• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제31회 추계학술대회논문집
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• pp.341-344
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• 2008

Numerical simulations have been carried out for a supersonic two-dimensional flow over open, rectangular cavities (length-to-depth ratios are L/D = 1.0) in order to investigate the effect of non-equilibrium condensation of moist air on supersonic flows around the cavity for the flow Mach number 1.83 at the cavity entrance. In the present computational investigation, a condensing flow was produced by an expansion of moist air in a Laval nozzle. The results obtained showed that in the case with non-equilibrium condensation for L/D = 1.0, amplitudes of oscillation in the cavity became smaller than those without the non-equilibrium condensation. Furthermore, the occurrence of the non-equilibrium condensation reduced the peaks of power spectrum density and the frequency of the flow field oscillation increased in comparison with the case of $S_0$ = 0.

• 설비공학논문집
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• 제12권3호
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• pp.277-283
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• 2000

The heat transfer characteristics for air jet vertically impinging on a flat plate which had a set of hybrid rod were investigated experimentally. The rod had a cross section made with a half of circular cross section and that of rectangular and was installed in front of the plate. The heating surface was given constant heat flux value of 1020 W/$m^2^{\circ]C$ and the problem parameters investigated were jet Reynolds number, nozzle-to-plate spacing and the rod size. The local and local average Nusselt number characteristics were found to be dependent on the rod size because the flow was disturbed by installing the rod. Higher convective heat transfer rate occurred in the whole plate as well as in the stagnation region.

• Journal of Biosystems Engineering
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• 제34권6호
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• pp.404-410
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• 2009

This study was carried out to develop a self-propelled type explosive subsoiler for improving the root zone soil conditions in orchard and other forest fields. Prototype was designed to be able to inject air and other soil improving material such as lime into soil at the same time, and thus improve the air permeability and drainage of orchard soils to promote the root growth of tree for high quality fruit production. Soil penetration device of explosive subsoiler is composed of air hammer, penetration rob and air injection nozzle. To support the soil penetration device of explosive subsoiler to penetrate vertically, modified Scott-Russel mechanism was used. Timing control device for simultaneous injection of soil improving material with air was attached to the out side wall of air cylinder and as the cylinder move, the soil improving material was injected into soil at the same time. Turning radius of prototype was 2.2-2.3 m with good mobility in sloped land. It took approximately 1 minute for lime injection system to reach the optimum pressure of 9.9 kg/$cm^2$, average 10-20 seconds were required to rupture soil with the depth of 50 cm and 2-3 seconds were required for explosion, so all in all about 1 minute and 20 seconds were required for one cycle of explosion. Maximum soil rupture depth and diameter were 50 cm and 3-4 m respectively depending on the soil type and soil moisture content. For final design of explosive subsoiler inclination angle of lime hopper was increased from 60 degree to 70 degree and the shape of hopper was changed from rectangular cone to circular cone to solve the clogging problem of lime at out let. Agitating system operated by compressed air was attached to the metering device of the prototype, thus more than 90 cc of lime was discharged per cycle from metering device without clogging problems.

• 태양에너지
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• 제17권1호
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• pp.47-58
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• 1997

본 연구는 2차원 충돌공기분류계의 포텐셜코어 영역에서 열전달증진을 목적으로 노즐출구와 전열면사이에 메쉬를 설치한후 노즐출구 속도, 메쉬와 전열면사이의 간극, 노즐출구와 전열면사이의 거리를 변화시킬 때의 열전달특성을 메쉬를 설치하지 않은 경우와 비교 검토한 것으로 메쉬를 설치했을 때에는 분류가 전열면에 충돌하면서 소분류로 분할되어 발생하는 난류에 의해 충돌영역에서 열전달성능이 좋아지며, 또한 벽면분류영역으로 진행하면서 홀과 홀사이의 밑부분에서 일어나는 가속으로 인해 열전달성능이 향상된다. 특히 메쉬와 전열면사이의 간극을 변화시켰을 경우 정체점부근에서는 간극이 클수록, 벽면분류영역에서는 간극이 작을수록 전달성능은 향상되며 U=18m/s, H/B=2, C=1인 경우에는 메쉬를 설치하지 않은 평판보다 평균 약 44%의 열전달증진 효과과 있었다. 그리고 본 실험결과를 기존의 난류촉진체를 이용한 연구결과와도 비교 검토하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 춘계학술대회 논문집
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• pp.1051-1054
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• 2000

We developed the micro CSF (celebrospinal fluid) shunt valve with surface and bulk micromachining technology in polymer MEMS. This micro CSF shunt valve was formed with four micro check valves to have a membrane connected to the anchor with the four bridges. The up-down movement of the membrane made the CSF on & off and the valve characteristic such as open pressure was controlled by the thickness and shape of the bridge and the membrane. The membrane, anchor and bridge layer were made of the $O_2$ RIE (reactive ion etching) patterned Parylene thin film to be about 5~10 microns in thickness on the silicon wafer. The dimension of the rectangular nozzle is 0.2＊0.2 $\textrm{mm}^2$ and the membrane 0.45 mm in diameter. The bridge width is designed variously from 0.04 mm to 0.12 mm to control the valve characteristics. To protect the membrane and bridge in the CSF flow, we developed the packaging system for the CSF micro shunt valve with the deep RIE of the silicon wafer. Using this package, we can control the gap size between the membrane and the nozzle, and protect the bridge not to be broken in the flow. The total dimension of the assembled system is 2.5＊2.5 $\textrm{mm}^2$ in square, 0.8 mm in height. We could precisely control the burst pressure and low rate of the valve varing the design parameters, and develop the whole CSF shunt system using this polymer MEMS fabricated CSF shunt valve.

• 한국자기학회지
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• 제8권5호
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• pp.255-260
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• 1998

두께 10$\mu\textrm{m}$ 이하의 코발트계 극박형 비정질합금의 진공중 용탕급냉방법에 의한 제조조건과 자기적 특성에 대해 연구되었다. 구리 냉각롤의 회전 선속도를 55 m/s로 하였을 때, 0.05 kgf/cm2 이하의 용탕분사압 조건에서 극박형 리본이 얻어졌다. 합금 두께는 용탕분사 가스압력의 감소에 비례하여 직선적으로 감소하였으며, 이와 동시에 폭의 감소도 함께 일어났다. 이는 극박형 합금을 만들기 위해 용탕분사압을 극단적으로 감소시키면 노즐구의 양단부에서 용융금속과 노즐 사이의 마찰효과가 크게 나타나 유효분사압이 현저히 감소하는 데에 기인하는 것으로 해석되었다. 저주파(1 kHz) 실효투자율은 대략 2차 함수의 관계로 리본 두께의 감소에 따라 저하되었다. 반면 보자력은 두께의 감소에 반비례하여 증가하였는데, 이들 현상은 거의 전적으로 표면효과의 증대에 의한 자벽이동의 억제에 그 원인이 있는 것으로 판단되었다. 그러나 고주파(1 MHz) 실효투자율은 두께의 감소에 따라 증가하였는바 이는 와전류 발생이 억제되어 자기장 방향으로의 자화회전이 보다 용이해지기 때문으로 생각되었으며, 결과적으로 극박화에 의해 MHz 대역에서 우수한 저손실 성질을 나타내는 자심 특성의 실현이 가능하였다.

• 한국추진공학회지
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• 제24권6호
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• pp.1-9
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• 2020

케로신/액체산소를 추진제로 하는 직사각형 2열 오리피스를 갖는 1.5톤급 액체-액체 핀틀 분사기를 설계 및 제작하여 액체로켓엔진의 실운용 조건인 초임계 상태에서 핀틀 분사기의 연소성능 및 연소 안정성 검증 연소시험을 수행하였다. 연소시험결과 연소실 내부의 고혼합비 재순환 영역에서 생성되는 고온의 연소가스에 핀틀 팁이 손상되었다. 핀틀 팁으로 전달되는 열유속 또는 하중에 대한 냉각 성능을 증가시키기 위해 핀틀 분사기 내부에 인서트 노즐을 설치하였다. 연소시험 결과 인서트 노즐의 설치, AR 및 BF가 핀틀 팁 냉각 성능에 큰 영향을 주는 인자로 확인되었다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.109-114
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• 2008

This paper presents the development status of a subscale precooled turbojet engine "S-engine" for the hypersonic cruiser and space place. S-engine employs the precooled-cycle using liquid hydrogen as fuel and coolant. It has $23cm{\times}23cm$ of rectangular cross section, 2.6 m of the overall length and about 100 kg of the target weight employing composite materials for a variable-geometry rectangular air-intake and nozzle. The design thrust and specific impulse at sea-level-static(SLS) are 1.2 kN and 2,000 sec respectively. After the system design and component tests, a prototype engine made of metal was manufactured and provided for the system firing test using gaseous hydrogen in March 2007. The core engine performance could be verified in this test. The second firing test using liquid hydrogen was conducted in October 2007. The engine, fuel supplying system and control system for the next flight test were used in this test. We verified the engine start-up sequence, compressor-turbine matching and performance of system and components. A flight test of S-engine is to be conducted by the Balloon-based Operation Vehicle(BOV) at Taiki town in Hokkaido in October 2008. The vehicle is about 5 m in length, 0.55 m in diameter and 500 kg in weight. The vehicle is dropped from an altitude of 40 km by a high-altitude observation balloon. After 40 second free-fall, the vehicle pulls up and S-engine operates for 60 seconds up to Mach 2. High altitude tests of the engine components corresponding to the BOV flight condition are also conducted.

• 대한기계학회논문집B
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• 제24권2호
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• pp.306-315
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• 2000

An experimental study was conducted to examine the internal flow patterns inside the mixing chamber of effervescent atomizers. The mixing chamber has the rectangular cross section ($8mm{\times}2mm$) and made of transparent acrylic plate for flow visualization. The parameters tested were the air/liquid ratio (ALR), injection. pressure, and the nozzle orifice diameter. Three different flow regimes were observed; bubbly, annular, and intermittent flows. In the bubbly flow regime, the discharged mixture was disintegrated into drops through the bubble expansion and the ligament breakup. On the other hand, in the annular flow regime, the liquid annulus was disintegrated into small drops by the aerodynamic interaction between the phases due to the high relative velocities between the gas and the liquid. In the intermittent flow regime, the bubble-expansion/ligament-disintegration mode and the annulus-disintegration mode appeared alternatively. The correlations representing the transition criteria between the two-phase flow patterns within the mixing chamber were proposed based on the drift-flux models.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1626-1631
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• 2007

The purpose of the study is to simulate the displacement of the LCD glass during process of a large size imprint. During this process, a small temperature variation makes thermal stress, which causes the horizontal variation of mold and glass. During alignment process to fix the LCD glass on a alignment stage, the vertical displacement is made by the absorption pressure and the shear stress. This study simulates the horizontal displacement of mold and glass due to temperature variation, the vertical displacement depending on the shape of absorption surface fixing the LCD glass in the alignment process, and the horizontal and vertical displacement which occurs in the LCD glass at the alignment process. Algor which is a FEM code for a framework simulation was applied. Temperature variation above ${\pm}$ $0.1^{\circ}C$ on mold and glass causes the horizontal displacement of 150nm due to thermal expansion. The vertical displacement due to the circular is ten times of the case of rectangular absorption nozzle. The displacement of the LCD glass in the alignment process is about 49nm.