• 한국정밀공학회지
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• 제25권12호
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• pp.125-131
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• 2008

In the past, precision optical glass lenses were produced through multiple processes such as grinding and polishing, but mass production of aspheric lenses requiring high accuracy and having complex profile was rather difficult. In such a background, the high-precision optical GMP processes were developed with an eye to mass production of precision optical glass parts by molding press. Generally because the forming stage in a GMP process is operated at high temperature above $570^{\circ}C$, thermal stresses and deformations are generated in the aspheric glass lens mold that is used in GMP process. Thermal stresses and deformations have negative influences on the quality of a glass lens and mold, especially the height of the deformed glass lens will be different from the height of designed glass lens. To prevent the problems of a glass lens mold and the glass lens, it is very important that the thermal stresses and deformations of a glass lens mold at high forming temperature are considered at the glass molds design step. In this study as a fundamental study to develop the molds used in an aspheric glass lens fabrication, a heat transfer and a thermal stress analysis were carried out for the case of one cavity glass lens mold used in progressive GMP process. Finally using analysis results, it was predicted the height of thermally deformed guide ring and calculated the height of the guide ring to be modified, $64.5{\mu}m$. This result was referred to design the glass lens molds for GMP process in production field.

• 한국분말재료학회지
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• 제26권4호
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• pp.290-298
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• 2019

$TiO_2$-particles containing Co grains are fabricated via thermal hydrogenation and selective oxidation of TiCo alloy. For comparison, $TiO_2$-Co composite powders are prepared by two kinds of methods which were the mechanical carbonization and oxidation process, and the conventional mixing process. The microstructural characteristics of the prepared composites are analyzed by X-ray diffraction, field-emission scattering electron microscopy, and transmission electron microscopy. In addition, the composite powders are sintered at $800^{\circ}C$ by spark plasma sintering. The flexural strength and fracture toughness of the sintered samples prepared by thermal hydrogenation and mechanical carbonization are found to be higher than those of the samples prepared by the conventional mixing process. Moreover, the microstructures of sintered samples prepared by thermal hydrogenation and mechanical carbonization processes are found to be similar. The difference in the mechanical properties of sintered samples prepared by thermal hydrogenation and mechanical carbonization processes is attributed to the different sizes of metallic Co particles in the samples.

• 분석과학
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• 제27권5호
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• pp.254-260
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• 2014

본 연구에서는 열처리 공정에서 발생하는 폐기물 중 무기물질류 15 종과, 유기물질류 24 종 (PCDD/PCDFs, PAHs)에 대한 배출 특성을 파악하고자 수행하였다. 납 열적 야금에서 발생하는 폐기물 (EWC 10 04)에서 규제 무기금속물질류 중 Pb은 가장 높은 농도를 보였다. 이는 EWC 10 04에서 분진으로 인한 결과로 판단된다. 아연 열적 야금에서 발생하는 폐기물(EWC 10 05)에서 규제 무기금속물질류 중 Zn이 높은 농도로 나타나 EWC 10 05에서 분진으로 인한 결과로 판단되며, 또한 구리 열적 야금에서 발생하는 폐기물(EWC 10 06)에서 Cu가 65,177 mg/kg으로 규제기준 (100 mg/kg)보다 651 배 높게 나타난 것은 EWC 10 06에서 분진으로 인한 결과로 판단된다. 분진은 다이옥신 0.0005~11.748 ng-TEQ/g으로 검출되었고, 소각재는 0.0027 ng-TEQ/g로 나타났다. 다이옥신의 규제기준을 초과하는 시료는 없는 것으로 조사되었다. PAHs의 함량은 Naphthalene는 ND~118.9 mg/kg, Phenanthrene는 ND~9.6 mg/kg, Benzo[b]fluoranthene은 ND~48.4 mg/kg, Benzo[a]pyrene는 ND~62.6 mg/kg, Fluoranthene는 ND~10.7 mg/kg, Benzo[a]anthracene는 ND~11.5 mg/kg의 범위로 나타났다.

• Structural Engineering and Mechanics
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• 제83권5호
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• pp.645-654
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• 2022

Environmental thermal loads such as vertical and lateral temperature gradients are significant factors that must be taken into account when designing the bridge. Different models have been developed and used by countries for simulating thermal gradients in bridge codes. In most of the codes only vertical temperature gradients are considered, such as Iranian Standard Loads for Bridge code (ISLB), which only considers the vertical gradient for bridge design proposes. On the other hand, the vertical gradient profile specified in ISLB, has many lacks due to the diversity of climate in Iran, and only one vertical gradient profile is defined for whole Iran. This paper aims to get the both vertical and lateral gradient loads for the concrete box girder using experimental analysis in the capital of Iran, Tehran. To fulfill this aim, thermocouples are installed in experimental concrete segment and temperatures in different location of the segment are recorded. A three dimensional finite element model of concrete box-girder bridge is constructed to study the effects of thermal loads. Results of investigation proved that the effects of thermal loads are not negligible, and must be considered in design processes. Moreover, a solution for reducing the negative effects of thermal gradients in bridges is proposed. Results of the simulation show that using one layer polyurethane insulation can significantly reduce the thermal gradients and thermal stresses.

• 에너지공학
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• 제13권2호
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• pp.112-117
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• 2004

휘발성 유기물질은 도장공정, 염색, 건조공정 등 화학공정에서 발생하는 저발열량 가스이다 VOCs의 특징은 발열량이 150kcal/㎥ 이하이며 착화를 위한 활성화 에너지가 높고 발생 에너지가 낮다는 것이다. 따라서 연소 안정성은 낮아지고 처리공정은 고에너지 소비공정이 된다. Cyclone연소시스템은 연소기 내에 강한 선회 유동을 만들어서 에너지를 순환시켜 활성화에너지를 낮추어주고 열밀도가 높아 일반적인 swirl 연소 시스템에 비해 고온의 연소온도를 유지할 수 있으며 혼합성을 향상시킨다 본 논문에서는 휘발성 유기물질의 열산화를 위해 최적의 cyclone 연소시스템을 개발하는 것을 목적으로 수행되었으며 특별히 설계된 연소기에서 연소온도와 배가스 조성에 미치는 swirl number의 영향을 정립하였다.

• 한국축산식품학회지
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• 제40권3호
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• pp.323-337
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• 2020

This study was conducted to investigate whether adding different levels of raw or differently processed chickpea into different diets of laying quails affected live weight, feed intake, feed efficiency, egg weight and internal and external egg quality. Chickpea was used as raw, autoclaved or microwave-processed, and it was involved in the diets on two different levels (20% and 40%). The sample was divided into 7 groups including the control, 20% and 40% raw, 20% and 40% autoclaved, and 20% and 40% microwave-processed groups. 336 ten-week-old female laying quails were used in the study, and the experiment continued for 19 weeks. In the study, the differences among the groups were insignificant in terms of live weight, feed intake, feed efficiency, egg weight and egg quality characteristics such as shell thickness, shell weight, yolk weight, yolk color and albumin index. The differences were significant in terms of the shape index, Haugh unit (p<0.05) and yolk index (p<0.01). Consequently, it was observed that different thermal processes on chickpeas did not usually have a significant effect on the yield performance of the quails, and the results that were obtained were similar to the other groups. However, it was determined that some egg quality characteristics were affected by the autoclaving and microwaving processes. Between the thermal processes, it may be stated that autoclaving provided better results.

• Journal of Ship and Ocean Technology
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• 제11권3호
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• pp.14-23
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• 2007

Welding processes cause undesirable problems, such as residual stresses and deformations due to the thermal loads imposed by local heating, melting, and cooling processes. This paper presents a computational modeling technique to simulate the Gas Metal Arc Welding (GMAW) process, emphasizing the effect of the melting bead on the residual stress distribution. Both a three-bar analogy and a three-dimensional thermo-mechanical finite element analysis are carried out in order to explain the effect. Element (de)activation, enthalpy, and adjustment of the reference temperature of thermal strain are considered with respect to the effect of the weld filler metal added to the base metal during a thermo-elastic-plastic analysis. Stress distributions obtained by the present study are compared with measured values and available data from other studies. The effect of the melting bead on the residual stress distribution is discussed and demonstrated.

• Environmental Engineering Research
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• 제16권1호
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• pp.1-9
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• 2011

During automotive painting, volatile organic compounds (VOCs) associated with the paint solvents are emitted to the atmosphere. Most VOC emissions come from spraying operations via the use of solvent-based paints, as the spraybooth air picks up gaseous solvent compounds and overspray paint materials. The VOCs consist of aromatic and aliphatic hydrocarbons, ketones, esters, alcohols, and glycolethers. Most VOCs (some hydrophilic VOCs are captured and retained in the water.) are captured by an adsorption system and thermally oxidized. In this paper, the processes involved in automotive painting and in VOC control are reviewed. The topics include: painting operations (briefly), the nature of VOCs, VOC-control processes (adsorption, absorption, biological removal, and thermal oxidation) and energy recovery from VOCs using a fuel reformer and a fuel cell, and the beneficial use of paint sludge.

• 한국연소학회지
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• 제4권2호
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• pp.51-62
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• 1999

NOx formation in turbulent flames is strongly coupled with temperature, superequilibrium concentration of O radical, and residence time. This implies that in order to accurately predict NO level, it is necessary to develop sophisticated models able to account for the complex turbulent combustion processes including turbulence/chemistry interaction and radiative heat transfer. The present study numerically investigates the turbulent nonpremixed hydrogen jet flames using the laminar flamelet model. Flamelet library is constructed by solving the modified Peters equations and the turbulent combustion model is extended to nonadiabatic flame by introducing the enthalpy defect. The effects of turbulent fluctuation are taken into account by the presumed joint PDFs for mixture fraction, scalar dissipation rate, and enthalpy defect. The predictive capability of the present model has been validated against the detailed experimental data. Effects of nonequilibrium chemistry and radiative heat loss on the thermal NO formation are discussed in detail.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.93-104
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• 1999

NOx formation in turbulent flames is strongly coupled with temperature, superequilibrium concentration of O radical, and residence time. This implies that in order to accurately predict NO level, it is necessary to develop sophisticated models able to account for the complex turbulent combustion processes including turbulence/chemistry interaction and radiative heat transfer. The present study numerically investigates the turbulent nonpremixed hydrogen jet flames using the laminar flamelet model. Flamelet library is constructed by solving the modified Peters equations and the turbulent combustion model is extended to nonadiabatic flame by introducing the enthalpy defect. The effects of turbulent fluctuation are taken into account by the presumed joint PDFs for mixture fraction, scalar dissipation rate, and enthalpy defect. The predictive capability of the present model has been validated against the detailed experimental data. Effects of nonequilibrium chemistry and radiative heat loss on the thermal NO formation are discussed in detail.