• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.9 no.4
• /
• pp.135-143
• /
• 1989

The experimental study on the shape and behavior of bubbles in U-tube deep shaft of 32m has been performed. According to the results in this paper, the equivalent spherical diameter of bubbles was 0.422-0.722cm and the shape of bubbles was almost ellipsoidal for bubbles to be generated ta single-orifice of diameter 0.06cm in the downcomer of the deep shaft system. Gas hold-up and gas-liquid contact area of bubbles in the deep shaft was decreased in accordance with depth, Also downcomer velocity of bubbles was slower than circulation velocity of liquid and riser velocity of bubbles was fast than circulation velocity. The bubble-size-distribution of bubbles in the deep shaft was the logarithmic probability distribution. The number of bubbles in the deep shaft was decreased in accordance with depth and the number of bubbles in the downcomer is more than the bubbles in the riser.

• 한국전산유체공학회:학술대회논문집
• /
• 2010.05a
• /
• pp.376-379
• /
• 2010

Bubble rising phenomenon is widely founded in many industrial applications such as a stream generator in power plant. Many experimental and numerical researches have been already performed to predict dynamic behavior of the bubble rising process. Recently numerical approaches are getting popular since it can offer much detailed information which is almost impossible to obtain from the experiments. Rising bubble could penetrate through the top free surface which makes the problem much more complicate in addition to the phase changing effect even with latest numerical techniques. In this paper, the top free surface effect on rising bubble has been investigated. The gas-liquid interface was explicitly tracked using high-order Level Contour Reconstruction Method(LCRM) which is a hybridization of Front-Tracking and Level-Set method. Break-up behavior of rising bubble at free surface showed different characteristics with initial diameter of bubble.

• 한국전산유체공학회:학술대회논문집
• /
• 2011.05a
• /
• pp.10-13
• /
• 2011

A level set method is proposed to simulate the incompressible two-phase flow considering the effect of surface tension. For reinitialization of level set junction, a direct approach method is employed, instead of solving hyperbolic type equation. A mixed element is adopted, so that the continuity mid Navier-Stokes equations are solved by using the quadratic elements (six-node triangular element mid nine-node quadrilateral element), mid the level set function is solved by using the linear elements (three-node triangular element mid four-node quadrilateral element). In order to verify the accuracy mid robustness of the codes, the present methods are applied to a few benchmark problems. It is confirmed that the present results are in good qualitative mid quantitative agreements with the existing studies.

• Journal of the Society of Naval Architects of Korea
• /
• v.39 no.1
• /
• pp.16-27
• /
• 2002

A level-set method is used for analyzing the behaviors of gas bubbles in two fluids incompressible viscous flow domain. The governing equations are solved by using a finite volume method. The numerical results are verified by comparing with the experimental and other computational results. Computations for the deformations and motions of one or multi-bubbles in the flow domain with the initial undisturbed free interface are conducted. It can be seen that numerical results for different surface tension and density ratio arise very different behaviors of bubbles. When bubbles rise near the free interface, the free interface gives some great influence on the behaviors of bubbles. The present results computed by a level-set method give useful information about the properties of bubble motions and deformations.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.1 no.1
• /
• pp.17-25
• /
• 1977

The purpose of this paper is to clarify the effect of wall proximity on the terminal velocity of single air bubbles in vertical tubes. As an initial step, experiments were conducted to determine the terminal velocity, shape, and path of single air bubbles rising freely in water. The terminal velocity of air bubbles rising through water was measured in cylindrical tubes, rectangular tubes, and parallel plates respectively. The results of effect wall of cylindrical tubes were shown as a dimensionless plot, and may also be used to arrive at a decision regarding the minimum size of tube.

• Journal of Ocean Engineering and Technology
• /
• v.10 no.3
• /
• pp.117-124
• /
• 1996

A fluidized bed combustion chamber is widely used to incinerate waste material. The most important factor designing the incinerator is the flow characteristics in a fluidized bed, because combustion efficiency is influenced by the flow characteristics. This paper has invesitigated the flow characteristics of bubbles in fluidized bed by means of meassuring a pressure fluctuation in the fluidized bed. A pressure probe system has used to measure the pressure. The data concerned with bubble rising velocity, bubble size, distribution of bubbles and frequency of bubble generation or decay are obtained to find the flow characteristics of bubbles in the fluidized bed. The result obtained from this experimental study can be used to design the fuel feeding system of fluidized bed combustion type incinerator. And it is possible to predict the mixing of waste material and fluidizing material.

• Korean Chemical Engineering Research
• /
• v.48 no.3
• /
• pp.359-364
• /
• 2010

Three kinds of functional regions such as continuous slurry(${\varepsilon}_f$), bubble(${\varepsilon}_b$) and wake(${\varepsilon}_w$) regions were identified, and the individual phase holdups of each functional region were determined in a three-phase slurry bubble column of 0.152 m ID. The holdups of bubble and wake were measured by adopting the electrical resistivity probe method. Effects of gas velocity and solid concentration in the slurry phase on the individual holdups of functional regions in the column were discussed. The holdup of continuous slurry phase decreased but that of bubble or wake increased, with an increase in the gas velocity in the column. The increase of solid content in the slurry phase could lead to the increase in the holdup of continuous slurry phase but decrease in the bubble or wake holdup. The portion of wake holdup was in the range of 15~40% of the bubble holdup, which decreased with increasing gas velocity or solid content in the slurry phase. The individual holdups of three functional regions were well correlated with operating variables within this experimental conditions.

• Korean Chemical Engineering Research
• /
• v.50 no.3
• /
• pp.505-510
• /
• 2012

The gas hold-up has a strong relationship with the size distribution and rising velocities of bubbles in a bubble column. Therefore, many previous researchers have studied on the hydrodynamics focusing on the bubble size variation in bubble column. In this study, the bubble behavior was influenced by partitioning porous plates installed at a certain height in a trayed bubble column. The gas hold-up was increased in non-sparging region (H/D > 5) as well as sparging region. We identified the effect of the partitioning porous plate using three trayed bubble columns with different reactor geometries. Furthermore, the bubble break-up frequency and size distribution were observed before and after individual bubbles penetrated through the plate. The arrangement of the plates was also investigated using a 0.15-m-in-diameter bubble column. Based on the result, we applied this design concept to a 0.36-m-in-diameter, 22 m tall trayed bubble column and identified the effect of the partitioning porous plate on the gas hold-up increase.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.8
• /
• pp.633-643
• /
• 2015

In this study, we develop a highly efficient conical-air diffuser that generates fine bubble. By inserting a sufficient number of aerotropic microorganisms with dissolved oxygen from an air diffuser and minimizing the air-channel blockages within the air diffuser, we expect to improve the efficiency and durability of the decomposition process for organic waste. To upgrade the conventional air diffuser, we perform experiments and numerical analysis to develop a conical-type that generates fine bubble, and which is free from nozzle blockage. We complement the air-diffuser design by numerically analyzing the internal air-flow pattern within the diffuser. Then, by applying the diffuser to a mockup bioreactor, we experimentally and numerically study the bubble behavior observed in the diffuser and the 2-phase fluid flow in the bioreactor. The results obtained include statistics of the cord length and increased velocity, and we investigate the mechanisms of the fluid-flow characteristics including bubble clouds. Throughout the study, we systemize the design procedures for the design of efficient air diffusers, and we visualize the fluid-flow patterns caused by bubble generation within the mockup bioreactor. These results will provide a meaningful basis for further study as well as the detection of oxygen transfer and fluid-flow characteristics in real-scale bio-reactors using sets of air diffusers.

• Journal of Korean Society of Environmental Engineers
• /
• v.35 no.10
• /
• pp.710-716
• /
• 2013

New and renewable energy sources have drawn attention because of climate change. Many studies have been carried out in waste-to-energy field. Fast pyrolysis of waste lignocelluosic biomass is one of the waste-to-energy technologies. Bubbling fluidized bed (BFB) reactor is widely used for fast pyrolysis of the biomass. In BFB pyrolyzer, bubble behavior influences on the chemical reaction. Accordingly, in the present study, hydrodynamic characteristics and fast pyrolysis reaction of waste lignocellulosic biomass occurring in a BFB pyrolyzer are scrutinized. The computational fluid dynamics (CFD) simulation of the fast pyrolysis reactor is carried out by using Eulerian-Granular approach. And two-stage semi-global kinetics is applied for modeling the fast pyrolysis reaction of waste lignocellulosic biomass. To summarize, generation and ascendant motion of bubbles in the bed affect particle behavior. Thus biomass particles are well mixed with hot sand and consequent rapid heat transfer occurs from sand to biomass particles. As a result, primary reaction is observed throughout the bed. And reaction rate of tar formation is the highest. Consequently, tar accounts for 66wt.% of the product gas. However, secondary reaction occurs mostly in the freeboard. Therefore, it is considered that bubble behavior and particle motions hardly influences on the secondary reaction.