• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.32-40
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• 2002

The study of nonlinear gas transport in rarefied condition or associated with the microscale length of the geometry has emerged as an interesting topic in recent years. Along with the DSMC method, several fluid dynamic models that come under the general category of the moment method or the Chapman-Enskog method have been used for this type of problem. In the present study, on the basis of Eu's generalized hydrodynamics, computational models for diatomic gases are developed. The rotational nonequilibrium effect is included by introducing excess normal stress associated with the bulk viscosity of the gas. The new models are applied to study the one-dimensional shock structure and the multi-dimensional rarefied hypersonic flow about a blunt body. The results indicate that the bulk viscosity plays a considerable role in fundamental flow problems such as the shock structure and shear flow. An excellent agreement with experiment is observed for the inverse shock density thickness.

• Korean Journal of Food Science and Technology
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• v.15 no.4
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• pp.392-398
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• 1983

A pilot single-screw food extruder was constructed, and its mechanical properties and product characteristics were investigated by using corn grits. The screw rotational speed was varied and the changes in temperature profile of the barrel for the start-up period of operation were measured. The rate of heat generation for the start-up period was affected by the screw speed and feed rate. The screw speed resulted in a great influence on the estimated dough viscosity. The changes in the dough viscosity could indicate the on-set of termoplastic reaction in the barrel. The expansion ratio during the start-up period mainly depended on the barrel temperature and the degree of thermoplastic reaction in the barrel. The barrel temperatures for the gelatinization and burning of corn grits depended on the screw speed as well as the feed rate.

• Journal of Adhesion and Interface
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• v.16 no.1
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• pp.15-21
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• 2015

In this study, rheological properties and flow dynamics in roll coating process of basecoat paints have been investigated for automotive precoated metal (PCM) sheet applications. Various rheological properties for basecoats with three colors (black, blue, and silver), such as shear viscosity data at room temperature and elastic/viscous moduli under thermal curing condition, have been measured using a rotational rheometer. It is found that the relative portion of function groups inside basecoats and their viscosity level have greatly affected the formation of crosslinked networks by thermal curing. Also, operability coating windows for basecoats have been established in three-roll coating process system by observing their flow instabilities such as ribbing and cascade. It is confirmed that rheological approaches applied in this study have been usefully applied to develop environmentally-friendly PCM coating technology and optimally control the coating operations for non-Newtonian PCM paints.

• Korean Journal of Food Science and Technology
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• v.33 no.2
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• pp.221-225
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• 2001

Flow properties of red flower cabbage pigment solutions were determined over a wide range of temperatures ($20-50^{\circ}C$) and soluble solid concentrations (1-65%) using a cone and plate rotational viscometer. Flow properties of the pigment solutions were adequately described by the simple power law model. Within the tested ranges of concentration, temperature and shear rate, the flow behavior index (n) and the consistency index (K) of the solutions were in the ranges of 0.841-0.998 and $0.008-31.525\;Pa{\cdot}s^n$, respectively. The effect of temperature on the apparent viscosity of the solutions followed an Arrhenius type relationship. Activation energy of flow varied from 9.36 to 52.48 kJ/mol depending on the solid concentration and shear rate. The combined effect of temperature and concentration on the apparent viscosity at the shear rate of $100\;s^{-1}$ could be represented by a single equation as ${\ln}\;{\eta}_a\;=\;6.11\;-\;3103.94(1/T)\;-\;0.03C$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.2
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• pp.69-76
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• 2024

The rheological properties of fresh concrete significantly influence its manufacturing and performance. However, the diversification of newly developed mixtures and manufacturing techniques has made it challenging to accurately predict these properties using traditional empirical methods. This study introduces a multiscale rheological property prediction model designed to quantitatively anticipate the rheological characteristics from nano-scale interparticle interactions, such as those among cement particles, to micro-scale behaviors, such as those involving fine aggregates. The Yield Stress Model (YODEL), the Chateau-Ovarlez-Trung equation, and the Krieger-Dougherty equation were utilized to predict the yield stress for cement paste and mortar, as well as the plastic viscosity. Initially, predictions were made for the paste scale, using the water-cement ratio (W/C) of the cement paste. These predictions then served as a basis for further forecasting of the rheological properties at the mortar scale, incorporating the same W/C and adding the cement-sand volume ratio (C/S). Lastly, the practicality of the predictive model was assessed by comparing the forecasted outcomes to experimental results obtained from rotational rheometer.

• The Korean Journal of Food And Nutrition
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• v.34 no.5
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• pp.458-467
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• 2021

The effect of 16 cultivars on the quality of the rice porridge was investigated. The 'Geunnun' had the highest water absorption rate, but the 'Segyejinmi' yield (w/w) was the highest. The total sugar content of the rice porridge was 0.29~8.10%, showing significant variation among the cultivars. High amylose 'Dodamssal' and 'Hwaseonchalbyeo' glutinous rice displayed rotational viscosities of <20,000 cP. Rotational viscosities for boiled rice cultivars were 30,000~40,000 cP, representing an intermediate level, and the rotational viscosities of 'Geonyang2' and 'Hanareum4' were over 50,000 cP. These results suggest that the viscosity of rice porridge varies significantly among raw material cultivars. Among other variables affecting the texture profile of rice porridge, there were significant differences in hardness and gumminess among the cultivars. As a raw material, 'Baekokchal', a kind of glutinous rice, is known to be whiter than the non-glutinous rice, but after processing to porridge, it showed the lowest L value (71.1). Starch degrading enzyme activity was not significant in most types of rice porridges within 30 or 60 minutes. Therefore, enzymatic starch degradation is thought to be completed within 30 minutes. Among the tested raw materials, 'Miho' was 73.5 ㎍/mg, indicating the best digestibility in vitro.

• International Journal of Fluid Machinery and Systems
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• v.4 no.3
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• pp.341-348
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• 2011

The study of bacterial flagellar swimming motion remains an interesting and challenging research subject in the fields of hydrodynamics and bio-locomotion. This swimming motion is characterized by very low Reynolds numbers, which is unique and time reversible. In particular, the effect of rotation of helical flagella of bacterium on swimming motion requires detailed multi-disciplinary analysis. Clear understanding of such swimming motion will not only be beneficial for biologists but also to engineers interested in developing nanorobots mimicking bacterial swimming. In this paper, computational fluid dynamics (CFD) simulation of a three dimensional single flagellated bacteria has been developed and the fluid flow around the flagellum is investigated. CFD-based modeling studies were conducted to find the variables that affect the forward thrust experienced by the swimming bacterium. It is found that the propulsive force increases with increase in rotational velocity of flagellum and viscosity of surrounding fluid. It is also deduced from the study that the forward force depends on the geometry of helical flagella (directly proportional to square of the helical radius and inversely proportional to pitch).

• Laser Solutions
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• v.16 no.4
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• pp.12-16
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• 2013

For mass production of electronic devices, the processing of the printing roll is one of the most important key technologies for printed electronics technology. A roll of printing process, the gravure printing that is used to print the electronic device is most often used. The indirect laser processing has been used in order to produce printing roll for gravure printing. It consists of the following processing that is coating of photo polymer or black lacquer on the surface of printing roll, pattering using a laser beam and etching process. In this study, we have carried out study on the coating and etching for $25{\mu}m$ line width on the printing roll. To do this goals, a $4{\mu}m$ coating thickness and 20% average coating thickness of the coating homogeneity of variance is performed. The factors to determine the thickness and homogeneity are a viscosity of coating solution, the liquid injection, the number of injection, feed rate, rotational speed, and the like. After the laser patterning, a line width of $25{\mu}m$ or less was confirmed to be processed through etching and the chromium plating process.

• The Korean Journal of Rheology
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• v.1 no.1
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• pp.54-62
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• 1989

준희박과 농축용액에서 약간의 유연성을 갖는 강성막대형 고분자의 회전확산계수와 zero shear rate 점도를 예측하기 위해 한정된 강성 사슬모델이 제시되었다. 본 연구에서는 이제시된 모델을 분자량 분포를 갖는 다분산계로 확장시켰다. 분자들의 분자량 분포 (MW/Mn) 와 분포 함수를 알수 없기 때문에 해당분자에 가장 적당한 분자량 분포와 함수를 취하였다. 만약 이것들을 알고 있다면 제시된 모델로 회전확산계수와 zero shear rate 점도 등과 같은 인자들을예측할수 있었다. 단분산계의 경우와 같이 다분산계에서도 회전확산계수 의 평균분자 윤곽길이 의존도는 L-7 에 비례하는 것으로 나타났다. Doi와 Edwards 의 튜브 모델에 의한 L-9 과 다른 이유는 분자들의 거동을 관찰하기 위해 임의로 선정된 하나의 막 대형 고분자운동을 제약하는 정도가 심하지 않았으며 따라서 제약 완화시간도 훨씬 짧았기 때문이다. 더구나 점도와 회전 확산계수와 단분산계에서는 정성적으로 일치한데 제약 완화 시간도 훨씬 짧았기 때문이다. 더구나 점도와 회전적인 일치를 나타내었다. 이 모델로 기준 으로 하여 분자들의 길이와 종류에 관계없이 하나의 master curve를 그릴수 있었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.6
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• pp.497-504
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• 2015

In this paper, we study the propulsive behavior related to the flagellar motion of bacteria using a spring model. A commercial program was used to conduct simulations, and we verified the numerical technique by setting an additional rotating domain and conducting a parametric study. The numerical results are in good agreement with slender-body theory, although overall, they are not in agreement with resistive-force theory. We confirm the effect of the rotational velocity, pitch, helical radius, fluid viscosity, and, in particular, the distance from the wall on the propulsion of the spring.