Experimental and Numerical Study of Single Bubble Dynamics on a Hydrophobic Surface

2007 ◽  
Author(s):  
Youngsuk Nam ◽  
Gopinath Warrier ◽  
Jinfeng Wu ◽  
Y. Sungtaek Ju
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Growth Period ◽  
Hydrophobic Surface ◽  
Bubble Surface ◽  
Bubble Nucleation ◽  
Root Mean Square Roughness ◽  
Energy Harvesters ◽  
Enhanced Boiling

The growth and departure of single bubbles on two surfaces with very different wettability is studied using high-speed video microscopy and numerical simulation. Isolated artificial cavities of approximately 10μm diameter are microfabricated on a bare and a Teflon-coated silicon substrate to serve as nucleation sites. The bubble departure diameter is observed to be almost three times larger and the growth period almost 60 times longer for the hydrophobic surface than for the hydrophilic surface. The waiting period is practically zero for the hydrophobic surface because a small residual bubble nucleus is left behind on the cavity from the previous ebullition cycle. The experimental results are consistent with our numerical simulations. Bubble nucleation occurs on nominally smooth hydrophobic regions with root mean square roughness (Rq) less than 1 nm even at superheat as small as 3 °C. Liquid subcooling significantly affects bubble growth on the hydrophobic surface due to increased bubble surface area. Fundamental understanding of bubble dynamics on heated hydrophobic surfaces will help to develop chemically patterned surfaces with enhanced boiling heat transfer and novel phase-change based micro-actuators and energy harvesters.

Experimental and Numerical Study of Single Bubble Dynamics on a Hydrophobic Surface

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
Youngsuk Nam ◽  
Jinfeng Wu ◽  
Gopinath Warrier ◽  
Y. Sungtaek Ju
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Growth Period ◽  
Hydrophobic Surface ◽  
Bubble Surface ◽  
Bubble Nucleation ◽  
Root Mean Square Roughness ◽  
Energy Harvesters ◽  
Enhanced Boiling

The growth and departure of single bubbles on two smooth surfaces with very different wettabilities are studied using high-speed video microscopy and numerical simulations. Isolated artificial cavities of approximately 10 μm diameter are microfabricated on both a bare and a Teflon-coated silicon substrate to serve as nucleation sites. The bubble departure diameter is observed to be almost 3 times larger and the growth period almost 60 times longer for the hydrophobic surface than for the hydrophilic surface. The waiting period is practically zero for the hydrophobic surface because a small residual bubble nucleus is left behind on the cavity from a previous ebullition cycle. The experimental results are consistent with our numerical simulation results. Bubble nucleation occurs on nominally smooth hydrophobic regions with root mean square roughness (Rq) less than 1 nm even at superheat as small as 3°C. Liquid subcooling significantly affects bubble growth on the hydrophobic surface due to increased bubble surface area. Fundamental understanding of bubble dynamics on heated hydrophobic surfaces will facilitate the development of chemically patterned surfaces with enhanced boiling heat transfer performance and novel phase-change based micro-actuators and energy harvesters.

Single Bubble Dynamics on a Hydrophobic Surface

2007 ◽  
Author(s):  
Youngsuk Nam ◽  
Gopinath Warrier ◽  
Jinfeng Wu ◽  
Y. Sungtaek Ju
Keyword(s):  
Silicon Substrate ◽  
Bubble Dynamics ◽  
Growth Period ◽  
Hydrophobic Surface ◽  
Nucleation Site ◽  
Bubble Surface ◽  
Bubble Nucleation ◽  
Root Mean Square Roughness ◽  
Static Contact ◽  
Artificial Cavity

The growth and departure of single bubbles on two surfaces with very different wettability is studied using highspeed video microscopy. An artificial cavity of approximately 10μm diameter is microfabricated on a bare and a Teflon-coated silicon substrate to serve as a nucleation site. The static contact angle of water is approximately 40° on the bare silicon substrate and approximately 120° on the Teflon-coated substrate. The bubble departure diameter is observed to be almost three times larger and the growth period almost 60 times longer for the hydrophobic surface than for the hydrophilic surface. The waiting period is practically zero for the hydrophobic surface because a small residual bubble nucleus remains on the cavity from the previous ebullition cycle. Bubble nucleation occurs on nominally smooth hydrophobic regions with root mean square roughness below 4 nm even at superheat as small as 4 °C. Liquid subcooling significantly affects bubble growth on the hydrophobic surface due to the increased bubble surface area.

Thermal Bubble Dynamics Under the Effect of Acoustic Vibration

2009 ◽  
Author(s):  
Xiaopeng Qu ◽  
Huihe Qiu
Keyword(s):  
Heat Transfer ◽  
Acoustic Field ◽  
Vapor Bubble ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Bubble Dynamics ◽  
Acoustic Vibration ◽  
Micro Electro Mechanical System ◽  
Mems Technology ◽  
Enhanced Boiling

The effect of acoustic field on the dynamics of micro thermal bubble is investigated in this paper. The micro thermal bubbles were generated by a micro heater which was fabricated by standard Micro-Electro-Mechanical-System (MEMS) technology and integrated into a mini chamber. The acoustic field formed in the mini chamber was generated by a piezoelectric plate which was adhered on the top side of the chamber’s wall. The dynamics and related heat transfer induced by the micro heater generated vapor bubble with and without the existing of acoustic field were characterized by a high speed photograph system and a micro temperature sensor. Through the experiments, it was found that in two different conditions, the temperature changing induced by the micro heater generated vapor bubble was significantly different. From the analysis of the high speed photograph results, the acoustic force induced micro thermal bubble movements, such as forcibly removing, collapsing and sweeping, were the main effects of acoustic enhanced boiling heat transfer. The experimental results and theoretical analysis were helpful for understanding of the mechanisms of acoustic enhanced boiling heat transfer and development of novel micro cooling devices.

Synchronized High-Speed Video and Infrared Thermometry Study of Bubble Dynamics During Nucleate Boiling of Nanoemulsion

2017 ◽  
Author(s):  
Robert Stephenson ◽  
Jiajun Xu
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Bubble Dynamics ◽  
Nucleate Boiling ◽  
Bubble Nucleation ◽  
Heat Diffusion ◽  
Temperature History ◽  
Pure Ethanol ◽  
High Speed Video ◽  
Significant Difference

In this study, a combination of synchronized high-speed video (HSV) and infrared (IR) thermography was used to characterize the nucleation, growth and detachment of bubbles generated during nucleate boiling inside the nanoemulsion fluid. The Ethanol/Polyalphaolefin nanoemulsion fluid was formed by dispersing ethanol nanodroplets into base fluid Polyalphaolefin, in which these nanodroplets can serve as the pre-seed boiling nuclei. With this unique combination, it allows controlled nucleation, time-resolved temperature distribution data for the boiling surface and direct visualization of the bubble cycle to track bubble nucleation and growth. Data gathered included measurements of bubble growth versus time, as well as 2D temperature history of the heater surface underneath the bubbles. Our findings demonstrate a significant difference of bubble dynamics between the nanoemulsion fluid and pure ethanol, which may also account for the substantial increase in heat transfer coefficient and critical heat flux of nanoemulsion fluid. It is also observed here that the bubbles occurred inside the nanoemulsion fluid appear to be more uniform and two orders-of-magnitude larger in size. While the growth rate of the bubbles inside pure ethanol was found to be heat diffusion controlled at a coefficient around ½, which however, dropped to be around 0.3 for nanoemulsion fluid. Further study on this unique system will help reveal its heat transfer mechanisms.

The Influence of Acoustic Cavitation to Microscopic Material Removal in Polishing Process Based on Vibration of Liquid: A Numerical Study

2006 ◽  
Vol 532-533 ◽  
pp. 301-304 ◽  
Author(s):  
Zhong Ning Guo ◽  
Zhi Gang Huang ◽  
Xin Chen
Keyword(s):  
Material Removal ◽  
High Speed ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Dissipative Particle Dynamics ◽  
Thermal Conditions ◽  
Acoustic Cavitation ◽  
Ultrasonic Frequency ◽  
Polishing Process ◽  
Cavitation Phenomenon

In Polishing Process based on Vibration of Liquid (PVL), abrasive particles driven by polishing liquid will brush and etch workpiece to achieve material removal. Because the liquid is vibrated in ultrasonic frequency, polishing process will be greatly affected by cavitation phenomenon. The critical thermal conditions and high-speed liquid jet produced by bubble dynamics may damage workpiece. A refined Dissipative Particle Dynamics method is applied to study the effect of acoustic cavitation on PVL. Validity of the numerical simulation is tested according to experimental results.

STUDY OF LEIDENFROST MECHANISM IN DROPLET IMPACTING ON HYDROPHILIC AND HYDROPHOBIC SURFACES

2013 ◽  
Vol 21 (04) ◽  
pp. 1350028 ◽  
Author(s):  
SEOL HA KIM ◽  
JUN YOUNG KANG ◽  
HO SEON AHN ◽  
HANG JIN JO ◽  
MOO HWAN KIM
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Hydrophobic Surface ◽  
Bubble Nucleation ◽  
Hydrophilic Surface ◽  
Water Droplets ◽  
Time Resolved ◽  
Droplet Dynamics ◽  
Different Shapes ◽  
Time Resolved Imaging

Water droplets, 2 mm in diameter, were allowed to fall freely onto hydrophobic and hydrophilic heated surfaces, and their impacts were imaged using high-speed cameras to investigate the droplet dynamics and heat transfer. As the heating power increased, the water droplets evaporated faster, eventually hovering over the surface due to the formation of a boiling film when the Leidenfrost point (LFP) was reached. The heat transfer from the surface into the droplet was evaluated, and LFP transition phenomena were investigated using time-resolved imaging of both side and bottom views. The hydrophilic surface showed a higher heat transfer rate and a higher LFP than the hydrophobic surface did. Furthermore, the droplet dynamics revealed very different shapes depending on the surface wettability; vigorous bubble nucleation and growth was observable for the hydrophilic surface, but not the hydrophobic surface. The rebound behavior of the droplets was analyzed based on the droplet free energy, including kinetic, potential, and surface energy terms.

Acoustic Driven Micro Thermal Bubble Dynamics in a Microchannel

2009 ◽  
Author(s):  
Xiaopeng Qu ◽  
Huihe Qiu
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Video Recording ◽  
Digital Camera ◽  
Microfluidic Devices ◽  
Acoustic Vibration ◽  
Micro Electro Mechanical System ◽  
Bubble Nucleation ◽  
Potential Applications ◽  
Micro Mixer

Understanding the effects of acoustic vibration on micro thermal bubble dynamics in a microchannel is the key to develop acoustic-thermal-bubble based microfluidic devices. For that purpose, in the current research, a series of experiments were carried out to study the acoustic-thermal-bubble dynamics in a microchannel. The thermal bubble was generated by a micro heater which was fabricated by MEMS (Micro-Electro-Mechanical-System) technique. Using a high-speed digital camera, the thermal bubble dynamics was studied in two different conditions: normal condition and acoustic condition. Through theoretical analysis, the whole bubble dynamic process in two conditions can be roughly divided into four steps, which are bubble nucleation, satellite bubbles movement, bubble evolution, and bubble shrinkage and remove. The effects of acoustic vibration on all these four steps were found to be significant. The mechanisms behind these effects are discussed by analyzing the high speed video recording results. The current experimental investigation has some potential applications in microfluidic devices, and a prototype of micro mixer based on acoustic-thermal-bubble was successfully tested.

Bubble Dynamics Observed in a Gas-Liquid Venturi Flow

2011 ◽  
Author(s):  
Wataru Nishi ◽  
Masanori Nogami ◽  
Hiroyuki Takahira
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Propagation Speed ◽  
Video Camera ◽  
Bubble Surface ◽  
Liquid Jets ◽  
Pressure Waves ◽  
Two Phase ◽  
Pressure Transducers ◽  
Two Bubbles

The present study deals with the experiments for the gas-liquid two-phase flow inside an acrylic Venturi tube using a high-speed video camera. Some interesting phenomena on the bubble dynamics are observed in the tube. First, the volume and surface oscillations of two interacting bubbles are observed in converging section of the tube when one bubble enters the throat. The volume oscillation of the bubble that enters the throat is caused by the detachment of the tip of the downstream surface of the bubble. The pressure wave irradiated from the bubble that enters the throat induces the volume and surface oscillations of the bubble that remains at the converging section. The parametric excitation is the reason for the surface oscillations. Second, the bubble deformations at the throat in a Venturi or a converging tube are investigated. The experiments show that two kinds of liquid jets are formed on the bubble surface; one is a forward jet that develops from the upstream surface to the downstream surface and the other is a counter jet in which the direction of the jet is opposite to the forward jet. It is shown that the counter jet occurs only when the distance between two bubbles in the throat is sufficiently short. The interactions between two bubbles cause the counter jet. It is also shown that the velocity of the forward jet becomes faster when the bubble is pinched off more upstream in the converging section. Finally, the propagations of the pressure waves are measured with pressure transducers. The impulsive pressure associated with the collapse of cavitation bubble cloud is measured when a bubble enters the throat of the tube. Also, the propagation speed of pressure waves is evaluated with the cross-correlation function. The results show that the propagation speed and damping of the pressure waves are dependent on the number density of bubbles at the downstream part in the tube.

scholarly journals A Numerical and Experimental Study of Wall Pressure Caused by an Underwater Explosion Bubble

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Yingyu Chen ◽  
Xiongliang Yao ◽  
Xiongwei Cui
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Underwater Explosion ◽  
Rigid Wall ◽  
Numerical Results ◽  
Wall Pressure ◽  
Bubble Collapse ◽  
Strong Impact ◽  
Jet Impact

The bubble dynamics behaviors and the pressure in the wall center are investigated through experimental method and numerical study. In the experiment, the dynamics of an underwater explosion (UNDEX) bubble beneath a rigid wall are captured by high-speed camera and the wall pressure in the wall center is measured by pressure transducer. To reveal the process and mechanism of the pressure on a rigid wall during the first bubble collapse, numerical studies based on boundary element method (BIM) are applied. Numerical results with two different stand-off parameters (γ=0.38 and γ=0.90) show excellent agreement with experiment measurements and observations. According to the experimental and the numerical results, we can conclude that the first peak is caused by the reentrant jet impact and the following splashing effect enlarged the duration of the first jet impact. When γ=0.38, the splashing jet has a strong impact on the minimum volume bubble, a number of tiny bubbles, formed like bubble ring, are created and collapse more rapidly owing to the surrounding high pressure and emit multi shock waves. When γ=0.90, the pressure field around the bubble is low enough only a weak rebounding bubble peak occurs.

NUMERICAL STUDY OF BUBBLE DYNAMICS ON SURFACE WITH SWITCHABLE WETTABILITY

2018 ◽  
Author(s):  
Lei Zhang ◽  
Tao Wang ◽  
SeolHa Kim ◽  
Yuyan Jiang
Keyword(s):  
Bubble Dynamics ◽  
Numerical Study
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