• Korean Journal of Optics and Photonics
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• v.20 no.5
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• pp.266-271
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• 2009

We designed a thermo-optic switch based on a directional coupler with not only a high extinction ratio but also significantly low power consumption. The switch operates by using the thermo-optic effect of the polymer which the refractive index changes by heating the electrode. If the electrode is not powered (OFF), the input light will be coupled completely to the other waveguide. When the electrode is powered at a certain level (ON), input light launched into the input waveguide will remain in that waveguide due to the lower index adjusted in the other waveguide. The switch based on the directional coupler was designed using the generalized extinction ratio curve and the lateral shift of the input waveguide. The coupling length is 1,610 ${\mu}m$ and the extinction ratios are -28 and -30 dB for ON and OFF states, respectively. The electrode structures were optimized by thermal analysis. The transported heat into the waveguide is increased, as the electrode width (w) is increased and the center distance between the electrode and the waveguide (d) is decreased. Also, because the heat generated in the electrode affects the other waveguide, the temperature difference between two waveguides is varied as the given w and d. There are specific conditions which have the maximum of the temperature difference. That of the temperature difference is increased as the width and the temperature of the electrode are increased. Especially, when the switch is designed using the condition with the maximum of the temperature difference for switching, the temperature of the electrode can be decreased. We expect this condition will be the novel method for the reduction of the power consumption in a thermo-optic switch.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.3
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• pp.171-178
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• 2008

Metal filter elements were newly introduced to the high temperature filter(HTF) system in the low- and intermediate-level radioactive waste vitrification plant. In order to evaluate the performance of various metal materials as filter media, elements made of AISI 316L, AISI 904L, and Inconel 600 were included to the test set of filter elements. At the visual inspection to the elements performed after completion of each test, a few dark spots were observed on the surface of some elements. Especially they were found much more at the AISI 316L elements than others. To check the dark spots are the corrosion phenomena or not, two kinds of analyses were performed to the tested filter elements. Firstly, the surfaces or the cross sections of filter specimens cut out from both normal area and dark spot area of elements were analyzed by SEM/EDS. The results showed that the dark spots were not evidences of corrosion but the deposition of sodium, sulfur and silica compounds volatilized from waste or molten glass. Secondly, the ring tensile strength were analyzed for the ring-shape filter specimens cut out from each kind of element. The result obtained from the strength tested showed no evidence of corrosion as well. Conclusionally, depending on the two kinds of analysis, no evidences of corrosion were found at the tested metal filter elements. But the dark spots formed on the surface could reduce the effective filtering area and increase the overall pressure drop of HTF system. Thus, continuous heating inside filter housing up to dew point will be required normally. And a few long-period test should be followed for the exact evaluation of corrosion of the metal filter elements.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.7
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• pp.492-507
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• 2010

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2009. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends of thermal and fluid engineering have been surveyed as groups of general thermal and fluid flow, fluid machinery and piping, and new and renewable energy. Various topics were covered in the field of general thermal and fluid flow such as an expander, a capillary tube, the flow of micro-channel water blocks, the friction and anti-wear characteristics of nano oils with mixtures of refrigerant oils, etc. Research issues mainly focused on the design of micro-pumps and fans, the heat resistance reliability of axial smoke exhaust fans, and hood systems in the field of fluid machinery and piping. Studies on ground water sources were executed concerning two well type geothermal heat pumps and multi-heat pumps in the field of new and renewable energy. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics and industrial heat exchangers. Researches on heat transfer characteristics included the heat transfer in thermoelectric cooling systems, refrigerants, evaporators, dryers, desiccant rotors. In the area of industrial heat exchangers, researches on high temperature ceramic heat exchangers, plate heat exchangers, frosting on fins of heat exchangers were performed. (3) In the field of refrigeration, papers were presented on alternative refrigerants, system improvements, and the utilization of various energy sources. Refrigeration systems with alternative refrigerants such as hydrocarbons, mixed refrigerants, and $CO_2$ were studied. Efforts to improve the performance of refrigeration systems were made applying various ideas of suction line heat exchangers, subcooling bypass lines and gas injection systems. Studies on heat pump systems using unutilized energy sources such as river water, underground water, and waste heat were also reported. (4) Research trend in the field of mechanical building facilities has been found to be mainly focused on field applications rather than performance improvements. In the area of cogeneration systems, papers on energy and economic analysis, LCC analysis and cost estimating were reported. Studies on ventilation and heat recovery systems introduced the effect on fire and smoke control, and energy reduction. Papers on district cooling and heating systems dealt with design capacity evaluation, application plan and field application. Also, the maintenance and management of building service equipments were presented for HVAC systems. (5) In the field of architectural environment, various studies were carried to improve indoor air quality and to analyze the heat load characteristics of buildings by energy simulation. These studies helped to understand the physics related to building load characteristics and to improve the quality of architectural environment where human beings reside in.

• Journal of the Korean Society of Groundwater Environment
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• v.7 no.1
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• pp.32-46
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• 2000

Hydrogeochemical and isotope ($\delta$$^{18}$ O, $\delta$D, $^3$H, $\delta$$^{13}$ C, $\delta$$^{34}$ S, $^{87}$ Sr/$^{86}$ Sr) studies of various kinds of waters (thermal groundwater, deep groundwater, shallow groundwater, and surface water) from the Yusung area were carried out in order to elucidate their geochemical characteristics such as distribution and behaviour of major/minor elements, geochemical evolution, reservoir temperature, and water-rock interaction of the thermal groundwater. Thermal groundwater of the Yusung area is formed by heating at depth during deep circlulation of groundwater and is evolved into Na-HCO$_3$type water by hydrolysis of silicate minerals with calcite precipitation and mixing of shallow groundwater. High NO$_3$contents of many thermal and deep groundwater samples indicate that the thermal or deep groundwaters were mixed with contaminated shallow groundwater and/or surface water. $\delta$$^{18}$ O and $\delta$D are plotted around the global meteoric water line and there are no differences between the various types of water. Tritium contents of shallow groundwater, deep groundwater and thermal groundwater are quite different, but show that the thermal groundwater was mixed with surface water and/or shallow groundwater during uprising to surface after being heated at depths. $\delta$$^{13}$ C values of all water samples are very low (average -16.3$\textperthousand$%o). Such low $\delta$$^{13}$ C values indicate that the source of carbon is organic material and all waters from the Yusung area were affected by $CO_2$ gas originated from near surface environment. $\delta$$^{34}$ S values show mixing properties of thermal groundwater and shallow groundwater. Based on $^{87}$ Sr/$^{86}$ Sr values, Ca is thought to be originated from the dissolution of plagioclase. Reservoir temperature at depth is estimated to be 100~1$25^{\circ}C$ by calculation of equilibrium method of multiphase system. Therefore, the thermal groundwaters from the Yusung area were formed by heating at depths and evolved by water-rock interaction and mixing with shallow groundwater.

• Journal of Food Hygiene and Safety
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• v.13 no.3
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• pp.278-293
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• 1998

The purposes of this study were to develop Hazard Analysis Critical Control Point-based standardized recipe applicable to cook/chilled Broiled Spanish Mackerel in school foodservice operations and to establish reasonable shelf-life limits by assessing food quality during chilled storage period of 5 days. HACCP for the production of menu items was identified in simulation study. At each critical control point, time-temperature profile was recorded and microbiological analysis was done. Also chemical analyses and sensory evaluation were conducted for 5 days of chilled storage. The results of time-temperature measurement of Broiled Spanish Mackerel by each production phase showed satisfactory condition that met the standards. Broiled Spanish Mackerel showed excellent microbiological quality from raw ingredient phase ($TPC:2.58{\pm}0.12\;Log\;CFU/g$) to holding phase ($TPC:2.70{\pm}0.42\;Log\;CFU/g$). Coliform (0.84 Log MPN/g) and fecal coliform (0.84 Log MPN/g) were detected from marinating phase ($TPC:3.82{\pm}0.52\;Log\;CFU/g$). After heating, only few mesophiles were detected ($TPC:1.83{\pm}0.49\;Log\;CFU/g$). No psychrophiles, coliforms and fecal coliforms were detected. In the phases after rapid chilling, during chilled storage and after reheating and distribution, almost none of the above microbes were detected. Salmonella and Listeria monocytogenes were not detected in all production phases. The pH immediately after cooking was 6.65 and then increased significantly to 6.81 on the third day of chilled storage (p<0.001). Acid value did not show significant changes while total volatile based nitrogen (TVBN) dramatitically increased during storage periods (p<0.01). In the result of sensory evaluation, general acceptability points had been rated high in the first day of storage, and then, the points were decreased significantly on the third day (p<0.05). General acceptability points ranged from 8.86 to 10.68. Accordingly, Broiled Spanish Mackerel is highly recommendable cook/chill system. Considering the DHSS standards for storage, the ideal shelf-life recommended for Broiled Spanish Mackerel is within 4 days excluding cooking day. For Broiled Spanish Mackerel, critical control points were purchasing and receiving of frozen Spanish Mackerel, heating, chilling, chilled storage, reheating and distribution.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.58.1-58.1
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• 2010

In solar cell module manufacturing, single solar cells has to be joined electrically to strings. Copper stripes coated with tin-silver-copper alloy are joined on screen printed silver of solar cells which is called busbar. The bus bar collects the electrons generated in solar cell and it is connected to the next cell in the conventional module manufacturing by a metal stringer using conventional hot air or infrared lamp soldering systems. For thin solar cells, both soldering methods have disadvantages, which heats up the whole cell to high temperatures. Because of the different thermal expansion coefficient, mechanical stresses are induced in the solar cell. Recently, the trend of solar cell is toward thinner thickness below 180um and thus the risk of breakage of solar cells is increasing. This has led to the demand for new joining processes with high productivity and reduced error rates. In our project, we have developed a new method to solder solar cells with a laser heating source. The soldering process using diode laser with wavelength of 980nm was examined. The diode laser used has a maximum power of 60W and a scanner system is used to solder dimension of 6" solar cell and the beam travel speed is optimized. For clamping copper stripe to solar cell, zirconia(ZrO)coated iron pin-spring system is used to clamp both joining parts during a scanner system is traveled. The hot plate temperature that solar cell is positioned during lasersoldering process is optimized. Also, conventional solder joints after $180^{\circ}C$ peel tests are compared to the laser soldering methods. Microstructures in welded zone shows that the diffusion zone between solar cell and metal stripes is better formed than inIR soldering method. It is analyzed that the laser solder joints show no damages to the silicon wafer and no cracks beneath the contact. Peel strength between 4N and 5N are measured, with much shorter joining time than IR solder joints and it is shown that the use of laser soldering reduced the degree of bending of solar cell much less than IR soldering.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.4
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• pp.39-46
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• 2017

This paper presents the fabrication of ceramic insulation layer on metallic heat spreading substrate, i.e. an insulated metal substrate, for planar type heater. Aluminum alloy substrate is preferred as a heat spreading panel due to its high thermal conductivity, machinability and the light weight for the planar type heater which is used at the thermal treatment process of semiconductor device and display component manufacturing. An insulating layer made of ceramic dielectric film that is stable at high temperature has to be coated on the metallic substrate to form a heating element circuit. Two technical issues are raised at the forming of ceramic insulation layer on the metallic substrate; one is delamination and crack between metal and ceramic interface due to their large differences in thermal expansion coefficient, and the other is electrical breakdown due to intrinsic weakness in dielectric or structural defects. In this work, to overcome those problem, selected metal oxide buffer layers were introduced between metal and ceramic layer for mechanical matching, enhancing the adhesion strength, and multi-coating method was applied to improve the film quality and the dielectric breakdown property.

• Korean Journal of Soil Science and Fertilizer
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• v.41 no.6
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• pp.379-386
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• 2008

Calcined clay granules (pellet) have been used as a soil conditioner. The space among the pellets can secure drainage of water in soil and, simultaneously, can keep water for plants in the inner pore of that. However, the usage of the pellet has been restrained because fabrication of that requires a high energy and cost for heating over the temperate of $1000^{\circ}C$. Recently, SCS(Self-propagating Combustion and Sintering) method was developed and this method use the combustion energy of the preliminary mixed combustible. The SCS method is suitable to fabrication of small porous aggregate and requires a very low cost. This research applied the SCS method to coal refuses for fabrication of soil conditioner pellets. The coal refuses were pulverized under the size of $100{\mu}m$ and the pulverized powders were pelletized to the size of 4~6mm. The pellets were heated at the temperature of $1200^{\circ}C$ in the SCS furnace that was specially prepared for this research. Characteristics of the pellets were investigated and were compared with that of ordinary calcined clay pellet of kaolin; porosity, pore size distribution, bulk density, pH and etc.. Characteristics of the moisture retention in the pellets were measured by the centrifugal method: ASTM D425-88. The pellets of the coal refuses showed the higher values of the field capacity and the plant-available water than that of kaolin pellet. These results suggest the very low cost process that can utilize the coal refuses and can fabricate the lightweight porous soil conditioner of the very high plant-available water.

• Journal of Energy Engineering
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• v.27 no.2
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• pp.1-13
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• 2018

The proportion of natural gas-fueled power generation is expanding due to the change of domestic energy policy pursuing reduction of dust and increasing clean energy consumption. Natural gas fuels used for the combined-cycle power plants and the district-heating power plants are operated at high temperature and high pressure in the fuel supply system. Accidents due to leakage of the gas such as fire and explosion should be prevented by applying risk management techniques. In this study, risk assessment was performed on the natural gas fuel supply system of a combined power plant based on the API RP 581 RBI code. For the application of the API RBI code, lines and segments of the evaluation target system were identified. Operational data and input information were analyzed for the calculations of probability of failure and consequence of failure. The results of the risk assessment were analyzed over time from the initial installation time. In the code-based evaluation, the gas fuel supply system was mainly affected by thinning, external damage, and mechanical fatigue damage mechanisms. As the operating time passes, the risk is expected to increase due to the external damage caused by the CUI(Corrosion Under Insulation).

• Journal of Korean Society of Environmental Engineers
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• v.36 no.4
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• pp.231-236
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• 2014

Sawdust, produced as an wood by-product, is usable biomass as liquid fuels if decomposed to monomer unit, because the chemical structure are similar to high octane materials found in gasoline. In this study, parameters of thermochemical degradation by acetone-solvolysis reaction of sawdust such as the effect of reaction temperature, reaction time and type of solvent on conversion yield and degradation products were investigated. The liquid products by acetone-solvolysis from sawdust produced various kind of ketone, phenol and furan compounds. The optimum sawdust conversion was observed to be 88.7% at $350^{\circ}C$, 40min. Combustion heating value of liquid products from thermochemical conversion processes was as high as 7,824 cal/g. The energy yield and mass yield in acetone-solvolysis of sawdust was 60.8% and 36.4 g-oil/100g-sawdust after 40 min of reaction at $350^{\circ}C$, respectively. The major components of the acetone-solvolysis products, that could be used as liquid fuel, were 4-methyl-3-pentene-2-one, 1,3,5-trimethylbezene, 2,6-dimethyl-2,5-heptadiene-4-one, 3-methyl-2-cyclopenten-1-one as ketone compounds.