• 한국전산유체공학회지
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• 제19권1호
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• pp.21-26
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• 2014

Butterfly valve is a valve that controls fluid flow depending on the size of the opening angle. In general, the size of the opening angle of the valve increases, the fluid flow has also increased sharply. However, sometimes, in a specific piping system, a particular operating condition is needed that the fluctuation of the fluid flow should not have large amount although the size of opening angle of the valve become larger. In butterfly value, the shape of a typical thin plate, it is impossible to control a minute fluid, but in thick plate type, it is possible. In this study, we got the fluid flow control characteristics and pressure drop through both a numerical method and an experimental method about thick plate type. The numerical result and experimental result of flow coefficient show a similar pattern. In addition, we could find that minute fluid flow control was possible in the area of small size of the opening angle.

• Journal of Mechanical Science and Technology
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• 제16권8호
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• pp.1144-1153
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• 2002

A hybrid performance prediction method is proposed in the present study. A channel diffuser is divided into four subregions: vaneless space, semi-vaneless space, channel, and channel exit region. One-dimensional compressible core flow and boundary layer calculation of each region with an incidence loss model and empirical correlation of residuary pressure recovery coefficient of a channel predict the performance of diffusers. Three channel diffusers are designed and tested for validating the developed prediction method. The pressure distributions from an impeller exit to the channel diffuser exit are measured and discussed for various operating conditions from choke to nearly surge conditions. The strong non-uniform pressure distribution which is caused by impeller-diffuser interaction is obtained over the vaneless and semi-vaneless spaces. The predicted performance shows good agreement with the measured performance of diffusers at a design condition as well as at off-design conditions.

• 한국유체기계학회 논문집
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• 제2권1호
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• pp.64-72
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• 1999

CSCM upwind flux difference splitting compressible Navier-Stokes method has been used to predict the transonic flows in a centrifugal compressor diffuser. The modified cyclic. TDMA and the mass flux boundary conditions were used as boundary conditions of the diffuser analysis. Broad flow separation on the suction surface near the hub and shroud was observed from the results of the mass flow rates 5.8, 6.0 and 6.2kg/s at 27000 rpm. The three-dimensional flow analysis predicted successfully that the static pressure increased and the total pressure decreased through the flow passage of the channel diffuser when compared to two-dimensional analysis due to the strong effect of the three-dimensional flow. The mass averaged loss coefficients and pressure coefficients were also studied.

• Nuclear Engineering and Technology
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• 제36권4호
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• pp.285-294
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• 2004

Pressure wave propagation in the discharge piping with a sparger submerged in a water pool, following the opening of a safety relief valve, is analyzed. To predict the pressure transient behavior, a RELAP5/MOD3 code is used. The applicability of the RELAP5 code and the adequacy of the present modeling scheme are confirmed by simulating the applicable experiment on a water hammer with voiding. As a base case, the modeling scheme was used to calculate the wave propagation inside a vertical pipe with sparger holes and submerged within a water pool. In addition, the effects on wave propagation of geometric factors, such as the loss coefficient, the pipe configuration, and the subdivision of sparger pipe, are investigated. The effects of inflow conditions, such as water slug inflow and the slow opening of a safety relief valve are also examined.

• 한국군사과학기술학회지
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• 제3권2호
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• pp.23-34
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• 2000

Three dimensional, compressible, mass weighted averaging of Favre, Navier-Stokes system with k-$\varepsilon$ turbulence, is numerically discretized to compute three dimensional multiple jet interaction flow fields for a hybrid projectile containing three rocket motors in the ogive section. Numerical flow field computations have been made for angled nose jets and rockets at supersonic speed using multiblock structured grid. The jet conditions include very high jet to free stream pressure ratio and high temperature. It is shown that the strength of nozzle stagnation pressure affects the flow field near the side nozzle and the high stagnation pressure increases total amount of drag by a few percent. However, minor drag loss due to the pressure drag might be fully overcomed by an additional axial thrust. The results of present study can be applied for the design of future hybrid projectile.

• 대한기계학회논문집B
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• 제26권7호
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• pp.919-926
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• 2002

Down scaled combustor undergoes increased heat loss that results in incomplete combustion or quenching of the flame as a consequence. Therefore, effect of enhanced heat loss should be understood to design a MEMS scale combustion devices. Existing combustion models are inadequate for micro combustors because they were developed for analysis of regular scale combustor where heat loss can be ignored during the flame propagation. In this research a combustion model is proposed in order to estimate the heat loss and predict quenching limit of flame in a down scaled combustor. Heat loss in the burned region is expressed in a convective form as a product of wall surface area, heat transfer coefficient and temperature difference. Comparison to the measurements showed satisfactory agreement of the pressure and temperature drop. Quenching is accounted for by introducing a correlation of quenching parameter and heat loss. The present model predicted burnt fraction of gases with reasonable accuracy and proved to be applicable in thermal design of a micro combustor.

• 한국추진공학회지
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• 제7권2호
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• pp.15-22
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• 2003

본 연구에서는 2차원 압축성 Navier-Stokes 방정식을 사용하여 $30^{\cire}$ 경사진 터빈익의 냉각구를 통한 유출계수를 예측하였다. 내/외부 유동이 유출계수에 미치는 영향을 알아보기 위하여 외부유동만 존재하는 경우, 내부유동만 존재하는 경우 그리고 내/외부 유동이 없는 3가지 경우에 대하여 수치해석을 수행하였으며. 실험결과와 비교하였다. 본 연구의 수치해석결과는 유출계수를 잘 예측하였으며, 외부유동은 유출계수를 감소시키고, 내부유동은 냉각구내에서의 전압손실과 경계층의 영향을 감소시켜 특정 구간에서 유출계수를 증가시킨다는 것을 알았다.

• Journal of Advanced Marine Engineering and Technology
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• 제37권4호
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• pp.358-367
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• 2013

본 논문에서는 타공판으로 구성된 필터의 전부 또는 일부를 다공성 매질로 대체하고 Forchheimer 법칙에 따라 판의 수직방향과 횡방향으로 손실계수를 부과하여 스트레이너를 지나는 유동의 압력 강하량를 정확히 예측할 수 있는 다공성모델링 기법을 적용하고 그 유효성을 확인하였다. 먼저 간단한 파이프 유동 해석을 통하여 수직방향 손실계수를 구하였다. 이어 필터 내에 반복되는 타공판 형상과 유동손실특성을 공유할 수 있는 단위주기 형상을 설정하고, 설정된 단위형상에 대하여 원형과 다공성모델 수치모사를 각각 수행한 후, 얻어진 두 결과를 서로 비교하여 횡방향 손실계수를 구하였다. 적용된 다공성모델링 기법을 검증하기 위하여 스트레이너 전체형상에 대하여 다공성모델 수치모사를 수행하였으며, 그 해석결과를 원형 수치모사 결과와 직접 비교하였다. 비교 결과, 다공성모델링 기법은 압력 강하량과 유동특성을 비교적 정확히 예측하였으며 계산비용과 직결되는 노드 수는 약 3~4배 정도 줄일 수 있었다.

• 한국가스학회지
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• 제2권1호
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• pp.47-52
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• 1998

천연가스 공급배관내의 이물질을 제거하기 위하여 한국가스공사에서는 현재 250um 공극 크기를 갖는 금속 스트레이너형의 필터를 사용하고 있다. 하지만 배관내의 이물질 크기를 조사한 결과 필터 공극 크기보다 작은 이물질이 상당량 있는 것으로 파악되었으며. 따라서 이들 이물질로 인하여 필터 후단부의 각종 밸브류나 계 량 측정 기기들에 악영향을 미치고 있는 실정이다. 미세한 크기의 이물질들을 없애기 위해서는 필터의 공극 크기를 줄여야 하는데. 이 경우에는 필터 전, 후단의 차압발생으로 인하여 원하는 유량의 가스를 공급하기 어려운 일이 생길 수 있으므로 차압발생을 신중히 고려하여 필터 공극 크기를 결정하여야한다. 본 연구에서는 손실계수 K를 이용하여 가스필터의 성능평가 방법을 제시하였다.

• 한국해양공학회지
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• 제2권2호
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• pp.130-137
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• 1988

This thesis introduced that character of a treatment technique for a mading synthetic resin Hifiow-Ring. The material system of packings make an experiment air$NH_{3}$/air$H_{2}SO_{4}$, $SO_{2}$-air/NaOH, $NH_{3}$-air/$/H_{2}SO_{4}$ under general conditions. Lattices packing compared with conventional packings was proved low pressure loss and high separation efficiency for high loading per trans unit. And an inflow materal tested for absorption and rectification, it made an experiment under a range regular temperature, low energy and small amount of money. That made possible in simple equation, volume material tranfer coefficient$\beta_{L}$ . a by absorption or $\beta_{V}$ .a calculated in all range loading. The peculiarity pressure loss $\Delta\;P/NUT_{ov}$ for Hiflow-ring contributed to a fall cost of energy, a grade number of a vacuum rectification and absorption calculation.