• Applied Chemistry for Engineering
• /
• v.25 no.2
• /
• pp.147-151
• /
• 2014

In many polymer processing operations, the diffusion of small molecules in polymeric materials plays an important role. The fundamental physical property required to design and optimize processing operations is the mutual diffusion coefficient. To investigate the transport properties of polymer/solvent systems at infinite dilution, capillary column inverse gas chromatography (CCIGC) is often employed. In this study, diffusion and partition coefficients of cyclic solvents in styrene/butadiene/styrene (SBS) block copolymer were measured over a wide temperature range using the CCIGC technique.

• Journal of Korea Technical Association of The Pulp and Paper Industry
• /
• v.34 no.3
• /
• pp.17-24
• /
• 2002

An unsteady-state moisture diffusion through cellulosic fibers in paper was characterized from the moisture sorption experiment and the mathematical modeling. The sorption experiment was conducted by exposing thin dry paper specimens to a constant temperature-humidity environment. Oven dried blotting papers and filter papers were used as test samples and the gains of their weights were constantly monitored and recorded as a function of sorption time. For a mathematical approach, the moisture transport was assumed to be an one-dimensional diffusion in thickness direction through the geometrically symmetric structure of paper. The model was asymptotically simplified with a short-term approximation. It gave us a new insight into the moisture uptake phenomena as a function of square root of sorption time. The fiber-phase moisture diffusivities(FPMD) of paper samples were then determined by correlating the experimental data with the unsteady-state diffusion model obtained. Their values were found to be on the order of magnitude of $10^{-6}-10^{-7}cm^2$/min., which were equivalent to the hypothetical effective diffusion coefficients at the limit of zero porosity. The moisture sorption curve predicted from the model fairly agreed with that obtained from the experiment at some limited initial stages of the moisture uptake process. The FPMD value of paper significantly varied depending upon the current moisture content of paper. The mean FPMD was about 0.7-0.8 times as large as the short-term approximated FPMD.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.2
• /
• pp.193-204
• /
• 1998

Numerical analysis was performed with multicomponent transport properties and detailed reaction mechanisms for axisymmetric 2-D CH$_{4}$ jet diffusion flame. Calculations were carried out twice with the $C_{2}$-Thermal Mechanism including $C_{2}$ and thermal NO reactions and the $C_{2}$-Full Mechanism including prompt NO reactions in addition to the above $C_{2}$-Thermal NO mechanism. The results show that the flame structures such as flame temperature, major and minor species concentration are indifferent to respective mechanisms. The production path of Thermal NO is dominant comparing with that of Prompt NO in total NO production of pure CH$_{4}$ jet diffusion flame. This is because thermal NO mechanism mainly contributes to positive formation of NO in the whole flame region, but Prompt NO mechanism contributes to negative formation in the fuel rich region. In addition, 0$_{2}$ penetration near the nozzle outlet affects the flame structures, especially N0$_{2}$ formation characteristics.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.10 no.5
• /
• pp.113-123
• /
• 2011

Recently, the global warming problem has arised around world, many nations has set up a various regulations for decreasing $CO_2$. In particular, $CO_2$ emissions reduction effect is very powerful in transport part, so there is a rising interest about development of green car, or electric vehicle in auto industry. For this reason, it is important to make a strategy for charging infra and forcast electric power demand, but it hasn't introduced about demand forecasting electric vehicle. Thus, this paper presents a demand forecasting for electric vehicles using choice based multigeneration diffusion model. In this paper, it estimates innovation coefficient, immitation coefficient in Bass model by using hybrid car market data and forecast electric vehicle market by year using potential demand market through SP(Stated Preference) experiment. Also, It facilitates more accurate demand forecasting electric vehicle market refelcting multigeneration diffusion model in accordance with attribute progress in development of electric vehicle. Through demand forecasting methodology in this paper, it can be utilized power supply and building a charging infra in the future.

• Nuclear Engineering and Technology
• /
• v.20 no.4
• /
• pp.233-240
• /
• 1988

The hafnium shroud is used to control the excess reactivity and power distribution in KMRR. The core analysis is performed by the diffusion code VENTURE using the 5 group macroscopic cross sections homogenized for an assembly. Investigated are the applicability of the diffusion calculation by homogenized cross sections to the analysis of control assembly which features unusual geometry such that hafnium shroud surrounds a multiplying medium inside. Comparative calculation is performed for the excess reactivity and power levels by the transport code TWOTRAN. The results show the acceptability of the diffusion calculation by the homogenized cross sections without significant error.

• Proceedings of the Membrane Society of Korea Conference
• /
• 1997.10a
• /
• pp.69-70
• /
• 1997

Polyimides and related polymers, when synthesized from aromatic monomers, have generally rigid chain structures resulting in a low gas permeability. The rigidity of polymer chains reduces the segmental motion of chains and works as a good barrier against gas transport. To overcome the limit of use as materials of gas separation membranes due to low gas permeability, block copolymers with the incorporation of flexible segments like siloxane linkage and ether linkage have been studied. These block copolymers have microphase-separated structures composed of microdomains of flexible poly(dimethylsiloxane) or polyether segments and of rigid polyimides segments. In case of rigid-flexible block copolymers, the characteristics of both phases for gas permeation are of great difference. The permeation of gas molecules occurs favorably through microdomains of flexible segments, whereas those of rigid segments hinder the permeation of gas molecules. Accordingly the increase of content of flexible segments in a rigid polymer matrix will increase the gas permeability of the membrane linearly. However, this prediction does not satisfy enough many experimental results and in particular the drastic increase of the permeability is observed in a certain volume fraction. It was proposed that the gas transport mechanism is dominated by diffusion rather than gas solubility in a certain content of flexible phase if solution-diffusion mechanism is adopted. However, the transition from solubility-dependent to diffusion-dependent cannot be explained by the understanding of mechanism itself. Therefore, we consider an effective chemical path which permeable phase can form in a microheterogenous medium, and percolation concept is introduced to describe the permeability transition at near threshold where for the first time a percolation path occurs. The volume fraction of both phases is defined as V$_{\alpha}$ and V$_{\beta}$ in block copolymers, and the volume of $\beta$ phase in the threshold forming geometrically a traversing channel is defined as V$_{\betac}$. The formation mechanism of shortest chemical channel is schematically depicted in Fig. 1.

• Membrane Journal
• /
• v.12 no.4
• /
• pp.207-215
• /
• 2002

The hindered diffusion in confined spaces is an important phenomenon to understand in a micro-scale the filtration mechanism determined by the particle motion in membrane pores. Compared to the case of spherical colloids, both the theoretical investigations and the experiments on the hindered diffusion of polyelectrolytes is actually more difficult, due to lots of relevant parameters resulting from the complicated conformational properties of the polyelectrolyte chain. We have successfully performed the Brownian dynamics simulations upon a single polyeiectrolyte confined in a slit-like pore, where a coarse-grained bead-spring model incorporated with Debye-Huckel interaction is properly adopted. For the given sizes of both the polyelectrolyte and the pore width, the hindered diffusion coefficient decreases as the solution ionic concentration decreases. It is evident that a charge effect of the pore wall enhances the hindered diffusion of polyelectrolyte. Simulation results allow us to make sense of the diffusive transport through the micro-pore, which is restricted by the influences of the steric hindrance of polyelectrolytes as well as the electrostatic repulsion between the polyelectrolytes and pore wall.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.5B
• /
• pp.557-562
• /
• 2006

In order to predict the dispersion of suspended sediment arising from dredging operation in port and navigation channel, a hybrid model for dispersive transport of turbidity plume was developed using Lee's(1998) hybrid method. Using hybrid modeling scheme advection-diffusion equation was solved by the forward particle-tracking method for advection process and by the fixed Eulerian grid method for diffusion process. To examine numerical model simulation in accuracy, the simulated results for 1-D, 2-D, and 3-D cases were compared with the analytical solutions including Kuo, et al's (1985) 3-D mathematical model. The model results were in a good agreement with the analytical solutions and mathematical model for the dispersion of turbidity plume.

• Journal of Environmental Science International
• /
• v.1 no.1
• /
• pp.19-33
• /
• 1992

The high oxidants, which occur the daily maximum concentrations in the afternoon, are transported into the other region via long range transport mechanisms or trapped within the shallow mixing boundary layer and then removed physically (deposition, transport by mountain wind, etc.) and chemically (reaction with local sources). Therefore, modeling formation of photochemical oxidants requires a complex description of both chemical and meteorolog ital processecs . In this study, as a part of air quality studies, we reviewed various aspects of photochemical modeling on the basis of currently available literature. The result of the review shows that the model is based on a set of coupled continuity equations describing advection, diffusion, transport, deposition, chemistry, emission. Also photochemical oxidant models require a large amount of input data concerned with all aspects of the ozone life cycle. First, emission inventories of hydrocarbon and nitrogen oxides, with appropriate spatial and temporal resolution. Second, chemical and photochemical data allowing the quantitative description of the formation of ozone and other photochemically-generated secondary pollutants. Third, dry deposition mechanisms particularly for ozone, PAN and hydrogen peroxide to account for their removal by absorption on the ground, crops, natural vegetation, man-made and water surfaces. Finally, meteorological data describing the transport of primary pollutants away from their sources and of secondary pollutants towards the sensitive receptors where environmental damage may occur. In order to improve our present study, shortcomings and limitation of existing models are pointed out and verification Process through observation is emphasized.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.5
• /
• pp.397-403
• /
• 2015

In this study, water distribution inside a proton exchange membrane fuel cell (PEMFC) was measured experimentally. Water distribution is non-uniform because of vigorous chemical reaction and mass transport and has been difficult to measure experimentally. Therefore, much research relied on indirect measuring methods or numerical simulations. In this study, several mini temperature-humidity sensors were installed at the channel for measuring temperature and humidity of the flowing gas throughout the channel. Only one of two electrode channels was humidified externally, and the humidity distribution on the other side was measured, enabling the observation of water transport characteristics under various conditions. Diffusion through the membrane became more vigorous as the temperature of the humidifier rose, but at high current density, electro-osmotic drag became more effective than diffusion.