Water bubble inside a microchannel

[Excom]

Hi

I need to calculate the force needed to move a water bubble inside a microchannel. Initially, the bubble is at rest and then the air pressure is increased on one side of the bubble.

I am new in microfluidic and need some help about where to start in order to solve this problem.

Thanks

 

[nona]

hi
i didn't understand for you
can you tall us whether more,please
thanks

 

[Excom]

I have a water bubble inside at microchannel. There is air on both sides of the bubble. I then increase the air pressure on one side of the bubble. The air pressure on the other sides is not changed. How much do I have to increase the pressure before the bubble starts to move?

 

[Andy Resnick]

This is a great question! I'm not sure I have an answer, but let's see..

What are forces involved? We can ignore gravity. So it's really wetting: the air/water/glass common line must move in order for the bubble to move. Now, wetting is not understood and there are a lot of microscopic models that have been proposed, but macroscopically, we can maybe estimate:

Young's equation relates the contact angle and interfacial energies. To make the text here easier, let's assume the contact angle is 90 degrees (It's not, but you can work this out later). The air-water interfacial energy is 70 dyn/cm, so multiply this by the circumference of the bubble and you have a certain force to overcome in order to move the contact line. Now, if the glass surface is dirty or otherwise rough all bets are off, but for now, let's just consider the surface to be clean, flat, chemically homogeneous, etc. And I've neglected the air-glass and water-glass interfacial energies.

Then the required pressure difference will be 2*70*2*pi*r/(2*pi*r^2)= 140/r dyn/cm^2. As the channel size goes down, r decreases, requiring a larger pressure difference- that agrees with reality, at least.

It's fairly easy to measure- try it out and see how well it agrees, I'm curious.

 

[PJC01]

for reaching out for help with your microfluidic problem. The movement of a water bubble inside a microchannel can be calculated using the principles of fluid mechanics and pressure differentials. The force required to move the bubble will depend on several factors such as the size of the bubble, the dimensions of the microchannel, and the properties of the fluid being used.

To start, you will need to determine the pressure differential that needs to be applied to the bubble in order to move it. This can be calculated using the Young-Laplace equation, which relates the pressure inside a bubble to its surface tension and curvature. You will also need to consider the frictional forces acting on the bubble as it moves through the microchannel.

Once you have determined the necessary pressure differential, you can then use the Navier-Stokes equations to calculate the force required to move the bubble. These equations describe the motion of a fluid and can be solved numerically using computational fluid dynamics (CFD) software.

It is important to note that the behavior of bubbles in microchannels can be complex and may require additional considerations such as surface tension gradients and wall effects. Therefore, it is recommended to consult with an expert in microfluidics or use specialized simulation software to accurately model the movement of the bubble.

I hope this information helps guide you in solving your problem. Good luck with your research!