• The Transactions of the Korean Institute of Electrical Engineers P
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• v.61 no.1
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• pp.13-17
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• 2012

Ionization and Attachment Coefficients in pure $CH_4$, $CF_4$ and mixtures of $CF_4$ and Ar, have been analyzed over a range of the reduced electric field strength between 0.1 and 350[Td] by the two-term approximation of the Boltzmann equation (BEq.) method and the Monte Carlo simulation (MCS). The calculations of electron swarm parameters require the knowledge of several collision cross-sections of electron beam. Thus, published momentum transfer, ionization, vibration, attachment, electronic excitation, and dissociation cross-sections of electrons for $CH_4$, $CF_4$ and Ar, were used. The results of the Boltzmann equation and the Monte Carlo simulation have been compared with the data presented by several workers. The deduced transport coefficients for electrons agree reasonably well with the experimental and simulation data obtained by Nakamura and Hayashi. The energy distribution function of electrons in $CF_4$-Ar mixtures shows the Maxwellian distribution for energy. That is, f(${\varepsilon}$) has the symmetrical shape whose axis of symmetry is a most probably energy. The proposed theoretical simulation techniques in this work will be useful to predict the fundamental process of charged particles and the breakdown properties of gas mixtures.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.685-692
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• 2003

A numerical simulation of flame propagation in a micro combustor was carried out. Combustor has a sub -millimeter depth cylindrical internal volume and axisymmetric one-dimensional was used to simplify the geometry. Semi-empirical heat transfer model was used to account for the heat loss to the walls during the flame propagation. A detailed chemical kinetics model of $H_2/Air$ with 10 species and 16 reaction steps was used to calculate the combustion. An operator-splitting PISO scheme that is non-iterative, time-dependent, and implicit was used to solve the system of transport equations. The computation was validated for adiabatic flame propagation and showed good agreement with existing results of adiabatic flame propagation. A full simulation including the heat loss model was carried out and results were compared with measurements made at corresponding test conditions. The heat loss that adds its significance at smaller value of combust or height obviously affected the flame propagation speed as final temperature of the burnt gas inside the combustor. Also, the distribution of gas properties such as temperature and species concentration showed wide variation inside the combustor, which affected the evaluation of total work available of the gases.

• Applied Chemistry for Engineering
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• v.25 no.2
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• pp.147-151
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• 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 ILASS-Korea
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• v.22 no.4
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• pp.175-184
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• 2017

The numerical investigation on the effects of water-mist characteristics has been carried out for the fire suppression mechanism. The FDS are used to simulate the interaction of fire plume and water mists, and program describes the fire-driven flows using LES turbulence model, the mixture fraction combustion model, the finite volume method of radiation transport for a non-scattering gray gas, and conjugate heat transfer between wall and gas flow. The numerical model is consisted of a rectangular enclosure of $L{\times}W{\times}H=1.5{\times}1.5{\times}2.0m^3$ and a water mist nozzle that be installed 1.8 m from fire pool. In the present study, the parameters of nozzle for simulation are the droplet size and the spray velocity. The droplet size influences to fire flume on fire suppression more than the spray velocity because of the effect of the terminal velocity. The optimal condition for fire suppression is that the droplet size and the spray velocity are $100{\mu}m$ and 20 m/s respectively.

• Korean Membrane Journal
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• v.1 no.1
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• pp.65-72
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• 1999

The surface of polypropylene membrane was modified by plasma treatment using Ar,$N_{2}$, $NH_{2}$ and $O_{2}$ Permeabilities for $CO_{2}$, $N_{2}$ and separation factor for $CO_{2}$ relative to $N_{2}$ were measured. The permeation experiments were performed by a variable volume method at $25^{\circ}C$ and 0.303MPa. The effects of the plasma conditions such as treatement time power input gas flow rate and pressure in the reactor on the transport properties of modified membrane were investigated. The surface of the plasma treated membrane was analyzed by means of FTIR-ATR XPS and AFM. The surface structure of the plasma treated membrane was fairly different from that of the untreated membrane. Although the permeation rates for both $CO_{2}$ and $N_{2}$ decreased with increasing plasma treatement time the separation factor was found to be improved by the plasma treatement. The operating conditions of plasma treatement imposed on membranes had notable effect on the permeability and separation factor.

• Membrane Journal
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• v.26 no.2
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• pp.152-158
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• 2016

The Chlor-alkali (CA) membrane cell is a major electrolysis system to produce valued chemicals such as chlorine gas and sodium hydroxide. The CA membrane process has been attracted in the industries, since it has relatively low energy consumption when compared with other CA processes. The key component in CA process is perfluorinated sulfonic acid ionomer membranes, which provide ion-selectivity and barrier properties to produced gases. Unfortunately, there is limited information to determine which factors should be satisfied for CA applications. In this study, the influences of PFSA membranes on CA performances are disclosed. They include ion transport behaviors, gas evolution capability, and chemical/electrochemical resistances under CA operation conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.5
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• pp.477-485
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• 2012

Fluid flow and heat transfer in horizontal ducts are strongly coupled with large changes in thermodynamic and transport properties near the critical region as well as the gravity force. Numerical analysis has been carried out to investigate convective heat transfer in horizontal rectangular ducts for water near the thermodynamic critical point. Convective heat transfer characteristics, including velocity, temperature, and the properties as well as local heat transfer coefficients along the ducts are compared with the effect of proximity on the critical point. When there is flow acceleration because of a density decrease, convective heat transfer characteristics in the ducts show transition behavior between liquid-like and gas-like phases. There is a large variation in the local heat transfer coefficient distributions at the top, side, and bottom surfaces, and close to the pseudocritical temperature, a peak in the heat transfer coefficient distribution resulting from improved turbulent transport is observed. The Nusselt number distribution depends on pressure and duct aspect ratio, while the Nusselt number peak rapidly increases as the pressure approaches the critical pressure. The predicted Nusselt number is also compared with other heat transfer correlations.

• Progress in Superconductivity and Cryogenics
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• v.23 no.2
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• pp.1-5
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• 2021

We have investigated the electrical transport properties of polycrystalline tantalum nitride (TaN_x) films. Various compositions of tantalum (nitride) thin films have been deposited on SiO₂ substrates by reactive DC magnetron sputtering while changing the ratio of nitrogen partial pressure. The substrate temperature was maintained at 283 K during deposition. X-ray diffraction analyses indicated the presence of α-Ta and β-Ta phases in the Ta film deposited in pure argon atmosphere, while fcc-TaN_x phases appeared in the sputtering gas mixture of argon and nitrogen. The N/Ta atomic ratio in the film increased ranging from 0.36 to 1.07 for nitrogen partial pressure from 7 to 20.7%. The superconducting transition temperatures of the TaN_x thin films were measured to be greater than 3.86 K with a maximum of 5.34 K. The electrical resistivity of TaN_x thin film was in the range of 177-577 𝜇Ωcm and increased with an increase in nitrogen content. The upper critical filed at zero temperature for a TaN_0.87 thin film was estimated to exceed 11.3 T, while it showed the lowest T_c = 3.86 K among the measured superconducting TaN_x thin films. We try to explain the behavior of the increase of the residual resistivity and the upper critical field for TaN_x thin films with the nitrogen content by using the combined role of the intergrain Coulomb effect and disorder effect by grain boundaries.

• Membrane Journal
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• v.3 no.2
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• pp.60-69
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• 1993

The polyamic acid (PAA) based on 3,3', 4,4'-benzophenonetetracarboxylic dianhydride(BTDA)-3,3', 4,4'-dipheylsulfonetetracarboxylic dianhydride(BAPP), 2,2-bis(4-[4-aminophenoxyl]phenyl) propane(DSDA)-3,3', 4,4'-dipheylsulfonetetracarboxylic dianhydride(BAPP), and 3,3',4,4'-benzophenonetetracarboxylic dianhydride(BTDA)-4,4'-oxydianiline(4,4'-ODA) was synthesised. The casted PAA films were partially imidised and the permeation properties of these PAA films for $O_2$ and $N_2$ were investigated according to the degree of imidisation. When the degree of imidisation was increased by curing, the permeabilities of the PAA films were increased for a while and then decreased. These results show that the increase of gas permeation by the disappearence of strong hydrogen bond is larger than the decrease of gas permeation by the dense effect. The decrease of hydrogen bond between molecular chains of PAA suddenly increases the vibration of the chain to make holes but the compaction in polymer chain gradually decreases the gas permeation. The largest values of permeability of BTDA-BAPP, DSDA-BAPP and BTDA-4,4'-ODA film was 8.3, 0.3 and 0.8 barrer respectively, and the imidisation content corresponding to the values of the largest permeability was 37, 47 and 55% each. But the permselctivities of the PAA films were not changed by the variation of the degree of imidisation.

• Membrane Journal
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• v.22 no.1
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• pp.1-7
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• 2012

We make a studyof the hydrogen permeability and chemical stability of $Nb_{56}Ti_{23}Ni_{21}$ metal alloy membrane. For this purpose, we produced the $Nb_{56}Ti_{23}Ni_{21}$ membrane which has 10 mm diameter and 0.5 mm thick, and experiment the hydrogen transport properties under two kinds of feed gas ($H_2$ 100%; $H_2$ 60% + $CO_2$ 40%) at $450^{\circ}C$C with variation of absolute pressure.The maximum hydrogen permeation flux was $5.58mL/min/cm^2$ in the absolute pressure 3 bar under pure hydrogen. And each case of feed gases about gas composition, the permeation fluxes were satisfied with Sievert's law, and the hydrogen permeation flux decreased with decrease of hydrogen partial pressure irrespective of temperature and pressure. After permeation test, we experiment the stability and durability of $Nb_{56}Ti_{23}Ni_{21}$ alloy membrane for carbon dioxide by XRD analysis.