The generation of single, monodisperse compound droplets is shown in these fluid dynamics videos. In an apparatus designed to produce single compound droplets, a piezoelectric diaphragm generates a pressure pulse from a voltage waveform input to eject a droplet. In the method presented, oil is allowed to flow into the water nozzle with the pressure pulse ejecting both fluids as a compound droplet. Experiments were performed to demonstrate how changes in water pressure affect compound droplet compositions. It was found that increasing the water pressure decreased the thickness of the compound droplet's oil layer.
We investigate imbibition of a monodisperse emulsion into a low-aspect ratio microfluidic channel with the height h comparable to the droplet diameter d. For confinement ratio d/h = 1.2, the tightly confined disk-like droplets in the channel move more slowly compared to the average suspension velocity. Behind the meniscus that drives the imbibition, there is a droplet-free region, separated from the suspension region by a sharp concentration front. The suspension exhibits strong droplet density and velocity fluctuations, but on average, the suspension domain remains uniform. For weaker confine…
The influence of drop formation due to micro rib-like structures, viz., the Junction Gutters (JGs) within a standard microfluidic T-junction, is numerically investigated. Hydrodynamic conditions that lead to various flow regimes are identified characterized by the Capillary number (Ca) and velocity ratios of the dispersed and continuous phases (q) within a standard T-junction. Subsequently, under such conditions, a range of gutter configurations is introduced in the standard channel. The results predict that the introduction of JGs can favourably alter the formation frequency and morphology of…
Forced generation of simple and double emulsions in all-aqueous system
我们报告了一种易于实施的方法，允许直接生成水包水（w/w）单一乳液。该方法依赖于驱动乳液分散相流动的压力的直接扰动。由于瑞利-高原不稳定性引起的扰动的增长，所产生的内射流被诱导破碎成液滴[L。Rayleigh，Proc. R. Soc. London 29，71-97（1879）];这导致单分散液滴的形成。通过在改性的微流体装置上实施该方法，我们直接产生水包水包水（w/w/w）双重乳液，其对封装液滴的大小和数量具有良好的控制。我们的方法提出了一种将基于液滴的微流体应用于完全基于水的系统的新途径。
Effects of low-temperature chemistry induced by ultrafine water droplet evaporation on reaction front development from an ignition spot with temperature gradient are studied in this work. The Eulerian-Eulerian method is used to simulate the gas-liquid two-phase reactive flows and the physical model is one-dimensional spherical reactor with stoichiometric gaseous n-heptane/air mixture and ultrafine monodisperse water droplets (initial diameter 5 micrometres). Homogeneous ignitions of two-phase mixtures are first simulated. The water droplets can complete evaporation in the reactor prior to igni…
Deformation and breakup of a ferrofluid compound droplet migrating in a microchannel under a magnetic field: A phase-field-based multiple-relaxation time lattice Boltzmann study
This work has explored interface evolution and pinch-off mechanism of the droplet formation in two-phase flow through cross-flow microfluidic device. The two-dimensional mathematical model equations have been solved using the finite element method under the squeezing regime ($Ca_c < 10^{-2}$) for wide range of flow rates ($Qr = 0.1 - 10$) and fixed contact angle ($θ=135^o$). The droplet formation process has been classified into various instantaneous stages as initial, filling, squeezing, pinch-off and stable droplet through microscopic visualization of interface evolution in phase profiles. T…
We use direct numerical simulation to study the temporal evolution of a perturbation localized on the turbulent layer that typically separates a cloud from the surrounding clear air. Across this shearless layer, a turbulent kinetic energy gradient naturally forms. Here, a finite perturbation in the form of a local initial temperature fluctuation is applied to simulate a hydrodynamic instability inside the background turbulent air flow. A numerical initial value problem for two diametrically opposite types of drop population distributions is then solved. Specifically, we consider a mono-dispers…
Effects of surface viscosities on the motion of a droplet enclosing a translating particle
Santa Clara University（圣克拉拉大学）；Towson University（托森大学）；National University of Singapore（新加坡国立大学）；Nanjing University of Aeronautics and Astronautics（南京航空航天大学）；New Jersey Institute of Technology（新泽西理工学院）
Onsager-variational-principle-based Lattice Boltzmann Model For Three-phase Dielectric Fluid Flows
College of Science, National University of Defense Technology（国防科技大学理学院）；School of Mathematics and Physics, China University of Geosciences（中国地质大学数学与物理学院）
The effect of a spatially uniform magnetic field on the shear rheology of a dilute emulsion of monodispersed ferrofluid droplets, immersed in a non-magnetizable immiscible fluid, is investigated using direct numerical simulations. The direction of the applied magnetic field is normal to the shear flow direction. The droplets extra stress tensor arising from the presence of interfacial forces of magnetic nature is modeled on the basis of the seminal work of G. K. Batchelor, J. Fluid Mech., 41.3 (1970) under the assumptions of a linearly magnetizable ferrofluid phase and negligible inertia. The …
Droplet encapsulating bubble: Investigation of droplet spreading dynamics and bubble encapsulation time
School of Mechanical Engineering, Iran University of Science and Technology（伊朗理工大学机械工程学院）；Department of Mechanical Engineering, University of California, Riverside（加州大学河滨分校机械工程系）
Compound particles are a class of composite systems in which solid particles encapsulated in a fluid droplet are suspended in another fluid. They are encountered in various natural and biological processes, for e.g., nucleated cells, hydrogels, microcapsules etc. In this work, we analyze the flow in and around a concentric compound particle and investigate the deformation and reorientation dynamics of the confining drop and its stability against breakup in imposed linear flows. We obtain analytical expressions for the flow fields upto O(Ca) (capillary number) and the deformed shape of the conf…
