• Title/Summary/Keyword: single air bubble

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Thermal Performance Evaluation of the Window Systems with Air-bubble Sheets (단열시트(뽁뽁이)의 종류 및 부착위치에 따른 창호의 단열성능 평가)

  • Hwang, Je;Jeong, Ah Hee;Jeon, Byung Heoun;Ahn, Young Chull
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.27 no.9
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    • pp.463-467
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    • 2015
  • The air-bubble sheet has been widely used to wrap fragile products for long-distance transportation. The further usage of the air-bubble sheet as a thermal-insulation material for the reduction of the thermal conductivities of window systems has occurred because of its low price, in addition to its thermal-conductivity properties. In this study, the thermal performances of a variety of commercial air-bubble sheets according to various applications were evaluated. The experiments were performed with single-glazed and double-glazed windows and three types of air-bubble sheets of different air volumes. U-values are used and were calculated for the determination of the thermal performances that are based on the KS F 2278. The maximum decrease of the U-value was measured as 1.092 when a sheet was attached onto the frame of single-glazed window. The square-like air-bubble sheet that contains the largest air volume shows the highest thermal-resistance value. Double layers of the air-bubble sheets show better performances than those of the single layers on both sides of the windows.

Investigation on Shapes and Acoustic Characteristics of Air Bubbles Generated by an Underwater Nozzle (수중 노즐에서 발생하는 기포의 형상 및 음향 특성 연구)

  • Kim, Jong-Chul;Oh, Joon-Seok;Cho, Dae-Seung
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.16 no.2 s.107
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    • pp.190-197
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    • 2006
  • It is well known that the acoustic characteristics of the sea are significantly affected by bubbles which have their own inherent characteristics at the undersea. In this study, the shape and acoustic characteristics of air bubbles generated by an underwater nozzle are calculated numerically, and are measured with a high speed camera and a hydrophone at various air flow rates in the experimental apparatus. As a result of analysis, the shape calculated numerically well matched with measured values at low flow rates, but in case of relatively higher flow rates. the use of correction coefficient is needed for more accurate estimation of the bubble shape. And also the rising velocity of a single bubble is constant regardless of both the bubble size and the flow rate. and the acoustic signal generated when the bubble is produced by an underwater nozzle has the same characteristic of natural frequency of the bubble pulsation, and is agreed with Minnaert's equation if the correction coefficient is considered in accordance with the flow rate.

Effect of a Silicone Defoamant on the Motion of Single Air Bubbles Rising in Lubricant

  • Shim, Joosup;Cho, Wonoh;Chung, Keunwoo;Kim, Woung Woon
    • 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.

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Flow Visualization of Magnetic Particles under the external magnetic field in bubbly flow using Single Plane Illumination Microscopy - MicroPIV (Single Plane Illumination Microscopy - MicroPIV를 이용한 버블 유동에서 외부 자계 영향을 받는 자성입자 가시화)

  • Lee, Changje;Cho, Gyeong-rae;Lee, Sangyoup
    • Journal of the Korean Society of Visualization
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    • v.19 no.1
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    • pp.36-42
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    • 2021
  • This study measured the velocity of magnetic particles inside the power generation using external heat sources. Single Plane Illumination Microscopy (SPIM) was used to measure magnetic particles that are simultaneously affected by bubbly flow and magnetic field. It has the advantage of reducing errors due to particle superposition by illuminating the thin light sheet. The hydraulic diameter of the power generation is 3mm. Its surface is covered with a coil with a diameter of 0.3 mm. The average diameter of a magnetic particle is 200nm. The excitation and emission wavelengths are 530 and 650nm, respectively. In order to find out the flow characteristics, a total of four velocity fields were calculated in wide and narrow gap air bubbles, between the wall and the air bubble and just below the air bubble. Magnetic particles showed up to 8.59% velocity reduction in the wide gap between air bubbles due to external magnetic field.

A Study on Destratification System Using Bubble Plume: Dimensional Analysis and Design Methodology (버블 플룸을 이용한 탈성층의 평가: 차원해석 및 설계방법론의 제시)

  • Kim, Sung-Hoon;Kim, Jae-Yun;Park, Heekyung
    • Journal of Korean Society of Water and Wastewater
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    • v.19 no.6
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    • pp.827-837
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    • 2005
  • In this study, we derived a new non-dimensional variable including bubble size and air diffusing area by Buckingham's theorem for making a practical correlation with experimental results. Firstly, we drew a relationship between a non-dimensional variable, $NH/u_s$, which has a form of Froude number and destratification efficiency with a simple theoretical consideration. Then we derived two non-dimensional variables by Buckingham's ${\pi}$-theorem and equating them with a form of $Fr_N$ for making single parameter to correlate overall destratification efficiency. As the result, the single parameter Be number shows a correlations with destratification efficiencies obtained from laboratory and pilot experiments. Also, for the practical applications, we conducted multiple regression analysis using Be and tank area to make predictive equations about destratification efficiency. The result also shows a successful correlations with destratification efficiency ($R^2$>0.9, p<0.001). Using this equation, we proposed a new design methodology with respect to bubble diffusing area.

Field Application to Evaluate the Effect of Various Surface Covered Curing Blankets on Temperature Profile and Crack Occurrence of the Concrete under Hot Weather Condition (서중환경에서 표면피복 양생재 종류변화가 콘크리트의 초기 온도이력 및 균열발생에 미치는 영향에 관한 현장적용성 평가)

  • Han, Min-Cheol;Lee, Sang-Woon
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.34 no.5
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    • pp.27-34
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    • 2018
  • Concrete placed under hot weather condition suffers from larger slump loss, rapid moisture evaporation due to high air temperature. Proper measures for material, transportation and curing should be taken to prevent the quality deterioration of the concrete under hot weather condition. In Korea, Although the period of hot weather concrete in Korea occupies only 2 months, there are a lot of quality problems including plastic, drying shrinkage and cold joint. Therefore, the objective of this paper is to investigate and compare the temperature history and crack occurrence of the concrete, which was placed in the actual apartment house construction field under hot weather condition, in response to the application of surface covered curing blankets including PE film, single layer clear bubble sheet, white colored bubble sheet and aluminum metalized bubble sheet. Test results indicated that the application of white colored bubble sheet and aluminum metalized bubble sheet showed most favorable results in terms of reduction in temperature rise and crack occurrence as well as easiness in handling. But, due to light reflection by aluminum metalized bubble sheet, it is believed that white colored bubble sheet is preferable.

The Effect of Second Order Refraction on Optical Bubble Sizing in Multiphase Flows

  • Qiu, Huihe;Hsu, Chin-Tsau;Liu, Wei
    • Journal of Mechanical Science and Technology
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    • v.15 no.12
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    • pp.1801-1807
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    • 2001
  • In multiphase flne the bubble size and velocity. To achieve this, one of approaches is to utilize laser phase-Doppler anemometry. However, it was found that the second order refraction has great impact on PDA sizing method when the relative refractive index of media is less than one. In this paper, the problem of second order refraction is investigated and a model of phase-size correlation to eliminate the measurement errors is introduced for bubble sizing. As a result, the model relates the assumption of single scattering mechanism in conventional phase-Doppler anemometry. The results of simulations based on this new model by using Generalized Lorenz Mie Theory (GLMT) are compared with those based on the conventional method. An optimization method for accurately sizing air-bubble in water has been suggested.

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A Study on the Interaction between Particles and Surrounding Fluid (입자와 주위유체와의 상호작용에 관한 연구)

  • ;T.Kurihara;H. Monji;G. Matsui
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.2
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    • pp.108-115
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    • 2002
  • The fundamental mechanism of a dispersed two-phase flow was investigated. Experiments were carried out to understand how the particles behaves under the influence of the particle size, shape, metamorphoses (bubble) and buoyancy of a single particle which is ascending from the standstill water. Two CCD cameras were employed for image processing of the behavior of the particles and the surrounding flow, which was interpreted with the technique of correlation PIV (Particle Image Velocimetry) and PTV (Particle Tracking Veloci- metry), respectively The experimental results showed that the large density difference bet- ween a particle and water caused high relative velocity and induced zigzag motion of the particle. Furthermore, the turbulence intensity of a bubble was about twice the case of the spherical solid particle of similar diameter.

Effects of Entrained Air on the Characteristics of a Small Screw-type Centrifugal Pump (공기 흡입이 소형 스크류식 원심펌프의 특성에 미치는 영향)

  • Kim, You-Taek;Tanaka, Kazuhiro;Lee, Young-Ho;Matsumoto, Yoichiro
    • The KSFM Journal of Fluid Machinery
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    • v.2 no.3 s.4
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    • pp.37-44
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    • 1999
  • In a screw-type centrifugal pump, the pump head deteriorates from single-phase flow to the choke due to an increased air entrainment at a wide tip clearance compared to that of a narrow tip clearance. Moreover, at a narrow tip clearance, the pump head became partially higher in a two-phase flow than that of a single-phase flow near the best efficiency point in low void fraction region. Therefore, we observed the internal flow pattern by using a stroboscope and we measured the mean size of bubbles from the images obtained with a high speed camera. Then, we investigated the influences of the mean size of bubbles, tip clearances and flow patterns on pump performance.

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THEORETICAL STUDY OF MOTION OF SMALL SPHERICAL AIR BUBBLES IN A UNIFORM SHEAR FLOW OF WATER

  • MEHDI, SYED MURTUZA;KIM, SIN
    • Nuclear Engineering and Technology
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    • v.47 no.1
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    • pp.126-134
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    • 2015
  • A simple Couette flow velocity profile with an appropriate correlation for the free terminal rise velocity of a single bubble in a quiescent liquid can produce reliable results for the trajectories of small spherical air bubbles in a low-viscosity liquid (water) provided the liquid remains under uniform shear flow. Comparison of the model adopted in this paper with published results has been accomplished. Based on this study it has also been found that the lift coefficient in water is higher than its typical value in a high-viscosity liquid and therefore a modified correlation for the lift coefficient in a uniform shear flow of water within the regime of the $E\ddot{o}tv\ddot{o}s$ number $0.305{\leq}Eo{\leq}1.22$ is also presented.