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1.Introduction - A peek through the keyhole
1.Introduction - A peek through the keyhole
I am doing my undergraduate thesis work under the supervision of Professor Dr. A.B.M Toufique Hasan Sir on the topic "Droplet dynamics in an Isolated Surface Discontinuity". The work is still ongoing and there is a long journey ahead, but I'm enjoying my research work a lot. Here. in short, I'll try to explain what my thesis is all about.
2. Microfluidic T Junction
2. Microfluidic T Junction
A schematic figure of a T junction is shown. Here, two channels are connected as the way shown in the figure. The channel connected in one side is called side channel and the other channel is called main channel. A microfluidic T junction is the same thing except, its geometrical scale is in the micrometer (10-6 m) scale.
A schematic figure of a T junction is shown. Here, two channels are connected as the way shown in the figure. The channel connected in one side is called side channel and the other channel is called main channel. A microfluidic T junction is the same thing except, its geometrical scale is in the micrometer (10-6 m) scale.
For droplet formation, two different fluids flow in the two channels. The fluid that flows in the main channel is called continuous or carrier fluid. The fluid that flows in the side channel is called dispersed fluid. The other side of the main channel is the common outlet for both fluids.
For droplet formation, two different fluids flow in the two channels. The fluid that flows in the main channel is called continuous or carrier fluid. The fluid that flows in the side channel is called dispersed fluid. The other side of the main channel is the common outlet for both fluids.
3. Forces acting on a Droplet
3. Forces acting on a Droplet
Now, what happens when dispersed fluid from side channel enters the main channel? Obviously, the continuous fluid flow will distort the flow of dispersed fluid towards the outlet! Eventually, main channel will be blocked by the dispersed flow.
Now, what happens when dispersed fluid from side channel enters the main channel? Obviously, the continuous fluid flow will distort the flow of dispersed fluid towards the outlet! Eventually, main channel will be blocked by the dispersed flow.
Here comes the interesting part. Now due to blockage, a pressure difference will build up, which will push the dispersed fluid blockage towards outlet. Shear stress from continuous fluid will also act the same way. On the other hand, interfacial tension will pull the dispersed fluid back and resist the above two pushing forces.
Here comes the interesting part. Now due to blockage, a pressure difference will build up, which will push the dispersed fluid blockage towards outlet. Shear stress from continuous fluid will also act the same way. On the other hand, interfacial tension will pull the dispersed fluid back and resist the above two pushing forces.
Analogy of the Droplet Formation mechanism to a tug of war game
4. Analogy of Acting Forces to a Tug of war Game (2 vs 1)
4. Analogy of Acting Forces to a Tug of war Game (2 vs 1)
You can imagine this pushing and pulling back scenario of the 3 forces as a tug of war game where at one side, there are two players and on the other side, there is only one.
You can imagine this pushing and pulling back scenario of the 3 forces as a tug of war game where at one side, there are two players and on the other side, there is only one.
The two players are like forces due to shear stress and pressure difference from blockage of channel, pushing the dispersed flow towards the outlet. The single person holding back is like the force due to interfacial tension, which is responsible for holding the dispersed flow back and balancing the other two forces.
The two players are like forces due to shear stress and pressure difference from blockage of channel, pushing the dispersed flow towards the outlet. The single person holding back is like the force due to interfacial tension, which is responsible for holding the dispersed flow back and balancing the other two forces.
5. Dynamic Equilibrium & Emergence of the Droplet
5. Dynamic Equilibrium & Emergence of the Droplet
Although this pulling back or balancing effect creates a sort of dynamic equilibrium. The dispersed phase still continues to grow and the blockage still continues to move towards the outlet slowly. As a result, the connection of the blockage with the side channel starts thinning which is called neck.
Although this pulling back or balancing effect creates a sort of dynamic equilibrium. The dispersed phase still continues to grow and the blockage still continues to move towards the outlet slowly. As a result, the connection of the blockage with the side channel starts thinning which is called neck.
Now in practical sense, 2 against 1 is always an unfair ratio and 2 have the upper hand always, of course in a rope pulling game. No matter how strong the single person is. Similarly, at one stage, interfacial tension cannot balance the other two, thus the dynamic equilibrium falls apart, the neck connecting the plug with the side channel dispersed flow breaks. Thus this broken plug of dispersed flow takes the shape of a droplet and moves toward the outlet.
Now in practical sense, 2 against 1 is always an unfair ratio and 2 have the upper hand always, of course in a rope pulling game. No matter how strong the single person is. Similarly, at one stage, interfacial tension cannot balance the other two, thus the dynamic equilibrium falls apart, the neck connecting the plug with the side channel dispersed flow breaks. Thus this broken plug of dispersed flow takes the shape of a droplet and moves toward the outlet.
After the rupture of the neck, the dispersed flow connection retracts or coils back into the side channel. Eventually, dispersed flow again enters the main channel and the whole droplet formation cycle starts again.
After the rupture of the neck, the dispersed flow connection retracts or coils back into the side channel. Eventually, dispersed flow again enters the main channel and the whole droplet formation cycle starts again.
6. Four Stages of Droplet Formation
6. Four Stages of Droplet Formation
The cycle of the formation of a droplet can be divided into 4 Stages:
The cycle of the formation of a droplet can be divided into 4 Stages:
Stage-I: Entering Stage
Stage-II: Blocking Stage
Stage-III: Elongation Stage
Stage-IV: Break-up Stage
7. Video of Droplet Formation Cycles for 50 ms (mili-second)
7. Video of Droplet Formation Cycles for 50 ms (mili-second)
8. Conclusion - A Perpetual Journey through the Path of Research
8. Conclusion - A Perpetual Journey through the Path of Research
This is the overall scenario of a droplet formation. I have only shown you how this phenomenon works. What we do for research purpose is try to perceive why this phenomena works this way and what would happen if any condition changes. Hopefully, you have enjoyed and understood what I have just shown.
Just imagine the vastness of such majestic phenomena are out there, waiting for us to grab and perceive that knowledge and to unearth the secrets they hold. I would rather say it's a true privilege to be able to follow the path of research.
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