• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.12
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• pp.1193-1199
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• 2012

A cup burner experiment was performed to investigate the effect of the oxidizer velocity and concentration on flame instability near extinction. Heptane was used as a fuel and air diluted by nitrogen and carbon dioxide was used in the oxidizer stream. Two types of flame instabilities at the flame base and at axial downstream were observed near extinction. The instability at the flame base could be characterized by cell, swing, and rotation modes, and the cell mode changed to the rotation mode through the swing mode as the oxidizer velocity increased. To assess the parameters for the flame instability, the initial mixture strengths, Lewis number, and adiabatic flame temperature were investigated under each condition. The Lewis number might be the most important among them, but it is impossible to generalize because of the insufficient number of cases. Furthermore, the axial periodic flickering motion disappeared at low and high oxidizer velocities near extinction. This resulted from the fact that low oxidizer velocity induced evaporated fuel velocity below the critical velocity and high velocity made the reacting fuel velocity comparable.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.6
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• pp.1775-1781
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• 2008

The effects of the type of curing agent on the swelling of the natural rubber(NR) sponge applicable to the self-sealing layer of a helicopter fuel tank were investigated. The curing systems employed were peroxide and mixed ones of sulfur and peroxide. The NR compounds were prepared in a kneader and a roll-mill. The compounds were partially cured in a press at high pressure and subsequently cured fully with expansion in another press at atmospheric pressure. The apparent density of the NR sponge was measured and the cell structure was observed with scanning electron microscopy. The swelling experiments were performed at room temperature using toluene, iso-octane, and an aircraft fuel as a solvent. More rapid volume swelling of the NR sponge cured by peroxide was achieved than cured by sulfur and peroxide with similar amount of curing agent added in rubber compounds. The apparent density and cell structure of the sponge were extremely sensitive to the amount of peroxide, which influences again the swelling behavior of the NR sponge. It is important to control properly two reactions of decomposition of foaming agent and crosslinking of NR in the mold to obtain rapid swelling of the NR sponge on contact of the fuel.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.361-369
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• 2011

The effect of an increase in the temperature of inlet air on the performance of a membrane humidifier for a PEMFC (Polymer Electrolyte Membrane Fuel Cell) vehicle was investigated both experimentally and numerically. A shell-and-tube type gas-to-gas humidifier with Nafion membrane was tested. The experimental result showed that water transfer varies nonlinearly with the temperature elevation. Numerical analysis based on detailed modeling was also conducted in simplified geometry of a single tube to explain this nonlinear behavior. The simulation revealed that the local water flux varies nonlinearly and dramatically along the tube. The analysis was based on the inverse relationship between the increase in temperature and decrease in relative humidity, both of which seriously affect the water conductivity of the membrane.

• Nuclear Engineering and Technology
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• v.39 no.1
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• pp.9-20
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• 2007

Design study on the Gas Turbine High Temperature Reactor 300-Cogeneration (GTHTR300C) aiming at producing both electricity by a gas turbine and hydrogen by a thermochemical water splitting method (IS process method) has been conducted. It is expected to be one of the most attractive systems to provide hydrogen for fuel cell vehicles after 2030. The GTHTR300C employs a block type Very High Temperature Reactor (VHTR) with thermal power of 600MW and outlet coolant temperature of $950^{\circ}C$. The intermediate heat exchanger (IHX) and the gas turbine are arranged in series in the primary circuit. The IHX transfers the heat of 170MW to the secondary system used for hydrogen production. The balance of the reactor thermal power is used for electricity generation. The GTHTR300C is designed based on the existing technologies of the High Temperature Engineering Test Reactor (HTTR) and helium turbine power conversion and on the technologies whose development have been well under way for IS hydrogen production process so as to minimize cost and risk of deployment. This paper describes the original design features focusing on the plant layout and plant cycle of the GTHTR300C together with present development status of the GTHTR300, IHX, etc. Also, the advantage of the GTHTR300C is presented.

• Applied Chemistry for Engineering
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• v.34 no.3
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• pp.307-312
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• 2023

In this study, a catalytic oxidation-heat recovery system was designed that can remove unreacted with a concentration of about 1% to 6% in the exhaust gas of hydrogen fuel cells and recover heat to ensure safety in the hydrogen economy. The safety system was devised by filling hydrogen oxidation catalysts at room temperature that can remove unreacted hydrogen without any energy source, and an exhaust-heat recovery device was integrated to efficiently recover the heat released from the oxidation reaction. Through CFD analysis, variations in pressure and fluid within the system were shown depending on the filling conditions of the hydrogen oxidation system. In addition, it was found that waste heat could be recovered by optimizing the temperature of the exhaust gas, flow rate, and pressure conditions within the heat recovery system and securing hot water above 40 ℃ by utilizing the exhaust gas oxidation heat source above 300 ℃. Through this study, it was possible to confirm the potential of utilizing hydrogen processes, which are applied in small to medium-sized systems such as hydrogen fuel cells, as a safety system by evaluating them at a pilot scale. Additionally, it could be a safety guideline for responding to unexpected hydrogen safety accidents through further pilot-scale studies.

• Journal of the Korean Electrochemical Society
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• v.3 no.2
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• pp.115-120
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• 2000

All solid-state thin film micro-batteries consisting of lithium metal anode, an amorphous LiPON electrolyte and cathode of vanadium oxide have been fabricated and characterized, which were fabricated with cell structure of $Li/LiPON/V_2O_5Pt$. The effect of various oxygen partial pressure on the electrochemical properties of vanadium oxide thin films formed by d.c. reactive sputtering deposition were investigated. The vanadium oxide thin film with deposition condition of $20\%\;O_2/Ar$ ratio showed good cycling behavior. In in-siか process, the LiPON electrolyte was deposited on the $V_2O_5$ films without breaking vacuum by r.f. magnetron sputtering at room temperature. After deposition of the amorphous LiPON, the Li metal films were grown by a thermal evaporator in a dry room. The charge-discharge cycle measurements as a function of current density and voltage variation revealed that the $Li/LiPON/V_2O_5$ thin film had excellent rechargeable properly when current density was $7{\mu}A/cm^2$. and cut-off voltage was between 3.6 and 2.7V In practical experiment, a stopwatch ran on this $Li/LiPON/V_2O_5$ thin film micro-battery. This result means that thin film micro-battery fabricated by in-siか process is a promising for power source for electronic devices.

• Korean Journal of Materials Research
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• v.9 no.11
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• pp.1075-1082
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• 1999

Composite air electrodes of 50/50 vol% LSM- YSZ where LSM =$\textrm{La}_{1-x}\textrm{Sr}_{x}\textrm{MnO}_{3}$(0$\leq$x$\leq$0.5) were prepared by colloidal deposition technique. The electrodes were then examined by scanning electron microscopy (SEM) and studied by ac impedance spectroscopy in order to improve the performance of a solid oxide fuel cell (SOFC). Reproducible impedance spectra were confirmed by using the improved cell, consisting of LSM- YSZ/YSZ/LSM-YSZ. These spectra were a strong function of operating temperature and the stable conditions for the cells were typically reached at $900^{\circ}C$. The typical spectra measured for an air//air cell at $900^{\circ}C$ were composed of two arcs. Addition of YSZ to the LSM electrode led to a pronounced decrease in cathodic resistivity of LSM-YSZ composite electrodes. Polishing the electrolyte surface to eliminate the influences of surface impurities could further reduce cathode resistivity. The cathodic resistivity of the LSM-YSZ electrodes with catalytic interlayer (Ni or Sr) was much smaller than that of LSM-YSZ electrodes without catalytic interlayer. In addition, the cathodic resistivity of the LSM-YSZ electrodes was a strong function of composition of electrode materials, the electrolyte geometry, and applied current.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.3.1-3.1
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• 2010

Water splitting reaction using photocatalysts is of great interest in the utilization of solar energy [1]. In the present work, visible light-responsive $TiO_2$ thin films (Vis-$TiO_2$) were prepared by a radio frequency magnetron sputtering (RF-MS) deposition method and applied for the separate evolution of $H_2$ and $O_2$ from water as well as the photofuel cell. Special attentions will be focused on the effect of HF treatment of Vis-$TiO_2$ thin films on their photocatalytic activities. Vis-$TiO_2$ thin films were prepared by an RF-MS method using a calcined $TiO_2$ plate and Ar as the sputtering gas. The Vis-$TiO_2$ thin films were then deposited on the Ti foil substrate with the substrate temperature at 873 K (Vis-$TiO_2$/Ti). Vis-$TiO_2$/Ti thin films were immersed in a 0.045 vol% HF solution at room temperature. The effect of HF treatments on the activity of Vis-$TiO_2$/Ti thin films for the photocatalytic water splitting reaction have been investigated. Vis-$TiO_2$/Ti thin films treated with HF solution (HF-Vis-$TiO_2$/Ti) exhibited remarkable enhancement in the photocatalytic activity for $H_2$ evolution from a methanol aqueous solution as well as in the photoelectrochemical performance under visible light irradiation as compared with the untreated Vis-$TiO_2$/Ti thin films. Moreover, Pt-loaded HF-Vis-$TiO_2$/Ti thin films act as efficient and stable photocatalysts for the separate evolution of $H_2$ and $O_2$ from water under visible light irradiation in the presence of chemical bias. Thus, HF treatment was found to be an effective way to improve the photocatalytic activity of Vis-$TiO_2$/Ti thin films. Furthermore, unique separate type photofuel cell was fabricated using a Vis-$TiO_2$ thin film as an electrode, which can generate electrical power under solar light irradiation by using various kinds of biomass derivatives as fuel. It was found that the introduction of an iodine ($I^-/{I_3}^-$) redox solution at the cathode side enables the development of a highly efficient photofuel cell which can utilize a cost-efficient carbon electrode as an alternative to the Pt cathode.

• Elastomers and Composites
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• v.52 no.3
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• pp.180-186
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• 2017

In this work, the effect of low-temperature dehydration of a poly(styrene-co-styrenesulfonic acid) (PSSA) membrane was investigated by differential scanning calorimetry, fourier transform infrared spectroscopy (FT-IR), electron magnetic resonancespectroscopy (EMR), and $^1H$- and $^{13}C$ solid-state nuclear magnetic resonance spectroscopy. These analyses were performed at room temperature for powdered PSSA specimens with and without dehydration and the following key observations were made. First, FT-IR analysis showed that low-temperature dehydration not only transformed the [${SO_3}^-{\cdots}H^+$] ionic pair in the non-hydrated PSSA to an $SO_3H$ group, but also induced the formation of -C=C- double bonds in the dehydrated PSSA. Second, the ${-SO_3}^{\bullet}$ radical was unambiguously identified by EMR spectroscopy. Third, H-abstraction was detected by $^1H$ magic-angle spinning spectroscopy. Finally, an unexpected color shift from white for the non-hydrated PSSA to a yellowish brown for the dehydrated sample was observed. In order to explain these experimental results, it was proposed that the formation of the intermediate hydrogen ($H^{\bullet}$) or hydroxyl radical ($HO^{\bullet}$) species was initiated by the dehydration process. The sespecies attacked the $SO_3H$ group and the tertiary proton at the ${\alpha}-carbon$, resulting in the formation of $-SO^{\bullet}$ radicals and -C=C- double bonds, which correlated with the color shift in the dehydrated PSSA sample. The semechanisms are useful for understanding the simultaneous loss of an aromatic ring and -SO- groups in the PSSA fuel cell membrane.

• Journal of Hydrogen and New Energy
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• v.23 no.6
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• pp.670-677
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• 2012

Perovskite-type oxides such as doped barium zirconate ($BaZrO_3$) show high proton conductivity and chemical stability when they are exposed to hydrogen and water vapour containing atmospheres, thus it can be applicable to the hydrogen separation and the fuel cell electrolyte membranes. However the high temperature ($1700-1800^{\circ}C$) and long sintering times (24h) are generally required to prepare the fully densified $BaZrO_3$ pellets. These sintering conditions lead to the limitation of the grain size growth and the degradation of conductivity due to the acceleration of BaO evaporation at $1200^{\circ}C$. Here we demonstrate NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ with lower calcination and sintering temperature, less experimental procedure and lower process cost than the conventional mixing method. The stoichiometry of $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ was optimized by the control of excess amount of Ba (5mol%) to minimized BaO evaporation. We found that the crystal size of NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ was increased with increase of calcination temperature from XRD analysis. NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ powder was calcined at $1000^{\circ}C$ for 12h when its showed the highest conductivity of $3.3{\times}10^{-2}s/cm$.