• Journal of the Korean Society of Visualization
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• v.3 no.1
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• pp.20-25
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• 2005

An x-ray PIV (Particle Image Velocimetry) technique was developed fur measuring quantitative information on flows inside opaque conduits and/or opaque-fluid flows. To check the performance of the x-ray PIV technique developed, it was applied to a liquid flow in an opaque Teflon tube. To acquire x-ray images suitable for PIV velocity field measurements, the refraction-based edge enhancement mechanism was employed with seeding detectable tracer particles. The amassed velocity field data obtained were in a reasonable agreement with the theoretical prediction. The x-ray PIV technique was also applied to get velocity fields of blood flow and to measure size and velocity of micro-bubbles simultaneously, and to visualize the water refilling process in bamboo leaves. The x-ray PIV was found to be a powerful transmission-type flow imaging technique fur measuring quantitative information of flows inside opaque objects and various opaque-fluid flows.

• Journal of Environmental Science International
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• v.26 no.3
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• pp.303-309
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• 2017

Aeration with low energy micro-bubble generation and $UV/H_2O_2$ processes was introduced to verify the possibility of oxidation treatment for acid mine drainage. During 10 hours of aeration with micro-bubbles, Fe and As concentrations were decreased to 18.1 and 61.8%, respectively, while Cu, Cd, Al were kept at influent concentrations. Other heavy metals such as Mn, Cr, Pb, Zn, and Ni concentrations fluctuated due to the repetition of oxidation and release. Twenty days of aeration indicated the oxidation possibility for Cu, Cd, and Al. With the employment of $UV/H_2O_2$ processes, more than 77% of Cu and Fe removed, whereas slightly more than 30% of Cd and Al removed.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.2
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• pp.109-115
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• 1994

This paper presents a new concept to reduce turbulent frictional drag by injecting micro-bubble into near the buffer layer of turbulent boundary layer on flat plate. The concentrations of micro bubble distribution in the boundary was calculater by eddy viscosity equations in the governing equations. When near region of the buffer layer of turbulent boundary layer is filled with micro-bulle of air and viscous of the region is kept low, the velocity profile in the near region should be changed substantially. Then the Reynolds stress in the region becomes less, which guide to lower velocity gradient there. It results in reduction of velocity gradient at the viscous sublayer, which gives the reduction of shear stress at the wall.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.4
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• pp.471-478
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• 2011

A series of laboratory experiments carried out to investigate the particle separation efficiency and flotation characteristics using $CO_2$ bubbles. The primary objective of this study was to find out the feasibility of $CO_2$ bubbles as an applicable unit of flotation process in tap-water and wastewater treatment plant. The fundamental measurements were conducted to characterize the $CO_2$ bubble from the physical viewpoint in water including bubble size distribution and rising velocity under various operational conditions. In addition, the removal efficiency of solid was experimented using the lab scale plant applied $CO_2$ bubbles, namely the dissolved carbon dioxide flotation (DCF) process. The DCF process using carbon dioxide bubble, which is an advantage as the decrease and the reuse of Green-House gas, can be a promising technology as an water treatment process. On the other hand, the further research to decrease the bubble size distribution of $CO_2$ is required to enhance the particle separation efficiency.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.4
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• pp.134-140
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• 2009

The feasibility of electrochemical drilling and milling on stainless steel are investigated using tungsten microelectrode with $10{\mu}m$ in diameter. For the development of environmentally friendly and safe electrochemical process, citric acid solution is used as electrolyte. A few hundred nanoseconds duration pulses are applied between the microelectrode and work material for dissolution localization. Tool fracture by Joule heating, micro welding, capillary phenomenon, tool wandering by the generated bubbles are observed and their effects on micro ECM are discussed. Occasionally, complex textures including micro pitting corrosion marks appeared on the hole inner surface. Metal growth is also observed under the weak electric conditions and it hinders further dissolutions for workpiece penetration. By adjusting appropriate pulse and chemical conditions, micro holes of $37{\mu}m$ in diameter with $100{\mu}m$ in depth and 26Jim in diameter with $50{\mu}m$ in depth are drilled on stainless steel 304. Also, micro grooves with $18{\mu}m$ width and complex micro hand pattern are machined by electrochemical milling.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1203-1210
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• 2003

Emission of ultrasonic vibration to turbulent flow promotes the turbulence generation due to the resonantly oscillating pressure field and thereby induced cavitation. In addition, ultrasonic vibration is well transmitted through water and not dissipated easily so that the micro-bubbles involved in the fluid induce the gaseous cavitation if the bubbles are resonated with the ultrasonic field. In the present study, we found through LDV measurement that the gaseous cavitation induced by ultrasonic vibration to CO$_2$saturated water flow in the rectangular cross-sectioned straight duct enhances turbulence much more than the case of non-ultrasonic or normal ultrasonic conditions without gaseous cavitation. We also found that the fluctuating velocity component induced by emitting the ultrasonic vibration in normal direction of a rectangular channel flow can be redistributed to stream-wise component by the agitation of gaseous cavitation.

• Composites Research
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• v.28 no.2
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• pp.70-74
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• 2015

In this paper, carbon nanotubes (CNTs) and micro glass bubbles (GBs) have been incorporated into a polyamide6 (PA6) matrix to impart thermoelectric properties. The spaces created in the matrix by GBs allows the formation of "segregated" CNT network. The tightly bound CNT network, if controlled properly, can serve as a conductive path for electron transport, while prohibiting phonon transport, which would provide an ideal configuration for thermoelectric applications. The CNTs and GBs were dispersed in a nylon-formic acid solution using horn sonication followed by coagulation in deionized water, and nanocomposite panels were fabricated using a hot press. The performance of nanocomposite panels was evaluated from thermal and electrical conductivities and Seebeck coefficient, and a thermoelectric figure of merit as high as 0.016 was achieved.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1464-1469
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• 2004

In this study, micro square heaters having dimensions of $65{\times}65{\mu}m^2$and $100{\times}100{\mu}m^2$ were fabricated and bubble nucleation experiments on the heaters were performed. Bubble nucleation temperature was also measured using a bridge circuit and the photographs of bubble nucleation and subsequent growth were taken by a camera with a flash unit. Measured bubble nucleation temperatures were found to be closer to the superheat limit of working fluid (FC-72). Also quasi-1D analyses for the square heaters were performed. The quasi-1D analysis yielded proper temperature distribution of the square heater at steady state, however failed to predict the temperature rise up to the steady state. Similar time dependent temperature can be obtained with proper value of thermal diffusivity. For the $100{\times}100{\mu}m^2$ square heater, nucleation of several bubbles was observed while only one bubble was observed to be nucleated on $65{\times}65{\mu}m^2$ heater.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.6
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• pp.447-452
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• 2011

In this study, the polymeric membrane module is used as a diffuser and an image analysis technique based on visual information is applied to get bubble characteristics. The bubble size generated passed through polymeric membrane module was smaller from 30 to 64% than that of air stone, and bubble volume over 70% was ranged from 0.2 to 0.82 mm. But over 80% the bubbles from air stone diffuser ranged from 0.77 to 1.08 mm. The air stone and polymeric membrane module used as diffuser for a flotation system. The floc size inside the flotation reactor using air stone diffuser was bigger than that of the polymeric membrane module, which means that the micro-bubbles generated from polymeric membrane module could provide better opportunities for collisions between colloidal particles than those from air stone diffuser. Therefore, there is a possibility to apply the polymeric membrane module as a diffuser to increase the removal efficiency in the flotation process. Also, the image analysis technique used in this study could be applied as a useful analytical tool for acquisition of an information about the bubble characteristic.

• Journal of Environmental Health Sciences
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• v.2 no.1
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• pp.25-28
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• 1975

The main purpose of the aeration units in activated sludge process is to enable micro-organisms to metabolize the constituents of the waste effectively by supplying sufficient oxygen for their respiration. Normally, aeration is achieved by bringing the mixture of waste and sludge into intimate contact with air. The main type of aeration unit is diffused air unit in which air is injected into the liquid in the form of bubbles. The object of these laboratory studies is to compare the performance of three laboratory scale aeration systems at various depths of submergence, aerating water with and without the addition of a surface active agent.