liquid ejectors.