• 한국식품과학회지
• /
• 제27권5호
• /
• pp.799-806
• /
• 1995

고유점도가 3.75 dL/g인 감귤류 펙틴 용액의 전단점도 및 점탄성에 대한 농도의존성을 연구하였다. 전형적인 자수법칙 흐름 현상이 2.0% 이상의 펙틴 농도에서 관찰되었으며, 전단점도의 전단속도 의존성은 농도의 증가에 따라 더욱 뚜렷하게 나타났다. ${\eta}_{sp.o}$ 대 $C[\eta]$를 양대수 좌표에 그렸을 때 묽은 영역에서 진한 영역으로의 전이를 나타내는 $C^{*}[\eta]$는 약 4.0이었으며, 이때 ${\eta}_{sp.o}$의 값은 약 10.0을 나타내었다. 묽은 용액$(C[\eta]과 진한 용액$(C[\eta]>C^{*}[\eta])$에서 ${\eta}_{sp.o}$ $C[\eta]$의 기울기는 각각 1.1과 4.5였다. 전단점도를 ${\eta}/{\eta_0}$ 대 ${\gamma}/{\gamma}_{0.8}$에 대하여 그렸을 때 $2{\sim}5%$의 농도에서는 잘 중첩되었으나, 6%의 고농도에서는 중첩곡선에서 벗어나는 현상을 보였다. 펙틴 용액의 점탄성을 조사한 결과 전 농도범위에서 손실탄성률$(G^{\prime\prime})$의 값이 저장탄성률$(G^\prime)$보다 훨씬 높은 값을 보여 점성이 전체 점탄성을 지배하는 것으로 나타났다. 저 농도에서 전단점도는 복소점도와 거의 비슷한 값을 보여 Cox-Merz 법칙에 잘 부합하였으나, 농도가 높아질수록 두 값은 차이를 보였다.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2001년도 춘계학술대회 논문집
• /
• pp.124-128
• /
• 2001

Two-dimensional solidification analysis during rheology forming process of semi-solid aluminum ahoy has been studied Two-phase fluid flow model to investigate the velocity field and temperature distribution is proposed. The unposed mathematical model is applied to the die shape of the two type. To calculate the velocities and temperature fields during rheology forming process, the each governing equation correspondent to the liquid and solid region are adapted. Theoretical model on the basis of the two-phase flow model is the mixture rule of solid and liquid phases. This approach is based on the liquid and solid viscosity.

• Wind and Structures
• /
• 제25권4호
• /
• pp.381-395
• /
• 2017

Nonlinear vibration and instability of cylindrical shell conveying fluid-nanoparticles mixture flow are studied in this article. The surrounding elastic medium is modeled by Pasternak foundation. Mixture rule is used for obtaining the effective viscosity and density of the fluid-nanoparticles mixture flow. The material properties of the elastic medium and cylindrical shell are assumed temperature-dependent. Employing first order shear deformation theory (FSDT), the motion equations are derived using energy method and Hamilton's principal. Differential quadrature method (DQM) is used for obtaining the frequency and critical fluid velocity. The effects of different parameters such as volume percent of nanoparticles, boundary conditions, geometrical parameters of cylindrical shell, temperature change, elastic foundation and fluid velocity are shown on the frequency and critical fluid velocity of the structure. Results show that with increasing volume percent of nanoparticles in the fluid, the frequency and critical fluid velocity will be increases.

• 한국유체기계학회 논문집
• /
• 제17권4호
• /
• pp.47-52
• /
• 2014

An inducer is forward-attached to an impeller to improve the suction performance. This paper described the experimental and numerical investigations on the concept of NPSH similarity about the inducer scale. As Reynolds number decreased for the same scale inducer, the hydraulic performance is slightly reduced because of the viscosity. The suction performance similarity is in good agreement. For different scale inducers, the NPSH similarity did not follow the conventional rule which is proportional to the square of the inducer diameter. A cavity of two times scale inducer grows faster under cavitation inception, and the head is more drop as the fluid passes blades. Because of the simplified cavitation model and vapor pressure, the NPSH similarity dose not have an accuracy. This study suggested an empirical formula for the NPSH similarity.

• Nonlinear Functional Analysis and Applications
• /
• 제26권2호
• /
• pp.347-371
• /
• 2021

A plethora of applications from mathematical programmings, such as minimax, mathematical programming, penalization and fixed point problems can be framed as variational inequality problems. Most of the methods that used to solve such problems involve iterative methods, that is why, in this paper, we introduce a new extragradient-like method to solve pseudomonotone variational inequalities in a real Hilbert space. The proposed method has the advantage of a variable step size rule that is updated for each iteration based on previous iterations. The main advantage of this method is that it operates without the previous knowledge of the Lipschitz constants of an operator. A strong convergence theorem for the proposed method is proved by letting the mild conditions on an operator 𝒢. Numerical experiments have been studied in order to validate the numerical performance of the proposed method and to compare it with existing methods.

• Preventive Nutrition and Food Science
• /
• 제14권3호
• /
• pp.233-239
• /
• 2009

The effects of guar gum (GG) and xanthan gum (XG) at different concentrations (0, 0.2, 0.4, and 0.6% w/w) on the rheological properties of Korean waxy rice starch (WRS) pastes were evaluated under both steady and dynamic shear conditions. The flow properties of WRS-gum mixtures were determined from the rheological parameters of the power law model. The addition of GG and XG to WRS resulted in an increase in the apparent viscosity ($\eta_{a,100}$) and consistency index (K) values obtained from power law model. The flow behavior index (n) values of the WRS-XG mixtures decreased with an increase in gum concentration while there was only a marginal difference between n values for the WRS-GG mixtures. Dynamic moduli (G', G", and $\eta^*$) values in the WRS-gum mixture systems also increased with an increase in gum concentration. WRS-XG mixtures had higher dynamic moduli and lower tan $\delta$ (ratio of G"/G') values than WRS-GG mixtures, indicating that the higher dynamic rheological properties of WRS-XG can be attributed to an increase in the viscoelasticity of the continuous phase in the starch-gum mixture systems, which was due to the higher viscoleastic properties of XG compared to GG. The dynamic ($\eta^*$) and steady shear ($\eta_a$) viscosities of the WRS-XG paste at a 0.2% gum concentration followed the Cox-Merz superposition rule.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집B
• /
• pp.83-89
• /
• 2000

This paper presents a pressure drop correlation for evaporation and condensation of alternative refrigerant with oil in micro-fin tubes. The correlation was developed from a data base consisting of oil-free pure and mixed refrigerants in micro-fin tube; Rl25 R134a. R32 R410a(R32/R125 50/50% mass), R22, R407c(R32/R125/R134a, 23/25/52% mass) and R32/R134a(25/75% mass). The micro-fin tube used in this paper had 60 0.2mm high fins with a 18 helix angle. The cross sectional flow area $(A_c)$ was $60.8 mm^2$ giving an equivalent smooth diameter$(D_e)$ of 8.8mm. The hydraulic diameter $(D_h)$ was estimated to the 5.45mm. The new correlation was obtained by replacing the friction factor and the tube-diameter in Bo Pierre correlation by a friction factor derived from pressure drop data for a micro-fin tube and the hydraulic diameter, respectively. This correlation was also used to predict some pressure data with a lubricant after using a mixing viscosity rule of lubricants and refrigerants. As a result, the new correlation was also well predicted to the measured data within a mean deviation of 19.0%.

• 폴리머
• /
• 제24권6호
• /
• pp.810-819
• /
• 2000

Poly(p-hydroxybenzoate) (PHB)/poly(ethylene terephthalate) (PET) 8/2 공중합 폴리에스터 액정고분자와 poly(ethylene 2,6-naphthalate) (PEN), PET를 용융방사하여 인장탄성률을 측정하고, 55$^{\circ}C$ ο-chlorophenol 에서 2시간 동안 모재인 PEN/PET부분을 용출시킨 후, 용출되지 않은 PHB 피브릴을 전자현미경으로 조사하였다. 모재고분자 속에 존재하는 피브릴이 단섬유일 때 적용하는 Halpin-Tsai식과 피브릴이 연속상일 경우 적용하는 혼합의 법칙을 사용하여 이론적인 탄성률을 계산하고, 측정된 탄성률과 비교하였다. 이론적 탄성률과 측정된 탄성률의 차이를 보정하기 위하여 무차원 점도비 상수 (K)를 정의하고, K를 적용하여 기존의 식을 변형하였다. 변형된 Halpin-Tsai식과 혼합의 법칙을 통해 계산된 이론적인 탄성률은 용융방사를 통해 제조된 복합재료의 탄성률 계산에 더 적합함을 확인하였다.

• 폴리머
• /
• 제28권6호
• /
• pp.460-467
• /
• 2004

폐폴리(염화 비닐) 수지 [waste poly(vinyl chloride), RPVC]와 폐폴리에틸렌 수지 (waste polyethylene, RPE)를 용융 블렌드하여 이들의 형태학적 특성과 유변학적 성질을 관찰하였다. 대수 가감 법칙 (Log additivity rule)으로 계산된 값과 측정된 토크 변화를 비교해보면, 고분자 블렌드는 서로 비상용성을 나타내는 음의 편차 거동을 보였다. 평형판 레오미터와 모세관 레오미터를 사용하여 측정한 블렌드의 유변학적 성질은 용융 상태에서 전단 속도가 증가함에 따라 전단 점도가 감소하는 경향을 보였다. RPVC/RPE 블렌드에 상용화제를 첨가하면 단순 블렌드보다 전단 점도가 증가하였으며 이는 상용성이 증가하여 분산상 크기가 감소하는 것을 확인하였다. 전단 점도 측정 후 얻은 시료를 전자 현미경으로 관찰해 보면 전단속도가 증가함에 따라 분산상의 크기가 약간씩 커지는 것이 관찰되었고 또한, 시료의 표면층보다 내부의 분산상이 커지는 것이 관찰되었다.

• 한국미생물·생명공학회지
• /
• 제20권2호
• /
• pp.203-206
• /
• 1992

Demeclocycline 생산균주를 세포 융합하여 얻은 변이주를 이용하여 demethyltetracycline을 생산하기 위한 발효조건에 대해 연구한 결과, 발효 최적온도는 $25^{\circ}C$였고, 초기pH는 6.7였으며 발효기간 중 pH를 일정하게 조절하면 생산성이 저하되었다. 또한 식균량이 많을 수록 초기 당 소모와 점도가 높았는데, 이는 식균량이 증가함에 따라 발효가 급격히 진행됨을 나타냈다. 식균량은 5(v/v)일 때 생산성이 가장 높았으며 전배양 시간과 전배양 pH가 중요한 요인임을 밝혔다.