Stabilizing a bubble in a water tunnel

In summary, the conversation is about finding the required flow rate to stabilize a sinking bubble in a water tunnel. The calculation for the velocity of the sinking bubble is discussed, as well as the need for active control or a position-dependent flow velocity to stabilize the bubble. A sketch of the setup is requested for better understanding, and the calculation for the drag on a bubble with flow is also mentioned.
  • #1
Ninet
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Hello,

I am trying to find the required flow rate for stabilization of a bubble (to control the sinking and rising of bubble) in the water tunnel. I found the velocity of sinking bubble in the water (when the flow rate is zero) but I am not sure how to use that to find flow rate of my system to control the sinking and rising of bubble. I would greatly appreciate any help. Thank you.

Here is how I calculated velocity of sinking bubble:

FBD--> W (weight) = D (drag) + B (Buoyancy)

W= γAir * V , V= volume
B= γwater* V
Drag=(1/2)* ρ*U^2* (π/4)*(D^2)*Cd , where ρ= density of Water, U= velocity, D= bubble's diameter and Cd= drag coefficient
Cd (Drag Coefficient)= 24/ Re
Re= ρ*U*D*(1/μ)

U (Velocity) = (SG bubble]-1)*(γwater)*D^2*(1/18)*(1/[μwater)
 
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  • #2
Maybe I am missing something, but can't you just multiply the flow velocity by the cross-section of the tunnel (and the density of water for mass flow)?
 
  • #3
Sorry, I think I didn't explain the problem very well. I am trying to determine the the flow velocity in a way that can stabilize a sinking bubble in a tunnel. (Tunnel is tapered and the size is fixed)
 
  • #4
To make it stable, I guess you'll need some active control, or a position-dependent flow velocity (=a position-dependent width of your tunnel or some other way to change the current flow).
Otherwise, even tiny deviations from the "right" flow will get your bubble to the bottom or the top after a while.
 
  • #5
well, first I want to calculate the maximum flow velocity in my system to figure out required pump. I am not sure how to calculate the flow velocity based on the shape of the tunnel and the sinking rate of bubble.
 
  • #6
If you know how fast your bubble sinks without flow, then your flow velocity upwards at the position of the bubble has just to be this velocity. It is not constant over the cross-section, but that's probably an issue that can be sorted out later.

It would help to get more context. Do you have a sketch of the setup?
 
  • #7
Thank you mfb for your help. I think my calculation for velocity of sinking bubble without flow should be correct. But then as you said when there is a flow the flow velocity changes in different cross section of tunnel. I draw a basic sketch of tunnel and the rectangle in the sketch is the desired range to keep the bubble stable. Also, how can I calculate drag on a bubble when there is a flow?
 

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  • #8
If the object is sinking without flow, the current position is instable - upwards flow increases with height.

Also, how can I calculate drag on a bubble when there is a flow?
All you need is the velocity relative to the fluid. As the bubble velocity is supposed to be zero, this is just the velocity of the fluid.
 
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1. What is a water tunnel and why is it used in bubble stabilization experiments?

A water tunnel is a controlled flow channel filled with water that is used to simulate real-life fluid dynamics and study the behavior of different objects, such as bubbles. It is used in bubble stabilization experiments because it provides a realistic and controlled environment for studying the effects of various factors, such as flow velocity and surface tension, on bubble stability.

2. How do you create a stable bubble in a water tunnel?

To create a stable bubble in a water tunnel, the first step is to generate the bubble using a bubble generator or by injecting air into the water. Then, the flow rate, water temperature, and surface tension must be carefully controlled to achieve the right balance for the bubble to maintain its shape and position in the water flow. Other factors, such as the shape and size of the bubble, can also affect its stability.

3. What techniques are used to measure bubble stability?

There are various techniques used to measure bubble stability, such as high-speed photography or video recording to track the movement and shape of the bubble over time. Pressure sensors can also be used to measure the internal pressure of the bubble, which can indicate its stability. Additionally, advanced techniques like laser interferometry and image analysis software can provide more precise data on bubble stability.

4. What factors can influence the stability of a bubble in a water tunnel?

The stability of a bubble in a water tunnel can be affected by various factors, including flow velocity, surface tension, temperature, bubble size and shape, and the properties of the surrounding fluid. Changes in any of these factors can cause the bubble to become unstable, leading to changes in its shape or position in the water flow.

5. How can the results of bubble stabilization experiments in a water tunnel be applied in real-world applications?

The results of bubble stabilization experiments in a water tunnel can be used to improve our understanding of bubble dynamics and the factors that affect bubble stability. This knowledge can then be applied in various industries, such as oil and gas, where bubbles can cause problems in pipelines or underwater structures. It can also be used in biomedical research to study the effects of bubbles in blood flow and develop treatments for conditions like decompression sickness.

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