It's a common phenomenon in life that the water doesn't boil and the boiling water doesn't ring. Many mothers realize this Law and don't know the reason. Let me answer it for you. Let's have a look!
One convection
There are two kinds of changes in the process of water being heated: 1. The temperature of the lower layer of water rises, the density decreases, it will float upward, and the temperature of the upper layer will sink when the temperature is low. Therefore, with the extension of heating time, the temperature of the upper layer will be higher than that of the lower (not the lowest layer), and the water temperature in the middle is the lowest. This phenomenon is called convection [1]; 2 the solubility of air decreases with the increase of water temperature, and bubbles will overflow from the bottom layer and rise to the water surface with the convection of water. The water convection mode is a cycle of rising in the middle and falling on both sides. In the process of rising, the bubble is a process from the lower layer (low temperature) to the upper layer (high temperature). The internal pressure of the bubble expands and breaks due to the increase of temperature. Therefore, before the water is boiled, the bubble breaks before reaching the surface, causing the oscillation and sound of the water surface. The higher the temperature of the upper layer, the more and faster the bubble breaks, So the sound is getting louder and louder from the bubble overflow to the process before the water boils.
Secondary boiling
When the water boils, the water temperature is basically uniform and the internal pressure of bubbles is basically stable. They will not break in the water and can reach the surface. However, not all bubbles can reach, or some bubbles break in the water. Therefore, it is an illusion that the boiling water will not sound, and the boiling water will also sound, but there is not so much sound.
Three phenomena
In order to better understand this statement, give a few small questions to help explain. 1. When boiling water, you will find that the temperature is very high by touching the surface before it is opened, but if you stir it, the water temperature will drop, indicating that the water temperature below is low. 2. For the boiler boiling water, the hot water port is opened in the middle and upper part rather than directly in the lower port, because the water discharged from the lower port is basically not hot. 3 We can also see that the bubbles come out from both sides of the teapot first, and then from the middle, because the temperature difference in the middle is large, and the bubbles have burst before coming out. The temperature difference around is small, and some bubbles can come out.