Acoustically excited oscillating bubble on a flexible structure and its energy-harvesting capability

Jinpyo Jeon,홍지우,Sang Joon Lee,Sang Kug Chung 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.3

When a bubble oscillates under the action of an acoustic field, it generates a cavitational microstreaming flow around it. We here explore oscillation dynamics of a bubble hanging on a flexible structure (i.e., piezocantilever) by acoustic excitation, and assess the suitability of the proposed method to micro-energy harvesting systems. We preferentially investigate the characteristics of bubble oscillation, such as the maximum amplitude and resonant frequency by varying the applied frequency and bubble size. The amplitude of the oscillating bubble is found to be maximized at the resonant frequency depending on the bubble size. Additionally, we measured the electrical outcome generated from bubble oscillation-induced microstreaming and resultant vibration of the piezocantilever, as functions of the applied frequency, bubble size, and distance between the bubble and piezoactuator. The generated voltage is considerably dependent of the applied frequency and bubble size. Meanwhile, it is inversely proportional to the distance between the bubble and piezoactuator. Finally, we found that the electrical output can be can be improved by increasing the number of bubbles. This work will provide a new framework for the fundamental design of bubble-mediated micro-energy harvesters and microsensors.

Bubble dynamic parameters during subcooled flow boiling under uniform and non-uniform transverse heat distribution

Al-Yahia, Omar S.,Yoon, Ho Joon,Jo, Daeseong Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.143 No.-

<P><B>Abstract</B></P> <P>Bubble behaviors and their interactions with each other affect the two-phase flow characteristics. In this study, experiments are conducted to investigate the bubble characteristics during subcooled flow boiling under uniform and non-uniform transverse heat flux distribution. The non-uniform heat flux distribution creates non-uniform bubble characteristics on the heated surface as opposed to under uniform heating. The working fluid is demineralized water that flows through a narrow rectangular channel heated from one side. The experimental loop used in the study operates at low pressure. A wide range of experimental operating conditions, such as inlet temperature (35–65 °C), thermal power (500–6250 W), and mass flow rates (0.03–0.13 kg/s), are applied to the upward flow channel. The bubble behaviors are visualized using a high-speed camera (2200 fps) at a resolution of 512 × 512 pixels. The results indicate that the bubbles exhibit different departure diameters, nucleation site density distributions, and bubble departure frequencies. In the uniform case, bubbles are generated uniformly across the whole transverse direction of the heated surface. In the non-uniform case, more bubbles are generated where the heat flux is concentrated, which disturbs the flow velocity profile in the transverse direction. The differences in bubble generation in the transverse direction result in differences in the two-phase flow instability through the heated channel. As a result, new empirical correlations are proposed based on the experimental results to estimate the bubble departure diameter, nucleation site density, and bubble departure frequency. The correlations are applicable for both heated surface conditions, uniform and non-uniform, under low-pressure conditions. CFD analysis using ANSYS FLUENT incorporates the RPI wall boiling model is conducted to validate the empirical correlations. Comparison of the CFD calculations with the experimental data for void fraction, wall temperature, and bulk temperature show good agreement. The simulation results show an accurate prediction of the ONB (Onset of Nucleate Boiling) and OFI (Onset of Flow Instability).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bubble behaviors have a significant influence on two-phase flow. </LI> <LI> Numerous discrepancies in the bubble parameters appear at different heating conditions. </LI> <LI> Bubble parameters are highly dependent on the local thermal hydraulic parameters. </LI> <LI> Accurate prediction of bubble parameters is critical for two-phase modeling. </LI> <LI> New empirical correlations can accurately predict the bubble parameters under uniform and non-uniform heating cases. </LI> </UL> </P>

인공기포 존재 환경에서의 양상태 잔향음 예측을 위한 해상 실험 분석 및 모델링 연구

양원준,오래근,배호석,손수욱,김다솔,최지웅 한국음향학회 2022 韓國音響學會誌 Vol.41 No.4

Bubbles generated by various causes in the ocean are known to persist for long periods of time. Although the volume occupied by bubbles in the ocean is small, the presence of bubbles in ocean due to resonance and attenuation greatly affects the acoustic properties. Accordingly, bistatic reverberation experiment was performed in the ocean where artificial bubbles exist. A number of transducers and receivers were installed on 6 buoys arranged in a hexagonal shape, and blowing agents were dropped in the center of the buoy to generate bubbles. For reverberation modeling that reflects acoustic characteristics changed by bubbles, the spatial distribution of bubbles was estimated using video data and received signals. A measurement-based bubble spectral shape was used, and it was assumed that the bubble density within the spatial distribution of the estimated bubble was the same. As a result, it was confirmed that the bubble reverberation was simulated in a time similar to the measured data regardless of the bubble density, and the bubble reverberation level similar to the measured data was simulated at a void fraction of about 10-7 ~ 10-6.8. 해양에서 다양한 원인에 의해 발생된 기포들은 해수 중 오랜 시간 잔존하는 것으로 알려져 있다. 이러한 기포들이 해양환경에서 차지하고 있는 부피는 매우 작지만 공진, 감쇠 등으로 인해 해수 중 기포의 존재는 음향 특성에 큰 영향을 미친다. 이에 따라 본 논문에서는 인공기포가 존재하는 해양 환경에서의 양상태 잔향음 실험을 수행하였다. 다수의송수신기들이 육각형 형태로 배치된 6개의 부이에 설치되었으며, 부이 중앙에 발포제를 투하하여 인공기포를 발생시켰다. 발생된 기포에 의해 변화하는 음향 특성을 반영한 잔향음 모델링을 위해 영상자료와 수신신호를 이용하여 기포의 공간적인 분포를 추정하였다. 측정치 기반의 기포 분포 형태를 이용하였으며, 추정한 기포의 공간적 분포 내에서의기포 밀도는 동일하다고 가정하여 기포 밀도의 변화에 따른 모의 결과를 측정치와 비교, 분석하였다. 그 결과 기포에의한 잔향음 모의결과가 실측값과 유사한 시간대에 모의되었으며, 약 10-7 ~ 10-6.8의 기포율에서 실측값과 유사한 기포잔향음 준위가 모의됨을 확인하였다.

On-line Measuring Method of Effective Bulk Modulus in Hydraulic System Based on Frequency Analysis

Chen, Yingshu,Wang, Nan,Gu, Lichen Korean Society for Fluid machinery 2018 International journal of fluid machinery and syste Vol.11 No.1

Based on the gas-liquid phase flow theory, an indirect method is proposed to on-line measure the effective bulk modulus by constructing the mathematical model which reveals the relationships of the effective bulk modulus, bubble volume fraction, pressure and natural frequency. The natural frequency of hydraulic fluid is a key parameter for measuring effective bulk modulus utilizing the model, so it is online measured by the proposed pseudo-excitation method. The frequency response function is obtained by solving the amplitude spectrum functions of pseudo-excitation signal and the response signal, and the natural frequency is obtained. The numerical simulation and experiment are carried out, and we can deduce from the analysis of simulation and experimental results that the effective bulk modulus in hydraulic system can be easily online measured by the proposed indirect method.

On-line Measuring Method of Effective Bulk Modulus in Hydraulic System Based on Frequency Analysis

Yingshu Chen,Nan Wang,Lichen Gu 한국유체기계학회 2018 International journal of fluid machinery and syste Vol.11 No.1

Based on the gas-liquid phase flow theory, an indirect method is proposed to on-line measure the effective bulk modulus by constructing the mathematical model which reveals the relationships of the effective bulk modulus, bubble volume fraction, pressure and natural frequency. The natural frequency of hydraulic fluid is a key parameter for measuring effective bulk modulus utilizing the model, so it is online measured by the proposed pseudo-excitation method. The frequency response function is obtained by solving the amplitude spectrum functions of pseudo-excitation signal and the response signal, and the natural frequency is obtained. The numerical simulation and experiment are carried out, and we can deduce from the analysis of simulation and experimental results that the effective bulk modulus in hydraulic system can be easily online measured by the proposed indirect method.

A Study on the Characteristics of Two-Phase Flow by Driven Bubbles in a Liquid Bath

Oh, Yool-Kwon,Seo, Dong-Pyo The Society of Air-Conditioning and Refrigerating 2005 International Journal Of Air-Conditioning and Refr Vol.13 No.1

In the present study, the characteristics of upward bubble flow were experimentally investigated in a liquid bath. An electro-conductivity probe was used to measure local volume fraction and bubble frequency. Since the gas was concentrated at the near the nozzle, the flow parameters were high near the nozzle. In general their axial and radial values tended to decrease with increasing distance. For visualization of flow characteristics, a Particle Image Velocimetry (PIV) and a thermo-vision camera were used in the present study. The experimental results showed that heat transfer from bubble surface to water was largely completed within z = 10 mm from the nozzle, and then the temperature of bubble surface reached that of water rapidly. Due to the centrifugal force, the flow was more developed near the wall than at bubble-water plume. Vortex flow in the bottom region was relatively weaker than that in the upper region.

Active control of low-frequency noise in bubbly water-filled pipes

노응휘,우상범,이동주,송민호,이재완,이훈기,엄원석,장하다,이근상,박영철,서영수 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.7

This paper describes an active silencer system for low-frequency noise in water-filled pipes, with implementation in marine vessels and structures in mind. Active noise control in underwater environment has its unique challenges arising from bubbles. In this light the effect of bubbles on active noise control in water-filled pipes is explored, and a design guideline for a robust active silencer is proposed. The silencer consists of an underwater sound source, an error hydrophone, and an electronic controller programmed with an adaptive filter. The adaptive filter is updated using the filtered-x least mean square algorithm. Estimation of the incoming noise is performed using an adaptive notch filter. The performance of the active silencer is tested for pure tone noises below 500 Hz in a water-filled pipe connected to a reservoir. Notable reduction of noise is achieved with varying degrees of success at different bubble fractions.

Air-Water 모델에서 가시화를 통한 유동특성에 관한 연구

임태훈,박근욱,서동표,정낙규,김진흥,오율권 朝鮮大學校 機械技術硏究所 2002 機械技術硏究 Vol.5 No.2

In the air-water model, the characteristics of flow parameters were experimentally investigated. An electro-conductivity probe was used for measuring flow parameters such as local volume fraction and bubbles frequency. The flow parameters were very high at the near nozzle. For visualization of flow characteristics, a camera technique method and a thermo vision camera were adopted in the present study. The experimental results shows that the heat transfer from bubble surface to water is almost achieved within z=10[mm〕 from the nozzle. Then the temperature of bubble surface teaches to the water temperature in a short time. The camera and argon illumination laser were applied to the water circulation zone for flow visualization. The flow was more developed near the wall than at bubble-water plume. Voltex flow in the bottom region was relatively weaker than in the upper region.

Acoustic energy harvester using an acoustically oscillating bubble-induced propulsion force

D. Jang(장대성),S. K. Chung(정상국),J. P. Jeon(전진표) 한국가시화정보학회 2017 한국가시화정보학회 학술발표대회 논문집 Vol.2017 No.11

Characteristics of Bubble Departure Frequency in a Low-Pressure Subcooled Boiling Flow

EUH, Dongjin,OZAR, Basar,HIBIKI, Takashi,ISHII, Mamoru,SONG, Chul-Hwa Atomic Energy Society of Japan 2010 Journal of nuclear science and technology Vol.47 No.7

<P>In order to measure the bubble departure frequency, a flow visualization system was set up on a vertical annulus test section with a heater rod by using a high-speed camera. In this study, we developed an efficient methodology of image processing for obtaining the bubble departure frequency data. Bubble nucleation was investigated under various thermal hydraulic conditions of water, which correspond to pressures from 167 to 346 kPa, mass fluxes from 214 to 1869 kg/m<SUP>2</SUP>s, heat fluxes from 61 to 238 kW/m<SUP>2</SUP>, and subcooling degrees from 7.5 to 23.4 K. The characteristics of bubble departure frequency were analyzed with the present data. The measured data was compared with models available in existing literature and a more plausible model was proposed.</P>