• Nuclear Engineering and Technology
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• 제49권4호
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• pp.692-699
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• 2017

The determination of the shape and rising velocity of gas bubbles in a liquid pool is of great importance in analyzing the radioactive aerosol emissions from nuclear power plant accidents in terms of the fission product release rate and the pool scrubbing efficiency of radioactive aerosols. This article suggests a simple parameterization for the gas bubble rising velocity as a function of the volume-equivalent bubble diameter; this parameterization does not require prior knowledge of bubble shape. This is more convenient than previously suggested parameterizations because it is given as a single explicit formula. It is also shown that a bubble shape diagram, which is very similar to the Grace's diagram, can be easily generated using the parameterization suggested in this article. Furthermore, the boundaries among the three bubble shape regimes in the $E_o-R_e$ plane and the condition for the bypass of the spheroidal regime can be delineated directly from the parameterization formula. Therefore, the parameterization suggested in this article appears to be useful not only in easily determining the bubble rising velocity (e.g., in postulated severe accident analysis codes) but also in understanding the trend of bubble shape change due to bubble growth.

• Korean Chemical Engineering Research
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• 제54권4호
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• pp.543-547
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• 2016

직경 0.152 m이고 높이 2.5 m인 전해질용액 기포탑에서 기포의 크기(chord length)와 상승속도 등 기포의 물성에 대해 고찰하였다. 기포의 크기와 상승속도는 이중저항탐침법을 사용하여 측정하였다. 기체와 액체의 유속 그리고 액상의 이온강도가 기포의 크기와 상승속도에 미치는 영향을 결정하였다. 기포의 크기는 기체의 유속이 증가함에 따라 증가하였으나 액체의 유속과 액상의 이온강도가 증가함에 따라서는 감소하였다. 기포의 상승속도는 기체의 유속이 증가함에 따라 증가하고 액상의 이온강도가 증가함에 따라 감소하였으나 액체유속의 변화에 따라서는 약한 최대값을 나타내었다. 기포의 크기와 상승속도는 운전변수들의 상관식으로 잘 나타낼 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• 제18권5호
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• pp.24-28
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• 1994

In the present paper, the behavior of bubbles in a fluidized bed has been investigated experimentally. The bubble size, distribution of bubble, bubble rising velocity and pressure fluctuation in the fluidized bed are obtained at different air velocity. The results are discussed and compared study the effect of air velocity on the behavior of a bubbles in fluidized bed.

• 한국입자에어로졸학회지
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• 제13권1호
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• pp.1-10
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• 2017

본 총설에서는 액체층을 통과하는 기포의 크기, 형상, 상승속도를 결정하기 위한 이론들을 살펴보았다. 액체의 물리적 특성과 기포의 유량으로부터 기포의 크기, 형상, 상승속도를 체계적으로 계산하는 여러 가지 이론식 및 모수식들을 살펴보고, 각각의 장단점을 정리하였다. 이 분야에서 발표된 초기 저작들에서는 주로 반복계산을 통해 기포의 형상과 상승속도를 결정하는 기법들이 사용되었으나, 최근에 발표된 논문들에서는 간단한 모수식을 통해 기포의 형상과 상승속도를 반복계산 없이 쉽게 구하는 기법들이 제시되고 있다. 이러한 기법들은 매우 다양한 물리적 특성을 가지는 실험결과들과의 비교에서도 우수성을 보여주고 있어, 관련 분야의 연구에 매우 유용한 도구로 사용할 수 있을 것으로 보인다.

• Korean Chemical Engineering Research
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• 제55권5호
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• pp.698-703
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• 2017

Bubble flow characteristics in fluidized beds were analyzed by CPFD simulation. A fluidized bed, which had the size of $0.3m-ID{\times}2.4m-high$, was modeled by commercial CPFD $Barracuda^{(R)}$. Properties of bed material were $d_p=150{\mu}m$, ${\rho}_p=2,330kg/m^3$, and $U_{mf}=0.02m/s$. Gas was uniformly distributed and the range of superficial gas velocity was 0.07 to 0.16 m/s. Two other geometries were modeled. The first was a three-dimensional model, and the other was a two-dimensional model of $0.01m{\times}0.3m{\times}2.4m$. Bubble size and rising velocity were simulated by axial and radial position according to superficial gas velocity. In the case of three-dimensional model, simulated bubble rising velocity was different from correlations, because there was zigzag motion in bubble flow, and bubble detection was duplicated. To exclude zigzag motion of bubble flow, bubble rising velocity was simulated in the two-dimensional model and compared to the result from three-dimensional model.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3015-3020
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• 2007

An experimental study of the dynamic characteristics of the free rising oblate spherical bubble is investigated. As noted by Saffman, the characteristics of the spiral motion are defined with parameters of the spiral frequency, spiral radius, and rising velocity. High speed camera recorded every detail information of free rising bubble. The spiral number, the bubble rise velocity, and the angular velocities were measured for the bubble size between 1.0mm to 20.0mm in diameter. In order to make clear trajectory, we employed the Fast Fourier Transformation for the normal digital camera data to synchronize with the high speed camera data. It was found that the spiral number suggested here was monotonically decreased as the bubble size increases. The present observation, however tells us that previous Saffman's formulation shows a good agreement with the trend, but over estimated spiral number. Therefore, it is recommended that Saffman's theoretical study is needed to be improved.

• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1810-1820
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• 2021

Study of single bubble behavior under rolling motions can prove useful for fundamental understanding of flow field inside the modern small modular nuclear reactors. The objective of the present study is to simulate the influence of rolling conditions on single rising bubble in a liquid using multiphase Moving Particle Semi-implicit (MPS) method. Rolling force term was added to 2D Navier-Stokes equations and a computer program was written using C language employing OpenACC to port the code to GPU. Computational results obtained were found to be in good agreement with the results available in literature. The impact of rolling parameters on trajectory and velocity of the rising bubble has been studied. It has been found that bubble rise velocity increases with rolling amplitude due to modification of flow field around the bubble. It has also been concluded that the oscillations of free surface, caused by rolling, influence the bubble trajectory. Furthermore, it has been discovered that smaller vessel width reduces the impact of rolling motions on the rising bubble. The effect of liquid viscosity on bubble rising under rolling was also investigated and it was found that effects of rolling became more pronounced with the increase of liquid viscosity.

• 대한기계학회논문집B
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• 제31권11호
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• pp.904-911
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• 2007

A measurement technique fur void fraction has been proposed using a time-resolved two-phase PIV system and the bubble dynamics has been investigated in gas-liquid two-phase flows. For the three-dimensional evaluation of the bubble information, both the images from the front and side views are simultaneously recorded into a high speed CCD camera by reflecting the side view image on a $45^{\circ}$ oriented mirror to be juxtaposed with the front view image. Then, a stereo-matching technique is applied to calculate the void fraction, bubble size and shape. To obtain the rising bubble velocities, the 2-frame PTV method was adopted. The present technique is applied to freely rising bubby flows in stagnant liquid. The results show that the increase of bubble flow rate gives rise to the increase of bubble size and rising velocity at first. If it goes over a certain level, the rising velocity becomes constant and the horizontal velocity grows bigger instead due to the obstruction of other bubbles.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2105-2108
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• 2003

The characteristics of upward bubble flow were experimentally investigated in a liquid bath. In the present study, a thermal-infrared camera and high speed CCO camera were used to measure their temperature and local rising velocity, respectively. Heat transfer from bubble surface to water is largely completed within z=10mm from the nozzle, and then the temperature of bubble surface reaches that of water rapidly. The rising velocity of bubble was calculated for two different experimental conditions: 1) bubble flow without kinetic energy 2) with kinetic energy. Bubble flow without kinetic energy starts to undergo the effect of inertia force 10cm away from the nozzle. Whereas, kinetic energy is dominant before 30 cm away from the nozzle in bubble flow, but after this point, kinetic energy and inertial force are applied on bubble flow at the same time.

• 한국가시화정보학회지
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• 제8권3호
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• pp.41-48
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• 2010

A visualization study to evaluate bubble motion in a tab water filled cylindrical tank with a varying flow rate of compressed air is conducted. The flow rate of compressed air varies from 1 to 5 L/min. Time resolved images are acquired by a high speed camera in 10 bit gray level at 100 fps and the measurement volume is irradiated by a 230 W halogen lamp. It is observed that there are three different regions; the bubble formation region, the rising bubble region and the free surface region. During the rise of bubble, the shape is changed as if an elastic body. Based on the binarized bubble image, the mean diameters of rising bubbles are estimated at beneath of the free surface. As the gas flow rate increases, the mean diameter is increased and the rising velocity also increases with buoyancy force.