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Numerical Investigation of The Electrocoalescence of Moving Microdroplets using Direct and Alternating Electric Fields

Behnam Bilondi, Amir Ali | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58729 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Mohammadi, Ali Asghar
  7. Abstract:
  8. Droplet coalescence in microfluidic systems plays a crucial role in a wide range of engineering applications. The investigation of droplet coalescence using electric fields is of particular importance due to its high controllability, fast response, and weak dependence on channel geometry and flow rates. In this study, a three-dimensional computational fluid dynamics (CFD) modeling of the electro-coalescence of moving deionized water droplets in mineral oil under the influence of direct and alternating electric fields was performed. In addition, dimensional analysis based on the Buckingham π theorem and phenomenological modeling were conducted to achieve a better understanding of the mechanisms governing droplet formation and coalescence. Two asymmetric electrodes were placed on both sides of the main channel to generate a non-uniform electric field. The phase-field, momentum, continuity, and electrostatic equations were solved in a fully coupled manner using the COMSOL Multiphysics software. The results showed that in the absence of an electric field, none of the droplets coalesced with each other. When a direct electric field was applied at low voltages, only a small number of droplets coalesced. As the field strength increased, the number of coalescence events also increased, until at 1200 V and above, all pairs of droplets entering the main channel coalesced. Under alternating electric fields, a similar trend was observed: at low peak voltages, coalescence occurred only for the first few droplet pairs entering the main channel, while the subsequent droplets did not coalesce. From a peak voltage of 900 V onward, all droplet pairs coalesced. The droplet coalescence ratio exhibited a different behavior with changes in frequency. At low frequencies, the coalescence ratio was low. With increasing frequency within a certain intermediate range, the coalescence ratio increased, and then decreased again at higher frequencies.
  9. Keywords:
  10. Droplets Coalescence ; Computational Fluid Dynamics (CFD) ; Microfluidic System ; Electrocoalescence ; Microdroplets

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