• 에너지공학
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• 제23권4호
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• pp.9-18
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• 2014

시험방법 중 현재 국내 자동차 연비계산 방법은 차대동력계에 시험차량을 설치한 후, 주어진 시험모드(FTP-75 & HWFET 모드 등)에 따라 차량을 주행하여 측정되어지는 배출가스 결과를 가지고 계산에 의해 연비를 구하는 방식인 카본발란스 측정법(Carbon balance method)을 이용하고 있다. 이때 사용하고 있는 카본발란스 측정법은 시험방법 개발 당시의 표준연료에 대해 연료물성을 구하고, 이때 구하여진 상수 값과 시험에서 측정되어진 THC, CO, $CO_2$ 값을 가지고 계산하게 된다. 그러므로 시험할 때마다 매번 바뀌게 되는 사용 연료의 연료물성 특성은 정확히 고려되지 않게 된다. 주어진 시험연료에 따라 엔진성능 및 배출가스 결과가 변하게 되고, 많은 대체연료가 나오고 있는 현 시점에서 시험연료의 물성 특성을 연비계산 시에도 고려해야만 된다고 생각된다. 본 연구에서는 기존에 사용하고 있는 카본발란스법과 실제 시험에 사용된 연료의 유량을 측정하는 유량측정 방법을 이용한 결과를 비교하여, 시험에 사용된 연료의 물성 특성을 고려할 수 있는 방법을 연구함으로서, 다양해지고 있는 연료의 물성 특성을 고려해 줄 수 있는 개선된 연비측정 방법을 검토해 보고자 한다.

• 한국환경과학회지
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• 제17권11호
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• pp.1243-1253
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• 2008

The seasonal variations of picoplankton including Prochlorococcus, Synechococcus and Picoeukayotes around Ulneung Island were investigated by flow cytometry in spring, summer and autumn in 2006. All groups of picoplankton showed clear seasonal patterns in population abundance. Among the group, Synechococcus showed the most prominent seasonal variation during the study period. The maximal abundance of Synechococcus occurred in summer and the lowest in autumn. The seasonal distribution of Prochlorococcus displayed the reverse tendency with that of Synechococcus. The abundance of Prochlorococcus ranged from $2.9{\times}10^3$ cells/ml in summer to $311{\times}10^3$ cells/ml in autumn. However, the seasonal distribution of Picoeukaryotes was shown to be relatively constant, and the maximal abundance was $81.5{\times}10^3$ cells/ml in summer. The highest abundance of Picoeukaryotes occurred in summer and the lowest in autumn and the seasonal distribution in abundance of Picoeukaryotes showed a similar trend with that of Synechococcus. The estimated total carbon biomass of picoplankton were ranged from $74.7\;mg\;C/m^2$ to $1,055.9\;mg\;C/m^2$. The highest total carbon biomass occurred in summer, but lowest occurred in autumn. The pattern of the contribution of three picoplankton to total autotrophic picoplankton carbon is different. The contribution of Synechococcus to total autotrophic picoplankton carbon is increased to 75%, but the contribution of Prochlorococcus dropped to 12% in summer. The contribution of Picoeukaryotes is ranged from 24% in summer to 72.5% in spring.

• 한국해양공학회지
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• 제18권3호
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• pp.13-19
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• 2004

The structural behavior of a worn tire, attached to carbon fiber steel pile by current and wave forces, has been investigated through the numerical method. The finite element model has been developed, by considering that the composite material of rubber and cord is orthotropic, the rubber is isotropic, and that all the material behaves as linear elastic. The pressure distribution by wave and current, around the worn tire, has been estimated through the adjustment for the concept of flow separation. Also, the structural behavior of the worn tire has been examined, by comparing the situation wherein the space between the pile is reinforced, and tire as elastic and isotropic material, with the one left empty. Through this comparison, it is determined that the space between pile and tire has to be filled with elastic and isotropic material, in order to avoid the failure by wave and current action.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.1201-1206
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• 2003

A measurement device for gas flow rate using hot-wire module is developed for the utilization in low-accuracy industrial applications. The module has three wires of measuring and heating, and a bridge circuit is installed to detect electric current through the wire in the module. An amplification of the signal and conversion to digital output are conducted for the online measurement with a personal computer. In addition, temperature distribution in the module is numerically analyzed to examine the measured outcome from the module experiment. The flow rate of air and carbon dioxide gas is separately measured for the performance examination of the device. The experimental relation of measurement and flow agrees with the prediction from the numerical analysis. The outcome of the performance test indicates that the accuracy and reproducibility of the module is satisfactory for the purpose of industrial applications.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1018-1021
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• 2006

Powdered metal parts and components may be carburized successfully in a vacuum furnace by combining carburizing technology $VacCarb^{TM}$ with a hi-tech control system. This approach is different from traditional carburizing methods, because vacuum carburizing is a non-equilibrium process. It is not possible to set the carbon potential as in a traditional carburizing atmosphere and control its composition in order to obtain a desired carburized case. This paper presents test results that demonstrate that vacuum carburizing system $VacCarb^{TM}$ carburized P.M. materials faster than traditional steel with acceptable results. In the experiments conducted, PM samples with the lowest density and open porosity showed a dramatic increase in the surface carbon content up to 2.5%C and a 3 times deeper case. Currently the boost-diffusion technique is applied to control the surface carbon content and distribution in the case. In the first boost step, the flow of the carburizing gas has to be sufficient to saturate the austenite, while avoiding soot deposition and formation of massive carbides. To accomplish this goal, the proper gas flow rate has to be calculated. In the case of P.M. parts, more carbon can be absorbed by the part's surface because of the additional internal surface area created by pores present in the carburized case. This amount will depend on the density of the part, the densification grade of the surface layer and the stage of the surface. "as machined" or "as sintered". It is believed that enhanced gas diffusion after initial evacuation of the P.M. parts leads to faster carburization from within the pores, especially when pores are open . surface "as sintered" and interconnected . low density. A serious problem with vacuum carburizing is delivery of the carbon in a uniform manner to the work pieces. This led to the development of the different methods of carburizing gas circulation such as the pulse/pump method or the pulse/pause technique applied in SECO/WARWICK's $VacCarb^{TM}$ Technology. In both cases, each pressure change may deliver fresh carburizing atmosphere into the pores and leads to faster carburization from within the pores. Since today's control of vacuum carburizing is based largely on empirical results, presented experiments may lead to better understanding and improved control of the process.

• 설비공학논문집
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• 제15권7호
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• pp.557-562
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• 2003

Flue gas from apartment heating gas boiler is exhausted outside through an exhaust duct mounted horizontally in a vertical row on the wall. The flue gas includes nitrogen-oxides (NOx) and carbon monoxide. To investigate the possible entrainment of the flue gas into the apartments through the windows, a large eddy simulation (LES) based numerical method is utilized. Distribution of the velocity intensity and temperature around the exhaust ducts is presented for three numerical parameters: exhaust velocity, temperature of the flue gas, and exhaust duct length. The flow field visualized with particles inserted at the ends of the ducts is also presented. The results clearly show that the exhausted flue gas may flow into the apartments when the windows are open.

• 한국자동차공학회논문집
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• 제2권3호
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• pp.113-122
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• 1994

This paper describes the effects of combustion parameters on the characteristics of combustion products in swirling flow furnace. The concentration of combustion products and temperature distribution of flow field in the furnace have been investigated by numerical method. The fuel was injected into the furnace and the swirling device was constructed with three kinds of vane swirler at inlet port of furnace. The results of this study showed that the effect of combustion parameters on the concentration characteristics of carbon monoxide and nitrogen monoxide of combustion products. It was found that the pollutant formation wad dependent on the equivalence ratio and swirl intensity level.

• 한국대기환경학회지
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• 제33권1호
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• pp.1-10
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• 2017

Adsorption is a plausible technology using solid adsorbents for dry capture of carbon dioxide ($CO_2$). In general, narrow size distribution of tiny pores and surface chemical functionalities of solid adsorbents enhance the adsorption capacity of gaseous $CO_2$ molecules. In order to utilize the advantages of fibrous adsorbents, this work prepared activated carbon nanofibers (ACNFs) via the electrospinning process using a polymer precursor of polyacylonitrile (PAN). The spun fibers were 390 nm to 580 nm in thickness with an average surface area of $27.3m^2/g$. The surface structure was improved by a programmed thermal activation at $800^{\circ}C$ in $CO_2$ atmosphere. It was also found that the nitrogen-groups including pyrrole and pyridine were created during the activation facilitaing the selective adsorption as forming enhanced active sites. The finally obtained adsorption capacities were 2.74 mmol/g for pure $CO_2$ flow and 0.74mmol/g for 3000 ppm.

• KSBB Journal
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• 제18권5호
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• pp.385-392
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• 2003

초임계 이산화탄소를 이용한 효율적인 DDS 설계를 위한 기초연구로서 순수한 초임계 이산화탄소와 초임계 이산화탄소와 상용성이 있으면서 고분자에 대해서는 비용매로 작용하는 극성 공용매로 변형된 초임계 이산화탄소를 이용하여 생체분해성 고분자인 L-PLA의 미세입자 형성에 대하여 고찰하였다. L-PLA용액의 농도가 증가할수록 입자 크기는 증가하였으며, 약 4%이상의 농도에서는 입자들 간의 강한 응집으로 인하여 입자의 형태가 구형에서 섬유상으로 변화하였다. 침전기 내 초임계 유체의 온도가 높아짐에 따라 생성된 입자의 크기가 증가하였으며, 온도가 높아질수록 입자의 분포는 불균일하게 나타났다. 용액 유량이 증가함에 따라 전체적으로 구형 입자의 생성이 증가하였으며, 입자의 평균 크기는 증가하는 것으로 나타났다. 순수한 초임계 이산화탄소를 사용한 경우 모든 실험 조건에서 입자 회수율은 약 30∼40% 정도로 나타났다. 입자 회수율을 향상시키기 위해 극성 공용매를 초임계 이산화탄소와 혼합하여 입자를 제조하였다. 메탄올과 에탄올을 이산화탄소 대비 몰비 0.5로 혼합한 경우 회수율은 각각 80%와 70%로 매우 높은 값을 나타냈으며, 평균 직경 1 $\mu\textrm{m}$이하의 매우 작은 입자를 제조할 수 있었다.

• 한국물환경학회지
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• 제35권6호
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• pp.557-566
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• 2019

Paldang is a river reservoir in the Midwest of Korea, which is a drinking water source for the metropolitan area. Since the Paldang Reservoir is shallow, and has a short hydraulic residence time, its water quality is directly impacted by two incoming rivers, the north Han River (NHR) and the south Han River (SHR). The NHR has different seasonal patterns of water temperature from the SHR because the NHR is greatly impacted by the discharge water from upstream dams. The electrical conductivity (EC) and other material concentrations of the SHR are usually higher than those of the NHR because its basin is limestone-based. The difference in water temperature in the two rivers causes density flow, and the distribution of the EC within the reservoir can be an indicator for monitoring density flow. From the vertical gradient of the EC at the dam site, from spring to fall, it was confirmed that the SHR flowed into the upper layer, and the NHR flowed into the lower layer, and vice versa at other times. The relative difference (RD) of the EC between the upper layer and the lower layer at the dam site was used as an indicator for density flow. The RD of the EC showed a very significant correlation with the RD of total organic carbon (r = 0.70, p < 0.001) and the RD of total nitrogen (r = 0.58, p < 0.01). This relationship is based on the assumption that the difference in electrical conductivity and water quality between the SHR and the NHR is constant. However, in many cases this assumption is inconsistent. Thus, further study is needed on more suitable indicators to evaluate the impact of density flow on water quality.