Characteristics Of Bubble Motion Research Articles

Dynamic control of current and voltage waveforms and droplet transfer for ultrasonic-wave-assisted underwater wet welding

Ultrasonic vibration can change the dynamic behavior of the bubble and improve the process stability in underwater wet welding (UWW); thus, it has been attempted to profitably control metal transfer process. Arc signals about welding current and arc voltage together with the high-speed imaging detected in conventional UWW and ultrasonic-wave-assisted UWW (U-UWW) were used as information source for determining the droplet transfer mode. The results show that the change in the characteristics of bubble motion affects the droplet transfer process in U-UWW. During the short-circuiting transfer process in small arc voltage, the frequency of arc extinction and the peak of short-circuiting current are both decreased. During the droplet repelled transfer process in middle arc voltage, the droplet repulsive phenomenon is weakened, and the transfer frequency is increased from 7.9 Hz to 10.5 Hz at 34 V. Meanwhile, the droplet diameter is reduced and its transfer stability is improved. During the droplet repelled transfer process in high arc voltage, the frequency and duration time of arc extinction are both reduced. The underlying difference of droplet transfer process between conventional UWW and U-UWW was investigated by the two aspects including ultrasonic wave effect and dynamic bubble effect.

Geometry and Motion Characteristics of Bubbles Released in Liquid Cross Flow

To investigate the characteristics of the bubbles trapped in liquid cross flow, air was injected into flowing water circulated in a closed loop. High speed photography was used to record bubble images instantaneously. An image-processing code was specifically developed to identify bubbles in the images and to calculate bubble parameters. Effects of the water velocity and the flow rate of the injected air on bubble patterns were investigated. The results indicate that the inclination of bubble trajectory relative to the nozzle axis is enhanced as the water velocity rises. Meanwhile, bubble size varies inversely with the water velocity. The bubble profile tends to be rounded as the water velocity increases. Fluctuations of the bubble velocity are intensified as the water velocity decreases. As the balance between the external forces exerted on the bubble is reached, an approximately linear relationship between the velocities of the bubble and the water is manifested. For a given equivalent bubble diameter, the bubble terminal velocity is higher than that associated with quiescent water. At small Eötvös number, the consistency of the bubble aspect ratio in the liquid flow and quiescent water is revealed. The range of Eötvös number is extended considerably due to the flowing water. Values of Weber number are accumulated in a range within which high bubble aspect ratio is associated with relatively high water velocity.

Effects of initial bubble size on geometric and motion characteristics of bubble released in water

To seek and describe the influence of bubble size on geometric and motion characteristics of the bubble, six nozzles with different outlet diameters were selected to inject air into water and to produce different bubble sizes. High-speed photography in conjunction with an in-house bubble image processing code was used. During the evolution of the bubble, bubble shape, traveling trajectory and the variation of bubble velocity were obtained. Bubble sizes acquired varied from 0.25 to 8.69 mm. The results show that after the bubble is separated from the nozzle, bubble shape sequentially experiences ellipsoidal shape, hat shape, mushroom shape and eventually the stable ellipsoidal shape. As the bubble size increases, the oscillation of the bubble surface is intensified. At the stabilization stage of bubble motion, bubble trajectories conform approximately to the sinusoidal function. Meanwhile, with the increase in bubble size, the bubble trajectory tends to be straightened and the influence of the horizontal bubble velocity component on the bubble trajectory attenuates. The present results explain the phenomena related to relatively large bubble size, which extends the existing relationship between the bubble terminal velocity and the equivalent bubble diameter.

Continuous simulation of the whole process of underwater explosion based on Eulerian finite element approach

Underwater explosion is an extremely complex hydrodynamic problem and it is always divided into two stages and studied individually, i.e., shock wave stage and bubble motion stage. Actually underwater explosion is a continuous process and there are intensive interactions between the two stages in some cases, e.g. underwater explosion in the vicinity of the wall. In this paper, the Eulerian finite element formulation considering the fluid compressibility is applied to continuously simulate the process of underwater explosion based on the subroutine of ABAQUS. Firstly, the governing equation and its solution by the operator splitting approach are discussed. Then the free-field underwater explosion is continuously simulated, including shock wave propagation and the bubble expansion, contraction, collapse, jet and rebound. The applicability and reliability of this method are discussed by comparing with experimental results from Klaseboer [5]. Furthermore, the traditional treatments of the simulation initialized at the bubble motion stage are discussed. Finally, the underwater explosion near wall is investigated regarding the interactions of shock wave and bubble motion and the importance of the continuous simulation of underwater explosion on the bubble motion characteristics is summarized.

Research on Bubble Removal Mechanism of Screw-Propelled 3D Printer

The new screw-propelled 3D printer can realize 3D printing with granular plastic materials. The granular plastic material cost low and need not pay more attention on material flexibility. In this paper, the motion characteristics of bubbles produced in the printing processing of the screw-propelled 3D printer are studied. Through the analysis of the screw structure, and establish the corresponding three-dimensional model, the flow field of screw propulsion system is established by using FLUENT software. Through the simulation, the effects of the speed of the screw propeller, inlet pressure and screw pitch on the velocity of the bubble rise is studied. And the different locations of the bubble are concerned. In order to make the bubble escape from the fluid, a new structure of screw propeller is improved. The simulation result shows this improved structure can get a good performance to help to remove the bubbles in molt plastic material. And the fluid leakage can be compensated by increase the speed of the screw propeller.

Numerical Analysis of Bubble Motion Characteristics within Vertical Rectangular Micro Channels

In this paper, flow patterns transition criteria from bubble growth to confined bubbly flow, from isolated/confined bubbly flow to slug flow, and from slug flow to annular flow are numerical analyzed. The prediction of the theoretical model agrees well with experimental data. By carrying out comparative study, it is indicated that there is an apparent postponement of flow patterns transition of flow boiling in mini/micro-channel than that under adiabatic conditions.

Two-Phase Heat Transfer and Bubble Characteristics in a Microchannel Array

Heat transfer coefficients and bubble motion characteristics are reported for two-phase water flow in an array of 13 equally spaced microchannels over an area of 1 cm2. Each channel has Dh = 451 ± 38 μm, W/H = 0.8, and L/Dh = 22.2. Uniform heat flux is applied through the base, and wall temperatures are determined from the thermocouple readings corrected for heat conduction effects. The upper surface is insulated and transparent. Single-phase heat transfer coefficients are in a good agreement with comparable trends of existing correlations for developing flow and heat transfer, although a difference is seen due to the insulated upper surface. Two-phase heat transfer coefficients and flow characteristics are determined for 221 < G < 466 kg/m2s and 250 < q < 1780 kW/m2. Heat transfer coefficients normalized with mass flux exhibit a trend comparable to that of available studies that use similar thermal boundary conditions. Flow visualization shows expanding vapor slug flow as the primary flow regime with nucleation and bubbly flow as the precursors. Analysis of bubble dynamics reveals ∼t1/3 dependence for bubble growth. Flow reversal is observed and quantified, and different speeds of the vapor phase fronts are quantified at the leading and trailing edges of vapor slugs once the bubble diameter equals the channel width. Bubble formation, growth, coalescence, and detachment at the outlet of the array are best characterized by the Weber number.

Chaotic behavior of in-line bubbles rising with coalescences in non-Newtonian fluids: A multiscale analysis

The nonlinear dynamics of in-line bubbles rising with coalescence in non-Newtonian Carboxymethylcellulose sodium (CMC) fluids was studied through the techniques such as the multiresolution signal decomposition and the chaotic time series analysis. The temporary signals of bubble passages collected by an optical sensing device at different heights were investigated by a 12-level wavelet decomposition and the scalewise characteristics of bubble motion were extracted and analyzed. The chaotic time series analysis distinguished the periodicity or the deterministic chaos of bubble motion successsfully. The calculation of Kolmogorov entropy proves that in the ranges of experimental heights and gas flowrates, the bubble rising dynamics becomes more chaotic with the increase of height, and reaches the maximum chaotic extent in a certain height, while with the further increase of height, the chaotic extent decreases slowly. With the increase of gas flowrate, at the lower height, the bubble rising dynamics changes from periodicity to deterministic chaos, and at the higher heights it reaches the maximum chaotic extent in a certain gas flowrate; however, for both cases, it has little change in the higher gas flowrates. Moreover, with the increase of CMC concentration, the bubble rising dynamics becomes less chaotic when the height is beyond a certain value.

Effect of liquid properties on the growth and motion characteristics of micro-bubbles induced by electric fields in confined liquid films

The effect of liquid properties on gas bubble growth and motion characteristics in liquid films confined within a nanogap between a highly polished steel ball and a smooth glass disc under an electric field is reported. Experimental results show that the critical voltage for the appearance of bubbles has insignificant dependence on liquid viscosity and surface tension. The bubble size after detachment increases with liquid viscosity, and bubble instability and coalescence tend to occur when bubbles move some distance away from where they were formed. An increase in liquid surface tension results in larger bubbles at the growth stage. Also, the bubble motion characteristics are greatly influenced by liquid viscosity, and the dielectrophoresis force is demonstrated to be the dominant driving force for bubble movement. Theoretical models and analyses have been used to discuss the bubble formation and describe the bubble movement characteristics.

Effect of Plate Oscillation on Bubble Residence Time in an Aerated Stagnant Liquid

Gas transfer efficiency during absorption is an important factor in various technological processes involving the interaction between liquid and gaseous systems. It is known that gas bubble motion characteristics strongly affect the efficiency of mass transfer during gas absorption. A device for mechanical vibration of an aerated liquid was designed, based on a cylindrical column filled up with tab water and a plate oscillating in the vertical direction. The goal of the present study is to investigate the effect of vibration parameters such as amplitude, frequency and form of the applied signal on the efficiency of the oxygenation process. Bubble residence time in the liquid and bubble depth of submergence related to the oscillating plate surface were chosen as main parameters for measurements. Furthermore, experiments were conducted to study the effect of the design parameters of the vibrating plate on bubble motion characteristics. The resultant data show that bubble residence time and depth of submergence can be controlled by changing the amplitude, the frequency and the form of the vibration field applied.

Liquid Oxygenation Improvement by Interaction of Bubbles and Vibration Fields

AbstractGas bubble motion characteristics and bubble size are important factors in various technological processes involving the interaction between liquid and gaseous systems. The present work studies the effect of vibration fields on the characteristics of bubble motion and bubble size. Bubble retention time in the liquid (rise velocity) and bubble mean diameter were chosen as main parameters effecting the oxygen mass transfer rate. A device for mechanical vibration of the aerated liquid was used. The influence of the device design parameters on the chosen bubble parameters is studied experimentally and discussed in this work. The results obtained show the possibility of controlling bubble retention time and bubble size by employing vibration fields. Thus, by applying rather simple techniques, one can considerably improve the process of liquid oxygenation.

Visualization of Bubble‐Fluid Interaction by a Moving Object Flow Image Analyzer System

This paper deals with interaction between a bubble and fluid around it, visualized by a moving object flow image analyzer (MOFIA) consisting of a three-dimensional (3D) moving object image analyzer (MOIA) and two-dimensional particle image velocimetry (PIV). The experiments were carried out for rising bubbles of various sizes and shapes in stagnant water in a vertical pipe. In the MOFIA employed, 3D-MOIA was used to measure bubble motion and PIV to measure fluid flow. The 3D position and shape of a bubble and the velocity field were measured simultaneously. The experimental results showed that the interaction was characterized by the shape, size and density of a bubble. Concretely, they showed the characteristics of bubble motion, wake shedding, and flow field.

Domain-wall behavior in ion-implanted garnet layers for 1-μm bubble devices

Bitter pattern observations are reported on domain walls in ion-implanted garnet layers. Particular attention is given to the behavior of charged walls at the edge of nonimplanted disks and other elements and on the response of these walls to varying in-plane fields. The interaction between bubbles and charged walls has been observed and the propagation of bubbles around disks and along propagation tracks has been examined. The crystalline symmetry of the garnet layer has been found to give rise to significant orientation effects on the response of walls to external fields. From a study of wall behavior certain characteristics of bubble motion along propagation paths can be explained.