• Korea-Australia Rheology Journal
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• v.12 no.3_4
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• pp.165-173
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• 2000

Three-dimensional numerical simulation of isothermal/nonisothermal coextrusion process of two immiscible polymers through a rectangular channel has been done using the finite element method. The encapsulation phenomenon with the less viscous layer encapsulating the more viscous layer was investigated with the generalized Newtonian fluids. The interface position around the symmetric plane obtained by numerical simulation nearly coincided with the one observed in experiments, but the degree of encapsulation was less than the one observed experimentally. Open boundary condition method was found to be applied to the simulation of nonisothermal coextrusion process, however, the results are not far from those using the fully developed boundary condition, because the temperature development along the downstream direction is very slow in the case of convection dominated flow. When the inlet velocity is increased, the interface profile does not change in isothermal flow, while it moves upward in nonisothermal situation. The degree of encapsulation decreases along the downstream direction in nonisothermal flow. When the inlet temperature increases compared to the wall temperature, the outlet interface moves downward and the degree of encapsulation increases. The difference of degree of encapsulation between the simulation and the experiments seems to arise from the viscoelastic effect of the materials. It was concluded that the nonisothermal effect alone does not explain the complex coextrusion process and the viscoelastic effect needs to be considered.

• Composites Research
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• v.30 no.3
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• pp.202-208
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• 2017

Resin transfer molding (RTM) is a mass production process that allows the fabrication of composites ranging in size from small to large. Recently, fast curing resins with a curing time of less than about 10 minutes have been used in the automotive and aerospace industries. The viscosity of resin is bound up with the degree of cure, and it can be changed rapidly in the fast-cure resin system during the mold filling process. Therefore, it is advantageous to experimentally measure and evaluate the degree of cure because it requires much effort to predict the flow characteristics and cure of the fast curing resin. DMA and dielectric technique are the typical methods to measure the degree of cure of composite materials. In this paper, the resin flow and degree of cure were measured through the multi-channel dielectric system. A total of 8 channels of dielectric sensors were used and resin flow and degree of cure were measured and compared with each other under various pressure conditions.

• Membrane Journal
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• v.30 no.1
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• pp.21-29
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• 2020

In this study, we have established the optimum design condition of pore-filled anion-exchange membrane for all-vanadium redox flow battery (VRFB). From the experimental results, it was proven that the membrane design factors that have the greatest influence on the charge-discharge performance of VRFB are the ion exchange capacity, the porosity of substrate film, and the crosslinking degree. That is, the ohmic loss and the crossover of active materials in VRFB were shown to be determined by the above factors. In addition, two methods, i.e. reducing the ion exchange capacity at low crosslinking degree and increasing the crosslinking degree at high ion exchange capacity, were investigated in the preparation of pore-filled anion-exchange membranes. As a result, it was found that optimizing the crosslinking degree at sufficiently high ion exchange capacity is more desirable to achieving high VRFB charge-discharge performances.

• Journal of the Korean Institute of Gas
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• v.16 no.3
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• pp.42-47
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• 2012

In this paper, alternative natural refrigerant R290(Propane), R600(Butane), R717(Ammonia), R1270(Propylene) for freon refrigerant R22 were used working fluids for 2-stage compression and 1-stage expansion refrigeration system. The operating parameters considered in this study included evaporation temperature, condensation temperature, subcooling degree, superheating degree, mass flow rate ratio of inter-cooler. The main results were summarized as follows : The COP of 2-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling degree and mass flow rate ration of inter-cooler, but decreases with the increasing evaporating temperature, condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of 2-stage compression and 1-stage expansion refrigeration system using natural refrigerants have an effect on COP of this system. The COP of natural refrigerants was higher than the COP of freon R22 in this study, so points to be considered are the security, the attached facilities for natural refrigerants than COP.

• International Journal of Air-Conditioning and Refrigeration
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• v.7
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• pp.79-90
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• 1999

This investigation presents the experimental results of forced convection boiling heat transfer around a circular, electrically heated horizontal cylinder to subcooled water in cross flow. In these experiments, the following primary variables were included: heat flux, flow velocity, pressure and degree of subcooling at inlet. Local surface temperatures were measured at nine peripheral positions. Local surface temperature distributions are classified into four categories depending on the supplied heat flux. The effects of the boiling curve depending on the fluid velocity, degree of subcooling at inlet and pressure are presented.

• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.995-998
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• 2003

This paper reports the correlation between dielectric constant and degree of amorphism of the hybrid type Si-O-C thin films. Si-O-C thin films were deposited by high density plasma chemical vapor deposition using bistrimethyl- silylmethane(BTMSM, $H_{9}$C$_3$-Si-C $H_2$-Si-C$_3$ $H_{9}$) and oxygen precursors with various flow rate ratio. As-deposited film and annealed films at 40$0^{\circ}C$ were analyzed by XRD. The Si-O-C thin films were amorphous from XRD patterns. For quantitative analysis, the diffraction pattern of the samples was transformed to radial distribution function by Fourier analysis, and then compared with each other. The degree of amorphism of annealed films was higher than that of as-deposited ones. The dielectric constant varied in accordance with flow rate ratio of precursors. The lowest dielectric constant was obtained from the as-deposited film which has the highest degree of amorphism after annealing.

• Journal of Environmental Health Sciences
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• v.21 no.4
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• pp.37-43
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• 1995

The course of biodegradation of anionic surfactants, Linear Alkylbenzene Sulfonates(LAS), Sodium Lauryl Ethoxylate Sulfonate(SLES), and Sodium Lauryl Sulfonates(SLS), which are mainly used to make detergents and shampoo, was investigated. The degree of biodegradation was studied as a function of concentration, volumetric flow rate, and temperature in Naktong River. MethyleneBlue Active Substances(MBAS), Total Dissolved Organic Carbon(TOC), and Chemical Oxygen Demand(COD) were measured to evaluate the degree of biodegradation. The degree of biodegradation of LAS was highly dependent upon the concentration and was increased as the concentration was decreased and that of SLES and SLS was almost constant at the concentration of less than 200 ppm, but was much increased as the volumetric flow rate was increased or the temperature was increased.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.1
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• pp.57-65
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• 2003

As a compressed water is rapidly expanded through a nozzle, two-phase flow of vapor and liquid is formed in the nozzle due to the flash evaporation. In the present study, critical flow of two-phase fluids is analysized using an Isentropic-Homogeneous-Equilibrium model and a Leung model. Calculation results show that the choke of the two-phase flow can be two different types of continuous and discontinuous chokings. For the stagnation pressure below 10 Mpa it is found that the continuous choking, which is similar to the choking phenomenon of single-phase gas flow, is possible only when the degree of subcooling is less than 10K.

• Journal of Power System Engineering
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• v.20 no.2
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• pp.85-90
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• 2016

Coefficient of performance (COP) for two-stage compression system is investigated in this paper to develop seawater ice machine. The system performance is analyzed with respect to degrees of superheating and subcooling, condensing and evaporating temperatures, compression and mechanical efficiencies and mass flow ratio in an inter-cooler. The main results are summarized as follows : The COP of the system grows when the mass flow ratio, subcooling degree and evaporating temperature edge up. Contrariwise, the system performance descends in case that superheating degree and condensing temperature increase. The most effective factor for the COP is the mass flow rate ratio. Each refrigerant has different limitation for a value of the mass flow ratio in the inter-cooler because of difference in material property.

• Journal of Ship and Ocean Technology
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• v.12 no.1
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• pp.1-15
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• 2008

An edgetone is the discrete tone or narrow-band sound produced by an oscillating free shear layer, impinging on a rigid surface. In this paper, 2-dimensional edgetone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle is presented using lattice Boltmznan model with 21 bits, which is introduced a flexible specific heat ratio y to simulate diatomic gases like air. The blown jet is given a parabolic inflow profile for the velocity, and the edges consist of wedges with angle 20 degree (for symmetric wedge) and 23 degree (for inclined wedge), respectively. At a stand-off distance w, the edge is inserted along the centerline of the jet, and a sinuous instability wave with real frequency is assumed to be created in the vicinity of the nozzle exit and to propagate towards the downward. Present results presented have shown in capturing small pressure fluctuating resulting from periodic oscillation of the jet around the edge. The pressure fluctuations propagate with the speed of sound. Their interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. It is found that, as the numerical example, satisfactory simulation results on the edgetone can be obtained for the complex flow-edge interaction mechanism, demonstrating the capability of the lattice Boltzmann model with flexible specific heat ratio to predict flow-induced noises in the ventilating systems of ship.