• 한국식품과학회지
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• 제24권1호
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• pp.54-58
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• 1992

국내 시판용 옥수수 전분을 시료로 하여 그 호화액의 전분농도와 측정온도에 따른 리올로지 특성을 조사하였다. $4{\sim}9%$ 옥수수 전분 호화액의 리올로지 거동은 Herschel-Bulkley 식에 적합하였고, 항복응력을 갖는 의가소성 유체의 특성을 나타내었다. 전분농도의 증가로 의가소성은 증가하였으나 의가소성의 온도의존성은 보이지 않았고, 겉보기 점도와 항복응력은 모두 지수함수적인 농도 및 온도의존성을 나타내었다. 이들 농도 및 온도에 따른 유동특성을 해석한 결과, 옥수수 면분 호화액에서 졸-겔 전이와 같은 구조적 변화를 일으키는 농도 및 항복응력을 나타내기 시작하는 농도는 각각 $6.22{\sim}6.52%$ 및 $2.6{\sim}6.52%$이었다.

• 공업화학
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• 제19권4호
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• pp.421-426
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• 2008

본 연구에서는 다양한 조성의 다중벽 탄소 나노튜브/폴리스티렌 복합체들을 유화제를 이용한 용액공정을 이용하여 제조하였다. 이때, 분자량이 다른 3종의 폴리스티렌(PS-1 : ${\bar{M}}_n$ = 101500 g/mole, PS-2 : ${\bar{M}}_n$ = 89900 g/mole, PS-3 : ${\bar{M}}_n$ = 85000 g/mole)을 사용하였다. 복합체에서 매트릭스로 사용된 폴리스티렌의 임계흐름온도($T_{cf}{\sim}195^{\circ}C$) 이상과 이하인 $210^{\circ}C$ 및 $180^{\circ}C$에서의 열적 거동을 동적 유변측정기를 이용하여 측정하였다. 복합체의 저장 탄성율, 손실탄성율 및 용융점도는 복합체내에서 다중벽 탄소 나노튜브 함량이 증가함에 따라 증가하였으며, 용융점도의 경우에는 다중벽 탄소 나노튜브 함량이 2 wt%에서 5 wt% 사이에서 가장 큰 증가가 관찰되었다. $210^{\circ}C$의 유변특성 거동에 의하면, 특정 다중벽 탄소 나노튜브 함량에서 복합체의 점성 특성이 탄성특성으로 전이되는 현상이 관찰되었으며, 이때 다중벽 탄소 나노튜브 함량은 MWCNT/PS-1, MWCNT/PS-2 및 MWCNT/PS-3 조성에 대해 각각 3.5 wt%, 3.2 wt 및 3.0 wt%를 나타내었다.

• 한국식품과학회지
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• 제24권4호
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• pp.353-360
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• 1992

유통과정 중 발생가능한 요구르트의 품질변화를 알아보기 위하여 저장온도 (10 & $20^{\circ}C$)와 교반조건(100 & 200 rpm에서 각각 30분간 교반)을 달리한 요구르트의 저장기간에 따른 미생물학적, 물리화학적 및 관능적 특성을 조사하였다. 저장온도가 높고 저장기간이 길어짐에 따라 적정산도와 TCA soluble nitrogen이 증가되었고 pH, 유당 및 유산균 수는 감소되는 경향을 보였으나 교반조건에 따른 변화는 나타나지 않았다. pH, 적정산도 및 유산균 수는 $10^{\circ}C$ 저장시 15일 동안 변화가 없었으나 $20^{\circ}C$ 저장시는 큰 폭으로 감소되었다. 관능검사 결과 저장온도가 높고 저장기간이 길어짐에 따라 신맛은 증가하고 단맛은 감소되었으며 $10^{\circ}C$ 저장시는 15일까지, $20^{\circ}C$ 저장시는 3일까지 저장초기와 차이가 없었다. 이취의 발생은 $10^{\circ}C$ 저장시는 200 rpm으로 교반한 군에서 12일째부터, $20^{\circ}C$ 저장시는 교반조건에 상관없이 6일부터 이취가 발생되어 제품으로서의 가치를 상실하였다. 관능검사에 의한 견고성 평가결과는 consistometer로 측정한 결과와 잘 일치되었는데 200 rpm으로 교반한 경우는 교반하지 않은 군보다 견고성이 유의적으로 낮게 나타났으며, 저장온도가 높고 저장기간이 길어짐에 따라 증가되는 양상을 나타내었다. 이와 같은 결과로 유통과정 중 우수한 품질을 유지하기 위해서는 냉장저장 및 운반시의 충격을 가능한 피하는 것이 바람직하다고 본다.

• Earthquakes and Structures
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• 제26권4호
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• pp.261-267
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• 2024

With the increase in the exploitation depth of offshore oil and gas, it is possible to control the global buckling of deep-sea pipelines by the snake lay method. Previous studies mainly focused on the analysis of critical buckling force and critical temperature of pipelines under the snake-like laying method, and pipelines often suffer structural failure due to seismic disasters during operation. Therefore, seismic action is a necessary factor in the design and analysis of submarine pipelines. In this paper, the seismic action of steel pipes in the operation stage after global buckling has occurred under the active control method is analyzed. Firstly, we have established a simplified finite element model for the entire process cycle and found that this modeling method is accurate and efficient, solving the problem of difficult convergence of seismic wave and soil coupling in previous solid analysis, and improving the efficiency of calculations. Secondly, through parameter analysis, it was found that under seismic action, the pipe diameter mainly affects the stress amplitude of the pipeline. When the pipe wall thickness increases from 0.05 m to 0.09 m, the critical buckling force increases by 150%, and the maximum axial stress decreases by 56%. In the pipe soil interaction, the greater the soil viscosity, the greater the pipe soil interaction force, the greater the soil constraint on the pipeline, and the safer the pipeline. Finally, the pipeline failure determination formula was obtained through dimensionless analysis and verified, and it was found that the formula was accurate.

• 한국식품과학회지
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• 제33권6호
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• pp.686-692
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• 2001

전곡립을 이용한 기능성 식품개발을 위하여 현미, 현미찹쌀, 보리, 현미율무를 온도 $110{\sim}130^{\circ}C$, 수분함량 $15{\sim}25%$, 스크류속도 $200{\sim}300rpm$의 조건에서 압출성형하고, 반응표면분석법(RSM)을 이용하여 최적조건을 분석하였다. 압출공정에 의한 전곡립의 수용화 효과는 수분용해지수(WSI), 농도(수율), 고유점도를 측정하였으며, 수율과 고유점도를 동시에 고려하여 새로운 무차원군의 최적인자인 $([\eta])$를 적용하여 최적조건을 찾고자 하였다. 각 조건별 실험결과를 반응표면분석을 실시하여 본 결과, 종속변수들에 대한 결정계수$(R^2)$는 $0.936{\sim}0.984$ 범위로 나타났다. 현미의 경우에는 수용화 수율, 현미찹쌀은 고유점도, 보리와 현미율무는 수용화 수율과 고유점도에 대해서 모델식이 유의성을 나타내었다. 특히 독립변수 중에서는 수분함량이 가장 큰 영향을 보였다. 최적인자인 $([\eta])$에는 고유점도가 더 큰 영향을 미치므로, 현미의 경우에서는 유의성을 보이지 않았다. 현미의 경우를 제외하고 최적화 인자로 설정한 $([\eta])$의 최적값을 찾기 위하여 회귀분석을 한 결과 임계점은 스크류 속도는 약 300rpm, 수분함량은 20%, 온도는 $120^{\circ}C$인 지점에서 나타났다.

• Tribology and Lubricants
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• 제33권6호
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• pp.269-274
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• 2017

Currently, fuel efficiency becomes one of critical issues for automotive industries as concerns about environmental and energy problems grow. In an automatic transmission of an automobile, a drag torque due to a viscous drag of a fluid between friction and clutch plates is one of factors that degrade fuel economy. In this work, the drag torque characteristics of a wet clutch was experimentally investigated with respect to rotational speed, temperature of automatic transmission fluid (ATF), and gap between friction and clutch plates. The experimental results showed that drag torque increases to a certain level, and then decrease to the steady state value with increasing rotational speed. This behavior may be associated with two-phase flow of air and ATF at gap between friction and clutch plates. Also, it was found that the maximum drag torque value decreased as ATF viscosity decreases with increasing temperature. However, it was shown that the point at which the maximum drag torque occurs was not significantly affected by the ATF temperature. In addition, maximum drag torque was found to decrease as the gap between friction and clutch plates increased from 0.1 mm to 0.2 mm. Furthermore, it was observed that the generation of maximum drag torque was delayed as the gap increased. The outcomes of this work are expected to be helpful to gain a better understanding of drag torque characteristic of a wet clutch, and may therefore be useful in the design of wet clutch systems with improved performance.

• Tribology and Lubricants
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• 제32권1호
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• pp.1-8
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• 2016

This paper focuses on the thermal deformation induced preload change in the tilting pad journal bearing, using a three-dimensional (3D) thermo-hydro-dynamic (THD) approach. Preload is considered as a critical factor in designing the tilting pad journal bearing. The initial preload measured under nil external load and nil thermal gradient is influenced by two factors, namely, the thermal deformation and elastic deformation. Thermal deformation is due to a temperature distribution in the bearing pads, whereas the elastic deformation is due to fluid forces acting on the pads. This study focuses on the changes induced in preload and film clearance due to thermal deformation. The generalized Reynolds equation is used to evaluate the force of the fluid and the 3D energy equation is used to calculate the temperature of the lubricant. The abovementioned equations are combined by establishing a relationship between viscosity and temperature. The heat transfer within the bearing pads, the lubricant, and the spinning journal is calculated using the heat flux boundary condition. The 3D Finite Element Method (FEM) is used in modeling the (1) heat conduction in the spinning journal and bearing pads, (2) thermal gradient induced thermal distortion of the spinning journal and pads, and (3) viscous shearing, and heat conduction and convection in a thin film. This evaluation method has an increased fidelity, and it can prove to be a cost-effective tool that can be used by designers to predict the dynamic behavior of a bearing.

• Steel and Composite Structures
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• 제24권4호
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• pp.399-408
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• 2017

Of high strength bolts, the torque shear type bolt is known to be clamped normally when pin-tails are broken. Sometimes the clamping loads on slip critical connections considerably fluctuate from the required tension due to variation of torque coefficient. This is why the viscosity of lubricant affects the torque coefficient by temperature. In this study, the clamping tests of high strength bolts were performed independently at laboratory conditions and at outdoor environment. The temperatures of outdoor environment candidates were ranged from $-11^{\circ}C$ to $34^{\circ}C$ for six years. The temperature at laboratory condition was composed from $-10^{\circ}C$ to $50^{\circ}C$ at each $10^{\circ}C$ interval. At outdoor environment conditions, the clamping load of high strength bolt was varied from 159 to 210 kN and the torque value was varied from 405 to 556 Nm. The torque coefficients at outdoor environment were calculated from 0.126 to 0.158 when tensions were measured from 179 to 192 kN by using tension meter. The torque coefficients at outdoor environment conditions were analyzed as the range from 0.118 to 0.152. From these tests, the diverse equations of torque coefficient, tension dependent to temperature can be acquired by statistic regressive analysis. The variable of torque coefficient at laboratory conditions is 0.13% per each $1^{\circ}C$ when it reaches 2.73% per each $1^{\circ}C$ at outdoor environment conditions. When the results at laboratory conditions and at outdoor environment were combined to get the revised equations, the change in torque coefficient was modified as 0.2% per each $1^{\circ}C$ and the increment of tension was adjusted as 1.89 % per each $1^{\circ}C$.

• 한국분말재료학회지
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• 제24권3호
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• pp.223-228
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• 2017

Nanopowders provide better details for micro features and surface finish in powder injection molding processes. However, the small size of such powders induces processing challenges, such as low solid loading, high feedstock viscosity, difficulty in debinding, and distinctive sintering behavior. Therefore, the optimization of process conditions for nanopowder injection molding is essential, and it should be carefully performed. In this study, the powder injection molding process for Fe nanopowder has been optimized. The feedstock has been formulated using commercially available Fe nanopowder and a wax-based binder system. The optimal solid loading has been determined from the critical solid loading, measured by a torque rheometer. The homogeneously mixed feedstock is injected as a cylindrical green body, and solvent and thermal debinding conditions are determined by observing the weight change of the sample. The influence of the sintering temperature and holding time on the density has also been investigated. Thereafter, the Vickers hardness and grain size of the sintered samples have been measured to optimize the sintering conditions.

• 한국응용과학기술학회지
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• 제10권2호
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• pp.81-90
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• 1993

The Surfactants composed of acylated aterocollagen which is produced by the acylation of the side chain amino radicals of aterocollagen with an aliphatic acid having 12 to 18 carbon atoms will be discussed in this study. This condensation is done at moderate reaction temperature (<$25^{\circ}C$) in aqueous alkaline solution. The products of this reaction were identified by UV/VIS spectroscopy and infrared spectroscopy. For these compounds, surface active properties and physical properties including isoelectric point, Krafft point, surface tension, critical micelle concentration(cmc), foaming power, viscosity behaviour, water holding capacity, skin irritation and emulsifying power were measured respectively. The experimental results received that the products have a good emulsifying power, excellent water holding capacity while having low skin irritation. Thus, these derivatives will be expected to be used as an emulsifying agent for O/W type cosmetic emulsion.