• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.1
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• pp.79-87
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• 1998

Basic design of a 50USRT(175㎾) triple effect absorption chiller driven by hot gas has been carried out for both parallel and series flow cycles. Parallel flow cycle showed higher COP, however, the temperature in the generator was also higher than that in series flow cycle. Dynamic operation behavior of a parallel flow system at off-design conditions, such as the change in heat transfer medium temperature or the construction change of the system components, has been investigated in detail. It was found that the cooling capacity was seriously decreased by reducing hot gas flow rate and UA-value in the high temperature generator. However, the system COP was improved, because thermal load in the system components was reduced. The COP and the cooling capacity was found to be improved as cooling water temperature decreased or chilled water temperature increased. The optimum ratio of solution distribution could be suggested by considering the COP, the cooling capacity and the highest temperature in the system, which is critical for corrosion.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.50.1-50.1
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• 2011

Lead-free ceramics with a composition of 0.55 mol%$K_4CuNb_8O_23-(K_{1-x}Na_x)NbO_3$ (KCN-KNNx) where $0.45{\leq}x{\leq}0.60$ were synthesized by conventional ceramic processing. Results revealed that the addition of Na was effective in changing the microstructure and relative density of KCN-KNNx. Further, the addition of Na resulted in a slight shift of the phase transition temperatures (To-t and Tc) toward low values. A high mechanical quality factor (Qm) of 1850 was found atx=0.54, which might be due to the build-up of an internal bias field (Ei) within KCN. Thermal hysteresis in KNNx was confirmed with an increase in the Na content during the heating and cooling cycles, resulting from structural changes. Thus, KCN-KNNx with x=0.54 exhibits excellent piezoelectric properties with d33 (97 pC/N), kp (36%), and Qm (1850), being promising candidates for application in high-power piezoelectric devices.

• Korean Journal of Veterinary Service
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• v.27 no.3
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• pp.273-280
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• 2004

The studies were performed for the PRRS antigen and antibody detection from breeding farms, artificial insemination(AI) center and growing farms in Jeonbuk province. 1. Specific PRRS primers were successfully amplified ORF6 617bp and ORF7 448 bp on agarose gel. 2. RT-PCR method has been establish by commercial kit and the thermal cycler program consisted of 30 cycles: $95^{\circ}C$ for 30 sec, $45^{\circ}C$ for 30 sec, and $72^{\circ}C$ for 45 sec. 3. The results of PRRS antibody test by ELISA method in AI centers were $6.6\%,\;53.3\%$ and breeding farms $65\%,\;65\%\;and\;38.7\%$, respectively. The serological positive of the antibody in gilt higher than sow. 4. The sero-positive of the PRRS antibody showed average $21\%$ in domestic farms, $56.2\%$ in breeding farms, and $29.9\%$ in AI center.

• Journal of Electrochemical Science and Technology
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• v.2 no.2
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• pp.116-123
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• 2011

Herein, a novel preparation method of highly homogeneous carbon-silicon composite materials was presented. In contrast to conventional solvent evaporation method, a milled silicon-graphite or its oxidized material were directly reacted with petroleum-derived pitch precursor. After thermal reaction under high pressure, pitch-graphite-silicon composite was prepared. Carbon-graphite-silicon composite were prepared by an air-oxidization and following carbonization. From energy dispersive spectroscopy, it was observed that small Si particles were highly embedded within carbon, which was confirmed by disappearance of Si peaks in Raman spectra. Furthermore, X-ray diffraction and Raman spectra revealed that carbon crystallinity decreased when the strongly oxidized silicon-graphite was added, which was probably due to oxygen-induced cross-linking. From the anode application in lithium ion batteries, carbon-graphite-silicon composite anode displayed a high capacity ($565\;mAh\;g^{-1}$), a good initial efficiency (68%) and an good cyclability (88% retention at 50 cycles), which were attributed to the high dispersion of Si particles within cabon. In case of the strongly oxidized silicongraphite addtion, a decrease of reversible capacity was observed due to its low crystallinity.

• Journal of information and communication convergence engineering
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• v.6 no.1
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• pp.38-42
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• 2008

Highly sensitive and mechanically stable gas sensors have been fabricated using the microfabrication and micromachining techniques. The sensing materials used to detect the offensive $CH_3SH$ and $(CH_3)_3N$ gases are 1 wt% Pd-doped $SnO_2$ and 6 wt% $Al_2O_3$-doped ZnO, respectively. The optimum operating temperatures of the devices are $250^{\circ}C$ and $350^{\circ}C$ for $CH_3SH$ and $(CH_3)_3N$, respectively and the corresponding heater power is, respectively, about 55mW and 85mW. Excellent thermal insulation is achieved by the use of a double-layer membrane: i.e. $0.2{\mu}m$-thick silicon nitride and $1.4{\mu}m$-thick phosphosilicate glass. The sensors are mechanically stable enough to endure the heat cycles between room temperature and $350^{\circ}C$, at least for 30 days.

• International Journal of Fluid Machinery and Systems
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• v.5 no.2
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• pp.91-99
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• 2012

The Fighter aircraft transmission system consists of a light weight, High Speed Flexible Coupling (HSFC) known as Power Take-Off shaft (PTO) for connecting Engine gearbox (EGB) with Accessory Gear Box (AGB). The HSFC transmits the power through series of specially contoured metallic annular thin flexible plates whose planes are normal to the torque axis. The HSFC operates at high speed ranging from 10,000 to 18,000 rpm. The HSFC is also catered for accommodating larger lateral and axial misalignment resulting from differential thermal expansion of the aircraft engine and mounting arrangement. The contoured titanium alloy flexible plates are designed with a thin cross sectional profile to accommodate axial and parallel misalignment by the elastic material flexure. This paper investigates the effect of misalignment on the transmission characteristics of the HSFC couplings. A mathematical model for the HSFC coupling with misalignment has been developed for analyzing the torque transmission and force interaction characteristics. An extensive testing has been conducted for validating characteristics of the designed coupling under various misalignment conditions. With this the suitability of the model adapted for the design iteration of HSFC development is validated. This method will reduce the design iteration cycles of HSFC and can be extended for the similar development of flexible couplings.

• Journal of Korea Foundry Society
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• v.13 no.3
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• pp.268-275
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• 1993

In gravity die casting, die cooling systems are frequently employed with water cooling to remove the heat of the solidifying metal. Thermal modeling is an important technique in mold design for improving the productivity of the process. Computer simulation system which consists of pre-processor, main solidification simulator and post-processor has been developed for three dimensional solidification analysis of cyclic gravity die casting. The pre-processor is used for mesh generation in a PC system. The modified finite difference method is adopted for the main solidification simulation algorithm during all the casting cycles. The post-processor graphically presents the simulation results. Several experiments in automotive cast piston were carried out. The temperature variations in casting and mold with time are measured experimentally, and the results are compared with calculation results. The effects of cycle number on solidification pattern are also studied. Several experimental results for the prediction of shrinkage defects are compared with calculated results.

• Journal of Energy Engineering
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• v.18 no.2
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• pp.93-100
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• 2009

An exergy analysis is carried out for the regenerative wet-compression Brayton cycle which has a potential of enhanced thermal efficiency owing to the reduced compression power consumption and the recuperation of exhaust energy. Using the analysis model, the effects of pressure ratio and water injection ratio are investigated on the exergy efficiency of system, exergy destruction ratio for each component of the system, and exergy loss ratio due to exhaust gas. The results of computation for the typical cases show that the regenerative wet-compression gas turbine cycle can make a notable enhancement of exergy efficiency. The injection of water results in a decrease of exergy loss of exhaust gas and an increase of net power output.

• Journal of Hydrogen and New Energy
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• v.1 no.1
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• pp.1-8
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• 1989

The hydriding kinetic mechanism and the change of the hydriding reaction rate of $MmNi_{4.5}Al_{0.5}$ during the thermally induced hydrogen absorption-desorption cycling are investigated. Comparison of the reaction rate data which are obtained by the pressure sweep method with the theoretical rate equations suggests that the hydriding rate controlling step has changed from the dissociative chemisorption of hydrogen molecules at the surface to the hydrogen diffusion through the hydride phase with the increase of the hydriding fraction. These hydriding kinetic mechanism is not changed during the cycling. However, the intrinsic hydriding reaction rate of $MmNi_{4.5}Al_{0.5}$ after 5500 cycles increases significantly comparing with the activated one. It is suggested that the change of the hydriding kinetic behavior due to intrinsic degradation of $MmNi_{4.5}Al_{0.5}$ can be interpreted as follows ; the formation of nickel cluster at the surface of the sample and the host metal atom exchange in bulk by thermal cycling.

• The Journal of Advanced Prosthodontics
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• v.12 no.5
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• pp.283-290
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• 2020

PURPOSE. The present study aimed to evaluate the clinical applicability of monolithic zirconia (MZ) crowns of different thickness via determination of fracture resistance and marginal fit. MATERIALS AND METHODS. MZ crowns with 0.5, 0.8, 1.0, and 1.5 mm thickness and porcelain fused to metal (PFM) crowns were prepared, ten crowns in each group. Marginal gaps of the crowns were measured. All crowns were aged with thermal cycling (5 - 55℃/10000 cycle) and chewing simulator (50 N/1 Hz/lateral movement: 2 mm, mouth opening: 2 mm/240000 cycles). After aging, fracture resistance of crowns was determined. Statistical analysis was performed with one-way ANOVA and Tukey's HDS post hoc test. RESULTS. Fracture loads were higher in the PFM and 1 mm MZ crowns compared to 0.5 mm and 0.8 mm crowns. 1.5 mm MZ crowns were not broken even with the highest force applied (10 kN). All marginal gap values were below 86 ㎛ even in the PFM crowns, and PFM crowns had a higher marginal gap than the MZ crowns. CONCLUSION. The monolithic zirconia exhibited high fracture resistance and good marginal fit even with the 0.5 mm thickness, which might be used with reduced occlusal thickness and be beneficial in challengingly narrow interocclusal space.