• 대한기계학회논문집B
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• 제21권4호
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• pp.509-517
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• 1997

Results of flat plate compressible boundary layer calculation, based on discrete formulation of DSMC method, are presented in low Mach number and low Knudsen number range. The free stream is a uniform flow of pure nitrogen at various Mach numbers in low pressures (i.e. rarefied gas). Complete thermal accommodation and diffuse molecular reflections are used as the wall boundary condition, replacing unreal no-slip condition used in continuum calculations. In the discrete formulation of DSMC method, there is no need to use ad hoc assumptions on transport properties like viscosity and thermal conductivity, instead viscosity is calculated from values of other field variables (velocity and shear stress). Also the results are compared with existing self-similar continuum solutions. In all Mach number cases computed, velocity slip is most pronounced in regions near the leading edge where continuum formulation renders the solution singular. As the boundary layer develops further downstream, velocity slips asymptote to values that are between 10 to 20% of the magnitude of free stream velocity. When the free stream number density is reduced, so the gas more rarefied, the velocity slip increases as expected.

• 펄프종이기술
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• 제47권5호
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• pp.23-32
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• 2015

In this study, chemical and physical changes of dissolving pulps which have similar viscosity by dry milling and fractionation were investigated. We used two types of dissolving pulp made from wood and cotton linter fiber, respectively. Dry milling was executed by knife cutter and pulp powders were fractionated by sieve shaker into 4 grades. We analyzed fiber properties, crystallinity index, viscosity, molecular weight of pulp sheet and powders. It was found that poly-dispersity index of cotton linter pulp was smaller than that of wood pulp, meaning that cotton pulp has more narrow molecular weight distribution. It was assumed that these were related to exposure times to chemical treatment which cut cellulose chains not evenly. At least 4 times of chemical treatments for wood pulp were executed and only two times of chemical treatments for cotton linter pulp were done. After dry milling average molecular weight and crystallinity index of cotton linter pulp powders were reduced and these were related to fines content and shape of pulp powders.

• Journal of the Korean Wood Science and Technology
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• 제26권1호
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• pp.29-37
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• 1998

Alkali-soluble extracts were prepared from medium-sized barks of Radiata pine(Pinus radiata). There are difficulties in the production of extracts with uniform quality and in the preparation of adhesives with suitable viscosity. Ultrafiltration using an Amicon cell was subjected to fractionate extracts according to molecular sizes in order to overcome the above problem. The filtration efficiency was studied by using thin channel filtration systems. Adhesive manufacturing was also examined. Removal of particles greater than 0.45m from the extracts increased both filtration speed (flux) and yields of solids in the filtrates. Ultrafiltration with PM 10 membrane was very effective to fractionate and concentrate the extracts. Stiasny precipitates from the filtrates obtained by PM 10 membrane were very lower than that(83%) of the retentates. This ultrafiltration method was efficient for obtaining high yield purified phenolic compounds(mainly polyflavanoids) and thus important for preparing wood adhesives from barks. The extracts were shown excessive high viscosities at the concentrations required for adhesive formulation, but this high viscosity and short gelation time was reduced by lowering pH of the extracts and addition of urea. The highest bonding strength of plywoods(340g/$m^2$ of adhesive spreads) was achieved with adhesive formulated by 100parts of mixed alkali extracts and urea(70/30,w/w), 10parts of p-formaldehyde and 3.5parts of wheat flour at pH 6, and by hot pressing at the conditions of 12kg/$cm^2$ at $120^{\circ}C$ for 10 minutes.

• International Journal of Automotive Technology
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• 제4권2호
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• pp.95-100
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• 2003

Automobile industry has been developed rapidly as a key manufacturing industry in Korea. Meanwhile, air pollution is getting worse noticeably than ever. In the diesel emission, PM (Particulate Matter) and NOx (Nitrogen Oxides) have been exhausted with a great amount and the corresponding emission regulations are getting stringent. In order to develop low emission engines, it is necessary to research on better qualified fuels. Sulfur contained in fuel is transformed to sulfur compound by DOC (Diesel Oxidation Catalyst) and then it causes to the increase of sulfate-laden PM on the surface of catalyst. In this research, ULSD (Ultra Low Sulfur Diesel) is used as a fuel and some experimental results are investigated. ULSD can reduce not only PM but also gas materials because cetane value, flash point, distillation 90%, pour point and viscosity are improved in the process of desulfurization. However, excessively reduced sulfur may cause to decease lubricity of fuel and engine performance in fuel injection system. Therefore, it requires only modest adjusted amount of sulfur can improve engine performance and DOC, as well as decrease of emission.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2013년도 춘계 학술논문 발표대회
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• pp.305-307
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• 2013

In this paper, we test and evaluate in terms of workability the epoxy resin mortar and the EVA powder resin mortar used on the concrete structures. The initial viscosity of the epoxy resin mortar is lower than the EVA powder mortar, but after 20 minutes work can not be rapidly increased to 40 minutes. In the other hand, the EVA powder resin mortar is able to measure of viscosity for the past 40 minutes. In the flow test for evaluate workability, the flow of the epoxy resin mortar is rapidly decreased from 230 to 100 in the 90 minutes, but the flow of the EVA powder resin mortar is reduced to 198 to 175 that there is no significant change. In the coverage test of the pinhole on the concrete surface, the EVA powder mortar appears coverage in the all pinhole size but the epoxy resin mortar is not concealed from 2mm pinhole size.

• 한국식품과학회지
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• 제18권3호
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• pp.241-244
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• 1986

홍미삼을 추출하여 홍삼엑기스를 제조할 때 추출용매인 에탄올의 농도와 추출온도, 그리고 시간이 홍삼엑기스의 물리적 성질에 미치는 영향을 비교조사 하였다. 홍삼엑기스의 고유점도(固有粘度)는 에탄올의 농도가 증가함에 따라 현저히 감소되었고 추출온도의 상승과 추출시간외 경과에 따라 다소 증가되는 경향이었으나 그 폭은 크지 않았다. 한편 측정온도의 상승은 고유점도를 크게 감소시키나 에탄올 농도가 50% 이상되면서 그 감소폭은 현저히 줄어들었다. 홍삼엑기스의 탁도와 pH는 에탄올의 농도 증가와 추출시간의 결과에 따라 낮아졌고 온도 상승에서는 큰 차이가 없었다.

• 한국기계가공학회지
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• 제20권12호
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• pp.123-128
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• 2021

Liquid dispensing systems are extensively used in various industries such as display, semiconductor, and battery manufacturing. Of the many types of dispensers, drop-on-demand piezoelectric jetting systems are widely used in semiconductor industries because of their ability to dispense minute volumes with high precision. However, due to the problems of nozzle clogging and undesirable dispensing behavior in these dispensers, which often result in device failure, the use of highly viscous fluids is limited. Accordingly, we studied the behaviors of droplet formation based on changes in viscosity. The effects of surface energy and the inner diameters of needle-type nozzles were also studied. Results showed that nozzles with lower surface energies reduced the ejection volume of droplets when a smaller nozzle diameter (0.21 mm in this study) was applied. These results indicate that the hydrophobic treatment of nozzle surfaces and the use of smaller nozzle diameters are critical factors enabling the use of highly viscous fluids in precision dispensing applications.

• Geomechanics and Engineering
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• 제34권3호
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• pp.221-231
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• 2023

Biopolymer stabilization is a sustainable alternative to traditional techniques that cause a lesser negative impact on the environment during production and application. The study aims to minimize the biopolymer dosages by sizing the bio-additives to the nanoscale. This study combines the advantages of bio and nanomaterials in geotechnical engineering applications and attempts to investigate the behaviour of a low viscous biopolymer, nano sodium carboxymethyl cellulose (nCMC), to treat organic soil. Soil is treated with 0.25%, 0.50%, 0.75% and 1.00% of nano-bio additive, and its effect on the plastic behaviour, compaction characteristics, strength, hydraulic conductivity (HC) and compressible nature are investigated. The strength increased by 1.68 times after 90 days of curing at a dosage of 0.5% nCMC through the formation of gel threads connecting the soil particles that stiffened the matrix. The viscosity of 1% nCMC increased exponentially, deterring fluid flow through the voids and reduced the HC by 0.85 times after curing for 90 days. Also, beyond the optimum dosage of 0.50%, the nCMC forms a film around the soil particles that inhibits the inter-particle cohesion causing a reduction in strength. Experimental results show that nCMC can effectively substitute conventional additives to stabilize the soil.

• Applied Biological Chemistry
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• 제32권4호
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• pp.327-331
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• 1989

염소 처리량에 따른 박력분의 백도 및 pH 그리고 리올로지 특성에 미치는 영향에 대해 실험하였다. 염소 처리한 것과 무처리한 박력분의 표백의 정도는 처리량이 2 oz./cwt.까지 표백효과가 있었으나 그 이상부터는 표백효과가 없었고, pH는 처리량 증가에 따라 점차적으로 낮아졌다. Farinogram 특성에서 염소처리량 증가에 따라 흡수율과 반죽의 안정도가 높아진 반면에 MTI값은 감소하였으며, valorimeter value는 일정하지 않았다. Extensogram 특성에서 저항도, 최대저항도 및 신장저항도는 90분과 135분 동안 방치했을때 무처리한 것이 가장 컸으며, 처리량 1 os./cwt.인 것이 가장 낮았으나 2 oz./cwt. 처리의 경우 그 값이 다시 증가하는 경향을 나타냈다. Amylogram의 최고점도와 최고점도시 온도는 처리량 증가에 따라 점증적으로 상승하였으며, 특히 4 oz./cwt. 처리의 경우 최고 점도가 1,160BU로 급격히 상승하였다.

• 한국항공우주학회지
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• 제35권8호
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• pp.720-725
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• 2007

분사기형 배플이 설치된 연소기에 대하여 최적의 감쇠를 가지는 간극을 상온음향시험을 통하여 규명하였다. 먼저 상온 상압의 조건에서 배플의 간극에 따른 음향학적 특성을 파악하였다. 최적의 감쇠능력을 가지는 간극이 배플의 길이에 상관없이 일정하게 존재함을 발견하였다. 이런 현상의 주된 인자를 파악하기 위하여 연소 상황에서의 유체의 점성을 모사하는 상온 상태의 음향시험을 수행하였다. 이를 통하여 최적의 간극이 발생하는 이유가 점성 때문임을 밝혔다. 최적의 간극은 실제 연소기에서 배플의 길이를 감소시킬 수 있으므로 냉각 문제를 해결할 수 있는 하나의 방안으로 사용될 수 있을 것이다.