• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.11
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• pp.1570-1577
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• 2002

In order to investigate the characteristics of two-phase slug flow, an electromagnetic flowmeter with 240Hz triangular AC excitation was designed and manufactured. The signals and noise from the flowmeter were obtained, and analyzed in comparison with the observations with a high speed CCD camera. The uncertainty of the flowmeter under single-phase flow was $\pm$ 2.24% in real-time. For two-phase slug flow, electromagnetic flowmeter provided real-time simultaneous measurements of the mean film velocity around Taylor bubble and the relative location and the length of the bubble. Besides, it is an easier and cheaper method for measuring mean film velocity than others such as photochromic dye activation method or particle image velocimetry.

• Journal of the Korean Ceramic Society
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• v.23 no.4
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• pp.47-54
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• 1986

Since the wall mobility of bubble magnetic materials havin g the large q (q=Kac/2$\pi$$M_s^2$) like a $YFeO_3$ has been found to be proportional to the wall energy theoretically crystallographical direction dependence of wall energy calculated by the basis on the spin configuration of the bubble wall which lies in the ac plane was compared with the crystallographical direction dependence of wall mobility which was measured by the experiment. The sample was a single crystal of $YFeO_3$ which was cut into plate normal to the C axis and polished t a thickness of about 60${\mu}{\textrm}{m}$ The measurement of the wall mobility was carried out by optical system using the magneto-optic Faraday effect. From the good agreement of the crystallographical direction dependence of wall mobility and will energy it was found that the spin configuration of the bubble wall suggested is fair.

• Journal of the Korean Electrochemical Society
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• v.16 no.2
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• pp.70-73
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• 2013

Iridium oxide is well known as an electrocatalyst for the water oxidation. Recently, Dr. Bard's group observed the electrocatalytic behavior of individual nanoparticle of Iridium oxide using the electrochemical amplification method by detecting the single nanoparticle collisions at the ultramicroelectrode (UME). However, the electrocatalytic current is decayed as a function of time. In this study, we investigated that the reason of electrocatalytic current decay of water oxidation at Iridium oxide nanoparticles. We identified it is due to the bubble overpotential because the cyclic current decay and recovery were synchronized to the oxygen bubble growth and coming away from an Iridium disk electrode.

• Journal of the Korea Institute of Building Construction
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• v.16 no.3
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• pp.211-217
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• 2016

In this research, the performance of surface covering technique using a white-colored bubble sheet on reducing the cracking due to the plastic, and drying shrinkages for high rise building construction were evaluated by comparing the exposed surface without any surface treatment. From the results of the experiment conducted during fall season, desired results of decreased numbers, length, maximum width, and area of cracking were obtained without a significant difference on heat of hydration and cumulative temperature. Therefore, it is considered that the surface covering technique using bubble sheet is an appropriate method for preventing plastic and drying shrinkage cracking at fall season concrete construction.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.01a
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• pp.768-772
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• 2009

This paper proposes a method for measurement three-dimensional trajectories of bubbles generated around a swimmer's arms from stereo high-speed camera videos. This method is based on two techniques: two-dimensional trajectory estimation in single-camera images and trajectory pair matching in stereo-camera images. The two-dimensional trajectory is estimated by block matching using similarity of bubble shape and probability of bubble displacement. The trajectory matching is achieved by a consistensy test using epipolar constraint in multiple frames. The experimental results in two-dimensional trajectory estimation showed the estimation accuracy of 47% solely by the general optical flow estimation, whereas 71% taking the bubble displacement into consideration. This concludes bubble displacement is an efficient aspect in this estimation. In three-dimensional trajectory estimation, bubbles were visually captured moving along the flow generated by an arm; which means an efficient material for swimmers to swim faster.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.38.3-39
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• 2009

Equatorial Plasma Bubble (herafter, EPB) is a common feature in low-latitude F-region during the night time. Since EPB causes significant impacts on the satellite communication and navigation systems, its accurate forecast is highly demanded by the GNSS users. Thus, further understanding of these features and their configuration is a challenging issue in space weather studies. The day-to-day variability of the plasma bubble activity was investigated by analyzing the TIMED/GUVI, ROCSAT-1, DMSP, and CHAMP satellite data. The pre-reversal enhancement (PRE) is known as the most important single parameter for the onset of plasma bubbles but we do not know yet to what extent the day-to-day variability of the bubble activity can be attributed to the PRE. We obtained the magnitude of the PRE from ROCSAT-1 and the occurrence of bubbles in relation to the PRE was investigated by using the coincident observations of EPBs from TIMED/GUVI, DMSP, and CHAMP. By conducting one-to-one comparison of the PRE characteristics with the EPB occurrence we examined the role of the PRE in the onset of EPBs.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.643-652
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• 2005

Saturated nucleate pool boiling experiments for binary mixtures, which are consisted of refrigerant R11 and R113, were performed with constant wall temperature condition. Results for binary mixtures were also compared with pure fluids. A microscale heater array and Wheatstone bridge circuits were used to maintain the constant temperature of the heating surface and to obtain heat flow rate measurements with high temporal and spatial resolutions. Bubble growth images were captured using a high speed CCD camera synchronized with the heat flow rate measurements. The departure time for binary mixtures was longer than that for pure fluids, and binary mixtures had a higher onset of nucleate boiling (ONB) temperature than pure fluids. In the asymptotic growth region, the bubble growth rate was proportional to a value between $t^{\frac{1}{6}}$ and $t^{\frac{1}{4}}$. The bubble growth behavior was analyzed to permit comparisons with binary mixtures and pure fluids at the same scale using dimensionless parameters. There was no discernable difference in the bubble growth behavior between binary mixtures and pure fluids for a given ONB temperature. And the departure radius and time were well predicted within a ${\pm}30{\%}$ error. The minimum heat transfer coefficient of binary mixtures occurred near the maximum ${\mid}y-x{\mid}$ value, and the average required heat flux during bubble growth did not depend on the mass fraction of R11 as more volatile component in binary mixtures. Finally, the results showed that for binary mixtures, a higher ONB temperature had the greatest effect on reducing the heat transfer coefficient.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.6
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• pp.519-526
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• 2015

To measure the physical parameters of the simple microlayer model for the prediction of the heat flux and heat transfer rate due to the evaporation of the microlayer during nucleate boiling, the microlayer geometry was experimentally examined. The parameters, including initial thickness, moving velocity and microlayer radius, were measured by total reflection and interferometry techniques using a laser. Single-bubble nucleate boiling experiments were conducted using saturated water on a horizontal surface under atmospheric pressure. The geometric characteristics of the microlayer underneath the bubbles periodically nucleating at a nucleation site at an average heat flux of $200kW/m^2$ were analyzed. The experimental results in the present study show that the maximum initial thickness of the microlayer and the horizontal moving velocity are $5.4{\mu}m$ and 0.12 m/s, respectively.

• KSTLE International Journal
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• v.1 no.1
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• pp.52-58
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• 2000

The velocity and motion of single air bubbles rising through lubricant have been experimentally investigated to test the effect of silicon defoamant The investigation reveals that the velocity is markedly retarded by the addition of small amount of silicone defoamant. This retardation of rising velocity of air bubbles is proposed by increasing of Drag force or reducing of Buoyancy force around the surfaces of the bubbles.

• Elastomers and Composites
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• v.41 no.2
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• pp.116-124
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• 2006

Cloud-point data to $160^{\circ}C$ and 1,000 bar are presented with poly(ethylene-co-15.3 mole% octene) copolymers ($PEO_{15}$) in pure 1-octene and mixtures of ethylene - 1-octene. The cloud-point curves for $PEO_{15}$ - ethylene - 1-octene mixture dramatically increase in pressure to as high as 1,000 bar with an increasing ethylene concentration. At ethylene concentrations less than 18 wt%, the ternary mixture has bubble- and cloud-point curves. As the ethylene concentration of the ternary mixture increases, the bubble-point curve and the single-phase region reduce. The reduction in the single phase region with increasing ethylene concentrations is the result of reduced dispersion interactions between $PEO_{15}$ and the mixed solvent. The single-phase region decreases with increasing temperatures when ethylene concentrations are lower than 36 wt%, whereas the single-phase region increases with temperatures at ethylene concentrations greater than 50 wt%. At ethylene concentrations greater than 50 wt% the effect of the polar interactions of the mixed solvent, which is unfavorable to dissolve PEO, is greater than the effect of the density of the mixed solvent. Therefore, the cloud-point pressures increase with a decreasing temperature. However, at ethylene concentrations less than 50 wt%, the cloud-point pressures decrease with temperature, because the effect of the polar interactions is less than the density effect.