Eli5: when the water is in a state of rolling boil, why do the bubbles appear to ascend from particular pinholes in the bottom.

Question

These said pinholes change from each boiling session.

In: 139

Answer 1

When you boil water, the bottom of your pot isn’t perfectly flat! sometimes it has little bumps, holes, and slightly different metal content. These spots tend to get hotter and make it easier for water vapour bubbles to form – that’s why you see them at the same spots every time! As time goes on, those spots will eventually become pitted as the boiling of the water at the same places as well as concentrated steam heat (hotter than 100C!) accelerates rusting at those points.