Gravitational effect in evaporating binary microdroplets
arXiv:1902.01991 · doi:10.1103/PhysRevLett.122.114501
Abstract
The flow in an evaporating glycerol-water binary sub-millimeter droplet with Bond number Bo 1 is studied both experimentally and numerically. First, we measure the flow fields near the substrate by micro-PIV for both sessile and pendant droplets during the evaporation process, which surprisingly show opposite radial flow directions -- inward and outward, respectively. This observation clearly reveals that in spite of the small droplet size, gravitational effects play a crucial role in controlling the flow fields in the evaporating droplets. We theoretically analyze that this gravity-driven effect is triggered by the lower volatility of glycerol which leads to a preferential evaporation of water then the local concentration difference of the two components leads to a density gradient that drives the convective flow. We show that the Archimedes number Ar is the nondimensional control parameter for the occurrence of the gravitational effects. We confirm our hypothesis by experimentally comparing two evaporating microdroplet systems, namely a glycerol-water droplet and a 1,2-propanediol-water droplet. We obtain different Ar, larger or smaller than a unit by varying a series of droplet heights, which corresponds to cases with or without gravitational effects, respectively. Finally, we simulate the process numerically, finding good agreement with the experimental results and again confirming our interpretation.
References in corpus (9)
- Evaporative Deposition Patterns Revisited: Spatial Dimensions of the Deposit
- Order-to-disorder transition in ring-shaped colloidal stains
- Patterns Formation in Drying Drops of Blood
- Controlled uniform coating from the interplay of Marangoni flows and surface-adsorbed macromolecules
- How water droplets evaporate on a superhydrophobic substrate
- Evaporation-triggered microdroplet nucleation and the four life phases of an evaporating Ouzo drop
- Evaporating pure, binary and ternary droplets: thermal effects and axial symmetry breaking
- Evaporation-triggered segregation of sessile binary droplets
- Self-wrapping of an ouzo drop induced by evaporation on a superamphiphobic surface
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