• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.267-273
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• 2013

In order to provide effective operating conditions for the fan in a wet cooling tower with film fill, a new program to search for the minimum fan power was developed using a model of the optimal total annual cost of the tower based on Merkel's model. In addition, a type of design map for a cooling tower was also developed. The inlet water temperature and heat load were considered as key parameters. The present program was first validated using several typical examples. The results showed that for a given heat load, a three-dimensional graph of the fan power (z-axis), mass flux of air (x-axis, minimum fan power), and inlet water temperature (y-axis, maximum of minimum fan power) showed a saddle configuration. The minimum fan power increased as the heat load increased. The conventionally known fact that the most effective cooling tower operation coincides with a high inlet water temperature and low air flow rate can be replaced by the statement that there exists an optimum mass flux of air corresponding to a minimum fan power for a given inlet water temperature, regardless of the heat load.

• Membrane Journal
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• v.27 no.1
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• pp.68-76
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• 2017

Flat membrane with $0.4{\mu}m$ pore size was prepared with PVdF (polyvinylidene fluoride) nanofiber, which has the advantages such as excellent strength, chemical resistance, non-toxicity, and incombustibility. The spiral wound module was manufactured with the flat membrane and a woven paper. Hybrid water treatment process was composed of the PVdF nanofibers spiral wound microfiltration and granular activated carbon (GAC) adsorption column. Effect of GAC packing mass was investigated by comparing the case of recycling or discharging the treated water using the synthetic solution of kaolin and humic acid. After each filtration experiment, water back-washing was performed, and recovery rate and filtration resistances were calculated. Also, effect of GAC adsorption was compared by measuring turbidity and $UV_{254}$ absorbance. As a result, there was no effect of GAC packing mass on turbidity treatment rate; however, the treatment rate of $UV_{254}$ absorbance was 0.7~3.6% for recycling the treated water, and increased to 3.2-5.7% for discharging the treated water. In the case of recycling the treated water, reversible filtration resistance ($R_r$) and irreversible filtration resistance ($R_{ir}$) trended to decrease as increasing GAC packing mass; however, total fitration resistance ($R_t$) was almost constant, and recovery rate of water back-washing trended to increase a little.

• Solar Energy
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• v.10 no.2
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• pp.38-43
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• 1990

The present study was to investigate the use of a phase change material for hydronic radiant floor heating. Two identical unit test cells sized $1.8m^L{\times}1.8m^W{\times}1.8m^H$ were built and installed with specially designed $1.6cm^T{\times}9cm^W{\times}80cm^H$ aluminum Ondol-panels holding 1.25kg of calcium chloride hexahydrate(CCH) each. It was found that the Ondol-panel with CCH reduced the room temperature fluctuations and maintains the phase changing temperature for considerably long duration, $2{\sim}4$ times of heating hour, over no-CCH one.

• Journal of Energy Engineering
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• v.26 no.4
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• pp.84-91
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• 2017

Fiber reinforced plastic (FRP) is a typical plastic composite which is fabricated using fiber reinforcement with resin to represent the high strength properties. The mechanical properties of FRP should be determined by a fibrous material, and the studies about the role of fiber as a reinforcement has been an interested subject, whereas a study along the effect of filler is not so big. However, the filler effect must be considered on the properties of the composite, because the filler influence on the plastic or resin compound which reacts as a matrix material of the composite. Thus, in this work, we studied the filler effect with size and content using $3-6{\mu}m$ of ground calcium carbonate. The specimen was prepared by sheet molding compound (SMC) method, and the mechanical properties were compared with bending strength and tensile strength. As a result, it was confirmed that the size and contents of calcium carbonate affected the strength of composites, and the condition of $2.8{\mu}m$ which was the smallest size condition showed the highest strength.

• Journal of the Korean Wood Science and Technology
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• v.38 no.4
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• pp.298-305
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• 2010

The effects of wood species, chemical components, filler loading level, filler particle size, and coupling agent on the water absorption property of the wood flour filled polypropylene (PP) composites were investigated in this study. After 500, 1,000, 1,500, 2,000, 2,500 and 3,000 hr water immersion, Quercus (Quercus accutisima Carr.) and Maackia (Maackia amuresis Rupr. et Maxim) showed significantly lower water absorption properties compared to Larix (Larix kaempferi Lamb.). As wood flour loading increases from 10 to 50 wt%, most wood species showed increased water absorption after a given immersion period. Particle size of wood flour proved to have very significant effects on water absorption of the composites. The effect of coupling agent was positive in terms of lowering water absorption of the composites. As the treatment level of coupling agent increases, the water absorption of the composites decreases. The lowest water absorption was obtained at the lower wood flour loading (Maackia), smaller particle size and by the addition of coupling agent. Thickness swelling of the composites shows close dependency on water absorption.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.2
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• pp.62-71
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• 2000

The abandoned mines causing settlement of the surface above and collapse of the cavities are the major influencing factor on the stability of the nearby underground structures. To prevent the harmful effect, the backfill methods are commonly applied to the cavities although the design criteria and the analysis method are not properly addressed in some cases. An approximate analytical method together with the numerical technique is considered in this study to simulate the gradual deterioration of the rock masses around the cavities and, therefore, the influential zone to the underground structures passing through the cavities. Also considered in this study is the backfill effect on the stability of the rock masses around the cavities. Specifically, the incomplete backfill effect is compared with that of the idealized backfill method by adopting elasto-plastic analysis involving a strain softening material law.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.1
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• pp.109-116
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• 2012

This paper presents a study on the nonlinear behavior of an innovative bridge girder made from concrete-filled and tied tubular steel arch (CFTA) under static loading. Manufacturing of the CFTA girder may have defects which may highly affect the symmetry and performance of the structure. A simple method is proposed by using stiffness extracted from static test data to detect manufacturing defects of the CFTA girder. A three-dimensional finite element model was used in the numerical analysis in order to verify the method. The proposed method was experimentally validated through static tests of the CFTA girder. The application of the proposed method showed that it is effective in identifying invisible manufacturing defects of the CFTA girder, especially for mass production of a standard type in the factory.

• Journal of the korean Society of Automotive Engineers
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• v.7 no.4
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• pp.24-31
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• 1985

본 논문은 Comprex압력파 과급기(Pressure-wave Supercharger;이하 PWS)의 공기 역학적인 원 리에 대해 기술하였으며, 또 기체 동력학적인 현상들이 별도의 제어장치없이도 우수한 운전성과 낮은 연료소모율, 적은 배기 배출물을 형성하는 차량들에 대해 기계적으로는 간단하면서도 완벽 한 boosting장치를 만들어 내는데 어떻게 사용될 수 있는지를 설명하였다. 근본적인 목적은 종 래의 turbo charger와 동일이지만 Comprex PWS는 현재 응용되고 있는 승용차가 요구하는 여러 가지면, 즉 1) 부하변동에 대한 충진공기압의 빠른 응답성 2) 엔진속도 전영역에 걸친 높은 boost 효과 3) 배기배출물특성을 좋게할 수 있는 배기가스 재순환(EGR)효과 등에서 종래의 것과 구별된다. 따라서 PWS의 중요한 특징들을 기술하였으며 마지막으로 최근 자동차용 Diesel Engine에의 몇 가지 예를 보았다.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.483-486
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• 2003

본 연구는 운동장, 주차장, 도로측면, 보도, 기타 주거시설 등의 우수 찻집시설에 사용되는 콘크리트 구조물의 침투능 확보를 위한 투수성 찻집 구조물 개발에 관한 것이다. 투수성을 확보하기 위하여 일반 차집시설의 콘크리트 구조체 벽면에 천공을 하고 천공된 측구 내에 쇄석을 충진시켜 침투되는 우수의 수질도 개선할 수 있다. 본 제작방법은 별도의 침투소재를 사용하는 경우와 비교해 볼 때 경제성이 우수하며 동일시공방법과 규격으로 대체재로서 활용성이 높을 것으로 전망된다, 본 연구에서 개발하고 있는 여재를 이용한 침투시설은 침투능을 충분히 확보할 수 있음을 확인하였고 SS기준으로 27％∼86％의 제거율을 보였으며, COD기준 20％∼68％의 제거율을 나타냈으며, 탁도기준 29％∼88％의 제거율을 볼 수 이었다.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.09a
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• pp.220-223
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• 2001

본 연구에서는 endosulfan으로 오염된 토양을 in-situ flushing으로 정화시 발생되는 세척 유출수의 고정화 미생물에 의한 처리 효율 및 적용성을 검토하였다. 초기 endosulfan 농도 및 pH가 각각 5mg/L, 5.6인 세척유출수의 체류시간을 1, 3, 5시간으로 하여 고정화미생 물 충진 컬럼에 적용한 결과, 제거효율은 각각 62, 82, 89%로 체류시간이 증가될수록 향상되었으며 3가지 조건 모두 약 80시간 이후에 정상상태에 도달하였다. 체류시간 3시간에서 유입수내 endosulfan 농도를 50mg/L 및 100mg/L로 증가시킨 결과, 제거효율이 각각 70% 및 50% 부근까지 저하되었다. 유입수의 pH를 4.0과 9.0으로 변화시켜 실험한 결과 각각 73%와 66%의 제거효율을 나타내었다. pH 9.0보다 4.0에서 제거효율이 약간 높은 이유는 사용 배지의 pH가 약산성을 띠기 때문에 알칼리 상태보다 약산성에서 미생물의 활성이 높기 때문으로 판단된다. 유출수를 재순환 시킨 결과 제거효율이 90%까지 향상되는 것을 볼 수 있었으며, 이는 재 순환되는 유출수의 농도 저감 및 고정화 미생물과의 재 접촉에 기인하는 것으로 판단된다. 유입수에 공기를 주입한 결과, 유출수의 재순환 없이도 약 40시간 후에 93%의 제거효율을 보였으며 이는 미생물 활성의 증가에 기인하는 것으로 판단된다.