Bubble formation and scale dependence in free-surface air entrainment

Abstract

The air bubble entrainment and self–aeration phenomena in free-surface water flows reveal a rich interplay of fundamental science and engineering, and the size distribution of the entrained bubbles enhances the air–water gas flux, improves the gas transfer, and influences the cavitation erosion protection in high–speed flows. In the present study, we investigate the bubble–formation mechanism of free–surface air entrainment and the related microscopic bubble scale in the laboratory. This paper provides a quantitative description of bubble entrainment. The entrapment deformation of the local free surface over a period follows a power–law scaling and entrains a bubble when the entrapped surface becomes enclosed in the unstable movement period. Both the size scale and shape character of the entrapped free surface determine the size and skewness of the distribution of the air bubble. The entrapment deformation process confirms that the instability behaviour of the local air–water interface results in the onset of bubble entrainment. Further research is necessary to elucidate the instability criterion dominated by the interface instability and promote a new understanding of multiphase flow generation and development.

Tuning the Morphology of Protein–Inorganic Calcium–Phosphate Supraparticles via Directed Assembly

“…68 The high Re and Re ω cases had a high incidence of bubble formation, possibly due to more forceful and rapid expansion of the fluid film and more turbulence. 69 At lower values of Re ω and higher values of Re (Figure 3B), there were many incidences of smooth sliding flow regimes. This was likely because the relative contribution of rotational inertia was muted by gravity and axial inertia.…”

“…The Re numbers compare axial or rotational inertia to viscous drag forces . The high Re and Re ω cases had a high incidence of bubble formation, possibly due to more forceful and rapid expansion of the fluid film and more turbulence . At lower values of Re ω and higher values of R e (Figure B), there were many incidences of smooth sliding flow regimes.…”

“…These observations identified Re ω ∼ 75 as the turbulent flow transition regime. As Ir decreased, a transition from surging waves to plunging waves occurred, indicating the fluid flow around the curved bottom of the tubes may behave similarly to waves in a large body of water. , It should be noted that Fr and Ir use similar variables, but the interpretation of their values independently leads to different insights in the system’s mechanics. SI Figure S6 shows similar findings with alternative combinations of dimensionless parameters.…”

Mesoscale Analysis of Air-Water Two-Phase Flow

“…This will increase the probability for a small air bubble to form. Figure 4.19 shows the statistical relationships between d ab and the intensity and scale of deformation within a test range (Wei and Xu et al 2019). As demonstrated in Fig.…”

Communication-Efficient Algorithms for Solving Pressure Poisson Equation for Multiphase Flows using Parallel Computers

“…For concreteness, we focus on the Pressure Poisson PDE that arises from multiphase flows that are found in a wide range of applications, including bubble columns in the chemical industry, nuclear reactors, and various aspects of metal processing. Various strategies to model such flows have been discussed [1][2][3][4] . Solving the Pressure Poisson equation is usually the most time-consuming part of the numerical solution of the equations governing incompressible flows.…”