Study on Bubble Breakup Mechanism in a Venturi Tube

2011 ◽  
Author(s):  
Yasumichi Nomura ◽  
Shin-ichiro Uesawa ◽  
Akiko Kaneko ◽  
Yutaka Abe
Keyword(s):  
Flow Structure ◽  
High Speed ◽  
Pressure Profile ◽  
Venturi Tube ◽  
Pressure Recovery ◽  
Bubble Collapse ◽  
Bubble Behavior ◽  
Low Velocity ◽  
Breakup Mechanism ◽  
Bubble Breakup

Microbubbles are expected to be applied in various subjects such as engineering and medical fields. Thus, on-demand microbubble generation techniques with high efficiently are required. In the present study, the microbubble generator using a venturi tube (converging-diverging nozzle) is focused. Although this technique realizes generation of many tiny bubbles with less than several-hundred-micrometer diameter, there are several unsolved parts of flow structure in a venturi tube on bubble breakup behavior. The purpose of this study is to clarify the bubble breakup mechanism in a venturi tube for practical use. In the present study, using a high speed camera for detailed observation of bubble behavior, the following features were obtained. In low velocity conditions, bubbles are divided in several pieces with a jet penetrating from the top (downstream) to the bottom (upstream) part of the bubble. In high velocity conditions, bubbles collapse in countless microbubbles with a drastic bubble expansion and shrinkage. Also, in order to clarify the flow structure in a venturi tube, pressure profile is measured in detail. Under chocking condition, the pressure profile shows the tendency of supersonic flow in a Laval nozzle and sudden pressure gradient appears in the diverging section. There are strong correlations between bubble fission points and pressure recovery points. It is suggested that bubble collapse is strongly influenced with pressure recovery in the diverging section.

Bubble Breakup Phenomena in a Venturi Tube

2007 ◽  
Author(s):  
A. Fujiwara ◽  
K. Okamoto ◽  
K. Hashiguchi ◽  
J. Peixinho ◽  
S. Takagi ◽  
...  
Keyword(s):  
High Speed ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Pressure Change ◽  
Venturi Tube ◽  
Large Bubble ◽  
Breakup Process ◽  
Bubble Behavior ◽  
Bubble Breakup ◽  
Unstable Surface

Microbubble generation techniques have been proposed in former investigations. Here, we study an effective technique using air bubbly flow into a convergent-divergent nozzle (venturi tube). Pressure change in the diverging section induces bubble breakup. The purpose of this study is to clarify the effect of flow velocity at the throat with respect to the bubble breakup process and the bubble behavior in a venturi tube. Relations between generated bubble diameter and bubble breakup process are also described. Using high speed camera for detailed observation of bubble behavior, the following features were obtained. The velocity at the throat is expected to be of the order of the magnitude of the speed of sound of bubbly flow and a drastic bubble expansion and a shrink is induced. Besides, a liquid column appeared after the bubble flowing into the throat, and it grew up to stick to the bubble like in the form of a jet. This jet induced both unstable surface waves and the breakup of a single large bubble into several pieces.

scholarly journals Bubble Behavior and Flow Structure on Bubble Collapse Phenomena in a Venturi Tube

2013 ◽  
Vol 26 (5) ◽  
pp. 567-575 ◽  
Author(s):  
Shin-ichiro UESAWA ◽  
Akiko KANEKO ◽  
Yasumichi NOMURA ◽  
Yutaka ABE
Keyword(s):  
Flow Structure ◽  
Venturi Tube ◽  
Bubble Collapse ◽  
Bubble Behavior

0212 Interfacial instability and flow structure on bubble breakup in a micro-bubble generator with a venturi tube

2012 ◽  
Vol 2012 (0) ◽  
pp. 121-122
Author(s):  
Shinichiro Uesawa ◽  
Akiko Kaneko ◽  
Yasumichi Nomura ◽  
Naoya Tamura ◽  
Yutaka Abe
Keyword(s):  
Flow Structure ◽  
Interfacial Instability ◽  
Venturi Tube ◽  
Bubble Breakup ◽  
Micro Bubble

216404 Influence of Flow Structure in a Venturi Tube on Bubble Breakup Behavior

2011 ◽  
Vol 2011.17 (0) ◽  
pp. 417-418
Author(s):  
Yasumichi NOMURA ◽  
Akiko KANEKO ◽  
Shin-ichiro UESAWA ◽  
Yutaka ABE
Keyword(s):  
Flow Structure ◽  
Venturi Tube ◽  
Bubble Breakup

Highly aligned PAN nanofiber bundles prepared via a novel Venturi tube high-speed airflow drafting (VAD) method

2021 ◽  
pp. 130383
Author(s):  
Lei Li ◽  
Jingna Su ◽  
Yuanyuan Wang ◽  
Gang Wang ◽  
Zhichao Zhang ◽  
...  
Keyword(s):  
High Speed ◽  
Venturi Tube ◽  
Nanofiber Bundles ◽  
Pan Nanofiber

Performance of Conical Diffuser on Liquid Jet Gas Ejector

2014 ◽  
Vol 493 ◽  
pp. 145-150 ◽  
Author(s):  
Daru Sugati ◽  
Indarto ◽  
Purnomo ◽  
Sutrisno
Keyword(s):  
Void Fraction ◽  
Flow Rate ◽  
Rate Increase ◽  
Pressure Profile ◽  
Pressure Recovery ◽  
Liquid Jet ◽  
Recovery Coefficient ◽  
Final Value ◽  
Conical Diffuser ◽  
Pressure Recovery Coefficient

Liquid gas ejector uses liquid as the motive fluid and gas as the entrained fluid. The presence of gas in the liquid reduces the performance of the ejector, especially the diffuser. To observe the effect of entrained gas on the diffuser performance, a series of experiment was conducted.In this research, the motive flow rate was varied from 1.52 to 2.02 l/s and the entrained rate from 0.118 l/s to 0.944 l/s. Its effects on the pressure profile and pressure recovery were observed. If the entrained rate increase, the pressure of the throat upstream, as well as downstream, increase. In the diffuser, longer distance is needed for the pressure to reach its final value. Pressure recovery is mainly affected by void fraction. The higher the void fraction the lower the pressure recovery coefficient

Subcooled Boiling of Surfactant Solutions

2000 ◽  
Author(s):  
G. Hetsroni ◽  
M. Gurevich ◽  
A. Mosyak ◽  
R. Rozenblit ◽  
L. P. Yarin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Speed ◽  
Heated Surface ◽  
Pure Water ◽  
Video Camera ◽  
Subcooled Boiling ◽  
Bubble Behavior ◽  
Boiling Hysteresis

Abstract During subcooled boiling of pure water and water with cationic surfactants, the motion of bubbles and the temperature of the heated surface were recorded by both a high-speed video camera and an infrared radiometer. The results show that the bubble behavior and the heat transfer mechanism for the surfactant are quite different from those of clear water. Bubbles formed in Habon G solutions were much smaller man those in water and the surface was covered with them faster. Boiling hysteresis is found for degraded solutions. Dependencies of heat transfer coefficient for various solutions were obtained and compared. The boiling curves of surfactant are quite different from the boiling curve of pure water. Experimental results demonstrate that the heat transfer coefficient of the boiling process can be enhanced considerably by the addition of a small amount of Habon G. The experiments show that the limitations of the ER technique with respect to frequency response are outweighed by its unique capacity to measure wall temperature distribution with high spatial resolution over an area encompassing many nucleation sites and over long periods.

Air Bubble Entrainment, Breakup, and Interplay in Vertical Plunging Jets

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Numa Bertola ◽  
Hang Wang ◽  
Hubert Chanson
Keyword(s):  
High Speed ◽  
Point Explosion ◽  
Air Bubble ◽  
Bubble Breakup ◽  
Jet Impact ◽  
Bubble Entrainment ◽  
Bubble Interaction ◽  
Onset Velocity ◽  
Air Cavities ◽  
Interaction Behaviors

The entrainment, breakup, and interplay of air bubbles were observed in a vertical, two-dimensional supported jet at low impact velocities. Ultra-high-speed movies were analyzed both qualitatively and quantitatively. The onset velocity of bubble entrainment was between 0.9 and 1.1 m/s. Most bubbles were entrained as detached bubbles from elongated air cavities at the impingement point. Explosion, stretching, and dejection mechanisms were observed for individual bubble breakup, and the bubble interaction behaviors encompassed bubble rebound, “kiss-and-go,” coalescence and breakup induced by approaching bubble(s). The effects of jet impact velocity on the bubble behaviors were investigated for impact velocities from 1.0 to 1.36 m/s, in the presence of a shear flow environment.

scholarly journals The “Bag Breakup” Spume Droplet Generation Mechanism at High Winds. Part II: Contribution to Momentum and Enthalpy Transfer

2018 ◽  
Vol 48 (9) ◽  
pp. 2189-2207 ◽  
Author(s):  
Yu. Troitskaya ◽  
O. Druzhinin ◽  
D. Kozlov ◽  
S. Zilitinkevich
Keyword(s):  
High Speed ◽  
Aerodynamic Drag ◽  
Stable Stratification ◽  
Noticeable Increase ◽  
Wind Speeds ◽  
Breakup Mechanism ◽  
Hurricane Wind ◽  
Exchange Processes ◽  
Aerodynamic Drag Coefficient ◽  
High Winds

AbstractIn Part I of this study, we used high-speed video to identify “bag breakup” fragmentation as the dominant mechanism by which spume droplets are generated at gale-force and hurricane wind speeds. We also constructed a spray generation function (SGF) for the bag-breakup mechanism. The distinctive feature of this new SGF is the presence of giant (~1000 μm) droplets, which may significantly intensify the exchange between the atmosphere and the ocean. In this paper, Part II, we estimate the contribution of the bag-breakup mechanism to the momentum and enthalpy fluxes, which are known to strongly affect the development and maintenance of hurricanes. We consider three contributions to the spray-mediated aerodynamic drag: 1) “bags” as obstacles before fragmentation, 2) acceleration of droplets by the wind in the course of their production, and 3) stable stratification of the marine atmospheric boundary layer due to levitating droplets. Taking into account all of these contributions indicates a peaking dependence of the aerodynamic drag coefficient on the wind speed, which confirms the results of field and laboratory measurements. The contribution of the spray-mediated flux to the ocean-to-atmosphere moist enthalpy is also estimated using the concept of “reentrant spray,” and the equation for the enthalpy flux from a single droplet to the atmosphere is derived from microphysical equations. Our estimates show that a noticeable increase in the enthalpy exchange coefficient at winds exceeding 30–35 m s−1 is due to the enhancement of the exchange processes caused by the presence of giant droplets originating from bag-breakup fragmentation.

scholarly journals Tactile Occupant Detection Sensor for Automotive Airbag

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5288
Author(s):  
Naveen Shirur ◽  
Christian Birkner ◽  
Roman Henze ◽  
Thomas M. Deserno
Keyword(s):  
High Speed ◽  
Tactile Sensors ◽  
Low Velocity ◽  
Speed Test ◽  
Multi Stage ◽  
The Matrix ◽  
Contact Data ◽  
Single Sensor ◽  
Matrix Sensor ◽  
Contact Position

Automotive airbags protect occupants from crash forces during severe vehicle collisions. They absorb energy and restrain the occupants by providing a soft cushion effect known as the restraint effect. Modern airbags offer partial restraint effect control by controlling the bag’s vent holes and providing multi-stage deployment. Full restraint effect control is still a challenge because the closed-loop restraint control system needs airbag–occupant contact and interaction feedback. In this work, we have developed novel single and matrix capacitive tactile sensors to measure the occupant’s contact data. They can be integrated with the airbag surface and folded to follow the dynamic airbag shape during the deployment. The sensors are tested under a low-velocity pendulum impact and benchmarked with high-speed test videos. The results reveal that the single sensor can successfully measure occupant–airbag contact time and estimate the area, while the contact position is additionally identified from the matrix sensor.

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