• 터널과지하공간
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• 제28권6호
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• pp.596-608
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• 2018

도시 기반시설이 노후화됨에 따라 도시 재난 발생 가능성이 증가하고 있다. 특히, 하수관로, 상수도관망, 지하철 등 노후화된 지하 시설물은 도심지 지반함몰을 유발하는 잠재적 원인이 된다. 도심지 지반함몰은 토양 침식 혹은 유실로 인해 생성된 지하 공동이 확장하여 지역적이고 갑작스런 지반 붕괴까지 이르는 현상으로 정의할 수 있다. 이는 석회암과 같은 용해성 암반에서 발생하는 싱크홀과는 구분된다. 지반 거동과 관련된 전통적인 계측 방식은 좁은 측정 범위와 각 센싱 지점에서의 계측값을 제공하기 때문에 불특정 다수 지역에서 발생할 수 있는 지반함몰 감시체계로서 한계가 있다. 따라서, 도시에 발생하는 지하 공동에 의한 지반함몰을 예방하기 위한 감시체계로서는 적절하지 않으며 지반 내 물리적 환경변화를 감시할 수 있는 새로운 상시 영역 감시 기술이 필요하다. 본 연구에서는 비방사 유도 자기장(자기공명) 기반 감시 체계의 기술적 타당성을 실험적으로 검토하였다. 공기, 물, 흙 등 매질과 공진 주파수, 임피던스 그리고 송 수신기 거리 등과 같은 환경변수에 따른 경로 손실 변화를 측정하는 방식으로 이루어졌다. 이론적으로 자기장의 전달 특성은 매질의 밀도와 독립된 것으로 알려졌으나, 실험 결과 매질의 조건에 따라 경로 손실에 의미있는 차이를 보이는 것으로 나타났다. 또한, 매질의 물리적 환경변화에 따라 경로손실보다는 반사계수가 명확한 차이를 보였으며, 입력 반사계수가 출력 반사계수에 비해 보다 판별이 용이한 것으로 나타났다.

• 설비공학논문집
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• 제14권12호
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• pp.989-995
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• 2002

A new fluidized bed heat exchanger for exhaust gas heat recovery is developed. Compared to the existing ones, the present heat exchanger system is featured by the particle fluidization method which does not depend on conventionally used baffle plate with holes and by the multiple downcomer tubes to extract heat energy from hot particle during the time particles moves down to be fed again to the hot gas line. Particles are introduced to the main hot gas stream alongside the pipe circumference. The heat exchanger performance and pressure drop are evaluated through experiments for the present gas-to-water heat exchanger system.

• 한국유체기계학회 논문집
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• 제2권3호
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• pp.24-29
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• 1999

The ASME strainers have been newly installed at the suction side of each reactor coolant pump to get rid of the foreign materials which may damage the pump impeller or interfere with the coolant path of fuel flow tube or primary plate type heat exchanger. The strainer was designed in accordance with ASME SEC. III, DIV. 1, Class 3 and the structural integrity was verified by seismic analysis. The screen was designed in accordance with the effective void area from the result of flow analysis for T-type strainer. After installation of the strainer, it was confirmed through the field test that the flow characteristics of primary cooling system were not adversely affected. The pressure loss coefficient was calculated by Darcy equation using the pressure difference through each strainer and the flow rate measured during the strainer performance test. And these are useful data to predict flow variations by the pressure difference.

• 설비공학논문집
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• 제7권1호
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• pp.132-141
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• 1995

Characteristics of pressure-drop oscillations(PDO) in a boiling channel were studied numerically and compared with experimental data. Effects of initial and boundary conditions on PDO were investigated in terms of oscillation period and amplitude. The period and amplitude of PDO increased with increasing of the compressible volume in the surge tank and the heat input. PDO occurred within the specific range of the fluid temperature, at which oscillation period and amplitude diminished rapidly with the increase of the fluid temperature. The increase of the loss coefficient in fluid supply line resulted in slightly longer oscillation period and larger amplitude. Numerical results showed good agreement with the experimental data.

• International Journal of Air-Conditioning and Refrigeration
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• 제11권1호
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• pp.24-31
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• 2003

A new fluidized bed heat exchanger for exhaust gas heat recovery is do-veloped. Compared to the existing ones, the present heat exchanger system is featured by the particle fluidization method which does not depend on conventionally used baffle plate with holes and by the multiple downcomer tubes to extract heat energy from hot particles during the time particles moves down to be fed again to the hot gas line. Particles are introduced to the main hot gas stream alongside the pipe circumference. The heat exchanger performance and pressure drop are evaluated through experiments for the present gas-to-water heat exchanger system.

• 설비공학논문집
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• 제11권2호
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• pp.185-192
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• 1999

Effective thermal conductivities and pressure-drop-related properties of aluminum foam metals have been measured. The effects of porosity and cell size in the aluminum foam metal are investigated in detail. The porosity of the foam metal, considered in the present study, varies from 0.89 to 0.96 and the cell size from 0.65㎜ to 2.5㎜. The effective thermal conductivity is evaluated by comparing the temperature gradient of the foam metal with that of the thermal conductivity-known material. The pressure drop in the foam metal is measured by a highly precise electric manometer while air is flowing through the aluminum foam metal in the channel. The results obtained indicate that the effective thermal conductivities are found to be increased with a decrease in the porosity while the effective thermal conductivities ire little affected by the cell size at a fixed porosity. However, the pressure drop is strongly affected by the cell size as well as the porosity. It is seen that the pressure drop is increased as the cell size becomes smaller, as expected. The minimum pressure drop is obtained in the porosity 0.94 at a fixed cell size. A new correlation of the pressure drop is proposed based on the permeability and Ergun's coefficient for the aluminum foam metal.

• 대한기계학회논문집 C: 기술과 교육
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• 제5권2호
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• pp.97-104
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• 2017

본 논문에서는 휠로더 냉각성능 평가를 위한 열유동해석의 효율성 향상과 비용 저감을 위해서 흡배기구 다공판형상을 Porous media 기법을 이용하여 단순화하고 해석 정도를 확인하였다. 여기서 Porous media에 적용된 다공판형상의 유동손실계수는 시험데이터를 바탕으로 정의하였다. 또한 다공판형상의 유동손실계수를 해석적으로 정의하기 위해 단위형상에 대한 압력손실을 계산하고 시험결과와 비교하였다. 마지막으로 휠로더 흡배기구를 단순화한 해석모델의 냉각해석 결과와 실차 방열시험 결과를 비교하였다. 이 연구를 통해 휠로더 흡배기구 단순화 해석기법의 적용 가능성을 확인하였으며 냉각성능 평가 및 개선 연구를 효과적으로 수행할 수 있는 기반을 마련하였다.

• 한국안전학회지
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• 제9권4호
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• pp.119-124
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• 1994

The considerations in the noise control by enclosure are the rise of temperature and sound pressure, transmission loss, absorption coefficient of the materials, the structure of the soundproof panels, an opening and coincidence frequency. But it is very difficult that we obtain the accurate data about those in design, so, the noise reduction after enclosing does not correspond with the calculation. The difference of the noise reduction between the calculation and the measurement was 8.2dBA, and we can obtain the approximate result as the following formula which correct 10dBA, safely.

• 한국유체기계학회 논문집
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• 제4권4호
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• pp.28-36
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• 2001

Performance analysis is conducted on an axial-type turbine which is used for fire extinction by injecting water or steam into the turbine. Loss models developed by Hacker and Okapuu are applied for predicting the performance of turbine. Pressure loss generated through a turbine is converted to the thermal efficiency, and thermal and gas properties are calculated within a turbine passage. Total-to-total efficiency, total-to-static efficiency, static temperature at the exit of turbine, output power, flow coefficient, blade loading coefficient, and expansion ratio are predicted with changing the amount of injected steam and the rotational speed. The 74 kW class gas turbine developed at KIMM is chosen for performance analysis. The 74 kW class turbine consists of 1 stage like a current developing gas turbine for fire extinction. Water or steam is injected at the end of combustor, and results show that efficiency and output power are dependent on the temperature of injected water or steam and the static temperature at the exit is decreased.

• 한국항공우주학회지
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• 제32권8호
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• pp.64-71
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• 2004

측 추력(Lateral Jet)을 이용하여 자세를 제어하는 미사일 주위의 초음속 유동장 해석을 위하여 삼차원 Navier-Stokes 코드 (AADL3D)를 개발하고, 이를 이용한 수치해석 연구를 수행하였다. 분출 제트 압력, 분출 마하수 등을 포함하는 제트의 유동특성이 미사일에 미치는 수직력 및 피칭모멘트에 대한 영향을 알아보기 위한 사례연구를 수행하였으며, 공력 해석 결과 제트의 분출 압력과 분출 마하수 변화에 따른 서로 다른 수직력과 모멘트 변화 양상 및 그 원인을 확인할 수 있었다. 또한 대부분의 수직력 손실과 피칭모멘트 발생은 노즐 후방의 저압영역에 의한 것이며, 동일한 제트 추력일지라도 분출 마하수가 큰 경우가 분출 압력이 큰 경우보다 모멘트 발생 최소화에 유리함을 확인하였다.