Spatial and temporal scaling of unequal microbubble coalescence

Chen, Rou; Yu, Huidan; Zhu, Likun; Patil, Raveena M.; Lee, Taehun

doi:10.1002/aic.15504

Cited by 30 publications

(32 citation statements)

References 57 publications

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“…This observation resembles the behavior of microdroplets. [32][33][34] Also in our latest work, we showed that nanodroplets around the rim of a microcap demonstrated a coalescence preference with a similar exponent p = 2.08. 35 The coalescence preference was attributed to the balance of the capillary force (F = 2pgr min ) which brings the droplet together, against the force required to overcome the contact angle hysteresis.…”

Section: Dynamics Of Droplet Coalescencementioning

confidence: 74%

Growth dynamics of surface nanodroplets during solvent exchange at varying flow rates

et al. 2018

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Solvent exchange is a simple solution-based process to produce surface nanodroplets over a large area. The final size of the droplets is determined by both the flow and solution conditions for a given substrate. In this work, we investigate the growth dynamics of surface nanodroplets during solvent exchange by using total internal reflection fluorescence microscopy (TIRF). The results show that during the solvent exchange, the formation of surface nanodroplets advanced on the surface in the direction of the flow. The time for the number density and surface coverage of the droplets to reach their respective plateau values is determined by the flow rate. From the observed evolution of the droplet volume and of the size of individual growing droplets, we are able to determine that the growth time of the droplets scales with the Peclet number Pe with a power law ∝Pe-1/2. This is consistent with Taylor-Aris dispersion, shedding light on the diffusive growth dynamics during the solvent exchange. Further, the spatial rearrangement of the droplets during coalescence demonstrates a preference in position shift based on size inequality, namely, the coalesced droplet resides closer to the larger of the two parent droplets. These findings provide a valuable insight toward controlling droplet size and spatial distribution.

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Section: Dynamics Of Droplet Coalescencementioning

confidence: 74%

Growth dynamics of surface nanodroplets during solvent exchange at varying flow rates

et al. 2018

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“…The in-house, GPU-accelerated LBM code based on the free-energy model is used for all the simulation in this work. The reliability of this LBM model has been demonstrated in some application studies [30,35,34] previously through comparisons with analytical solutions and experimental/computational results. The spatial resolution was selected 600 2 through a convergence check [34].…”

Section: Computational Set-upmentioning

confidence: 93%

Mechanism of damped oscillation in microbubble coalescence

Chen

Zeng

2019

Computers & Fluids

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This work is part of our continuous research effort to reveal the underlying physics of bubble coalescence in microfluidics through the GPU-accelerated lattice Boltzmann method. We numerically explore the mechanism of damped oscillation in microbubble coalescence characterized by the Ohnesorge (Oh) number. The focus is to address when and how a damped oscillation occurs during a coalescence process. Sixteen cases with a range of Oh numbers from 0.039 to 1.543, varying in liquid viscosity from 0.002 to 0.08kg/(m • s) correspondingly, are systematically studied. First, a criterion of with or without damped oscillation has been established. It is found that a larger Oh enables faster/slower bubble coalescence with/without damped oscillation when (Oh < 0.477)/(Oh > 0.477) and the fastest coalescence falls at Oh ≈ 0.477. Second, the mechanism behind damped oscillation is explored in terms of the competition between driving and resisting forces. When Oh is small in the range of Oh < 0.477, the energy dissipation due to viscous effect is insignificant, sufficient surface energy initiates a strong inertia and overshoots the neck movement. It results in a successive energy transformation between surface energy and kinetic energy of the coalescing bubble. Through an analogy to the conventional damped harmonic oscillator, the saddle-point trajectory over the entire oscillation can be well predicted analytically.

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“…We explore the underlying physics in the global process of microbubble coalescence to support the design and optimization of the prototype. Prior to this work, we have studied the temporal and spatial scalings of air microbubble coalescence in water [19], the effects of the initial conditions on the neck growth [9] in the early coalescence, and the mechanism of damping oscillation in the post coalescence [14] through numerical simulations using the lattice Boltzmann method (LBM) [20,21].…”

Section: Introductionmentioning

confidence: 99%

General power-law temporal scaling for unequal-size microbubble coalescence

Chen

Zeng

et al. 2020

Phys. Rev. E

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We systematically study the effects of liquid viscosity, liquid density, and surface tension on global microbubble coalescence using lattice Boltzmann simulation. The liquid-gas system is characterized by Ohnesorge number Oh ≡ η h / √ ρ h σ r F with η h , ρ h , σ , and r F being viscosity and density of liquid, surface tension, and the radius of the larger parent bubble, respectively. This study focuses on the microbubble coalescence without oscillation in an Oh range between 0.5 and 1.0. The global coalescence time is defined as the time period from initially two parent bubbles touching to finally one child bubble when its half-vertical axis reaches above 99% of the bubble radius. Comprehensive graphics processing unit parallelization, convergence check, and validation are carried out to ensure the physical accuracy and computational efficiency. From 138 simulations of 23 cases, we derive and validate a general power-law temporal scaling T * = A 0 γ −n , that correlates the normalized global coalescence time (T *) with size inequality (γ) of initial parent bubbles. We found that the prefactor A 0 is linear to Oh in the full considered Oh range, whereas the power index n is linear to Oh when Oh < 0.66 and remains constant when Oh > 0.66. The physical insights of the coalescence behavior are explored. Such a general temporal scaling of global microbubble coalescence on size inequality may provide useful guidance for the design, development, and optimization of microfluidic systems for various applications.

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Spatial and temporal scaling of unequal microbubble coalescence

Cited by 30 publications

References 57 publications

Growth dynamics of surface nanodroplets during solvent exchange at varying flow rates

Growth dynamics of surface nanodroplets during solvent exchange at varying flow rates

Mechanism of damped oscillation in microbubble coalescence

General power-law temporal scaling for unequal-size microbubble coalescence

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