Abstract:
The article experimentally examines and theoretically
establishes the influence of electric field on the
evaporation kinetics of pendant droplets. It is
observed that the evaporation of saline-pendant
droplets can be augmented by the application of an
external alternating electric field. The evaporation
behaviour is modulated by an increase in the field
strength and frequency. The classical diffusion driven
evaporation model is found insufficient in predicting
the improved evaporation rates. The change in
surface tension due to field constraint is also unable
to explain the observed physics. Consequently, the
internal hydrodynamics of the droplet is investigated
through particle image velocimetry. The electric field
is found to induce enhanced internal advection, which
improves the evaporation rates. A scaled analytical
model is proposed to quantify the role of internal
electrohydrodynamics, electro-thermal and electrosolutal effects. Stability maps reveal that the advection
is caused nearly equally by the electro-solutal and
electro-thermal effects within the droplet. The model
is able to illustrate the influence played by the
governing thermal and solutal Marangoni number,
the electro-Prandtl and electro-Schmidt number, and
the associated electrohydrodynamic number. The
magnitude of the internal circulation can be predicted
by the proposed model, which validates the proposed
mechanism.
