• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.236-242
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• 2007

A theoretical and numerical investigation is performed on the flow in a micronozzle for precision-controlled seal dispenser. The working fluid is a highly viscous epoxy used as sealant in producing LCD panels, which contains a number of tiny solid spacers. Flow analysis is conducted in order to achieve the optimal design oj internal geometry of a nozzle. A simplified design analysis methodology is proposed for predicting the flow in the nozzle based on the assumption that the Reynolds number is much less than O(1). The parallel numerical computations are performed by using a CFD package FLUENT. Comparison discloses that the theoretical model gives a good prediction on the distribution of pressure and wall shear stress in the nozzle. However, the theoretical model has a difficulty in predicting the maximum wall shear stress as found in a limited region near edge by numerical computation. The theoretical and numerical simulations provide the good guideline for designing a dispensing micronozzle.

• Nuclear Engineering and Technology
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• 제23권3호
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• pp.275-284
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• 1991

핵연료봉의 정방형 또는 삼각형 배열내의 2차 난류 유동의 해석은 연료봉내의 온도분포와 열전달 과정의 해석에 있어서 중요한 문제이다. 비등방성 난류모델과 등방성 난류모델을 사용하여 속 도장을 구하였고 열수력학적 성질이 일정하다는 가정하에 지배방정식을 유한 요소법을 사용하여 수치해석적인 방법으로 해를 구하였다. 또한 연료봉 표면 근처에서는 유체의 유동이 난류가 아니기 때문에 축 방향 속도는 벽의 법칙에 의해서 계산하였다. 이러한 방법에 의해서 구해진 해는 실험 결과와 비교되었고 비교적 잘 일치하였다.

• 설비공학논문집
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• 제23권11호
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• pp.718-725
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• 2011

Characteristics of flow boiling heat transfer in microchannels were investigated experimentally. The microchannels consisted of 9 parallel trapezoidal channels with each channel having 205 ${\mu}m$ of bottom width, 800 ${\mu}m$ of depth, $3.6^{\circ}$ of sidewall angle, and 7 cm of length. Tests were performed with R113 over a mass velocity range of 150~920 $kg/m^2s$, heat flux of 10~100 $kW/m^2$ and inlet pressures of 105~195 kPa. Flow boiling heat transfer coefficient in microchannels was found to be dominated by heat-flux. However the effect of mass velocity was not significant. Contrary to macrochannel trends, the heat transfer coefficient was shown to decrease with increasing thermodynamic equilibrium quality. A new correlation suitable for predicting flow boiling heat transfer coefficient was developed based on the laminar single-phase heat transfer coefficient and the nucleate boiling dominant equation. Comparison with the experimental data showed good agreement.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.47-52
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• 2002

The supersonic flow around multi-stage rocket system is analyzed using 3-D compressible unsteady flow solver. A Chimera overset grid technique is used for the calculation of present configuration and grid around the core rocket is composed of 3 zones to represent fins in the core rocket. Flow solver is parallelized to reduce the computation time, and an efficient parallelization algorithm for Chimera grid technique is proposed. AUSMPW+ scheme is used for the spatial discretization and LU-SGS for the time integration. The flow field around multi-stage rocket was analyzed using this developed solver, and the results were compared with that of a sequential solver The speed-up ratio and the efficiency were measured in several processors. As a result, the computing speed with 12 processors was about 10 times faster than that of a sequential solver. Developed flow solver is used to predict the trajectory of booster in separation stage. From the analyses, booster collides against core rocket in free separation case. So, additional jettisoning forces and moments needed for a safe separation are examined.

• 한국전산유체공학회지
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• 제12권4호
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• pp.54-60
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• 2007

A theoretical and numerical investigation is performed on the flow in a micronozzle for precision-controlled sealant dispenser. The working fluid is a highly viscous epoxy used as sealant in producing LCD panels, which contains a number of tiny solid spacers. Flow analysis is conducted in order to achieve the optimal design of internal geometry of a nozzle. A simplified design analysis methodology is proposed for predicting the flow in the nozzle based on the assumption that the Reynolds number is much less than O(1). The parallel numerical computations are performed by using a CFD package FLUENT. Comparison discloses that the theoretical model gives a good prediction on the distribution of pressure and wall shear stress in the nozzle. However, the theoretical model has a difficulty in predicting the maximum wall shear stress as found in a limited region near edge by numerical computation. The theoretical and numerical simulations provide the good guideline for designing a dispensing micronozzle.

• 대한기계학회논문집B
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• 제28권7호
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• pp.780-788
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• 2004

This paper reports the fluid flow and heat transfer around a module cooled by forced air flow generated by a piezoelectric(PZT) cooling fan. The fluids are locally accelerated by a flexible PZT fan which deflects inside a fluid transport system of comparatively simple structure mounted on a PCB in a parallel-plate channel(450${\times}$80${\times}$700㎣). Input voltages of 20-100V and a resonance frequency of 23㎐ were used to vibrate the cooling fan. Input power to the module was 4W. The fluid flow around the module was visualized by using PIV system. The temperature distributions around a heated module were visualized by using liquid crystal film(LCF). The cooling effect using a PZT fan was independent of the vent area ratios at the channel inlet and was similar to the forced convection cooling. We found that the flow type was Y-shape and the cooling effect was increased by the wake generated by a piezoelectric cooling fan.

• Korea-Australia Rheology Journal
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• 제15권2호
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• pp.55-61
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• 2003

The steady shear flow properties of vaseline generally used as a base of the pharmaceutical dosage forms were studied in the consideration of wall slip phenomenon. The purpose of this study was to show that how slip may affect the experimental steady-state flow curves of semisolid ointment bases and to discuss the ways to eliminate (or minimize) wall slip effect in a rotational rheometer. Using both a strain-controlled ARES rheometer and a stress-controlled AR1000 rheometer, the steady shear flow behavior was investigated with various experimental conditions ; the surface roughness, sample preparation, plate diameter, gap size, shearing time, and loading methods were varied. A stress-controlled rheometer was suitable for investigating the flow behavior of semisolid ointment bases which show severe wall slip effects. In the conditions of parallel plates attached with sand paper, treated sample, smaller diameter fixture, larger gap size, shorter shearing time, and normal force control loading method, the wall slip effects could be minimized. A critical shear stress for the onset of slip was extended to above 10,000 dyne/$\textrm{cm}^2$. The wall slip effects could not be perfectly eliminated by any experimental conditions. However, the slip was delayed to higher value of shear stress by selecting proper fixture properties and experimental conditions.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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• pp.173-179
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• 2012

본 논문에서는 부분 흡입형 초음속 터빈의 로터 블레이드에 ${\pm}15^{\circ}$의 스윕 각도를 적용하여 그에 의한 효과와 공력 특성을 살펴보기 위해 정상상태 유동해석과 비정상상태 유동해석을 동시에 수행하고 그 결과를 비교해 보았다. 3차원 Navier-Stokes 유동해석에는 상용 코드인 FLUENT 6.3 Parallel을 사용하였다. 모든 계산 케이스들에서 정상상태 유동해석에 비해 비정상상태의 경우가 손실이 더욱 크게 나오는 결과를 나타내었다. 후방스윕(BSW)모델은 기준모델(NSW)에 비해 팁 간극으로 빠져나가는 누설 손실량을 줄이는데 큰 효과가 있었고 비정상상태 유동 해석에서는 로터 출구면 정효율의 증가현상이 더욱 뚜렷하게 나타났다.

• 한국지반환경공학회 논문집
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• 제25권4호
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• pp.21-28
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• 2024

본 연구에서는 SPH 해석을 위한 다면체영역분할 기법이 소개된다. SPH 기법은 유체 유동 모사를 위한 수치해석기법으로 무요소기법(meshless method) 중 하나이다. 유동성 지반 또는 고체-유체 상호작용 해석 등에 유용하게 쓰일 수 있다. SPH는 입자기반 해석이기 때문에 입자가 많을수록 결과의 정확도는 높아지지만 수치적 효율성은 떨어진다. 일반적으로 해석의 효율성을 높이기 위해 병렬 프로세싱 알고리즘과 함께 쓰이는데 직교좌표계 기반의 영역분할 기법이 대표적이다. 그러나 복잡한 기하학적 형태나 동적 경계조건에서 유동 모사 등을 병렬 해석하기 위해서는 직교좌표계 영역분할 방법이 적합하지 않다. 소개하는 다면체영역분할 기법은 이와 같은 문제에서 병렬효율성을 높일 수 있는 장점을 갖는다. 다양한 형태의 3차원 다면체 요소로 분할하여 문제에 적합하게 모델링할 수 있다. SPH 입자들의 물리적 값들은 smoothing 길이 이내의 주위 입자들 정보를 이용하여 계산된다. 영역분할 시 물리적으로 분리될 수 있는 입자정보들을 코어간 공유할 수 있는 방법과 병렬효율성이 떨어질 수 있는 cross-point에서의 정보공유 방법이 소개된다. 수치해석 예제를 통하여 제안된 방법의 병렬효율성은 12코어까지 95%에 근접하였다. 이후 코어가 증가할수록 코어간 공유되는 정보량이 많아져 병렬효율성이 떨어지는 문제가 발생되기도 하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.390-395
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• 2001

Cooling characteristics using convection and conduction heat transfer in a parallel channel with extruding heat sources are studied numerically. A two-dimensional model has been developed for numerical prediction of transient, compressible, viscous, laminar flow, and conjugate heat transfer between parallel plates with uniform block heat sources. The finite volume method is used to solve this problem. The considered assembly consists of two channels formed by two covers and one PCB which has three uniform heat source blocks. Five different cooling methods are considered to find efficient cooling method in a given geometry and heat source. The velocity and temperature fields, local temperature distribution along surface of blocks, and the maximum temperature in each block are obtained.