I'm watching water with air bubbles flow through transparent plastic tubing. The inner diameter is a few mm. Bubbles typically are the same diameter as the tubing, with length about the same or up to several cm long. I am not sure what kind of plastic the hose is made of, but it's quite flexible. The general water flow rate varies but, guessing by eye, is in the range of about 1cm/sec to 10cm/sec.
Often the bubbles will stick in one place, or break apart with one portion staying stuck. The next bubble along may dislodge, but then it may stay stuck at the same place. I assume there's some sort of contamination or electrostatic charges to explain this. What exactly is the physics of this? What relations are there between the type of plastic (or other material), properties of the fluid, temperature, flow rate and so on?
If the physics is understood well enough, is there a way to simulate this phenomenon numerically, as CFD or something? Does simulation software exist?
Best Answer
This is an example of nucleation; the phase transition is triggered by a (relatively) rough point on the fluid boundary, due to disruption of surface tension. In a system with smooth fluid boundaries, phase changes can be delayed due to the lack of nucleation sites.