• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.12
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• pp.1202-1208
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• 2010

The prediction of the required pressurant mass for maintaining the pressure of propellant tanks during propellant feeding is an important issue in designing pressurization system. The temperature of pressurant fed into propellant tank is the critical factor in the required pressurant mass and is one of the most crucial design parameters in the development of pressurization system including designing the weight of pressurant tanks and the size of heat exchanger. Hence a series of propellant drainage tests by pressurizing propellant stored in a cryogenic propellant tank have been performed with measuring the temperature distribution inside ullage and the required pressurant mass according to the temperature condition of pressurant. Results shows that the required pressurant mass decreases as the temperature of pressurant increases. However, the rate of the actual pressurant mass to the ideal required pressurant mass increases.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2012.04a
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• pp.66-69
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• 2012

Field Model에 의한 화재해석방법은 화재현상을 지배하는 망정식윤 직접 해석하기 때문에 Zone model에 비해 공간내의 상세 정보를 제공함과 동시에 다양한 화재형태에 내해 보편적인 적용이 가능하다. Field model은 해석영역을 구성하는 격자점에 대해 이산화된 지배 방정식을 해석하는 과정에서 차분방법이나 격자의 크기에 따라 수치오류가 발생할 수 있다. 특히 격자수는 계산시간에 영향을 미치는 가장 중요한 인자이기 때문에 효율적인 계산을 위해서는 격자크기의 최적화가 이루어져야 한다. 본 연구에서는 구획공간 화재의 최적 격자크기 선정을 위해 격자해상도(Grid Resolution)에 따른 해석결과의 독립성을 비교분석하고 이를 통해 구획공간화재에 대한 격자 최적화 방법에 대해 논의하고자 한다. 화재크기 및 특성 길이에 따른 격자의존성을 파악하기 위해 ISO-9705 표준화재실에 내해 적용된 격자크기는 최소 3 cm에서 최대 30 cm까지 총 7 종류의 격자크기에 대해 FDS 해석이 수행되었다. 해석결과, 환기량이 충분한 화재에 대해서도 격자해상도가 16보다 작은 경우 출입구의 유동은 격자에 따른 독립성을 확보하지 못하는 것으로 나타났으며 화재발열량이 증가함에 따라 독립적인 해석해를 얻기 위해서는 더 큰 격자해상도를 요구하는 것으로 나타났다. 따라서 현재 실무에서 격자최적화를 위해 사용되고 있는 격자선정법에 대한 재검토가 필요하며 화재특성 및 구획공간 조건에 따른 최적격자 조건을 도출하기 위한 추가적인 연구가 필요하다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.5
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• pp.683-690
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• 2021

The ventilation system of the engine room of a ship is generally installed to supply the combustion air necessary for the internal combustion engine and to remove the heat source generated in the engine room, and it must satisfy the international standard (ISO 8861) for the design conditions and calculation standards for the ventilation of the ship engine room. The response delay of the ventilation system including the fire detector is affected by the airflow formed inside the area and the location of the fire detector. In this study, to improve the initial fire detection response speed of a fire detector installed on a fishing vessel and to maintain the sensitivity of the installed detector, the smoke behavior was simulated using the air flow field inside the engine room, the amount of combustion air in the internal combustion engine, and the internal pressure of the engine room as variables. Analysis of the simulation results showed that reducing the flow rate in the air flow field and increasing the vortex by reducing the internal pressure of the engine room and installing a smoke curtain would accelerate the rise of the ceiling of the smoke component and improve the smoke detector response speed and ventilation system.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.2
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• pp.135-148
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• 2013

Recently, road tunnels have become longer and the plans for long and deep road tunnel have been underway in urban areas. These long and deep tunnel excavations include NATM and TBM. Shield TBM is applied to around 80% of traffic tunnels in Europe, and approximately 30% of them in other developed countries. However, as much of equipment is imported from foreign countries at high prices and distribution rate of TBM tunnel is considerably low in Korea, NATM excavation method is commonly used. To increase TBM tunnel, it is necessary to do assure economic feasibility with the supply-demand of TBM equipment. For this, the selection of standardized TBM diameter is urgently needed. Therefore, the study aims to estimate the standardized optimum section properties of TBM by examining TBM excavation cross section utilization depending on the volume of traffic, the number of lane and its cross-section type(single or double deck), and ventilation system.

• Journal of Bio-Environment Control
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• v.11 no.1
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• pp.5-11
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• 2002

In this study, new development of natural ventilation window was accomplished to control environment of greenhouse with no use of farced ventilation during hot season. The ventilation effect of developed ventilation window was investigated in experimental greenhouse which was designed using side wall panel and folding type panel fur natural ventilation. Folding panel type ventilation window was designed to open upper part of the side wall and top of the roof using two hinges which are located bottom of the side wall and the roof panel to grab one side of each panels and guide the other side along with the guidance rail. Developed ventilation window has top ventilation part with maximum moving distance X=ι (1-cos$\theta$)=848.5 mm and side ventilation part with maximum moving distance Y=ι/2 $\times$sin$\theta$=1,184.4 mm at 45$^{\circ}$ of theoretical opening angle. It took 4.5 minutes to open roof vent fully and temperature at 1.2 and 0.8 m height decreased after 1 minute from starting opening and became equilibrium state maintaining 3-4$^{\circ}C$ difference after 2 minutes from complete opening. Air exchange rate was 15.2~39.3 h$^{-1}$ which was more than 10~15 h$^{-1}$ of continuous type and Venlo type greenhouse. The descent effect of temperature by ventilation windows was two times higher than Venlo type greenhouse.

• Horticultural Science & Technology
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• v.33 no.5
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• pp.647-657
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• 2015

To investigate a method for calculation of the heating load for environmental designs of horticultural facilities, measurements of total heating load, infiltration rate, and floor heat flux in a large-scale plastic greenhouse were analyzed comparatively with the calculation results. Effects of ground heat exchange and infiltration loss on the greenhouse heating load were examined. The ranges of the indoor and outdoor temperatures were $13.3{\pm}1.2^{\circ}C$ and $-9.4{\sim}+7.2^{\circ}C$ respectively during the experimental period. It was confirmed that the outdoor temperatures were valid in the range of the design temperatures for the greenhouse heating design in Korea. Average infiltration rate of the experimental greenhouse measured by a gas tracer method was $0.245h^{-1}$. Applying a constant ventilation heat transfer coefficient to the covering area of the greenhouse was found to have a methodological problem in the case of various sizes of greenhouses. Thus, it was considered that the method of using the volume and the infiltration rate of greenhouses was reasonable for the infiltration loss. Floor heat flux measured in the center of the greenhouse tended to increase toward negative slightly according to the differences between indoor and outdoor temperature. By contrast, floor heat flux measured at the side of the greenhouse tended to increase greatly into plus according to the temperature differences. Based on the measured results, a new calculation method for ground heat exchange was developed by adopting the concept of heat loss through the perimeter of greenhouses. The developed method coincided closely with the experimental result. Average transmission heat loss was shown to be directly proportional to the differences between indoor and outdoor temperature, but the average overall heat transfer coefficient tended to decrease. Thus, in calculating the transmission heat loss, the overall heat transfer coefficient must be selected based on design conditions. The overall heat transfer coefficient of the experimental greenhouse averaged $2.73W{\cdot}m^{-2}{\cdot}C^{-1}$, which represents a 60% heat savings rate compared with plastic greenhouses with a single covering. The total heating load included, transmission heat loss of 84.7~95.4%, infiltration loss of 4.4~9.5%, and ground heat exchange of -0.2~+6.3%. The transmission heat loss accounted for larger proportions in groups with low differences between indoor and outdoor temperature, whereas infiltration heat loss played the larger role in groups with high temperature differences. Ground heat exchange could either heighten or lessen the heating load, depending on the difference between indoor and outdoor temperature. Therefore, the selection of a reference temperature difference is important. Since infiltration loss takes on greater importance than ground heat exchange, measures for lessening the infiltration loss are required to conserve energy.

• JOURNAL OF ELECTRICAL WORLD
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• s.277
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• pp.63-68
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• 2000

요 몇 해 사이에 고내압$\cdot$대용량 파워디바이스에서는 아주 새로운 진전이 일어나고 있다. 파워일렉트로닉스 장치의 소형화$\cdot$고효율화 및 제어의 고속화 등의 요구에 응할 수 있는 차세대의 새로운 소자가 출현하여 그 제품화가 비약적으로 진전되고 있는 것이다. 새로운 파워디바이스의 대표적인 것으로는 다음의 3가지를 들 수 있다. $\cdot$HVIGBT(High Voltage Insulated Gate Bipolar Transistor Module)$\cdot$HVIPM(High Voltage Intelligent Power Module)$\cdot$GCT(Gate Commutated Turn-off)사이리스터 이들의 파워디바이스를 종래의 GTO(Gate Turn-off) 사이리스터와 비교해 보면 다음과 같은 특징이 있다.(1)GTO 사이리스터가 필요로 했던 스나버회로가 없어도(Snabber-less)턴오프가 가능하며, di/dt 억제용 아노드리액터의 생략 또는 저감이 가능하기 때문에 반도체 부녀회로의 소형화를 기할 수 있다. (2)게이트파워와 전체손실(소자 및 주변회로를 포함)의 저감으로 에너지 절약을 도모할 수 있다. (3)스위칭주파수를 2$\~$3kHz 정도까지 높일 수 있다. 이런 장점 때문에 다음과 같은 용도에의 적용이 기대되고 있다. (1)신간선, 지하철 등의 전철 응용 (2)액티브필터, SVG(무효전력발생장치), SVC(무효전력보상장치) BTB, 가변속 양수발전 스위치 등의 전력응용 (3) 철강압연이나 제지공장용 등의 대용량공업용 컨버터$\cdot$인버터 응용 HVIGBT와 HVIPM은 전철분야에서 신간선의 추진용 컨버터$\cdot$인버터장치와 보조전원장치, 그리고 지하철의 추진용 인버터 장치나 보조전원장치 등에 채용되고 GCT 사이리스터는 전력용 주파수변환기 등에 실용화되고 있다.

• Tuberculosis and Respiratory Diseases
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• v.52 no.2
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• pp.156-165
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• 2002

Background: A tracheal stenosis is caused by mucosal ischemic injury related to a high cuff pressure ($P_{cuff}$) of the endotracheal tube. In contrast, aspiration of the upper airway secretion and impaired gas exchange due to cuff leakage is related to a low $P_{cuff}$. To prevent these complications, the $P_{cuff}$ should be kept appropriately because the appropriate $P_{cuff}$ appears to change according to the patient's daily respiratory mechanics. However, the constant cuff volume($V_{cuff}$) has frequently been instilled to the cuff balloon on a daily basis to maintain the optimal $P_{cuff}$ instead of monitoring the $P_{cuff}$ directly at the patients' bedside. To address the necessity of continuous $P_{cuff}$ monitoring, the change in the $P_{cuff}$ was evaluated at various $V_{cuff}$ levels on a daily basis in patients with long-term mechanical ventilation. The utility of mercury column sphygmomanometer for the continuous monitoring $P_{cuff}$ was also investigated. Method: The change in $P_{cuff}$ according to the increase in $V_{cuff}$ was observed in 17 patients with prolonged endotracheal intubation for mechanical ventilation for 2 week or more. This maneuver measured the change in $P_{cuff}$ daily during the mechanical ventilation days. In addition, the $P_{cuff}$ measured by mercury column sphygmomanometer was compared with the $P_{cuff}$ measured by an automatic cuff pressure manager. Results : There were no statistically significant changes of $P_{cuff}$ during more than 14 days of intubation for mechanical ventilation. However the $V_{cuff}$ required to maintain the appropriate $P_{cuff}$ varied from 1.9 cc to 9.6 cc. In addition, the intra-individual variation of the $P_{cuff}$ was observed from 10 $cmH_2O$ to 46 $cmH_2O$ at constant 3 cc $V_{cuff}$. The $P_{cuff}$ measured by the bedside mercury column sphygmomanometer is well coincident with that measured by the automatic cuff pressure manager. Conclusion: Continuous monitoring and management of the $P_{cuff}$ to maintain the appropriate $P_{cuff}$ level in order to prevent cuff related problems during long-term mechanical ventilation is recommended. For this purpose, mercury column sphygmomanometer may replace the specific cuff pressure monitoring equipment.

• KOREAN POULTRY JOURNAL
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• v.4 no.8 s.34
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• pp.57-60
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• 1972

여기 산란계 10,000수를 확보한 양계장 주인이 있다고 가정하자. 대부분 다른 사람과 마찬가지로 그도 사소한 일에 도저히 신경쓸 겨를이 없었으나 몇달전 주의를 환기, 첵크해보니 계란 1타스 생산에 약2kg의 사료가 소비됨을 알았다. 그는 사료소비가 약간 높다는 것을 알았지만 사료를 허비하여 비용이 올라가는 줄은 몰랐다. 어느날 부화장 세일즈맨이 와서 계란 1타스 생산에 필요한 기준 사료 요구량은 약 1.86kg라고 했다. 그때 그는 계란 1타스당 140g의 사료가 낭비됨을 알았다. 그래서 곰곰히 계산해보니 1년에 1마리가 계란 20타스 생산하면 1타스당 140g 손실이니 20타스면 2.8kg의 사료를 낭비하고 년간수당 140원의 돈을 버리고 있음을 알았다. 1마리당 140원의 손실은 10,000수면 140,000원의 돈을 매년 버리고 있음을 발견하고 깜짝 놀라지 않을 수 없었다. 다행이도 그는 사소한 사료의 손실이 수익에 얼마나 손해를 끼치게 되는가 알게된 것이다. 그때부터 그는 고용인에게 하루 1회 사료를 주던것을 2회로 나누어 주도록 하고 사료운반통은 좀더 서서히 끌도록 하였다. 지금 그는 계란 1타스당 1.86kg의 사료를 소비하고 있으며 사소한 손실에 신경을 쓴 댓가로 전보다 1년에 140,000원의 돈을 더 벌고 있다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.1
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• pp.29-39
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• 2017

In this research, thermal design data such as heat transfer coefficient on the wall surface required for ventilation system design which is to prevent the temperature rise in the underground utility tunnel that three sides are adjoined with the ground was investigated in numerical analalysis. The numerical model has been devised including the tunnel lining of the underground utility tunnel in order to take account for the heat transfer in the tunnel walls. The air temperature in the tunnel, wall temperature, and the heating value through the wall based on heating value(117~468 kW/km) of the power cable installed in the tunnel and the wind speed in the tunnel(0.5~4.0 m/s) were calculated by CFD simulation. In addition, the wall heat transfer coefficient was computed from the results analysis, and the limit distance used to keep the air temperature in the tunnel stable was examined through the research. The convective heat transfer coefficient at the wall surface shows unstable pattern at the inlet area. However, it converges to a constant value beyond approximately 100 meter. The tunnel wall heat transfer coefficient is $3.1{\sim}9.16W/m^2^{\circ}C$ depending on the wind speed, and following is the dimensionless number:$Nu=1.081Re^{0.4927}({\mu}/{\mu}_w)^{0.14}$. This study has suggested the prediction model of temperature in the tunnel based on the thermal resistance analysis technique, and it is appraised that deviation can be used in the range of 3% estimation.