Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A24: Bubbles: Taylor Bubbles and Rising Bubbles I |
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Chair: Sheldon Green, University of British Columbia Room: 606 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A24.00001: Linear Stability of Taylor Bubbles in Downward Flowing Liquids Habib Abubakar, Omar Matar A Taylor bubble rising against a downward flowing liquid in vertical pipes is known to lose its symmetric shape when the velocity of the liquid exceeds a critical value. The influence of the liquid flow conditions, characterised by the dimensionless E$\ddot{\rm o}$tv$\ddot{\rm o}$s number, Eo, and inverse viscosity number, N$_{\rm f}$, on the onset of transition from symmetric to asymmetric bubble shape, is examined using linear stability analysis. To gain insight into the underlying mechanism, an `energy' budget analysis is carried out to isolate the most dominant energy term that drives the instability. The analysis shows that the driving mechanism is dependent on whether or not the effect of surface tension can be neglected. For negligible surface tension effects, the instability originates from within the bubble and the dominant source of energy that drives the instability is related to perturbations in the bubble pressure. In the case of strong surface tension, the mechanism is related to disturbances connected to the interfacial stress condition. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A24.00002: Numerical Modelling of Phase-change: Application to Evaporating Taylor Bubbles in Superheated Rectangular Microchannels Yan Delaure, Thomas Abadie, Omar Matar In micro-structured devices, the high surface to volume ratio leads to enhanced transport phenomena and the design of micro heat-exchangers requires some fundamental understanding on the dynamics and transfer phenomena taking place. The present study therefore aims at presenting a simple but accurate continuous model for modelling phase change in microfluidic devices within a finite volume Navier-Stokes flow solver. The proposed model is based on a Level Set method for capturing the interface on a fixed structured cartesian mesh and a continuous surface force method for the capillary force. The temperatures are solved in each phase in a sharp way in order to estimate the temperature gradients and the interfacial heat flux accurately. The accuracy of the phase change model is assessed with the analytical solution of the growth of a bubble in a superheated liquid. The evaporation rate of bubbles in superheated rectangular microchannels is investigated in the liquid film regime and the effects of geometry (aspect ratio) are studied. The effects of liquid superheat and operating conditions and thereby liquid film and thermal boundary layer thicknesses are discussed in terms of wall and interfacial heat fluxes. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A24.00003: Quantitative Phase Field Simulations of Turbulent Two-Phase flows Nathan Lafferty, Arnoldo Badillo, Omar Matar Turbulent two-phase flows are ubiquitous and fundamental in our society. We find them in ordinary tasks such as cooking (boiling), but also in more complex systems such as internal combustion engines, power stations, and atmospheric flows just to name a few. A better understanding of the interaction between turbulent structures and interfaces, will contribute to the derivation of more accurate models, which can then be used in the optimization of current technologies or aid in the development of new ones. To assess the capabilities of the Phase-Field model in predicting turbulent two-phase flows, we simulate the dynamics of a Taylor bubble rising in a cylindrical pipe. The simulations lead to the formation of a complex turbulent pattern in the wake of the Taylor bubble, which is strongly coupled to the dynamics of the bubble skirt. We observed important changes in the turbulent structures, as we vary the level of resolution of the surface tension force. We compare our prediction of bubble rise velocity, mean velocity profiles and turbulent fluctuations with direct experimental measurements. We discuss our findings, in terms of a recently developed analytical expression for the physical error in the calculation of the surface tension force. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A24.00004: Violent Expansion of a Rising Taylor Bubble Guangzhao Zhou, Andrea Prosperetti Because of the gradually decreasing hydrostatic pressure, a Taylor bubble expands as it rises in a long vertical conduit such as are encountered in volcanoes and deep-water oil drilling. In some situations, the expansion becomes violent, with a rapid increase of the bubble volume and a possibly catastrophic ejection of liquid from the mouth of the conduit. The mechanism of this process is analyzed with a 1-D drift-flux model and a simpler dynamic model. The results of the two models agree with each other. A simple but useful criterion for the occurrence of the violent expansion is obtained from a quasi-equilibrium model. The important nondimensional parameters involved in the process are identified and, on their basis, the energy budget for the rising bubble is clarified. The effect of gas diffusing from the liquid into the rising bubble is also considered and deficiencies in the current state of knowledge about this aspect of the problem are identified. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A24.00005: How fast do bubbles rise in strong turbulence with a high energy dissipation rate? Rui Ni, Ashwanth Salibindla, Ashik Ullah Mohammad Masuk We carried out an experimental study on the rise velocity of finite-size bubbles from 1 mm to 10 mm in diameter in strong turbulence. The turbulence generated in our facility targets an energy dissipation rate close to the one typically experienced in oceanic environments, which is orders-of-magnitude larger than most existing laboratory facilities. To uncover the mechanisms of bubble-turbulence interaction and its effect on the bubble rising velocity, simultaneous measurements of both the dispersed and the carrier phases in 3D were obtained. The results suggest that the bubble rising velocity shows an interesting transition: small bubbles rise much slower and large bubbles rise faster than that in the quiescent medium. In addition, the transition is at the point when bubble deformation becomes important. A simple model is introduced to quantify this transition and use it to infer both the lift and drag coefficients. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A24.00006: Path transition of a spiraling rising bubble: a wake-controlled process by imposing magnetic fields Jie Zhang, Long Chen, Mingjiu Ni The path transition of a spiraling bubble under the influence of magnetic fields are investigated. It is found that the rising path of a spiral bubble can be controlled manually by imposing magnetic fields in different directions and magnitudes. To detect what happens to the bubble when magnetic fields are applied, two research strategies have been adopted. First we look into details at the evolution of the wake vortices after imposing magnetic fields, and we will show the path transitions are closely related to the wake evolutions. Second, by calculating the time histories of the forces experienced by the bubble in presence of external magnetic fields, the results also reveal how the forces and the vortex patterns are coupled during path transition. Generally, the present study aims to provide the possibility of controlling the motion of bubbles, and potentially, this possibility conveys us that the key to control the bubble motion is to reconstruct the wake vortices by changing the flow field. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A24.00007: Laboratory Experiments on Air Bubbles Rising through Carbopol Capped with Water Kai Zhao, Edmund Tedford, Marjan Zare, Ian Frigaard, Gregory Lawrence We have conducted a series of laboratory experiments bubbling air through a Carbopol solution capped with water. These experiments were conducted to better understand methane ebullition, and its effects on turbidity, in a pit lake. The first bubble is the largest and drags Carbopol into the water. Subsequent bubbles are smaller and follow the path of the first bubble, creating a tube within the Carbopol into which water flows. For a range of Carbopol concentrations we investigate the size and shape of the bubbles, their rise trajectory, the amount of Carbopol dragged into the water, and the evolution of the tubes. Higher concentrations of Carbopol can support deeper tubes without collapsing. These tubes resemble the pockmarks observed in the pit-lake bed. [Preview Abstract] |
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