posted on 2024-02-27, 18:55authored byArnov Paul, Apurba Roy, Purbarun Dhar
We probe the evaporation mechanisms of wettability-moderated,
confined
capillary bridges and bulges. For the first time, we explore the internal
Marangoni hydrodynamics and external Stefan advection dynamics in
the surrounding gaseous domain due to evaporative effects. A transient
simulation approach based on the level set (LS) method and the Arbitrary
Lagrangian–Eulerian (ALE) framework was adopted to computationally
model the capillary bridge profiles and evaporation phenomenon with
generic contact line dynamics (both CCR and CCA modes). The governing
equations corresponding to the transport processes in both the liquid
and gaseous domains are simulated in a fully coupled manner with appropriate
boundary conditions to precisely trace the liquid–vapor interface
and the three-phase contact point during evaporation. The effect of
the bridge confinement phenomenon, i.e., the extent of confined ambient
surrounding the liquid–vapor interface between the solid surfaces,
is explored. Also, the role of wetting state and contact line dynamics
during CCR and CCA modes of evaporation were probed, and good agreement
with experimental observations was noted. Results show that the evaporation
rate is primarily dictated by the confinement phenomenon, and wettability
effects play a marginal role. A higher confinement curtails the evaporation
rate due to an increased local vapor concentration around the liquid
bridges. However, the wetting state substantially affects the internal
Marangoni effect dynamics and the Stefan advection dynamics due to
its explicit influence on the nonuniform evaporative flux along the
liquid–vapor interface. Between superhydrophobic confinements,
the contact lines are confined in the wedge-shaped region, thereby
locally augmenting the vapor concentration. As a result, the large
evaporative flux near the bulge region develops a higher temperature
gradient, thereby inducing upscaled thermal Marangoni flow compared
to hydrophilic confinements. These findings may have significant implications
for the efficient designing and development of thermofluidic systems
involving thermal transport, mixing, and deposition of dissolved particles
in liquid bridges.