scholarly journals A simulation study of the forward and backward thermocapillary migration of fluids in a microchannel

2020 ◽  
Vol 3 (4) ◽  
pp. first
Author(s):  
Long Thanh Le ◽  
Khuong Huu Nguyen
Keyword(s):  
Heat Source ◽  
Water Droplet ◽  
Thermocapillary Convection ◽  
Liquid Droplet ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Immiscible Fluids ◽  
Cold Side ◽  
Free Interface ◽  
Thermocapillary Migration

In this study, the forward and backward thermocapillary migration of fluids in a microchannel is numerically investigated. Both the upper wall and the lower wall of the microchannel are set to be an ambient temperature. Two 40mW heat sources activated periodically are placed on the left side and the right side of the droplet in a microchannel. When the heat source is turned on, a pair of asymmetric thermocapillary convection vortices is formed inside the droplet. The isotherms inside the droplet are extremely distorted by the thermocapillary convection. The forward and backward thermocapillary migration results in the net thermocapillary momentum which drives a water droplet moves from the hot side of the open channel to the cold side. The temperature gradient at the free interface on the side of acting heat source is always smaller than that on the cold side. The actuation velocity of the liquid droplet first increases significantly, and then decreases continuously for various interval times. The dynamic contact angle of a water droplet is strongly affected by the forward and backward oil flow motion and the net thermocapillary momentum inside the droplet. It is alternated due to the pressure difference acting on the free interface between two immiscible fluids during actuation process.

scholarly journals Numerical investigation of the thermocapillary migration of a water droplet in a microchannel by applying a heat source

2020 ◽  
Vol 3 (SI1) ◽  
pp. First
Author(s):  
Le Thanh Long ◽  
Jyh Chen Chen ◽  
Nguyen Huy Bich
Keyword(s):  
Contact Angle ◽  
Heat Source ◽  
Water Droplet ◽  
Stokes Equations ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Initial Position ◽  
Immiscible Fluids ◽  
Two Phase ◽  
Thermocapillary Migration

The migration of a small droplet has been developed during the last two decades due to its applications in industry and high technology such as MEMS and NEMS devices, Lap-On-a- chip, transportation of fluids and so on. There have many studies on this topic in which the energy source as a driving force for the moving of a droplet is quite a difference like heating, magnetics, pressure, electric, laser, and so on. In this study, the numerical computation is used to investigate the transient thermocapillary migration of a water droplet in a micro-channel under the effect of heating source. For tracking the evolution of the free interface between two immiscible fluids, we employed the finite element method with the two-phase level set technique to solve the Navier-Stokes equations and continuity equation coupled with the energy equation. Both the upper wall and the bottom wall of the microchannel are set to be ambient temperature. 40mW heat source is placed at a distance of 1 mm from the initial position of a water droplet. When the heat source is turned on, a pair of asymmetric thermocapillary convection vortices is formed inside the droplet, and the thermocapillary on the receding side is smaller than that on the advancing side. The temperature gradient inside the droplet increases quickly at the initial times and then decreases versus time. Therefore, the actuation velocity of the water droplet first increases significantly and then decreases continuously. Furthermore, the results also indicate that the dynamic contact angle is strongly affected by the oil flow motion and the net thermocapillary momentum inside the droplet. The advancing contact angle is always larger than the receding contact angle during the actuation process.

Numerical Study of a Small Droplet Movement in a Microchannel under Heat Source

2019 ◽  
Vol 894 ◽  
pp. 104-111
Author(s):  
Thanh Long Le ◽  
Jyh Chen Chen ◽  
Huy Bich Nguyen
Keyword(s):  
Contact Angle ◽  
Heat Source ◽  
Water Droplet ◽  
Stokes Equations ◽  
Numerical Study ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Initial Position ◽  
Immiscible Fluids ◽  
Two Phase

In this study, the numerical computation is used to investigate the transient movement of a water droplet in a microchannel. For tracking the evolution of the free interface between two immiscible fluids, we employed the finite element method with the two-phase level set technique to solve the Navier-Stokes equations coupled with the energy equation. Both the upper wall and the bottom wall of the microchannel are set to be an ambient temperature. 40mW heat source is placed at the distance of 1 mm from the initial position of a water droplet. When the heat source is turned on, a pair of asymmetric thermocapillary convection vortices is formed inside the droplet and the thermocapillary on the receding side is smaller than that on the advancing side. The temperature gradient inside the droplet increases quickly at the initial times and then decreases versus time. Therefore, the actuation velocity of the water droplet first increases significantly, and then decreases continuously. The dynamic contact angle is strongly affected by the oil flow motion and the net thermocapillary momentum inside the droplet. The advancing contact angle is always larger than the receding contact angle during actuation process.

scholarly journals Study of Fluids Motion in a Microchannel under Heat Source

2020 ◽  
Vol 2 (SI2) ◽  
pp. First
Author(s):  
Long Thanh Le
Keyword(s):  
Contact Angle ◽  
Heat Source ◽  
Water Droplet ◽  
Stokes Equations ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Immiscible Fluids ◽  
Navier Stokes ◽  
Two Phase ◽  
Receding Contact Angle

In this study, the numerical computation is used to investigate the transient thermocapillary migration of a water droplet in a Microchannel. For tracking the evolution of the free interface between two immiscible fluids, we employed the finite element method with the two-phase level set technique to solve the Navier-Stokes equations coupled with the energy equation. Both the upper wall and the bottom wall of the microchannel are set to be an ambient temperature. The heat source is placed at the left side of a water droplet. When the heat source is turned on, a pair of asymmetric thermocapillary convection vortices is formed inside the droplet and the thermocapillary on the receding side is smaller than that on the advancing side. The temperature gradient inside the droplet increases quickly at the initial times and then decreases versus time. Therefore, the actuation velocity of the water droplet first increases significantly, and then decreases continuously. The dynamic contact angle is strongly affected by the oil flow motion and the net thermocapillary momentum inside the droplet. The advancing contact angle is always larger than the receding contact angle during actuation process.

Bridge Dynamics for Capillary-Based Liquid Deposition

2012 ◽  
Author(s):  
Artur Lutfurakhmanov ◽  
Yechun Wang ◽  
Douglas L. Schulz
Keyword(s):  
Experimental Data ◽  
Contact Line ◽  
Liquid Droplet ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Non Invasive ◽  
Contact Line Motion ◽  
Liquid Deposition ◽  
Good Agreement ◽  
Bridge Dynamics

A new capillary-based lithography technique of liquid droplet deposition is further developed. Main advantage of this method in comparison with others techniques is that it is non-invasive both to the substrate and to the writing tip. The method is studied both theoretically and experimentally. To adequately describe bridge dynamics between the capillary and the substrate, proper boundary conditions must be set in the model for the liquid-surface interface. Based on literature review, two laws of contact line motion are identified: Tanner’s law and Blake’s equation. These two approaches are tested in multiple experiments with different retraction speeds from 3 microns/s to 300 microns/s. Analysis of the experimental data show that both Tanner’s and Blake’s equation can describe the correlation between the contact line velocity and the dynamic contact angle. In addition, both laws are employed in the direct numerical simulation of the bridge dynamics using 3D spectral boundary element method. Modeling results are compared with experimental data and show good agreement.

Droplet Oscillation After Impact on a Solid Surface

2016 ◽  
Author(s):  
Yina Yao ◽  
Shuai Meng ◽  
Cong Li ◽  
Xiantao Chen ◽  
Rui Yang
Keyword(s):  
Contact Angle ◽  
Spray Deposition ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Oscillation Period ◽  
Droplet Spreading ◽  
Oscillation Phenomenon ◽  
The Impact

Droplet spreading and oscillation occur when a liquid droplet impacts on the solid surfaces. This process is vital in many industrial applications, such as ink-jet printing technologies, spray coating and agricultural spray deposition. However, the researches that have been done mainly focused on the spreading process, and less attention has been paid to the droplet oscillation phenomenon, which has influence on the solidification and evaporation process. Therefore, the study on droplet oscillation phenomenon after the impact is necessary and valuable. This paper aims at analyzing the droplet oscillation phenomenon using VOF method. Since the contact angle varies dramatically in the dynamic process, a dynamic contact angle model is introduced to improve the simulation accuracy. The dynamic contact angle model has been verified by comparing the numerical results with experimental and theoretical results. In order to study the factors that may influence the droplet oscillation period, different droplet diameters and impact velocities are utilized in this simulation. The results show that the oscillation period presents a positive relationship with droplet diameter. However, the impact velocity has no apparent influence on the oscillation period, which agrees well with the theoretical analysis.

Numerical analysis on dynamics and thermodynamics of a supercooled water droplet considering the dynamic contact angle

2021 ◽  
Vol 33 (10) ◽  
pp. 102101
Author(s):  
Yongkui Wang ◽  
Qing Wang ◽  
Lei Ju ◽  
Duanfeng Han ◽  
Yanzhuo Xue
Keyword(s):  
Contact Angle ◽  
Numerical Analysis ◽  
Water Droplet ◽  
Dynamic Contact Angle ◽  
Supercooled Water ◽  
Dynamic Contact

Investigation of behavior of the dynamic contact angle in a problem of convective flows

2017 ◽  
Vol 5 (4) ◽  
pp. 27-42
Author(s):  
O.N Goncharova ◽  
◽  
I.V. Marchuk ◽  
A.V. Zakurdaeva ◽  
◽  
...  
Keyword(s):  
Contact Angle ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Convective Flows
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