• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.8
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• pp.855-860
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• 2011

We numerically simulated a dissolved air flotation (DAF) tank to predict the performance of the pilot facility. The flow was assumed to be two-dimensional and two-phase. The velocity distributions in the separation zones of differently shaped DAFs were compared to find the effect of the shape on the performance. The results showed that the typical flow pattern that appeared in a well-designed DAF-tank was generated in the separation zone of the base model. This flow pattern could be maintained while the baffle height was sufficiently tall regardless of the other geometric parameters. However, the baffle height and angle, the contact zone width, and the perforated plate affected the uniformity of the downward flow in the separation zone. Except for the baffle height, the base model used in this study showed a better uniformity of downward flow than did other models with different geometric parameters.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.3
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• pp.172-177
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• 2014

Low pressure air flotation (LAF) pilot plant for sludge thickening was installed in Chung Nam N.S. municipal waste water treatment plant to verify its application possibility. Effects of operating conditions such as coagulant dosages and microbubble water ratio on thickening of the mixed sludge were examined. Microbubbles which were generated in the chamber of $1.5kgf/cm^2$ by high speed collision method with foaming agent were used to float sludge. Solid loading of $30kg/m^2/hr$, solid contents in thickened sludge of 60,300 mg/L and SS removal efficiency of 99% were obtained through long period operating LAF in conditions of mixed sludge concentration of 14,400 mg/L, coagulant dosage of 27.6 mg/L, foaming agent addition of 4.0 mg/L and microbubble water injection ratio of 9.7%.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.5
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• pp.649-655
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• 2004

The behavior of biological particles in DAF (dissolved air flotation) process was analyzed by employing PBT (Population balance theory). After decline growth phase of activated sludge, the value of the initial collision-attachment efficiency was increased over than 0.35 corresponding relatively high value in the whole life cycle of microorganism. For practical application of DAF as a solid separation process. It is desirable that microbial particles should be operated to perform high solid removal efficiency in biological wastewater treatment.

• Journal of Korean Society of Water and Wastewater
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• v.16 no.6
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• pp.655-662
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• 2002

Separation characteristics of inorganic particles occurred during heavy rainwater were investigated in DAF (dissolved air flotation) process. In order to remove the inorganic particles effectively, the collision and flotation efficiencies were examined from a hydrodynamic point of view. Generally, the collision efficiency increased with floc size under the variation of fluid dynamic conditions including inertial force. However, more precise model should be required to analysis the collision efficiency expressed both the physical properties for inorganic particles and hydrodynamic conditions for a reactor.

• Journal of Navigation and Port Research
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• v.36 no.3
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• pp.157-162
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• 2012

A planing craft is designed specifically to achieve comparatively high speed on the surface of the water. The frictional resistance of planing craft can be reduced further by injecting air to the craft's bottom. In this paper, the resistance characteristics of high speed planing crafts with & without air injection at the bottom were compared by sea model-test method. As a result, we conformed that planing craft with air injection has much greater the effect of resistance reduction.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.985-988
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• 2008

Maglev is a system that a train runs levitated above a rail. Therefore it is very important to maintain a constant levitation gap for achieving serviceability and ride comfort. This study is a cooperation research subject of the 3-1 subject, performance improvement of maglev track structures, of the Center for Urban Maglev Program in Korea, started in 2006. The aim of this study is development of rapid constructions of bridge superstructure for maglev. At present, precast deck is widely used because of its superiority to cast-in-place concrete on quality and the term of works. The research group suggested basic systems of maglev guideway with PSC-U type and trapezoidal open steel box type girder, and precast deck, cooperating with Korea Railroad Research Institute, the managing institute of the 3-1 subject. In this study, full-scale structure was fabricated for structural safety evaluation of precast decks and rail, and a static performance test of those structures was performed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.75-81
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• 2012

Autoignited lifted flames in laminar jets with hydrogen-enriched methane fuels have been investigated experimentally in heated coflow air. The results showed that the autoignited lifted flame of the methane/hydrogen mixture, which had an initial temperature over 920 K, the threshold temperature for autoignition in methane jets, exhibited features typical of either a tribrachial edge or mild combustion depending on fuel mole fraction and the liftoff height increased with jet velocity. The liftoff height in the hydrogen-assisted autoignition regime was dependent on the square of the adiabatic ignition delay time for the addition of small amounts of hydrogen, as was the case for pure methane jets. When the initial temperature was below 920 K, where the methane fuel did not show autoignition behavior, the flame was autoignited by the addition of hydrogen, which is an ignition improver. The liftoff height demonstrated a unique feature in that it decreased nonlinearly as the jet velocity increased. The differential diffusion of hydrogen is expected to play a crucial role in the decrease in the liftoff height with increasing jet velocity.

• The Science & Technology
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• v.32 no.3 s.358
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• pp.34-34
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• 1999

고양이가 32층아파트에서 떨어졌는데도 큰 부상없이 살았다고 하는데 왜 그럴까. 물체가 떨어질 때는 떨어지는 속도가 가속되는데 중력은 일정한데도 저항력이 커지므로 언젠가는 중력과 공기의 저항력이 맞비기게 되어 물체는 더 가속되지 않고 일정한 최종속도를 유지한다. 32층 아파트에서 떨어진 고양이의 최종 속도는 초속 18m정도가 되므로 고양이는 살 수 있는데 이러한 물리학의 원리를 고양이는 알고 있을까.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2015.10a
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• pp.439-440
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• 2015

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.306-313
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• 2006

Automated material handling system is being used as a method to reduce manufacturing cost in the semiconductor and flat panel displays (FPDs) manufacturing process. Those are considering switch-over from the traditional cassette system to single-substrate transfer system to reduce raw materials of stocks in the processing line. In the present study, the wafer transportation speed has been evaluated by numerical and experimental method for three propulsion nozzle array (face, front, rear) in an air levitation system. Test facility for 300 mm wafer was equipped with two control tracks and a transfer track of 1,500mm length. The diameter of propulsion nozzle is 0.8mm and air velocity of wafer propulsion is $50\sim150m/s$. We found that the experimental results of the wafer transportation speed were well agreed with the numerical ones. Namely, the predicted values of the maximum wafer transportation speed are higher than those values of experimental data by 16% and the numerical result of the mean wafer transportation speed is higher than the experimental result within 20%.