• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.707-714
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• 2014

CFT (Concrete-Filled Tube) is a type of steel column comprised of steel tube and concrete. Steel tube holds concrete and the concrete inside tube takes charge of compressive load. This study presents structural performance of the CFT column which has 73~100 MPa high strength concrete inside. Fluidity, mechanical compression, pump pressure test in flexible pipe were conducted for understanding properties of the high strength concrete. Material properties were achieved by various experimental tests, such as slump, slump flow, air content, U-box, O-Lot, L-flow. In addition, mock-up tests were conducted to monitor concrete filling, hydration heat, compressive strength. From construction sites in Sang-am dong and University of Seo-kang, long-term behaviors could be effectively predicted in terms of ACI 209 material model considering elastic deformation, shrinkage and creep.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2002.02a
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• pp.151-157
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• 2002

화석에너지에 대한 경제적 부담과 환경오염문제를 줄이기 위하여 열펌프의 성능계수향상을 위하여 냉온 공기열교환기(HEEVA)를 고안하였고, 이 열교환기의 열특성과 성능계수향상에 미치는 영향을 분석하기 위하여 냉.난방 실험을 수행하였다. HEEVA에 의한 찬 공기와 더운 공기의 온도변화, 전열량 및 냉온 공기열교환기 효율, 총열전달계수등을 측정분석하였고, 냉난방시 외기온에 따른 열펌프의 성능계수, 소비전력, 응축기.증발기 출구 공기토출 온도 변화를 측정 분석함으로서 다음과 같은 결과를 얻을 수 있었다. 1. 외기온이 -4~11$^{\circ}C$로 변할 때 열펌프의 난방과정에서 HEEVA 찬공기 입출구 온도차는 4.5$^{\circ}C$에서 9.$0^{\circ}C$로 증가하였으며, HEEVA에 의한 영향으로 2~6$^{\circ}C$상승된 공기가 증발기 입구로 유입되어 냉매증발을 촉진하였다. 2. 실온이 4~22$^{\circ}C$일 때 HEEVA 더운공기 입출구 온도차는 3$^{\circ}C$에서 7$^{\circ}C$로 증가하였으며, 응축기에 유입되는 공기온도를 3~8$^{\circ}C$낮게 함으로서 압축기 소모전력을 감소시켜 COP 상승 효과를 나타냈다. 3. 외기온과 실온변화에 따라 풍량 346m$^3$/hr의 찬 공기가 받은 열량과 풍량 747m$^3$/hr의 더운 공기가 준 열량간의 차는 50~150kcal/hr로 나타났으며, 더운 공기가 준열량과 찬 공기가 받은 열량의 비가 83~98% 이었으므로 HEEVA의 열 교환율은 91% 을 보였다. 4. 총합열전달계수는 이론값이 실험 값보다 1~3W/m$^2$K 크게 나타났으며, 이 결과는 두 값 사이에 10% 내.외의 편차로서 Nusselt수를 구하기 위한 Petukhov상관식의 자체오차 15%에 비해 크지 않은 오차범주에 속하며, 이론상의 총합열전달계수 유도식의 타당성을 입증한 것이라 하겠다. 5. HEEVA를 작동함으로서 난방시 COP가 HEEVA를 작동하지 않았을 경우보다 0.3~0.5 향상된 것으로 나타났다. 이것은 HEEVA가 겨울철 난방에 효율을 높일수 있는 것으로 판단된다.

• Journal of Korean Society on Water Environment
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• v.22 no.3
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• pp.534-539
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• 2006

The supply of oxygen for aeration is the largest energy consumer at activated sludge wastewater treatment plants. Replacement of less efficient aeration systems with fine pore aeration devices can save up to 50 percent of aeration energy costs. The purpose of this study was the diagnosis and evaluation of a domestic wastewater aeration system by the off-gas method which had been studied by US EPA and ASCE. For this study, an off-gas analyzer and its hood were made to collect off-gas. Also, a vacuum pump was connected to the analyzer to make suction of off-gas. Experiments were conducted at a domestic activated sludge wastewater treatment plant which had a single spiral roll aeration system installed with P.E tube diffuser. Data on OTE(f), SOTE(pw), OUR, and air flow rate were obtained from these experiments. In case of replacing an aeration system, it is recommended that it should be replaced with perforated membrane disc or ceramic disc fine bubble diffusers installed in a full floor coverage or grid pattern.

• Journal of the korean society of oceanography
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• v.36 no.1
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• pp.19-26
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• 2001

The biological pump is one of the important pumping mechanisms absorbing CO$_2$ from the atmosphere into the ocean and can be quantified by estimating new production. New production in the open ocean mostly depends on the supply of nitrate from the water below the mixed layer. While nitrate is affected by many biological processes, the helium isotope ($^3$He) is inert and has very simple physical properties. Using the $^3$He flux and the relation between $^3$He and NO${_3}\;{^-}$- within the thermocline, the nitrate flux supporting new production was estimated in the southern East Sea. The average ${\delta}^3$He within the mixed layer was -14$%_o$ and -l5.4$%_o$ in the winter and autumn, respectively. Through the year excess $^3$He occurs in the mixed layer except for a slight depletion of -17$%_o$ in summer. The $^3$He flux of 13$%_o$md$^{-1}$ associated with the concentration gradient at the air-sea interface was calculated from the product of the piston velocity and the excess $^3$He. Tritium decay within the mixed layer could support only 2$%_o$md$^{-1}$ of the flux. Thus, the remaining 11$%_o$md^{-1}$ could be attributed to the flux of tritiugenic $^3$He from the water below the mixed layer. Nitrate and $^3$He were positively correlated within the thermocline layer with the slope of 0.21 ${\mu}$mol kg$^{-1}$ $%_o\;^{-1}$. The annual nitrate flux estimated from the upward flux of $^3$He and the NO$_{3}\;{^-}$-$^3$He relation was 0.8${\pm}$0.2 mol(N) m$^{-2}$yr$^{-1}$. This flux corresponds to an annual new production of 64 g(C) m$^{-2}$yr$^{-1}$, which is consistent with that in the north-west Pacific.

• Smart Structures and Systems
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• v.18 no.3
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• pp.405-423
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• 2016

In this study, the feasibility of using telecommunication single-mode optical fiber (SMF) as a distributed fiber optic strain and crack sensor was evaluated in concrete pavement monitoring. Tensile tests on various sensors indicated that the $SMF-28e^+$ fiber revealed linear elastic behavior to rupture at approximately 26 N load and 2.6% strain. Six full-scale concrete panels were prepared and tested under truck and three-point loads to quantify the performance of sensors with pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA). The sensors were protected by precast mortar from brutal action during concrete casting. Once air-cured for 2 hours after initial setting, half a mortar cylinder of 12 mm in diameter ensured that the protected sensors remained functional during and after concrete casting. The strains measured from PPP-BOTDA with a sensitivity coefficient of $5.43{\times}10^{-5}GHz/{\mu}{\varepsilon}$ were validated locally by commercial fiber Bragg grating (FBG) sensors. Unlike the point FBG sensors, the distributed PPP-BOTDA sensors can be utilized to effectively locate multiple cracks. Depending on their layout, the distributed sensors can provide one- or two-dimensional strain fields in pavement panels. The width of both micro and major cracks can be linearly related to the peak strain directly measured with the distributed fiber optic sensor.

• Korean Journal of Agricultural Science
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• v.46 no.1
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• pp.33-44
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• 2019

This study was conducted to examine the components of phytoncide from a pine forest in the southern temperate zone. Recent studies have found that a large amount of phytoncide is released not only from cypress trees but also from pine trees. Because the amount released is the highest during summer, we selected a warm climate region in the southern temperate zone and measured the concentration in the month of August. To capture the phytoncide from the forest atmosphere, we used the adsorption tube method with a mini pump and successfully gathered 9 L of forest air at a flow rate of 150 mL/min. We performed duplicate sampling from two different tubes installed at the same location and derived the mean value. A gas chromatography/mass spectrometer detector with thermal desorption spectroscopy was utilized to perform quantitative and qualitative analyses of the captured material. The results showed that the average phytoncide particle of the pine forest in the southern temperate zone contained a number of components as follows in descending order: ${\alpha}$-Pinene (39%, $0.28ng/m^3$), followed by ${\beta}$-Pinene (16%, $0.11ng/m^3$), D-Limonene (8%, $0.06ng/m^3$), camphor (6%, $0.04ng/m^3$), camphene (6%, $0.04ng/m^3$), and p-Cymene (5%, $0.04ng/m^3$). There were also 13 additional phytoncide components in trace amounts. The results of this study are expected to provide a useful dataset for building a "Healing-forest".

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.4
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• pp.303-311
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• 2019

Reversible solid oxide fuel cell (RSOFC) has become a prospective device for energy storage and hydrogen production. Many studies have been conducted around the world focusing on system efficiency improvement and realization. The system should have not only high efficiency but also a certain level of simplicity for stable operation. External waste steam utilization was proved to remarkably increase the efficiency at solid oxide electrolysis system. In this study, RSOFC system coupled with waste steam was proposed and optimized in term of simplicity and efficiency. Ejector for fuel recirculation is selected due to its simple design and high stability. Three system configurations using ejector for fuel recirculation were investigated for performance of design condition. In parametric study, the system efficiencies at different current density were analyzed. The system configurations were simulated using validated lumped model in EBSILON(R) program. The system components, balance of plants, were designed to work in both electrolysis and fuel cell modes, and their off-design characteristics were taken into account. The base case calculation shows that, the system with suction pump results in slightly lower efficiency but stack can be operated more stable with same inlet pressure of fuel and air electrode.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.29 no.2
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• pp.176-184
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• 2019

Objective: This study aims to characterize airborne radon and thoron levels ($Bq/m^3$) generated from working environments in three subway stations in Seoul. Method: A radon and thoron detector (EQF3220) was used to monitor real-time airborne radon and thoron levels ($Bq/m^3$) and their daughters ($Bq/m^3$) every two hours. They were monitored not only in the driver's cabin of seven circulation lines, but also three offices, platforms, and water pump reservoirs in the three stations. Results: The average levels of radon and thoron were $67.9Bq/m^3$ (range; $7.2-619.4Bq/m^3$) and $44.4Bq/m^3$ (range; $4.3-819.2Bq/m^3$), respectively. Notably, higher than legal airborne radon levels ($600Bq/m^3$) were frequently monitored in the driver's cabin of seven circulation lines. Airborne radon levels monitored in the platforms and administrative offices were found to be over $100Bq/m^3$. The average equilibrium factors (F) were 0.12 and 0.06, respectively. The percentages detected were found to be 84.9 for radon and 72.4 for thoron, respectively. Conclusions: Significant airborne radon and thoron levels were frequently found to be generated in subway facilities including water reservoirs, platforms and driver's cabins. Further study is necessary to thoroughly investigate airborne radon and thoron in all subway stations and to devise proper measures.

• Journal of the Semiconductor & Display Technology
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• v.21 no.4
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• pp.18-22
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• 2022

Photovoltaics (PV) power generation efficiency is affected by meteorological factors such as temperature and wind speed. In general, it is known that the power generation amount decreases because photovoltaics panel temperature rises and the power generation efficiency decreases in summer. Photovoltaics Thermal (PVT) power generation has the ad-vantage of being able to produce heat together with power, as well as preventing the reduction in power generation efficien-cy and output due to the temperature rise of the panel. In this study, the amount of heat collected by season and time was calculated for photovoltaics thermal modules using the International Weather for Energy Calculations (IWEC) data provided by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). Based on this, we propose a method of predicting the temperature of the photovoltaics panel using thermal analysis and then calculating the flow rate of coolant to improve power generation efficiency. As the results, the photovoltaics efficiencies versus time on January, April, July, and October in Jeju of the Republic of Korea were calculated to the range of 15.06% to 17.83%, and the maxi-mum cooling load and flow rate for the photovoltaics thermal module were calculated to 121.16 W and 45 cc/min, respec-tively. Though this study, it could be concluded that the photovoltaics thermal system can be composed of up to 53 modules with targeting the Jeju, since the maximum capacity of the coolant circulation pump of the photovoltaics thermal system applied in this study is 2,400 cc/min.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.6
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• pp.667-672
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• 2023

This study proposes polymer electrolyte membrane fuel cell (PEMFC) based cogeneration system for greenhouse heating and cooling. The main scope of this study is to examine the proposed cogeneration system's suitability for the 660 m²-class greenhouse. A 25 kW PEMFC system generates electricity for two identical air-cooled heat pumps, each with a nominal heating capacity of 70 kW and a cooling capacity of 65 kW. Heat recovered from the fuel cell supports the heat pump, supplying hot water to the greenhouse. In cooling mode, the adsorption system provides cold water to the greenhouse using recovered heat from the fuel cell. As a result, the cogeneration system satisfies both heating and cooling capability, performing 175 and 145 kW, respectively.