THINGS AROUND US
6. Tiny bubbles while heating water...The bubble's been engineered to allow us to learn from within it. -Alexandra Adornetto
Bubbles are so fascinating, even the universe can be explained using a bubble. It contains so much scientific beauty in it. Bubbles can be produced in many ways naturally and manually, sometimes it is created when we don't notice or when we don't notice them. One such everyday scenario is while boiling water. Tiny bubbles are formed when the water just starts to heat and then it becomes big and vigorous while the water starts to boil. As bubbles have many sciences to observe in this we are going to observe only the cause of the tiny bubbles while heating water.
There are many things that we can learn from water. This is one of the interesting concepts to encounter. How does water boil? Is a good question to investigate in the sense of basic science and industrial applications. Now we are only concerned about the bubbles.
Take some water in a pan. As the water warms, air molecules are driven out of solution in the water (in basic sense water is a solution containing dissolved minerals and gases), collecting as tiny bubbles in crevices or the microscopic cracks along the bottom of the pan and the curved surface of the pan. The air bubbles gradually inflate (becomes big), and then they begin to pinch off from the crevices and rise to the top surface of the water. As they leave, more air bubbles form in the crevices and pinch off i.e., they come up towards the surface, until the supply of air in the water is depleted. The formation of air bubbles is a sign that the water is heating but has nothing to do with boiling, this is an important aspect to understand in this article.
Are microscopic cracks real?
Yes, these are real. Even the smoothest surface will have these irregularities. Here is an image from a scientific article that shows it.
These are mainly due to the corrosion of the surface by continuous use and manufacturing defect which can not avoid.
Why these tiny bubbles are formed?
Water that is directly exposed to the atmosphere boils at what is sometimes called its normal boiling temperature say 100° celsius when the air pressure is 1 atmosphere which is a normal condition. The water at the bottom of the pan is not directly exposed to the atmosphere so it remains liquid even when it superheats above 100°C by as much as a few degrees. During this process, the water is constantly mixed by convection as hot water rises and cooler water descends sometimes we can see this as a shadow moving inside the pan. As the temperature of the pan increaces, the bottom layer of water begins to vaporize(converts to gas), with water molecules gathering in small vapor bubbles in the crevices. This phase of boiling is signaled by pops, pings, and eventually buzzing. Every time a vapor bubble expands upward into slightly cooler water, the bubble suddenly collapses because the vapor within it condenses. Each collapse sends out a sound wave (Not always seen but happens at a small level), the ping you hear. Once the temperature of the bulk water increases, the bubbles may not collapse until after they pinch off from the crevices and ascend part of the way to the top surface of the water.
The bubble grows, pinches off, and then ascends through the water
If the temperature of the pan is still increased, the babel of collapsing bubbles first grows louder and then disappears. The noise begins to soften when the bulk liquid is sufficiently hot that the vapor bubbles reach the top surface of the water. There they pop open with a light splash. The water is now in full boil. Once the pan and bulk of water reach the boiling temperature, the vapor bubbles next become so abundant and pinch off from their crevices so frequently that they coalesce or merge, forming columns of vapor that violently and chaotically agitate (Churn) upward, sometimes meeting previously detached ‘‘slugs’’ of vapor.
The production of vapor bubbles and columns is called nucleate boiling because the formation and growth of the bubbles depend on crevices serving as nucleating sites (or sites of formation). https://en.wikipedia.org/wiki/Nucleate_boiling
