• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.12
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• pp.1033-1041
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• 2007

This paper studied the characteristics of performance and temperature in a unit cell of a planar type SOFC under various conditions by employing computational fluid dynamics (CFD). In order to derive thermal stress distribution and performance characteristics, the 3-D model simulation for a single channel was performed in various conditions which include interconnect materials $(LaCrO_3/AISI430)$, gas flow direction (co-flow/counter-flow) and inlet temperature (923 K/1173 K). From these results of a single channel, the most effective conditions were applied to the unit stack with multi-channel and the temperature distribution is displayed. Considering both thermal stress and performance, the best combination is 923 K inlet temperature, counter-flow and interconnector of stainless steel. As the end results, flow, thermal and current density distributions were found in the model with multi-channel applied to the best combination and were concentrated in the middle of channels than in the edge.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.11
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• pp.1013-1020
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• 2004

The hybrid system of gas turbine and fuel cell is expected to produce electricity more efficiently than conventional methods, especially in small power applications such as distributed generation. The solid oxide fuel cell (SOFC) is currently the most promising fuel cell for the hybrid system. To realize the conceptual advantages resulting from the hybridization of gas turbine and fuel cell, optimized construction of the whole system must be the most important. In this study, parametric design analyses for pressurized GT/SOFC systems have been peformed considering probable practical limiting design factors such as turbine inlet temperature, fuel cell operating temperature, temperature rise in the fuel cell and soon. Analyzed systems include various configurations depending on fuel reforming type and fuel supply method.

• Journal of the Korean Magnetics Society
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• v.18 no.6
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• pp.217-220
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• 2008

We have investigated the magnetic properties of $ErFe_2O_4$. Stoichiometric polycrystalline sample of $ErFe_2O_4$ was prepared by solid-state reaction method in a stream of CO/$CO_2$ gas. The X-ray power diffraction pattern shows that the diffraction peaks are indexed with respect to the rhombohedral structure with a space group of R3m. The temperature dependent magnetization for $ErFe_2O_4$ shows two-step phase transitions at about 220 and 250 K. The transition at 250 K is an antiferromagnetic transition and that at 220 K is a structural transition.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.43-47
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• 2014

NiO-doped hibonite pigments were synthesized by the solid state method to get stabilized blue color pigment in both oxidation and reduction atmospheres. Optimum substitution condition with NiO for hibonite blue pigment was investigated. Experimental results were comparable to those of previous cobalt-minimization studies performed with other phosphate- or oxide-based cobalt-containing ceramic pigments (having olivine ($Co_2SiO_4$), spinel ($CoAl_2O_4$), or with co-doped willemite ($(Co,Zn)_2SiO_4$) structures). Composition was designed varying the NiO molar ratio increasing with $SnO_2$. The optimum substitution content is 0.93 mole NiO with 0.75mole $SnO_2$. The characteristics of the synthesized pigment were analyzed by XRD, Raman spectroscopy, SEM, and UV-vis. Synthesized pigment was applied to a lime-barium glaze with 10 wt% each and fired at an oxidation atmosphere of $1250^{\circ}C/1h$ and a reducing atmosphere $1240^{\circ}C/1h$. Blue color was obtained with $L^*a^*b^*$ values at 43.39, -6.78, -18.20 under a reducing atmosphere and 41.66, -6.36, -14.7 under and oxidation atmosphere, respectively.

• Korean Journal of Materials Research
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• v.12 no.1
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• pp.21-26
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• 2002

In order to search new phosphors for plasma display panel(PDP), phosphate hosts which has a host excitation band at around 150nm were prepared and their luminescent properties were investigated. In the preparation of $YPO_4: Eu\; and\; (Y,Gd)PO_4: Eu$ phosphors, the effect of oxide and oxalate starting materials on prepared phosphors were compared in terms of relative emission intensities and particle characteristics. The results showed that oxalate starting materials gave better performance in emission intensities and smaller size and more round shape phosphors which would be more applicable for high resolution display. Additionally, Gd, V, Nb and Ta ions were doped to $YPO_4:Eu$ and the luminescent properties of the resulant solid solutions were investigated to find efficient sensitizer. Among these ions, Gd, V and Nb ions increased the emission intensities of parent phosphor to around 10%. While Nb ion gave the best result in emission intensities, CIE color coordinate were improved by doping V ion into $YPO_4:Eu$ phosphor to give x=0.6523, y=0.3406 compared to commercial sample.

• Transactions of the Korean hydrogen and new energy society
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• v.21 no.5
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• pp.405-411
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• 2010

A 5kW class SOFC cogeneration system consisted of a hot box part, a cold BOP (balance of plant) part, and a hot water reservoir. The hot box part contained a stack, a fuel reformer, a catalytic combustor, and heat exchangers. A cold BOP part was composed of blowers, pumps, a water trap, and system control units. A 5kW stack was designed to integrate 2 sub-modules. In this paper, the 5kW class SOFC system was operated using 2 short stacks connected in parallel to test the sub-module and the system. A short stack had 15 cells with $15{\times}15 cm^2$ area. When a natural gas was used, the total power was about 1.38 kW at 120A. Because the sub-modules were connected in parallel and current was loaded using a DC load, voltages of sub-modules were same and the currents were distributed according to the resistance of sub-modules. The voltage of the first stack was 11.46 V at 61A and the voltage of the second stack was 11.49V at 59A.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.301-308
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• 1999

The present study investigates numerically particle laden flow through compressor cascades and a rocket nozzle. Engines are affected by various particles which are suspending in the atmosphere. Especially in the case of aircraft aviating in volcanic, industrial and desert region including many particles, each components of engine system are damaged severely. That damage modes are erosion of compressor blading and rotor path components, partial or total blockage of cooling passage and engine control system degradation. Numerical prediction and experimental data, erosion rates are predicted for two materials - ceramic, soft metal - on compressor blade surface. Aluminum oxide ($Al_2O_3$) Particles included in solid rocket propelant make ablative the rocket motor nozzle and imped the expansion processes of propulsion. By the definition of particle deposition efficiency, characteristics of particles impaction are considered quantitatively Stoke number is defined over the various particle sizes and particle trajectories are treated by Lagrangian approach. Particle stability is considered by definition of Weber number in rocket nozzle and particle breakup and evaporation is simulated in a rocket nozzle.

• Journal of the Korean Ceramic Society
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• v.52 no.5
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• pp.304-307
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• 2015

To reduce the lateral conduction loss of thin-film-processed cathodes, the microstructure of the thin-film cathode is engineered to contain a denser bridging layer in the middle. By doing so, the characteristic crack-like pores that separate the cathode domains in thin-film-processed cathodes and hamper lateral conduction are better connected and, as a result, the sheet resistance of the cathode is effectively reduced by a factor of 5. This induces suppression of the lateral conduction loss and expansion of the effective current collecting area; the cell performance is improved by more than 30%.

• Journal of the Korean Ceramic Society
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• v.53 no.5
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• pp.511-520
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• 2016

Electrolyte-supported symmetric Ni-YSZ cermet electrodes of ca. $23{\mu}m$ were prepared by screenprinting and the impedance was measured as a function of humidity from 2% to 90% balanced in $H_2$ at a total flow rate of 50 sccm. The Ni felt current collector of 1 mm thickness exhibited a Gerischer-like gas concentration impedance in the low frequency range, which was similarly observed in the cermet-supported solid oxide cells, while the Pt paste collector exhibited only electrochemical polarization. The electrochemical polarization of both samples was modeled by a non-ideal diffusion-reaction transmission line model including CPEs with ${\alpha}$= 0.5. In the case of the Pt paste collector, all the Bisquert parameters exhibited humidity dependence to the -1/2 power, supporting a non-faradaic chemical reaction mechanism at three phase boundaries. Consequently, the surface diffusivity and reaction rate increased linearly with humidity. Less pronounced humidity dependence and somewhat lower utilization length with an Ni felt collector can be attributed to the diffusion-limited gas flow through the collector.

• Ceramist
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• v.22 no.2
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• pp.133-145
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• 2019

Thermoelectric energy conversion has attracted much attention because it can convert heat into electric power directly through solid state device and vice versa. Current research is aimed at increasing the thermoelectric figure of merit (ZT ) by improving the power factor and reducing the thermal conductivity. Although there have been significant progresses in increasing ZT of material systems composed of Bi, Te, Ge, Pb, and etc. over the last few decades, their relatively high cost, toxicity, and the scarcity have hindered further development of thermoelectrics to expand practical applications. In this paper, we review the current status of research in the fields of nanostructured thermoelectric materials with eco-friendly and low cost elements, such as skutterudites and oxides, for mid-high temperature applications, highlighting the strategies to improve thermoelectric performance.