Droplet formation in a T-shaped microfluidic junction

Question

1. What contributions have the authors mentioned in the paper "Droplet formation in a t-shaped microfluidic junction" ?

2. What have the authors stated for future works in "Droplet formation in a t-shaped microfluidic junction" ?

3. What is the unifying feature of all the phase-field models?

4. Why is it important to minimize the numerical error introduced by the grid number?

Accepted Answer

The authors have systematically examined the influence of capillary number, flow rate ratio, viscosity ratio and contact angle in the droplet generation process.

Accepted Answer

In this work, an improved phase field lattice Boltzmann model has been applied to study the droplet formation in a microfluidic T-junction.. In the next step, the authors will develop high-performance computational code using massive parallel processors to carry out 3D simulations which can capture both intermolecular and hydrodynamic effects in droplet dynamics. [ 1 ]

Accepted Answer

A unifying feature of all the phase-field models is the existence of a free-energy functional, which not only determines the equilibrium properties, but also strongly influences the dynamics of a multiphase system.

Accepted Answer

Since the grid number may significantly affect the simulation results of the phase field method, it is important to minimize the numerical error introduced by the grid number.

Accepted Answer

The intrusion of the continuous phase accentuates the influence of the contact line dynamics, which is thought to be indispensable for the droplet detachment.

Accepted Answer

The droplet deforms before detachment, and the necking of the dispersed phase is initiated once the continuous phase fluid intrudes into the upstream of the lateral channel.

Accepted Answer

Flow behavior in a microfluidic T-junction can be classified by a group of dimensionless parameters, which are commonly defined by the experimentally measurable variables e.g. the inter-facial tension, the inlet volumetric flow rates (Qc and Qd) and viscosities (ηc and ηd) of the two fluids.

Accepted Answer

(2)The equilibrium interface profile can be obtained from Eq. (2) at µ = 0, which leads to two stable uniform solutions φ = ±1 representing the coexisting bulk phases.

Accepted Answer

The capillary number, the flow rate ratio,the viscosity ratio and the contact angle have found to be important in droplet formation, and these parameters together control the complex droplet generation process.

Accepted Answer

The reason may be that the generated droplet at a small Ca is usually big, which has a large contact area with the channel surface, so that the wall surface plays a more significant role in the droplet generation.

Accepted Answer

the authors find that the wetting property has more significant effect on droplet size at small Ca, and its effect diminishes gradually when Ca increases.

Accepted Answer

They assume that the wall is a mixture of two fluids, thus having a certain value of the order parameter φw, so the derivatives of the order parameter at the surface boundary can be calculated using (9 points) regular finite difference stencils [30].

Accepted Answer

D. Influence of contact angleDue to high surface to volume ratio, fluid/surface interaction will significantly affect the droplet dynamics in microchannels.

Accepted Answer

In order to examine the influence of wetting properties on droplet formation, the authors simulate the droplet generation at different contact angles i.e. θw = 110 ◦, 130◦, 150◦ and 180◦.

Accepted Answer

Fig. 10 shows that the droplet diameter decreases as the contact angle increases, but the squeezing-to-dripping transition still occurs at the the same critical capillary number i.e. Ca=0.018 for different wetting conditions.

Accepted Answer

In the numerical solution, a sufficient number of grids are required to avoid spurious currents and numerical instability at the interface.

Accepted Answer

The influence of the flow rate ratio was numerically investigated in [17] for both squeezing and dripping regimes, where the critical capillary number of 0.015 was found for the squeezing and dripping transition.

Accepted Answer

their simulation results shown in Fig. 5 suggest that the droplet size also strongly depends on Ca in the squeezing regime, which is consistent with the experimental observations [14].

Droplet formation in a T-shaped microfluidic junction

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Most frequently asked questions

1. What contributions have the authors mentioned in the paper "Droplet formation in a t-shaped microfluidic junction" ?

2. What have the authors stated for future works in "Droplet formation in a t-shaped microfluidic junction" ?

3. What is the unifying feature of all the phase-field models?

4. Why is it important to minimize the numerical error introduced by the grid number?

5. What is the effect of the continuous phase on the droplet?

6. What is the effect of the necking of the dispersed phase fluid?

7. What is the simplest way to classify the flow behavior in a microchannel?

8. What is the equilibrium interface profile of a multiphase system?

9. What are the parameters that control the droplet generation process?

10. Why is the droplet size influenced by the contact angle?

11. What is the effect of the wetting property on droplet size at small Ca?

12. How can the authors calculate the order parameter at the surface boundary?

13. What is the effect of contact angle on droplet dynamics in microchannels?

14. How is the droplet formation influenced by the viscosity ratio?

15. What is the droplet diameter at the critical capillary number?

16. How many grids are required to avoid spurious currents and numerical instability at the interface?

17. How many drops are squeezing and dripping?

18. What is the critical capillary number in the squeezing regime?

Figures

Citations

Lattice-Boltzmann Simulation and Experimental Validation of a Microfluidic T-Junction for Slug Flow Generation

Dynamics of magnetic modulation of ferrofluid droplets for digital microfluidic applications

Droplet Production and Transport in Microfluidic Networks with Pressure Driven Flow Control

Measuring liquid-liquid volume composition in transparent tubing using a linear CMOS sensor

Numerical Study on Droplet Formation and Cell Encapsulation Process in a Micro T-junction via Lattice Boltzmann Method

References

Lattice BGK Models for Navier-Stokes Equation

Principles of Condensed Matter Physics

The Lattice Boltzmann Equation for Fluid Dynamics and Beyond by Sauro Succi (Clarendon Press, Oxford, 2001) ISBN 0 19 850398 9

Molecular theory of capillarity

Principles of condensed matter physics

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