• Current Optics and Photonics
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• v.3 no.3
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• pp.248-255
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• 2019

Spherical $CeO_2:Ho^{3+}/Yb^{3+}$ particles were synthesized using spray pyrolysis, and the upconversion (UC) properties were investigated with changing the preparation conditions and the infrared pumping power. The resulting particles had a size of about $1{\mu}m$ and hollow structure. The prepared $CeO_2:Ho^{3+}/Yb^{3+}$ particles exhibited intense green emission due to the $^5F_4/^5S_2{\rightarrow}^5I_8$ transition of $Ho^{3+}$ and showed weak red or near-IR peaks. In terms of achieving the highest UC emission, the optimal concentrations of $Ho^{3+}$ and $Yb^{3+}$ were 0.3% and 2.0%, respectively. The UC emission intensity of prepared $CeO_2:Ho^{3+}/Yb^{3+}$ particles had a linear relationship with crystallite size and concentration quenching was caused by dipole-dipole interaction between the same ions. Based on the dependency of UC emission on the pumping power, the observed green upconversion was achieved through a typical two-photon process and concluded that the main energy transfer from $Yb^{3+}$ to $Ho^{3+}$ was involved in the ground-state adsorption (GSA) process.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.207-214
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• 2004

Extra heavy vacuum residue oil has advantage as the fuel of a power plant in reducing the cost of power generation. Numerical study is conducted by the KIVA code to understand combustion, heat transfer and flow field characteristics in the test reactor. The combustion model of pulverized coal particles is adopted as the combustion process of extra heavy oil is similar to that of coal. As an initial phase of investigation parametric study is performed with respect to SMD and spray angle of injected spray droplets.

• Architectural research
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• v.10 no.1
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• pp.1-11
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• 2008

A Steel column with damaged spray-applied fire resistive material (SFRM) may exhibit reduced structural performance due to the effects of elevated temperature during fire events. Thus, the fire load behavior of steel columns with removed or reduced SFRM needs to be examined to predict the structural damage by fire. FEM analyses were performed for the flange thinning removal models in which the SFRM was reduced as a constant strip in thickness at the top flange of the column. The temperature results for all models obtained from the heat transfer analyses were included as an initial condition in the FEM structural analyses. In this study, the results of analysis show that even small remnants of SFRM led to an effective reduction of temperature at any given fire duration, and improved significantly the axial load capacity of a column as compared to the complete removal cases of SFRM.

• Journal of Korea Society of Digital Industry and Information Management
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• v.8 no.1
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• pp.47-53
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• 2012

Sensor networks and car networks that have different structure from that of conventional TCP/IP network require extreme network environment due to frequent change of connectivity. Because such extreme network environment has characteristics like unreliable link connectivity, long delay time, asymmetrical data transfer rate, and high error rate, etc., it is difficult to perform normally with the conventional TCP/P-based routing. DTNs (delay and disruption tolerant network) was designed to support data transfer in extreme network environment with long delay time and no guarantee for continuous connectivity between terminals. This study suggests an algorithm that limits the maximum number of copying transferred message to L by improving the spray and wait routing protocol, which is one of the conventional DTNs routing protocols, and using the azimuth and density data of the mobile nods. The suggested algorithm was examined by using ONE, a DTNs simulator. As a result, it could reduce the delay time and overhead of unnecessary packets compared to the conventional spray and wait routing protocol.

• Journal of Welding and Joining
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• v.22 no.2
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• pp.69-77
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• 2004

The Gaussian heat source has been widely used to simulate the heat flux of the welding we, and applied to calculating the temperature distribution of a workpiece. The conventional two-dimensional Gaussian heat source for the GMAW is modified in this work by decomposing the arc heat into heats of the cathode and metal transfer. The efficiency and effective arc radius of each heat source are determined analytically for the free-flight mode such as the globular and spray modes. The temperature distribution and weld geometry are calculated using the finite element method, and distribution of the drop heat is found to have significant effects on the penetration. The predicted results show good agreements with the available experimental results, especially with the penetration.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.684-690
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• 2003

A new electrostatic rotary atomizing painting equipment using air turbine was developed. Based on the overall design requirements of painting equipment basic design specifications of the equipment parts such as air turbine and atomizing disk are defined from the present conceptual design model. Air turbine is designed with the section profile of NACA airfoil, and its internal flow field is analyzed by commercial CFD code. Atomizing disk is designed to achieve the ligament type spray of paint with the use of visualization technique. Various experiments and tests are conducted to investigate the spray and the transfer characteristics of newly-designed painting equipment, and the measurement results are compared with the those of conventional painting equipments.

• Journal of ILASS-Korea
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• v.20 no.3
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• pp.135-140
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• 2015

Flame transfer function is used to determine the relationship between flow fluctuations and heat release perturbations in a lean premixed gas turbine combustor. The characteristics of flame transfer function are known to depend greatly on flame geometries in addition to other various flow conditions. However, it is not easy to experimentally measure the flame transfer function under various actual combustor operating conditions in terms of time and cost. The current research tries to model the flame transfer function using CFD(Computational Fluid Dynamics). From the results, it is shown that the calculated steady flame geometry can be exactly captured with consideration of the wall heat transfer and radiations. Also, unsteady analysis results show the close characteristics of the flame transfer function to the measured one in both gain and phase.

• Journal of ILASS-Korea
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• v.15 no.4
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• pp.202-207
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• 2010

Mist cooling is widely employed as a cooling technique of high temperature surfaces, and it has heat transfer characteristics similar to boiling heat transfer which has the convection, nucleate and film boiling regions. In the present study, mist cooling heat transfer was experimentally investigated for the mist flow impacting on the heated surfaces of mico-fins. The mist flow was generated by supersonic vibration. Experiments were conducted under the test conditions of droplet flow rate, $Q=6.02{\times}10^{-9}{\sim}3.47{\times}10^{-8}\;m^3/s$ and liquid temperature, $T_f=30{\sim}35^{\circ}C$. From the experimental results, it is found that an increase in the droplet flow rate improves mist cooling heat transfer in the both case of smooth surface and surfaces of micro-fins. Micro-fins surfaces enhance the mist cooling heat transfer. Besides, the experimental results show that an increase in the droplet flow rate decrease the heat transfer efficiency of mist cooling.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1994.04c
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• pp.30-30
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• 1994

• Nuclear Engineering and Technology
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• v.49 no.1
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• pp.124-133
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• 2017

In-vessel retention by passive external reactor vessel cooling under severe accident conditions is a viable approach for retention of radioactive core melt within the reactor vessel. In this study, a new and versatile coating technique known as "cold spray" that can readily be applied to operating and advanced reactors was developed to form a microporous coating on the outer surface of a simulated reactor lower head. Quenching experiments were performed under simulated in-vessel retention by passive external reactor vessel cooling conditions using test vessels with and without cold spray coatings. Quantitative measurements show that for all angular locations on the vessel outer surface, the local critical heat flux (CHF) values for the coated vessel were consistently higher than the corresponding CHF values for the bare vessel. However, it was also observed for both coated and uncoated surfaces that the local rate of boiling and local CHF limit vary appreciably along the outer surface of the test vessel. Nonetheless, results of this intriguing study clearly show that the use of cold spray coatings could enhance the local CHF limit for downward-facing boiling by > 88%.