Basic Concept | Thought Experiments | Real Experiments | Outstanding Issues | References/Links  


Lots of little bubbles vs. a few big ones.

In open water it's clear that a rising bubble pushes most of the water out of its path and leaves it behind. Just as in the Balloon thought experiment, if there was no tube, each balloon would move almost no water to the surface, but if it fit tight in the tube, it would move the entire contents of the tube from bottom to top.

Say we have a tube that will hold 100 gallons of water.

Now imagine 10 gallons of that capacity is gas, and the other 90 is water.

IFF all the gas entered the pipe from the bottom in an even distribution of same sized bubbles.

THEN the steady state of the system will have a linear increase in volume from bottom to top due to gas expansion under decreased pressure.

Larger bubbles are more buoyant than small bubbles so they rise faster. (Known)

Larger bubbles push more water. (Assumption challenged)

In any given cross section of the pipe, air bubbles will represent a certain AREA.

The relationship between cross section and Area is geometric in nature.

A large number of small bubbles represents the same crosectional area as a few large ones.

Surface area expands geometrically with increased numbers as well.

  • 2 three-inch bubbles has a surface area of 56sq/in and a volume of 28 in^3
  • 53,000 X 0.1-inch bubbles has a surface area of 1,680 in^3 with the same volume.

Surface area will determine how much disolves back into the water. (this begs for decreased surface are [bigger bubble].

Surface area is where the gas influences the water as "drag" (this begs for increased surface area [smaller bubbles]

Send your thoughts to