Non‐coalescence and chain formation of droplets under an alternating current electric field

Huang, Xin; He, Limin; Luo, Xiaoming; Xu, Ke; Lü, Yuling; Yang, Donghai

doi:10.1002/aic.17165

Cited by 15 publications

(13 citation statements)

References 30 publications

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“…Extensive work has been carried out in the past, exploring a range of voltages and types of waveforms, to improve the efficiency of electrocoalescers. The literature on the effect of waveforms, − frequency of the AC field, ,,− and strength of the electric field ,,,,, on electrocoalescence suggests sensitive dependence of droplet coalescence or chain formation on these parameters. Often, studies on electrocoalescence have conflicting claims on both optimal frequency as well as the effect of frequency on the performance, indicating high sensitivity to the experimental conditions and parameters.…”

Section: Introductionmentioning

confidence: 99%

Mitigating Noncoalescence and Chain Formation in an Electrocoalescer by Electric Field Modulation

Hasib

Anand

Naik

et al. 2022

Ind. Eng. Chem. Res.

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In the petroleum industry, dehydration and desalting of a crude oil−brine emulsion are critical to further processing and refining of crude. The process of dehydration and desalting is typically done in large units called electrocoalescers. Enhancing the performance of an electrocoalescer includes the ability to dehydrate the emulsion in a shorter time, that is to increase the rate of separation of water while keeping the operation safe. The work proposes the enhancement of separation based on AC electric field modulation. The modulated waveform is composed of a high amplitude electric field step, followed by a low amplitude electric field step, and the process is repeated. The work demonstrates the efficacy of the technique through several experiments and their analysis. The work includes designing and optimizing the electrical waveform and then demonstrating the faster kinetics of electrocoalescence achieved in comparison with the conventional practice. The main advantage of modulation is facilitation of chaining of drops during the high voltage period, followed by their effective coalescence in the low voltage period. The effect of the modulation field and period has been investigated, and optimization of the time periods of the high field and the low field steps is carried out. Our analysis indicates that an increase in the fraction of the total period spanned by the high field improves the water separation, while a relatively weaker dependence is found on the total period. The electric field was applied both in directions parallel and perpendicular to the gravity, and performances were compared. It was found that the parallel configuration was better than the perpendicular configuration.

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Section: Introductionmentioning

confidence: 99%

Mitigating Noncoalescence and Chain Formation in an Electrocoalescer by Electric Field Modulation

Hasib

Anand

Naik

et al. 2022

Ind. Eng. Chem. Res.

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“…Studies found that there are a few various forms of non-coalescence behavior, such as bounce, which does not increase the diameter of droplet and cause secondary droplets. 13 Also, it brings the droplets closer together, increasing the probability of collision. However, a few non-coalescence behaviors cause secondary droplets, which are not favorable for demulsification.…”

Section: Introductionmentioning

confidence: 99%

“…Obviously, this behavior evolution of droplets after contact does not work for demulsification. Studies found that there are a few various forms of non-coalescence behavior, such as bounce, which does not increase the diameter of droplet and cause secondary droplets . Also, it brings the droplets closer together, increasing the probability of collision.…”

Section: Introductionmentioning

confidence: 99%

“…Choi and Saveliev proposed an energy model about electric capillary numbers Ca e and fluid conductivities to describe oscillatory coalescence of droplets, which means a controlled fluid transfer from one droplet to another. Huang et al found that two droplets usually go through complete coalescence, partial coalescence, and non-coalescence as Ca e increases under an AC electric field. In addition, these three behaviors are also found in a DC electric field .…”

Section: Introductionmentioning

confidence: 99%

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Behavior Evolution of Droplets Suspended in Castor Oil under Alternating Current Electric Field

Jin

et al. 2022

Langmuir

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Electric fields, which can promote the approach of droplets and break the liquid film, are extensively used in the separation of the water phase in water-in-oil emulsions. However, there is an evolution of droplet behavior under an electric field. After the two droplets meet with each other, the electric force becomes undesirable, which would even cause breakup of the merged droplet. When the electric field strength E reaches a particular value, the final behavior of droplets is made, which goes against coalescence, and there are lots of behavior evolution types. Several research studies have studied on whether droplets coalesce and the critical condition, but few works have focused on the classification and mechanism of non-coalescence behaviors. In this paper, the behavior evolution of two single droplets suspended in castor oil under an alternating current electric field is studied by a high−speed camera. Six distinct behavior evolution modes are observed and summarized: coalescence, bounce, partial coalescence, partial rupture, coalescence−rupture, and rupture. The behavior evolution mode is influenced by the initial separation distance s 0 between droplets and the electric field strength. Moreover, there exist critical electric field strengths among different behavior evolution modes. As E gradually increases, two water droplets go through coalescence, partial coalescence, and coalescence−rupture in sequence when s 0 is small and coalescence, bounce, partial rupture, and rupture when s 0 is large. The mechanisms of behavior evolution are revealed by investigating the confrontation between electric force and capillary force in the condition with liquid bridge or pressure difference from the surrounding fluid and electric force in the condition without a liquid bridge. In addition, a cone−dimple mode of water droplets in castor oil is found, demonstrating the rationality of electric force theory.

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“…However, microscopic experiments found that water droplets no longer coalesce when the electric field strength is too high 14,15 . In serious cases, these non‐coalescing droplets form stable droplet chains along the direction of electric field and then cause the short‐circuit of electric field, seriously deteriorating the separation efficiency of oil and water 16–18 . Understanding the characteristics and mechanism of droplet non‐coalescence under the electric field are of great significance for optimizing the operating conditions of electric field and improving the demulsification efficiency of water‐in‐oil emulsion.…”

Section: Introductionmentioning

confidence: 99%

Effect of liquid bridge evolution on the droplet non‐coalescence under a DC electric field

Huang

et al. 2022

AIChE Journal

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The droplet non-coalescence characteristics and mechanism under a DC electric field are investigated by comprehensively using high-speed microscopic experiments, molecular dynamics simulations, and interface dynamics simulations. The researches show whether two droplets coalesce or not depends on the evolution of liquid bridge. The liquid bridge evolution is not only dominated by the electric force F E and the capillary force F i , but also slowed down by the viscous force. The relative strength of F E and capillary force F i relies on the electric capillary number Ca and the maximum liquid bridge radius R* max . The droplet non-coalescence is more likely to happen as the Ca increases or the R* max decreases. Furthermore, the critical value Ca c for droplet non-coalescence reduces as the R* max decreases. The ion transportation causes uneven distribution of ions and thus strengthens the F E , resulting in the non-coalescence. These results provide significant guidance for efficient demulsification of water-in-oil emulsion.

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Non‐coalescence and chain formation of droplets under an alternating current electric field

Cited by 15 publications

References 30 publications

Mitigating Noncoalescence and Chain Formation in an Electrocoalescer by Electric Field Modulation

Mitigating Noncoalescence and Chain Formation in an Electrocoalescer by Electric Field Modulation

Behavior Evolution of Droplets Suspended in Castor Oil under Alternating Current Electric Field

Effect of liquid bridge evolution on the droplet non‐coalescence under a DC electric field

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