• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.8
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• pp.305-310
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• 2016

A thermal storage systems was designed to correspond to the temporal or quantitative variation in the thermal energy demand, and most of its heat is stored using the latent and sensible heat of the heat storage material. The heat storage method using latent heat has a very complex phenomenon for heat transfer and thermal behavior because it is accompanied by a phase change in the course of heating/cooling of the heat storage material. Therefore, many studies have been conducted to produce an experimentally accessible as well as numerical approach to confirm the heat transfer and thermal behavior of phase change materials. The purpose of this study was to investigate the problems encountered during the actual heat transfer from an internal storage tank through simulation of the process of storing and utilizing thermal energy from the thermal storage tank containing charged PCM. This study used analysis methods to investigate the heat transfer characteristics of the PCM with simultaneous heating/cooling conditions in the rectangular space simulating the thermal storage tank. A numerical analysis was carried out in a state considering natural convection using the ANSYS FLUENT(R) program. The result indicates that the slope of the liquid-solid interface in the analysis field changed according to the temperature difference between the heating surface and cooling surface.

• Journal of Surface Science and Engineering
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• v.56 no.6
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• pp.386-392
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• 2023

In this work, we describe the reduction kinetics of gold nanoparticles synthesized by plasma discharge in aqueous solutions with varied voltages and precursor (HAuCl₄) concentrations. The reduction rate of [AuCl₄]^- was determined by introducing NaBr to the gold colloidal solution synthesized by plasma discharge, serving as a catalyst in the reduction process. We observed that [AuCl₄]^- was completely reduced when its characteristic absorption peak at 380 nm disappeared, indicating the absence of [AuCl₄]^- for ligand exchange with NaBr. The reduction rate notably increased with the rise in discharge voltage, attributable to the intensified plasma generated by ionization and excitation, which in turn accelerated the reduction kinetics. Regarding precursor concentration, a lower concentration was found to retard the reduction reaction, significantly influencing the reduction kinetics due to the presence of active H⁺ and H radicals. Therefore, the production of strong plasma with high plasma density was observed to enhance the reduction kinetics, as evidenced by optical emission spectroscopy.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.10a
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• pp.358-363
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• 1995

A study on passive cooling systems for concrete containment of advanced pressurized water reactors has been performed. The proposed passive containment cooling system (PCCS) consist of (1) condenser units located inside containment, (2) a steam condensing pool outside containment at higher elevation, and (3) downcommer/riser piping systems which provide coolant flow paths. During an accident causing high containment pressure and temperature, the steam/air mixture in containment is condensed on the outer surface of condenser tubes transferring the heat to coolant flowing inside tubes. The coolant transfers the heat to the steam condensing pool via natural circulation due to density difference. This PCCS has the following characteristic: (1) applicable to concrete containment system, (2) no limitation in plant capacity expansion, (3) efficient steam condensing mechanism (dropwise or film condensation at the surface of condenser tube), and (4) utilization of a fully passive mechanism. A preliminary conceptual design work has been done based on steady-state assumptions to determine important design parameter including the elevation of components and required heat transfer area of the condenser tube. Assuming a decay power level of 2%, the required heat transfer area for 1,000MWe plant is assessed to be about 2,000 ㎡ (equivalent to 1,600 of 10 m-long, 4-cm-OD tubes) with the relative elevation difference of 38 m between the condenser and steam condensing pool and the riser diameter of 0.62 m.

• Journal of Biosystems Engineering
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• v.30 no.4 s.111
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• pp.195-201
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• 2005

The output of Stirling engine is influenced by the regenerator effectiveness. The regenerator effectiveness is influenced by heat transfer and flow friction loss of the regenerator matrix. In this paper, in order to provide a basic data for the design of regenerator matrix, characteristics of heat transfer and flow friction loss were investigated by a packed method of matrix in the oscillating flow as the same condition of operation in a Stirling engine. As matrices, several kinds of combined wire screen meshes were used. The results are summarized as follows; The packed meshes with high mesh no. in the side of heater part of regenerator showed effective than the packed meshes with low mesh no. in the side of cooler part of regenerator. The temperature difference and pressure drop of the regenerator were not made by the specific surface area of wire screen meshes but by the minimum free-flow area to the total frontal area. Among the No. 150 single screen meshes, 200-60 combined meshes, the 200-150-100 combined meshes showed the highest in effectiveness.

• Journal of Surface Science and Engineering
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• v.46 no.1
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• pp.16-21
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• 2013

CIGS (Cu-In-Ga-Se) films were deposited on the Mo coated soda lime glass (Mo/SLG) by RF magnetron sputtering using a single sintered target with different chemical compositions. Heat treatment of the CIGS films were carried out under three different conditions, 1step ($350^{\circ}C$ for 2 hour and $550^{\circ}C$ for 2 hour) and 2step ($350^{\circ}C$ for 1 hour and $550^{\circ}C$ for 1 hour). In the case of CIGS films post-annealed on 2step method, grain size remarkably increased compared to other methods, indicating that chemical composition [Cu/(Ga+In) = 1] of CIGS films was same as CIGS target. After heat treatment by 2step method, band gap energy of the CIGS film deposited at RF 80 W showed 1.4 eV which is broadly similar to identical band gap energy (1.2 eV) of CIGS film prepared by evaporation method. Therefore, 2step heat treatment method could be expected to low temperature process.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.247-255
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• 2004

The cooling characteristic of water-air mixed spray for high water mass flux is not well defined, compared to that of highly pressurized spray. A series of research program was planned to develop the boiling correlation for whole temperature range in case of water-air mixed spray with high water mass flux. The cooling experiments of hot steel surface with initial temperature of 820$^{\circ}C$ were conducted in unsteady state with relatively high water mass flux. A computer program was developed to calculate the heat flux inversely from measured data by three inserted thermocouples. Finally the effects of water and air mass flux on the averaged film boiling heat flux and wetting temperature were studied. In this 1st report, it is found that the boiling curve was similar to that of highly pressurized spray and the decreased slope of heat flux in film boiling region with respect to surface temperature became steep by increasing air mass flux. Also it is shown that, by increasing air mass flux, the averaged heat flux in film boiling region was increased, and then saturated and the wetting temperature was increased, and then decreased. Finally when the heat flux in film boiling region is compared with that of highly pressurized spray, it is known that the cooling is improved by introducing air up to 60%.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1465-1468
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• 1997

In this study we investigated the aging characteristic such as leakage current, dielectric loss, contact angle, of EPDM for outdoor use by thermal treatment. And also observed the color change of surface, changing of chemical ingredient of the marterials by optical microscope. SEMI, FTIR and EDX at the section and surface. The test result show that leakage current is increased with thermal aging time. contact angle and dielectric loss is slightly decreased. Moreover, micro-void or crack in bulk is severely increased with aging time. However, the result affect to the tan $\delta$ at bulk of EPDM. It seems that carrier sources are removed by degassing with heat treatment.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.33 no.1
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• pp.21-27
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• 1984

Both of the isother mally and thermally stimulated surface potential decay characteristics(SPDC) have been investigated not only in corona charged polysulfone(PSF) which is one of heat resistant polymer, but also in corona charged polyethyleneterephthalate(PET) and polyfluoroethylene propylene(Teflon FEP) under the same experimental condition. PSF and PET shows similar SPDC in the high teperature region. Also the effect of polarity on SPDC observed from PSF and Teflon FEP shows almost the same phenomenon. From these results, we suggest that the mechanism on SPDC of PSF could be explained as the bulk conductivity from the characteristic analysis concerning PET and electron affivity from characteristic analysis concerning Teflon FEP.

• Transactions of Materials Processing
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• v.13 no.4
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• pp.319-325
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• 2004

Continuous casting machine has been experienced a rapid development to increase productivity with high casting speed and to meet consumer's strict demands for high quality. However, because most of defects and cracks are initially formed in mold and grown into surface cracks during the post process, more specific and clear investigations upon heat transfer mechanism between mold and solidified shell are necessarily needed. In this study heat transfer coefficients which shows the characteristic of heat transfer mechanism are calculated with temperatures measured in bloom mold using optimal algorithm, and thermal analysis are investigated using the calculated heat transfer coefficients. Finally uniformity of solidified shell is investigated for high carbon steel, 0.187%C from thermal analysis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.371-374
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• 2006

Heat transfer characteristic near a sharp fin in a supersonic flow was studied. Infra-red thermography was used to obtain the variation of surface heat transfer coefficient distribution. The attack angle of fin is ranged from $10^{\circ}\;to\;20^{\circ}$ and the oil flow method was also conducted to understand a flow field near a sharp fin.