Why gas bubbles appear to get stuck inside narrow vertical tubes | Hacker News Reader

Why gas bubbles appear to get stuck inside narrow vertical tubes

livescience.com

20 pointsekoutanov8 comments

I thought it was common sense that the bubble gets stuck because the liquid needs to flow down for the bubble to go up. The bubble’s pressure pushes the liquid against the wall so that it can flow down only very slowly. Surface tension stops the liquid from breaking the bubble and flowing down the center.

"But in this case, the researchers used a custom-made microscope that shines a light onto the sample and measures the intensity of the light that bounces back."

That's how eyes work as well. Well, they need a light source to help, but otherwise ...

Not always how a microscope works though.

This article has a nice little comparison of a few different methods, not all of which measure (only) reflection https://en.wikipedia.org/wiki/Dark-field_microscopy

There’s also a whole world of microscopy where emissions from the sample itself are measured, often because parts of it have been tagged with fluorescent probes.

You can even see it sometimes, bubble stuck, draining around it slowly. Really no surprise to me...

TL;DR:

"Some calculations suggested that the bubble is surrounded by an extremely thin layer of liquid touching the sides of the tube, which slowly diminishes in size and eventually disappears, Kolinski said. That thin layer would create resistance to the motion of the bubble as it tries to rise."

But actually they disproved this belief:

'The researchers indeed observed this very thin layer around the gas bubble and measured it to be about 1 nanometer thick. That's what quenches the movement of the bubble as theoretical work had predicted. But they also found that the liquid layer (which forms because the pressure in the gas bubble pushes against the walls of the tube) doesn't disappear, but rather stays at a constant thickness at all times.

Based on their measurements of the thin layer of fluid, they were also able to calculate its velocity. They found that the gas bubble isn't stuck at all but is rather moving "extraordinarily slowly," at a pace invisible to the naked eye'

There is also evaporation occurring on the top surface of the gas bubble, and condensation happening on the bottom.

Since there is a small pressure differential, there will be a net upwards movement.

It's a small effect, but it might dominate.

bubble stuck

please send help

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