• Title/Summary/Keyword: Solution viscosity

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On the dynamic instability analysis of mechanical face seals (기계평면시일의 동적 불안정성에 관한 연구)

  • 김청균;서태석
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.6
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    • pp.1509-1514
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    • 1990
  • To investigate the seal dynamic instability for a misaligned and coned mechanical face seal, the finite difference approximation was employed to solve the modified Reynolds equation for an incompressible fluid and temperature dependent viscosity. Using the solution, the results for axial force, transverse moment, restoring moment, and ratio of the transverse moment and the restoring moment are calculated for the whole range from zero to full angular misalignment. The results indicate that the transverse moment due to the angular misalignment and coning terms affects considerably the dynamic instability of face seals. It is shown that the simplified treatment of Reynolds equation using the narrow seal approximation overestimate the ratio of the transverse moment to the restoring moment especially at touch.

Secondary flows through an impeller of centrifugal compressor at design and off-design conditions (설계점 및 탈설계점에서의 원심압축기 회전차 내부 2차유동)

  • Choe, Yeong-Seok;Gang, Sin-Hyeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.11
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    • pp.3573-3588
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    • 1996
  • The flow through a centrifugal compressor impeller was calculated using the 3-dimensional Navier-Stokes solution method. A control volume method based on a rotating curvilinear coordinate system was used to solve the time-averaged Navier-Stokes equations, and a standard k-.epsilon. model was used to obtain eddy viscosity. Numerical results and experimental data were compared for the overall performance of the impeller, the pressure distributions along the shroud wall and the detailed flowfields at the design and off-design conditions, which showed good coincidence. The flow through the impeller is complex with the curvature of the streamlines and rotation. The development of secondary flows and the jet-wake flow characteristics, which is the main source of flow loss, was discussed. Calculation results show quite different patterns as the flow rate changes.

Physicochemical Properties of Gamma-Irradiated Corn Starch

  • Lee, Yong-Jin;Kim, Sun-Young;Lim, Seung-Taik;Han, Sag-Myung;Kim, Hye-Mi;Kang, Il-Jun
    • Preventive Nutrition and Food Science
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    • v.11 no.2
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    • pp.146-154
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    • 2006
  • Structural modification of corn starch by gamma irradiation was evaluated for under dry conditions at varied intensities from 0 to 40 kGy. Under scanning electron microscopy, the granule shape of corn starch was not significantly affected by the irradiation up to 40 kGy. In addition, X-ray diffraction and melting patterns of the irradiated starches were similar to those of the native starch, indicating that crystalline regions in the starch granules were not changed by irradiation. However, the pattern of gel permeation column chromatography showed a significant increase in partial hydrolysis of gamma irradiated starch samples. The degree of polymerization and the paste viscosity of irradiated starch samples dose-dependently decreased significantly with irradiation, and increased solubility and clarity were observed in the irradiated starch solution. In addition, the degree of retrogradation decreased as irradiation dose increased. Irradiation of corn starch has advantages over the ordinary acid or the enzyme hydrolysis modification methods. It does not affect the granular shape and crystalline phase of starch during hydrolysis, and the process can be carried out in dry state.

Calculation of 3-Dimensional Flow Through an Impeller of Centrifugal Compressor (원심압축기 회전차 내부의 3차원 유동해석)

  • ;;Kang, S. H.;Jeon, S. G.
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.10
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    • pp.2617-2629
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    • 1995
  • The flow through a centrifugal compressor rotor was calculated using the quasi-3-dimensional and fully 3-dimensional Navier-Stokes solution methods. The calculated results, obtained during the development of the computer codes for both methods are discussed. In the inviscid quasi 3-dimensional analysis, stream function formulation was used for the blade to blade (B-B) plane calculations, and the streamline curvature method was used for the meridional (H-S) plane calculations. In the viscous 3-dimensional flow analysis, a control volume method based on a general rotating curvilinear coordinate system was used to solve the time-averaged Navier-Stokes equations, and a standard k-.epsilon. model was used to obtain eddy viscosity. The quasi-3-dimensional analysis reasonably predicts the pressure distributions and requires much less computation time in the region where viscous effects are not strong; however, it fails to predict velocity field and loss mechanism through the impeller passage. The viscous 3-dimensional flow analysis shows reasonable pressure distributions and typical jet-wake flow field through the impeller passage. Secondary flow and total pressure distributions on cross-sectional planes explain the loss mechanisms through the impeller.

Experimental Studies on the Efficiency of Insamyunpye-Hwan (인삼윤폐환(人蔘潤肺丸)의 효능(效能)에 관(關)한 실험적(實驗的) 연구(硏究))

  • Rhee, Hyung-Koo
    • Korean Journal of Oriental Medicine
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    • v.2 no.1
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    • pp.314-326
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    • 1996
  • Experimental studies were done to research the clinical effect of Insamyunpye-H wan on viscousity of mucin solution, pulmonary thromboembolism, oxygen consumption in $O_3$-exposed and Lung TBA in rats and mice. The result was obtained as follows : 1. In the effect of viscosity sampled from mucin, Insamyunpye-Hwan was revealed to have a significant effect of decrease in the rate of viscousity (p<0.01). 2. In the effect of sodium aracdonic acid induced pulmonary thromboembolism, I samyunpye-Hwan was revealed to have an effect of increasing the number of survival, but were not significant 3. In the effect of ADP induced pulmonary thrornboembolism, Insamyunpye-Hw an was revealed to have an effect of increasing the number of survival, but were not significant 4. In the effect of oxygen cansumption values in rats exposed-$O_3$, Insarnyunpye-Hwan was revealed to have a significant effect (p<0.05). 5. In the effect of the lung TBA values in rats exposed-$O_3$, Isamyunpye-Hwan was revealed to have a significant effect (p<0.05). In connection with the results of the studies, Insamyunpye-Hwan is concluded to be effective on the treatment of cough and lung and respiratory organ damages.

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A Numerical Model of Large Scale Grid for Two-Dimensional Wake behind Bodies (저항물체 배후의 이차원 후류에 관한 대격자 수치모형)

  • 박일흠;이종섭;이문옥
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.10 no.2
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    • pp.83-92
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    • 1998
  • To evaluate the hydraulic resistance behind bodies in a large scale grid numerical model, a drag stress term which is formulated by the drag force is introduced in the depth-integrated Reynolds equations. And also, the applicability and problems of this model are discussed through various numerical experiments where the analytical solutions exist. In the case of a single body, the error range of velocity difference between analytical and numerical solutions is within $\pm$10% and the wake width behind the body shows a good agreement with the analytical solution. When the drag coefficient and the eddy viscosity are precisely decided, the numerical solutions behind a row of bodies will be efficiently used in real situations.

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Effect of Ionic Liquid on the Kinetics of Peroxidase Catalysis

  • Lee, Yoon-Mi;Kwon, O-Yul;Yoo, Ik-Keun;Ryu, Keun-Garp
    • Journal of Microbiology and Biotechnology
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    • v.17 no.4
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    • pp.600-603
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    • 2007
  • The effect of a water-miscible ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate $([BMIM][BF_4])$, on the horseradish peroxidase (HRP)-catalyzed oxidation of 2-methoxyphenol (guaiacol) with hydrogen peroxide $(H_2O_2)$ was investigated. HRP maintains its high activity in the aqueous mixtures containing various concentrations of the ionic liquid and even in 90% (v/v) ionic liquid. In order to minimize the effect of solution viscosity on the kinetic constants of HRP catalysis, the enzymatic reactions in the subsequent kinetic study were performed in water-ionic liquid mixtures containing 25% (v/v) ionic liquid at maximum. As the concentration of $[BMIM][BF_4]$ increased for the oxidation of guaiacol by HRP, the $K_m$ value increased with a slight decrease in the $K_{cat}$ value: The $K_m$ value increased from 2.8 mM in 100% (v/v) water to 22.5mM in 25% (v/v) ionic liquid, indicating that ionic liquid significantly weakens the binding affinity of guaiacol to HRP.

A Study on the Conditions of Demethyltetracycline Fermentation (Demethylteracycline 발효조건에 관한 연구)

  • 최남희;장덕진;양한철;양한철
    • Microbiology and Biotechnology Letters
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    • v.20 no.2
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    • pp.203-206
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    • 1992
  • Conditions of fermentation for the production of demethyltetracycline were examined using the mutant, which was obtained through the cell fusion of demeclocycline producing strains, The optimum temperature and the initial pH of broth for demethyltetracycline fermentation were $25^{\circ}C$ and 6.7, respectively. Unlike any other cases, the control of pH with alkali solution during the fermentation process affected the productivity. As a general rule, the larger the inoculum size the higher the early consumption of sugar and the viscosity of broth, which means that fermentation proceeds more rapidly as the inoculum size is increased. The highest productivity was shown when the inoculum size was 5% (v/v), and the phase of seed also influenced the fermentation. Among the parameters of pre-culture thus examined, pH was the most important factor.

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Modification of Physicochemical Properties of Naked Barley Starch by Heat-Moisture Treatment (수분-열처리에 따른 쌀보리 전분의 물리화학적 성질)

  • Kang, Kil-Jin;Park, Yang-Kyun;Lho, Il-Hwan;Kim, Kwan;Kim, Sung-Kon
    • Korean Journal of Food Science and Technology
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    • v.19 no.2
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    • pp.97-101
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    • 1987
  • Physicochemical properties of heat-moisture (18, 21, 24 and 27%) treated naked barley (Youngsanbori) starch indicated that crystailinity of the starch was decreased upon treatment and water-binding capacity drastically increased as the moisture level increased. The swelling power was decreased, but the solubility increased by heat-moisture treatment. Apparent viscosity in aqueous sodium hydroxide solution was repressed as moisture-treatment level increased. Amylograph hot paste vicosities were decreased upon treatment except initial pasting temperature.

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Effects of Solubilized Additives on the Microstructure and Its Rheological Properties of CTAB Solutions (CTAB 용액의 미세구조와 유변학적 물성에 대한 첨가제의영향)

  • 양승만
    • The Korean Journal of Rheology
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    • v.9 no.1
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    • pp.6-15
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    • 1997
  • 계면활성제용액에 서로 다른 기능을 하는 두 종류의 첨가제를 투입하여 미셀의 미 세구조 전이현상을 규명하였다. 양이온 계면활성제는 CMC 이상의 농도에서 2단계의 미세 구조 전이거동을 나타낸다. 우선 구형 미셀은 첨가제의 투입에 의하여 표면에서의 친수성기 간의 반발력이 감소됨으로써 실린더형 또는 디스크형미셀로 전이가 일어난다. 더욱 농도가 증가하면 이방성을 가지는 실린더형 미셀간의 중첩 또는 hooking 현상에 의한 두 번째 전 이가 일어난다. 이때 미셀 용액은 흔히 점탄성을 나타내거나 확연한 비뉴톤성 유체거동을 나타낸다. 본 연구에선 heptanol의 화확구조적 차이가 물성에 나타내는효과를 규명하고 wormlike 미셀을 형성하는 MaSal에 의한 점탄성 거동을 살펴보았다. Heptanol의 화학구조 의 영향을 보면 약친수성기인 OH기가 알킬그룹과 나란하게 존재하여 밀집된 구조를 가지 기 쉬운 primary heptanol이 가장효과적으로 미세구조 전이를 유도함을 관찰하였다. 다른 이성질 hetanol의 경우 secondary heptanol이 teriary heptanol에 비하여 효과적임을 보이지 만 화학재할수 있는 농도범위가 매우 좁아 대부분 영역에서 비뉴톤성거동을 나타냄을 확인 하였다. 즉 NaSal를 사용한 경우 실린더형 미셀이 존재할 수 있는농도범위가 매우 좁아 대 부분 영역에서 비뉴톤성 거동을 나타냄을 확인하였다. 즉 NaSal 이 첨가된 용액은 선형점탄 성거동을 보이며 몰비가 증가함에 따라 scission 과정이 관찰되었다. 또한 몰농도비에 따라 항복응력과 shear thickening 특징을 보이는데 이는 흐름장의 세기에 따라 미세구조 변화가 일어나기 때문이다.

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