• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.6
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• pp.113-131
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• 1998

The objective of the present study is to investigate the characteristics of the dividing flow in the laminar flow region. Using glycerine water solution(wt43%) for Newtonian fluid and the polymer of viscoelastic fluid(500wppm) for non-Newtonian fluid, this research investigates the flow state of the dividing tube in steady laminar flow region of the two dimensional dividing tube by measuring the effect of Reynolds number, dividing angle, and the flow rate ratio on the loss coefficient. In T- and Y-type tubes, the loss coefficients of the Newtonian fluid decreases in constant rate when the Reynolds number is below 100. The effect of the flow rate ratio on the loss coefficients is negligible. But when the Reynolds number is over 100, the loss coefficient with various flow rate ratios approach an asymptotic value. The loss coefficient of the non-Newtonian fluid for different the Reynolds number shows the similar tendency of the Newtonian fluid. And when the Reynolds number is over 300, the loss coefficient is approximately 1.03 regardless of flow rate ratio or the dividing angle. The aspect ratio does hardly influence the reattachment length and the loss coefficient of both Newtonian and non Newtonian fluid. The loss coefficient decreases as the Reynolds number increases. The loss coefficient of Newtonian fluid is larger than that of non-Newtonian fluid.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.9 s.174
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• pp.179-187
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• 2005

The characteristics of blood flow and the interaction between the blood vessel and blood flow play important roles in plaque cap rupture and the growth of atherosclerosis which may lead directly to a heart attack or a stroke. In this study, carotid arteries with different stenoses have been numerically simulated to investigate the wall shear stress(WSS) and the elastic motion of the vessel. Blood flow has been treated as physiological, laminar and incompressible flow. To model the shear thining behavior of the blood, the Carreau-Yasuda model has been employed but the viscoelasticity of blood has not been considered. The results show that the WSS of $severe(75\%)$ stenosis is much higher than those of $25\%\;and\;50\%$ stenosis in the region of stenosis. With the increase in the stenosis thickness, the expansion ratio of the center of the stenosis decreases while the expansion ratio of the upstream region of the stenosis increases.

• Journal of the Korean Society of Visualization
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• v.21 no.1
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• pp.110-118
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• 2023

Characterizing the extensional rheological properties of non-Newtonian fluids is crucial in many industrial processes, such as inkjet printing, injection molding, and fiber engineering. However, educational institutions and research laboratories with budget constraints have limited access to an expensive commercial extensional rheometer. In this study, we developed a custom-made extensional rheometer using a CO₂ laser cutting machine and 3D printer. Furthermore, we utilized a smartphone with a low-cost microscopic lens for achieving a high spatial resolution of images. The aqueous polyethylene-oxide (PEO) solutions and a Boger fluid were prepared to characterize their extensional properties. A transition from a visco-capillary to an elasto-capillary regime was observed clearly through the developed rheometer. The extensional relaxation time and viscosity of the aqueous PEO solutions with a zero-shear viscosity of over 300 mPa·s could be quantified in the elasto-capillary regime. The extensional properties of the solutions with relatively small zero shear viscosity could be calculated using a smartphone's slow-motion feature with increasing temporal resolution of the images.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.456-461
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• 2017

In this study, the rheological properties of nitromethane gel propellants on nano/micron sized gelling agent are investigated. Silicon dioxide is used as the gellant with 5 wt%, 6.5 wt% and 8 wt% concentration, respectively, where the measurements are conducted under steady-state shear flow conditions using a rotational rheometer. The nitromethane/silicon dioxide gel showed non-Newtonian flow behavior for the entire experimental shear rate ranges. The gel fuels with nano-sized gellant had a slightly higher viscosity than the gel fuels with micron-sized one for low shear rate range. Additionally, it was found that Herschel-Bulkley model can hardly describe the rheological behavior of nitromethane gel propellant, but the NM model(by Teipel and Forter-Barth) is better suited to explain the rheological behavior of nitromethane gel propellant.

• Journal of Aerospace System Engineering
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• v.11 no.4
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• pp.8-14
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• 2017

In this study, the production of proper emulsion fuel and the evaluation of its rheological stability in various experimental conditions were carried out. The W/O (water-in-oil) emulsion fuel was made using n-decane, pure water, and Span 80 was used as a surfactant. Increments of water volume ratio and fuel temperature were the factors, which boosted the phase separation of the emulsion fuel. Rheological characteristics for different water/oil volume ratio, temperature, and elapsed time after the fuel production were examined. As the water volume ratio in the fuel increased, the behavior of non-Newtonian fluid was observed. Viscosity declined as the fuel temperature increased due to the cohesion of water droplets in the fuel. The effect of elapsed time on viscosity was not severe for lower water ratio. However, gradual decrease of viscosity 3 hours after fuel production, in the case of ratio of 3:7, was clearly observed.

• Journal of the Korean Geotechnical Society
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• v.38 no.4
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• pp.5-20
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• 2022

To analyze the flow and density variations in debris flows, a two-phase finite volume model simplified with momentum equations was constructed in this study. The Hershel-Buckley rheology model was employed in this model to account for the internal and basal friction of debris flows and was utilized to analyze complex topography and entrainments of basal soil beds. In order to numerically solve the debris flow analysis model, a finite volume model with the Harten-Lax-van Leer-Contact method was used to solve the conservation equation for the debris flow interface. Case studies of circular dam failure, non-Newtonian fluid dam failure, and multiple debris flows were analyzed using the proposed model to evaluate shock absorption capacity, numerical isotropy, model accuracy, and mass conservation. The numerical stability and correctness of the debris flow analysis of this analysis model were proven by the analysis results. Additionally, the rate of debris flow with various rheological properties was systematically simulated, and the effect of debris flow rheological properties on behavior was analyzed.

• Applied Chemistry for Engineering
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• v.34 no.6
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• pp.603-607
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• 2023

Aqueous film forming foam (AFFF) is a critical fire suppression agent used in combating hydrocarbon fires. This type of fire suppressant is highly effective due to its ability to form a protective film, dissipate heat, inhibit combustion, and utilize a blend of chemical substances to extinguish fires. While these properties offer significant advantages in responding to hydrocarbon fires, AFFF is distinct in its deployment as it is dispensed in the form of foam. Therefore, the rheological analysis of AFFF foam using a rheometer plays a crucial role in predicting the spray characteristics of AFFF for combating hydrocarbon fires, and this is closely associated with effective fire suppression. In this study, we conducted rheometer experiments to confirm the non-Newtonian behavior (shear-thinning) of AFFF foam and obtained data on the form's stability. These experimental data are expected to contribute to enhancing the efficiency of fire suppression systems utilizing AFFF.