From droplets to waves: periodic instability patterns in highly viscous microfluidic flows

Hu, Xuesong; Cubaud, Thomas

doi:10.1017/jfm.2019.1009

“…For the external fluid L2, silicone oils are typically blended with a reference oil having η 2 = 97 cP according to the manufacturer’s guidelines to obtain the desired viscosity, which is then measured for accuracy using tube viscometers. The viscosity of the inner fluid L1 is also tested, and values of interfacial tension γ 12 and diffusion coefficient D 12 for each fluid pair are similar to previous work using the same oil and alcohol from manufacturers. , Overall, the use of water, methanol, and ethanol for L 1 enables wide variations of γ 12 for the immiscible fluid pairs A to C and employing isopropanol and silicone oil for the center fluid allows for the formation of partially and fully miscible fluid pairs D and E (Figure b).…”

Section: Experimental Methodssupporting

confidence: 54%

Role of Interfacial Tension on Viscous Multiphase Flows in Coaxial Microfluidic Channels

Dinh

¹

,

Cubaud

²

2021

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We experimentally investigate the influence of interfacial tension on liquid/ liquid microflows for fluids having large viscosity contrasts. A coaxial microdevice is employed to examine the situation where a less-viscous fluid is injected in a sheath of a more-viscous fluid using both immiscible and miscible fluid pairs. Data obtained from high-speed imaging reveal a variety of regular flow regimes, including dripping, jetting, wavy, core-annular, diffusive jet, mist, and inverted thread flow patterns. Flow maps are delineated over a wide range of injection flow rates, and an original methodology based on periodic pattern analysis is developed to clarify relationships between interfacial dynamics and fluid properties of multiphase materials. Specifically, we show the smooth evolution of droplet size and spacing at the transition between dripping and jetting flows and develop scaling relationships based on capillary numbers to predict droplet flow morphologies. For similar flow conditions, reducing interfacial tension leads to a significant decrease in droplet size. For miscible fluid pairs, diffusive jets are observed at low Pećlet numbers, whereas wavy core-annular flows are obtained at moderate Reynolds numbers for both immiscible and miscible fluids. This work provides a unifying description of the influence of interfacial properties on viscous microflow phenomena.

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“…21e, f]. A similar phenomenon of ligament formation and irregular evolution has recently been observed in microfluidic experiments of Hu and Cubaud [40].…”

Section: Flows With Re = 100supporting

confidence: 66%

“…Finally, in microfluidic experiments at the inverse capillary number can assume values of order 1 or larger, e.g. , by choosing ethanol and silicone oil with and mN/m [ 40 ]. In an inertial microfluidic setup, the bulk velocity is larger and inverse capillary numbers, , below one are feasible.…”

Section: Problem Setup and Numerical Methodologymentioning

confidence: 99%

“…Already in 2007, Guillot et al [ 39 ] investigated the formation of jets and droplets in core-annular microfluidic flows of immiscible fluids at low Reynolds numbers. Microfluidic experiments of Hu and Cubaud [ 40 ] addressed the formation of droplets via dripping and jetting in a quadratic microchannel with a less viscous center fluid. Moreover, at relatively high flow rates they only observed waves along the interface.…”

Section: Introductionmentioning

confidence: 99%

“…Most recently, Dinh and Cubaud [ 41 ] also studied the effect of surface tension continuing work in Ref. [ 40 ] but with coaxial microchannels. A detailed review of various active and passive drop generation techniques in microfluidics can be found in Ref.…”

Section: Introductionmentioning

confidence: 99%

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Instability of a liquid sheet with viscosity contrast in inertial microfluidics

Patel

¹

,

Stark

²

2021

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Flows at moderate Reynolds numbers in inertial microfluidics enable high throughput and inertial focusing of particles and cells with relevance in biomedical applications. In the present work, we consider a viscosity-stratified three-layer flow in the inertial regime. We investigate the interfacial instability of a liquid sheet surrounded by a density-matched but more viscous fluid in a channel flow. We use linear stability analysis based on the Orr–Sommerfeld equation and direct numerical simulations with the lattice Boltzmann method (LBM) to perform an extensive parameter study. Our aim is to contribute to a controlled droplet production in inertial microfluidics. In the first part, on the linear stability analysis we show that the growth rate of the fastest growing mode $$\xi ^{*}$$ ξ ∗ increases with the Reynolds number $$\text {Re}$$ Re and that its wavelength $$\lambda ^{*}$$ λ ∗ is always smaller than the channel width w for sufficiently small interfacial tension $$\Gamma $$ Γ . For thin sheets we find the scaling relation $$\xi ^{*} \propto mt^{2.5}_{s}$$ ξ ∗ ∝ m t s 2.5 , where m is viscosity ratio and $$t_{s}$$ t s the sheet thickness. In contrast, for thicker sheets $$\xi ^{*}$$ ξ ∗ decreases with increasing $$t_s$$ t s or m due to the nearby channel walls. Examining the eigenvalue spectra, we identify Yih modes at the interface. In the second part on the LBM simulations, the thin liquid sheet develops two distinct dynamic states: waves traveling along the interface and breakup into droplets with bullet shape. For smaller flow rates and larger sheet thicknesses, we also observe ligament formation and the sheet eventually evolves irregularly. Our work gives some indication how droplet formation can be controlled with a suitable parameter set $$\{\lambda ,t_{s},m,\Gamma ,\text {Re}\}$$ { λ , t s , m , Γ , Re } . Graphical Abstract

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On a New Spatial Discretization for a Regularized 3D Compressible Isothermal Navier–Stokes–Cahn–Hilliard System of Equations with Boundary Conditions

Balashov

¹

,

Злотник

²

2021

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From droplets to waves: periodic instability patterns in highly viscous microfluidic flows

Cited by 11 publications

References 43 publications

Role of Interfacial Tension on Viscous Multiphase Flows in Coaxial Microfluidic Channels

Role of Interfacial Tension on Viscous Multiphase Flows in Coaxial Microfluidic Channels

Instability of a liquid sheet with viscosity contrast in inertial microfluidics

On a New Spatial Discretization for a Regularized 3D Compressible Isothermal Navier–Stokes–Cahn–Hilliard System of Equations with Boundary Conditions

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