• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.617-624
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• 2015

The dissolved air flotation (DAF) system is a water treatment process that removes contaminants by attaching micro bubbles to them, causing them to float to the water surface. In the present study, two-phase flow of air-water mixture is simulated to investigate changes in the internal flow analysis of DAF systems caused by using different turbulence models. Internal micro bubble distribution, velocity, and computation time are compared between several turbulence models for a given DAF geometry and condition. As a result, it is observed that the standard ${\kappa}-{\varepsilon}$ model, which has been frequently used in previous research, predicts somewhat different behavior than other turbulence models.

• Korean Journal of Food Science and Technology
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• v.25 no.4
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• pp.391-394
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• 1993

For the automation of Tackjoo fermentation, a sensor measurable gas production during brewing and a controller were built. The performance tests were carried out at 10 litter Tackjoo fermentor, The sensor was consisted of a transparent acryl cell for bubble formation and photo-interrupter for the detection of bubbles of 0.018ml size. The fermentation controller was fabricated with a single chip microcomputer (MC68705R3) and provided with both the monitoring module of temperature measurement and the valve controling device for the cooling water circulation in coil type heat exchanger. The operation programs were developed and systemized in ROM. With this computer system, the gas production amount and rate were acquired during the Tackjoo fermentation. The fermentation curve based on the gas production rate showed a good agreement with that of alcohol concentration. The maximum rate of gas production was found after 24 hr at $30^{\circ}C$. The correlation equation between the gas production and alcohol concentration was established and used as the control algorithm of the fermentation.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.5
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• pp.481-487
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• 2012

Recently, the construction of the small Al alloy ships is an increasing trend in viewpoint such as the disposal issue of a retired ship, the enhancement of environmental regulation and resources recycling etc. for FRP ships. However, Al alloy ship which can achieve high speed by light weight in marine environment is exposed to a problem on materials damage by cavitation-erosion which is generated by large impact pressure with the collapse of air bubbles due to cavitation. Consequently, in this study, water cavitation peening technology was applied in Al alloy for ship to enhance durability life by preventing cavitation damage. So, the water cavitaton peening application time that presented the excellent cavitation characteristic investigated. The weight-loss of 5456-H116, 5083-H321 and 5052-O Al alloy at the optimum water cavitation peening time were improved to 42.11 %, 50.0 % and 25.7 %, respectively.

• Clean Technology
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• v.10 no.4
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• pp.195-201
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• 2004

Cellulase was modified with copolymer with polyethylene(PE)/polypropylene(PP) oxide and maleic anhydride(MA) by maleylation reaction, and modified cellulase was applied to the reprocessing of old newsprint (ONP). Cellulase of modified cellulase enhanced the detachment of ink particles by fibrillation of fiber. The copolymer, which acted as the surfactant formed bubbles and removed the ink particles in the floatation process. Modified cellulase showed the same deinking ability without excess dosage compared with the conventional method. And, it improved the physical properties including tensile strength, brightness, and whiteness compared with the conventional deinking process. The bond between the ink and fiber got stronger as the storage time increased, and it became very difficult to remove the ink particle. But, modified cellulase increased the deinking ability by 41% compared with the conventional process at the experiment of the ONP for 1 year storage time. It removed the yellowing and increased the whiteness and brightness as well as tensile strength and internal bond strength.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.42-53
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• 2008

The two dimensional PIV (particle image velocimetry) measurement technique is applied to water flow in a narrow cavitation tunnel. The nearly homogeneous and isotropic turbulent flows are generated by the honeycomb installed in the tunnel and visualized with a PIV technique. The velocities in the measurement plane at the tunnel centerline 184cm downward from the honeycomb were measured and calculated by an image correlation technique. The turbulent properties are evaluated and each term in the turbulent kinetic energy equation is calculated for the conditions with different internal pressures. Lowering the internal pressure gives an effect on the turbulent flow due to growing bubbles which are resolved in the water. The turbulent kinetic energy in the measurement plane is decayed much slower than those of other research results carried out with wind tunnels. With decreasing the tunnel internal pressures the turbulent intensities are increased about 1.5 times and the anisotropic tendency is also increased.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.1
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• pp.56-65
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• 2018

Pressure oscillation caused by the compressibility of entrapped air in dam break flow is analyzed using an open source code, which is a two-phase compressible code for non-isothermal immiscible fluids. Since compressible flows are computed based on a pressure-based method, the code can handle the equation of state of barotropic fluid, which is virtually incompressible. The computed time variation of pressure is compared with other experimental and computational results. The present result shows good agreements with other results until the air is entrapped. As the entrapped air bubbles pulsate, pressure oscillations are predicted and the pressure oscillations damp out quickly. Although the compressibility parameter of water has been varied for a wide range, it has no effects on the computed results, because the present equation of state for water is so close to that of incompressible fluid. Grid independency test for computed time variation of pressure shows that all results predict similar period of pressure oscillation and quick damping out of the oscillation, even though the amplitude of pressure oscillation is sensitive to the velocity field at the moment of the entrapping. It is observed that as pressure inside the entrapped air changes quickly, the pressure field in the neighboring water adjusts instantly, because the sound of speed is much higher in water. It is confirmed that the period of pressure oscillation is dominated by the added mass of neighboring water. It is found that the temperature oscillation of the entrapped air is critical to the quick damping out of the oscillations, due to the fact that the time averaged temperature inside the entrapped air is higher than that of surrounding water, which is almost constant.

• Korean Journal of Plant Resources
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• v.30 no.5
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• pp.549-555
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• 2017

The production of ginseng cultivation is decreasing due to shortage of cultivated land and climate change, so additional methods are needed. Therefore, the physiological and morphological characteristics of finebubble were analyzed by applying them to ginseng cultivation which is the representative crop of Korea. The application of fine bubble water to 2 year old ginseng showed that stem length and leaf were increased, and weight increased as main root increased in root. In particular, it is shown that the weight of roots increases with the increase of leaf size. This is because the total chlorophyll content is high and it is judged to be related to the increase of photosynthesis efficiency. When the results of this study were confirmed, it was confirmed that ginseng cultivation using fine bubbles showed no inhibition of growth of ginseng. According to the results of physiological characteristics and subdividing results, It was confirmed that the growth of about 10% to 15% of the growth was increased and that the growth of ginseng was increased by applying the fine bubble when growing ginseng.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.142-149
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• 2003

Blind hydraulic backfilling is a commonly used technique for subsidence control of the strata over unapproachable waterlogged underground excavations. In this investigation model studies on all the three variants of this technique, namely, hydro-pneumatic or air-assisted gravity backfilling, pumped-slurry backfilling and simple gravity backfilling, have been carried out in fully transparent models of the underground excavations. On examination of the filling process, it was revealed that in all the three cases, the basic process of filling occurs by sand transport along one or more meandering channels. The relative influence of sand, water and air flow rates on the area of filling from a single inlet point and the hydraulic pressure loss per unit length were studied in details. In hydro-pneumatic backfilling process, the air bubbles while moving upward through the meandering channels provide an additional buoyant force over and above the available hydraulic head. In this way the area of filling from a single borehole may be quite large even at small flow rates of water. During actual field implementation the injected air, if not released completely from the rise side holes, may cause troubles by way of creating potholes on the surface. The pumped-slurry technique has shown its capability of filling a relatively larger area at faster rate, especially when high-volume, low-pressure method was selected. But simple gravity filling was also found to be equally effective method as slurry pumping, especially when flow rates were high. In the second and third method discussed above, examination of variations of injection pressure was also done and its relation with physical phenomenon was also attempted. Some empirical relationships were also developed using multivariate regression with a view to help the practicing engineers.

• Applied Chemistry for Engineering
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• v.30 no.6
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• pp.652-658
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• 2019

Direct hydrazine fuel cells (DHFCs) have been considered to be one of the promising fuel cells because hydrazine as a liquid fuel possesses several advantages such as no emission of CO₂, relatively high energy density and catalytic activity over platinum group metal (PGM)-free anode catalysts. Judging from plenty of research works, however, regarding key components such as electrocatalysts as well as their physicochemical properties, it becomes quite necessary to understand better the underlying processes in DHFCs for the long term stability. Herein, we highlight recent studies of DHFCs in terms of a systematic approach for developing cost-effective and stable anode catalysts and electrode structures that incorporate mass transport characteristics of hydrazine, water and gas bubbles.

• Journal of the Korean Wood Science and Technology
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• v.33 no.6 s.134
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• pp.17-24
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• 2005

Korean pine (Pinus koraiensis Sieb.et Zucc.) boards of 30 mm thickness were treated by steaming and four different drying methods. Small specimens were taken from the sapwoods of the treated boards and their longitudinal liquid permeability was measured according to Darcy's law. The specimens were also extracted with alcohol and aceton solutions to examine the mechanism of liquid flow in wood. It was observed that specific permeability drastically decreases with measurement time, resulting in violation of Darcy's law. It may be due to that air bubbles formed under vacuum block flow paths in resin canals. The average specific permeabilities of non-extracted and extracted specimens are different from one treatment to another. It is supposed that the properties of residual resin in resin canals change depending on the conditions of treatments. Anatomical examination was conducted with a scanning electron microscope.