We often don’t think too much about the slowly rising bubbles in our favourite cola or soda. The pleasing sensation that these bubbles give on our tongues is why we gulp more soda down our throats after a pizza. The only other possible thing we want to do with these bubbles is the Mentos experiment. Replicated by millions around the world, the rising bubbles make for some cool volcano eruptions, orchestrated fountain performances and high-speed rockets from just bottles of cola/soda and a pack of Mentos. These bubbles represent the energy stored within the innocent bottle.
A popping bubble releases energy. This proves to be quite useful in many processes.
The process of bubble formation is known as cavitation. When subjected to rapid changes of pressure, cavities/voids (a.k.a. bubbles) are formed in a fluid. The pressure is relatively low in these cavities. When exposed to a higher pressure from the surrounding fluid, these voids implode or collapse. This sends out pressure waves.
The destructive power of bubbles can be observed easily. Coastal erosion has been generally accepted to be due to cavitation. Bubbles also are the main cause for the damaged boat propellers, engines, pumps and valves.
But that doesn’t mean bubbles are a bane. Pistol and mantis shrimp are known to use cavitation to kill their prey. There exists even a hypothesis that cavitation is responsible for the formation of diamonds. We use the same concept to break kidney stones in lithotripsy; water purification; and several industrial cleaning processes (such as cleaning jewellery).
Earlier this year, a team from Virginia Tech published new findings on how cavitation affects nearby particles with a size similar to that of the bubbles. High-speed video cameras unveiled two important observations – 1) Once a bubble pops, the particle moves towards the popped bubble; and 2) when a bigger bubble pops, several microbubbles appear and these clobber the approaching particle.
As smaller particles are attracted faster towards a popping bubble, the research team visualizes the use of bubbles to eventually clean the surfaces of agricultural produce. Dirt and microbes could be cleaned using this bubble technology.
Bubbles are not just bubbles anymore!