• 한국자동차공학회논문집
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• 제14권6호
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• pp.1-8
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• 2006

One of the most important subjects to develop a LPDi engine is to suppress the bubble generated inside the liquid LPG direct injector. For the purpose of this, the analogy visualization injector to visualize the generation and behaviors of bubble is manufactured, and the bubbling phenomenon and behaviors of bubble are visualized and investigated according to the change of the temperature around an injector wall, fuel pressure and a needle configuration. As results, it was found that the bubble inside the injector is generated around an injector hole and after rising by buoyancy it disappears around the top of a nozzle. The number of bubbles generated is little changed regardless of the lapse of time but it remarkably increases as the temperature around the injector increases. Also, it was known that as the sac volume in LPDi injector decreases the generation of bubble is more active and the rising velocity of bubble generated is increased.

• Korean Chemical Engineering Research
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• 제43권2호
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• pp.272-277
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• 2005

직경이 0.152 m이고 높이가 3.5 m인 기-액 향류 흐름 기포탑에서 기포의 물성과 흐름의 거동을 고찰하고 진단하였다. 기체와 액체의 유속 그리고 기포의 분산형태(even, wall-side, central or asymmetric distribution)가 반응기 내부에서 기포의 크기, 빈도수, 상승속도와 체류량 등 기포특성에 미치는 영향을 이중 전기 저항 탐침법을 이용하여 측정 검토하였다. 기포의 크기, 빈도수와 체류량은 기체나 액체 유속의 증가에 따라 증가하였다. 기포의 상승속도는 기체 유속의 증가에 따라 증가하였지만, 액체 유속의 증가에 따라서는 감소하였다. 기포 크기 분포의 균일성이나 체류량은 기포 분산판에서 기포의 분산형태가 균일분포에서 벽면, 중앙 그리고 비대칭 분산으로 변화함에 따라 감소하였다. 기포의 체류량과 분포에 대한 균일성을 고려하면, 기포의 중앙 분산 형태가 비대칭 분산 형태보다는 유리하며, 벽면 분산형태분산보다는 좋지 않았다.

• 한국가시화정보학회지
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• 제4권2호
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• pp.69-75
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• 2006

The microbubbles were used in various fields, such as turbulent control, drag reduction, material science and life science. The X-ray PTV using X-ray micro-imaging technique was employed to mea-sure the size and velocity of micro-bubbles moving in an opaque tube simultaneously. Micro-bubbles of $10{\sim}60{\mu}m$ diameter moving upward in an opaque tube (${\phi}$=2.7mm) were tested. Due to the different refractive indices of water and air, phase contrast X-ray images clearly show the exact size and shape of over-lapped microbubbles. In all of the working fluids tested (deionized water, tap water, 0.01 and 0.10M NaCl solutions), the measured terminal velocity of the microbubbles rising through the solution was proportional to the square of the bubble diameter. The rising velocity was increased with increasing mole concentration. The microbubble can be useful as contrast agent or tracer in life science and biology. The X-ray PTV technique should be able to extract useful information on the behavior of various bio/microscale fluid flows that are not amenable to analysis using conventional methods.

• 한국가시화정보학회지
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• 제10권2호
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• pp.14-19
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• 2012

An optical fiber probe system for measuring the local void fraction in the air-water two-phase flow was developed with a 1550 nm light source. Air was injected through a nozzle placed in the center of the bottom wall of a water-filled cylindrical tank. The optical fiber probe having a diameter of $125{\mu}m$ was sufficiently thin to resolve the air-water interface of the bubbly flows. To verify the performance of the optical fiber probe, the synchronized high speed visualization study using a high speed camera was carried out. Comparison between the optical signals and the instantaneous bubble diffraction images confirms that the optical fiber probe is very accurate to measure the void fraction in two-phase flows. The estimated bubble diameter and the rising velocity by the optical fiber probe have 1% and 5% of accuracy, respectively.

• 대한설비공학회지:설비저널
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• 제6권1호
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• pp.1-8
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• 1977

This paper describes an experimental investigation which has been carried out with distilled water with the range of heat flux and pressure covering 7,400-28,000kcal/$m^2/h$ and 0.42-1.0332kg/$cm^{2}abs$, respectively. In this experiment, Nickel coated mirror surface heater of 5 cm O.D. was used as a heating source. The conclusions summerized as follows;1. The useful correlation of the test data for the heat transfer coefficient is presented as a function of the pressure. $$a/a_{s}=c{\times}p\;0.18$$ where a is the heat transfer coefficient and $a_s$ is the heat transfer coefficient at atmospheric pressure and p is the pressure, C is constant. 2. The bubble diameter near the heating surface and rising velocity increased with the heat flux. 3. A decrease in pressure results in the decrease of the number of nucleation sites and the increase of the bubble volume. 4. Bubble rising velocity differences are incrased maximumly up to $200\%$ of that at atmopheric pressure.

• 대한기계학회논문집B
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• 제28권6호
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• pp.659-664
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• 2004

It is important to measure precisely the size and velocity of micro-bubbles used in various field. The synchrotron X-ray micro-imaging technique was employed to measure the size and velocity of micro-bubbles moving in an opaque tube simultaneously. Phase contrast images were obtained at interfaces of micro-bubbles between water and air due to their different refractive indices. The X-ray micro-imaging technique was found to measure an optical fiber with an accuracy of 0.2%. Micro-bubbles of 20∼60$\mu\textrm{m}$ diameter moving upward in an opaque tube (${\Phi}$＝2.7mm) were tested to measure bubble size and up-rising velocity. For DI water, the measured velocity of micro-bubbles is nearly proportional to the square of bubble size, agreed well with the theoretical result. In addition, the synchrotron X-ray micro-imaging technique can measure accurately the size and velocity of several overlapped micro-bubbles.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1744-1748
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• 2004

It is important to measure precisely the size and velocity of micro-bubbles used in various field. The synchrotron X-ray micro-imaging technique was employed to measure the size and velocity of micro-bubbles moving in an opaque tube simultaneously. Phase contrast images were obtained at interfaces of micro-bubbles between water and air due to their different refractive indices. The X-ray micro-imaging technique was found to measure an optical fiber with an accuracy of 0.2%. Micro-bubbles of $10{\sim}60{\mu}m$ diameter moving upward in an opaque tube (${\phi}=2.7mm$) were tested to measure bubble size and up-rising velocity. For DI water, the measured velocity of micro-bubbles is nearly proportional to the square of bubble size, agreed well with the theoretical result. In addition, the synchrotron X-ray micro-imaging technique can measure accurately the size and velocity of several overlapped micro-bubbles.

• 한국산업정보학회논문지
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• 제29권1호
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• pp.117-123
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• 2024

수중에서 발생한 기포는 주변 유체의 밀도와 압력 차이에 의해 상승하는 부력을 받는다. 또한 주변 유체와의 점성, 표면장력, 상승 속도 그리고 크기 차이에 따라 기포의 거동, 형상, 열교환 과정 등이 달라진다. 본 연구에서는 원기둥 수조 내 상승하는 고온 단일 기포의 속도 그리고 열전달 해석에 관한 연구를 수행하였다. 이를 위해 이론적 식을 통해 기포의 속도 그리고 온도 등을 계산하여 수치 해석 결과와 비교하기 위한 자료를 설정하였다. 그리고 상용 프로그램으로 수치 해석을 수행하였으며, 격자의 변화에 따른 수치 해석 결과의 안정성을 격자 수렴성 지수 계산을 통해 확인하였다. 수치 해석 결과 단일 기포의 상승 속도와 온도는 최소 격자의 크기가 기포 지름의 1/160이 될 때 수렴성을 보였으며, 온도 감소는 0.05초 이내에 주변 유체와 동일한 수준으로 감소하는 것을 확인하였다.

• Korean Chemical Engineering Research
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• 제49권1호
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• pp.83-88
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• 2011

점성슬러리 기포탑에서 작은 기포의 체류량 특성에 대해 고찰하였다. 정압 강하방법(Static pressure drop method)에 의해 구한 기포탑 내부전체 기포체류량과 이중저항탐침법(dual resistivity probe method)에 의해 구한 큰 기포의 체류량으로부터 기포탑 내부에 체류하는 작은 기포의 체류량을 구할 수 있었다. 기체유속, 연속액상의 점도 그리고 슬러리 상중에 포함된 고체입자의 분율이 전체 기체체류량, 큰 기포의 체류량 그리고 작은 기포의 체류량에 미치는 영향을 검토하였다. 점성슬러리 기포탑에서 작은 기포의 체류량은 기체의 유속이 증가하면 증가하였으나 연속액상의 점도와 슬러리상에 포함된 고체입자의 분율이 증가하면 감소하였다. 기포탑 내부에 체류하는 전체 기포 체류량 중 작은 기포 체류량의 분율은 기체유속이 증가하면 증가하였으나 연속액상의 점도와 슬러리상에 포함된 고체입자의 분율이 증가하면 감소하였다. 기포탑 내부에 체류하는 작은 기포는 큰 기포의 상승속도에 영향을 미치지 못하였다.

• 상하수도학회지
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• 제20권4호
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• pp.617-626
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• 2006

Compared with the sludge from gravity sedimentation, it is difficult for operations to settle the sludge occurred from dissolved-air-flotation (DAF). Even though there are some problems in treating DAF sludge with conventional gravity thickeners, those has been used until now. In this study, Solid Flux theory for gravity thickening was applied to the Solid Flux of DAF sludge through flotation in order to develop new methodology for treatment of DAF sludge. Also, characteristics of DAF sludge were investigated. From the experiment results, it was revealed that the higher the polymer dosage, at fixed the solid concentration, the greater the rising velocity becomes. When we applied solid flux theory, the relationship, which is similar to that of gravity thickening, has been achieved. Also, we could find the proper polymer dosage from the rising velocity is about 50 mg/L. Consequently, the limiting solid flux can be derived from the relationship between the total solid flux and the withdrawal velocity of DAF sludge. Furthermore, the factors, such as solid concentrations, bubble volume, pH, zeta potential, and temperature, have effects on the flotation and sedimentation for DAF sludge treatment.