• 폴리머
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• 제38권4호
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• pp.477-483
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• 2014

Poly(lactic acid) (PLA) and poly(${\varepsilon}$-caprolactone) (PCL) blends with various components for melt-blown non-wovens were prepared by a twin-screw extruder. Tributyl citrate (TBC) was added in order to improve the miscibility between PLA and PCL. The results showed that small circular particles of PCL were dispersed in PLA matrix uniformly. The addition of PCL had the heterogeneous nucleation effect on the crystallization of PLA and decreased thermal stability of PLA. The flow of pure PLA and blends approached to Newtonian liquid at a low shear rate and expressed more obvious viscoelasticity at a high shear rate.

• Preventive Nutrition and Food Science
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• 제22권1호
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• pp.56-61
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• 2017

Rheological properties of waxy barley flour (WBF) dispersions mixed with various gums (carboxyl methyl celluleose, guar gum, gum arabic, konjac gum, locust bean gum, tara gum, and xanthan gum) at different gum concentrations were examined in steady and dynamic shear. WBF-gum mixture samples showed a clear trend of shear-thinning behavior and had a non-Newtonian nature with yield stress. Rheological tests indicated that the flow and dynamic rheological parameter (apparent viscosity, consistency index, yield stress, storage modulus, and loss modulus) values of WBF dispersions mixed with gums, except for gum arabic, were significantly higher than those of WBF with no gum, and also increased with an increase in gum concentration. In particular, konjac gum at 0.6% among other gums showed the highest rheological parameter values. Tan ${\delta}$ values of WBF-xanthan gum mixtures were lower than those of other gums, showing that there is a more pronounced synergistic effect on the elastic properties of WBF in the presence of xanthan gum. Such synergistic effect was hypothesized by considering thermodynamic compatibility between xanthan gum and WBF. These rheological results suggest that in the WBF-gum mixture systems, the addition of gums modified the flow and viscoelastic properties of WBF, and that these modifications were dependent on the type of gum and gum concentration.

• 대한기계학회논문집B
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• 제30권11호
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• pp.1027-1034
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• 2006

In order to investigate flow characteristics of chicken blood in a micro tube of 100$\mu$m in diameter, in-vitro experiments were carried out using a micro-PIV technique. The micro-PIV system consists of a microscope, 2-head Nd:YAG laser, 12 bit cooled CCD camera and a delay generator. Chicken blood with 40% hematocrit was supplied into a micro tube using a syringe pump. The blood flow shows clearly the cell free layer near the tube wall and its thickness is increased with increasing the flow speed. The hemorheological characteristics of chicken blood, including shear rate and shear stress were estimated from the PIV velocity field data obtained. Since the aggregation index of chicken blood is less than 50% of human blood, non-Newtonian flow characteristics of chicken blood are smaller than those of human blood. As the flow rate increases, the degree of flatness in the velocity profile at the center region is decreased and the parabola-shaped shear stress distribution becomes to have a linear profile. Under the same flow rate, chicken blood shows higher shear stress, compared with human blood.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2095-2100
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• 2003

This Experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin-friction coefficients have been measured for fully developed flow of bentonite-water solution(5%) when the inner cylinder rotates at the speed $0{\sim}400rpm$. The results of present study reveal the relation of the bulk flow Reynolds number Re and Rossby number $R_o$ With respect to the skin friction coefficients. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. In all flow regime, the skin friction coefficient is increased by the inner cylinder rotation. The critical (bulk flow) Reynolds number $Re_c$ decreases as the rotational speed increases. Thus, the rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.

• Food Science and Biotechnology
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• 제15권6호
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• pp.871-876
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• 2006

Rheological behavior of commercial hot pepper-soybean paste (HPSP) was evaluated in small amplitude oscillatory and steady shear tests. Storage modulus (G'), loss modulus (G"), and complex viscosity (${\eta}^*$) as a function of angular frequency (${\omega}$), and shear stress (${\sigma}$) as a function of shear rate (${\gamma}$) data were obtained for 5 commercial HPSP samples. HPSP samples at $25^{\circ}C$ exhibited a non-Newtonian, shear-thinning flow behavior with high yield stresses and their flow behaviors were described by power law, Casson, and Herschel-Bulkley models. Time-dependent flow properties were also described by the Weltman, Hahn, and Figoni & Shoemaker models. Apparent viscosity over the temperature range of $5-35^{\circ}C$ obeyed the Arrhenius temperature relationship with activation energies (Ea) ranging 18.3-20.1 kJ/mol. Magnitudes of G' and G" increased with an increase in ${\omega}$, while ${\eta}^*$ decreased. G' values were higher than G" over the most of the frequency range (0.63-63 rad/sec), showing that they were frequency dependent. Steady shear viscosity and complex viscosity of the commercial HPSP did not fit the Cox-Merz rule.

• Preventive Nutrition and Food Science
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• 제21권4호
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• pp.367-372
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• 2016

To understand the effects of adding different gums (guar, xanthan, and locust bean gums) on naked barley flour (NBF), the rheological and pasting properties of NBF-gum mixtures were measured at different gum concentrations (0, 0.3, and 0.6% w/w). Steady shear rheological properties were determined by rheological parameters for power law and Casson models. All samples showed a clear trend of shear-thinning behavior (n=0.16~0.48) and had a non-Newtonian nature with yield stress. Consistency index, apparent viscosity, and yield stress values increased with an increase in gum concentration. Storage modulus values were more predominant than loss modulus values with all concentrations of gums. There is a more pronounced synergistic effect of elastic properties of NBF in the presence of xanthan gum. Rapid visco analyser pasting properties showed that the addition of gums resulted in a significant increase in the peak, breakdown, setback, and final viscosities, whereas the pasting temperature decreased.

• 대한기계학회논문집
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• 제18권10호
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• pp.2533-2542
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• 1994

This paper suggests a simple approach to determining the screw characteristics for a three0dimensional flow in a channel with a finite aspect ratio(ratio of a width to a depth, W/H) by introducing a Total Shape Factor($F_t$) to correct a two-dimensional flow analysis for a channel with an infinite aspect ratio. In the present study, the Total Shape Factor($F_t$) was defined as a ratio of a net flow rate obtained by the three-dimensional analysis to that by the two-dimensional analysis. In the proposed approach, the quantity, $ \frac{{\partial}F_t}{\partial(H/W)}$ turns out to be almost constant and to play an important role in understanding the effects of the flights. Therefore, $ \frac{{\partial}F_t}{\partial(H/W)}$ are extensively reported in this paper in terms of several dimensionless parameters. This simple approach with such database will be very useful for extruder designers to predict the screw characteristics.

• 한국기계가공학회지
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• 제16권1호
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• pp.42-50
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• 2017

A cerebral aneurysm is a ballooning arising from a weakened area in the wall of a blood vessel in the brain. In this study, the flow analysis of the blood vessel, including the cerebral aneurysm and the stent, was conducted to investigate the effect of the stent shape on reduction of blood flowing into the cerebral aneurysm. We used the Carreau model to describe Non-Newtonian behaviors of blood flow. Two kinds of stents, which had different cross angles were modelled by the commercial CAD program and the geometries of those stents were reflected in the analysis domain of the blood vessel. From the results of the flow analysis, we found that the blood flowing into the cerebral aneurysm was decreased as the cross angle of the stent was decreased.

• 한국미생물·생명공학회지
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• 제23권3호
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• pp.269-274
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• 1995

For the screening of a new functional exopolysaccharide, sugar composition and rheological properties of exopolysaccharide produced from Xanthomonas sp. EPS-1 were investigated. The average molecular weight of exopolysaccharide was determined to be approximately 2.l $\times$ 10$^{6}$ dalton. The new exopolysaccharide EPS-1 was composed of mannose, glucose, galactose and gluco- samine. IR analysis showed that the exopolysaccharide EPS-1 was assumed to be polymer with carbohydrates. NMR analysis showed that exopolysaccharide EPS-1 was presumed to be 4 units of sugar and trace of CH$_{3}$ group. Exopolysaccharide EPS-1 solution showed a characteristic of non-Newtonian fluid properties. At the concentration of 1.0%, the consistency index and the flow behavior index were shown at 10.8352 poise-sec and 0.4419, respectively. All dispersions were pseudoplastic fluids described accurately by Power-law model. Exopolysaccharide EPS-1 was highly viscous at low concentration, with good stability over a wide range of pH 5 to 13. The excellent compatibility of exopolysaccharide EPS-1 was represented with salts such as sodium chloride.

• 대한기계학회논문집B
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• 제20권4호
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• pp.1501-1509
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• 1996

Differential pressure devices such as an orifice and Venturi are widely used in the measurement of flow rate of fluid mainly due to cost effectiveness and easy installation. In the current study, the viscoelastic effect on discharge and loss coefficients of those flow meters were investigated experimentally. Aqueous solutions of Polyacrylamide (200, 500, and 800 ppm) as viscoelastic fluids were used. Discharge coefficient of an orifice for viscoelastic fluids increased significantly up to approximately 15-20% when compared with that for water, while loss coefficient decreased up to 10-25% depending on the diameter ratio, .betha.. Also, pressure recovery for viscoelastic fluids was extended much longer than that for water. On the other hand, discharge and loss coefficients of Venturi for viscoelastic fluids were found to be strongly dependent on the Reynolds number. In both flow meters, the concentration effect for discharge and loss coefficients was not observed at more over than 200 ppm of aqueous solution. Conclusively, orifice and Venturi flow meters should be calibrated very carefully in the flow rate measurement for viscoelastic fluids.