The dynamics of an evaporating droplet in an unsteady flow is of practical interest in many industrial applications and natural processes. To investigate the transport and evaporation dynamics of such droplets, we present a numerical study of an isolated droplet in an oscillating gas-phase flow. The study uses a one-way coupled two-phase flow model to assess the effect of the amplitude and the frequency of a sinusoidal external flow field on the lifetime of a multicomponent droplet containing a non-volatile solute dissolved in a volatile solvent. The results show that the evaporation process becomes faster with an increase in the amplitude or the frequency of the gas-phase oscillation. The liquid-phase transport inside the droplet also is influenced by the unsteadiness of the external gas-phase flow. A scaling analysis based on the response of the droplet under the oscillating drag force is subsequently carried out to unify the observed evaporation dynamics in the simulations under various conditions. The analysis quantifies the enhancement in the droplet velocity and Reynolds number as a function of the gas-phase oscillation parameters and predicts the effects on the evaporation rate.
more »
« less
HYDRODYNAMICALLY-INDUCED DROPLET MICROVORTICES FOR CELL PAIRING APPLICATIONS
We present a water-in-oil droplet microfluidic trap array capable of modulating the distance between co-encapsulated cell pairs through microvortex formation. We demonstrate that vortex shape and periodicity can be directly controlled by the continuous phase flow rate. Explicit equations for the recirculation time inside droplet microvortices were derived by approximating the velocity fields through analytic solutions for the flow inside and outside of a spherical droplet. Comparison of these expressions against Particle Tracking Velocimetry (PTV) measurements of K562 (leukemia) cells circulating inside 50 μm droplets showed excellent theoretical agreement.
more »
« less
- Award ID(s):
- 1841509
- NSF-PAR ID:
- 10316888
- Date Published:
- Journal Name:
- 25th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2021)
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)In this paper, we theoretically investigate the migration of a surfactant covered droplet in a Poiseuille flow by including the surface viscosities of the droplet. We employ a regular perturbation expansion for low surface Péclet numbers and solve the problem up to a second-order approximation. We represent the drop surface as a two-dimensional homogeneous fluid using the Bousinessq–Scriven law and employ Lamb's general solution to represent the velocity fields inside and outside the droplet. We obtain an expression for the cross-stream migration velocity of the droplet, where the surface viscosities are captured by the Bousinessq numbers for surface shear and surface dilatation. We elucidate the influence of the surface viscosities on the migration characteristics of the droplet and the surfactant redistribution on the droplet surface. Our study sheds light on the importance of including the droplet surface viscosities to accurately predict the migration characteristics of the droplet.more » « less
-
Water harvesting from air is desired for decentralized water supply wherever water is needed. When water vapor is condensed as droplets on a surface the unremoved droplets act as thermal barriers. A surface that can provide continual droplet-free areas for nucleation is favorable for condensation water harvesting. Here, we report a flow-separation condensation mode on a hydrophilic reentrant slippery liquid-infused porous surface (SLIPS) that rapidly removes droplets with diameters above 50 μm. The slippery reentrant channels lock the liquid columns inside and transport them to the end of each channel. We demonstrate that the liquid columns can harvest the droplets on top of the hydrophilic reentrant SLIPS at a high droplet removal frequency of 130 Hz/mm 2 . The sustainable flow separation without flooding increases the water harvesting rate by 110% compared to the state-of-the-art hydrophilic flat SLIPS. Such a flow-separation condensation approach paves a way for water harvesting.more » « less
-
Atomization of High Viscosity Liquids Using a Two-Fluid Counterflow Nozzle: Experiments and Modelingnull (Ed.)We study the enhanced atomization of viscous liquids by employing a novel two-fluid atomizer. The nozzle establishes a countercurrent flow configuration in which the gas and liquid are directed in opposite directions, establishing a two-phase mixing layer. Detailed measurements of droplet size distributions were carried out using laser shadowgraphy, along with high speed flow visualization. The measurements suggest that the liquid emerges as a spray with little further secondary atomization. The performance of this nozzle is compared to the ‘flow-blurring’ nozzle studied by other investigators for four test liquids of viscosity ranging from 1 to 133.5 mPa.s. The counterflow nozzle produces a spray whose characteristics are relatively insensitive to fluid viscosity over the range studied, for gas-liquid mass flow ratios between 0.25 and 1. To gain insight into the mixing process inside the nozzle, simulations are carried out using an Eulerian-Eulerian Volume of Fluid (VoF) approach for representative experimental conditions. The simulation reveals the detailed process of self-sustained flow oscillations and the physical mechanism that generate liquid filaments and final droplets.more » « less
-
In this work, we apply theoretical, computational and experimental fluid dynamics to characterize hydrodynamics micro-vortices formation in the dispersed phase at the flow-focusing microfluidic droplet generation junction. This interfacial hydrodynamic method can be exploited to trap cells inside the micro-vortices and later release them in a one-to-one manner to achieve high efficiency single-cell encapsulation inside droplets. This passive trap and release mechanism is controlled by the distance between the closed vortex streamline and the liquid-liquid interface (dgap) and, thus, fundamental understanding of the micro-vortices and parameters affecting their formation, trajectory and magnitude is necessary to achieve effective one-to-one encapsulation.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
