Boiling coffee scalded with freshly boiled coffee in the microwave

Zhuzhou News (Zhuzhou Evening News reporter Dai Ping) A netizen became addicted to coffee and did not bother to boil water. He directly put cold water into the microwave oven to heat it. After heating for a few minutes, I took out and poured into the coffee, and something unexpected happened: the plain boiled water of the coffee was bubbling and boiling violently, and the spilled boiling water scalded the netizen.

A colleague of the reporter also made coffee in the same way. She said that sometimes she was alone at home and didn't bother to boil water in a kettle. If she wanted to make a cup of coffee, she just put it in the microwave oven. "but I've never encountered a splash of boiling water." She said.

What will happen if you boil water in the microwave? The reporter conducted an experiment.

The water boiled in the microwave is mixed with the coffee and the water bubbles out.

Photo taken by reporter Zhang Yuan

The heated water taken out of the microwave oven stirred with a spoon and began to bubble.

Photo taken by reporter Zhang Yuan

Experimental equipment: glass, water, microwave oven, spoon, coffee

Location of the experiment: office on the sixth floor of the Evening News

Experiment 1:

The reporter picked up a glass of cold water in the water cooler and heated it in the microwave oven for three and a half minutes.

In the process of heating, the reporter observed through the translucent front door of the microwave oven and found that the water in the cup was relatively calm.

When the heating time was up, the reporter took the glass out of the microwave oven with gloves and poured the prepared coffee into the cup. The coffee had just been put into the boiling water and there was little reaction.

About 2 seconds later, the boiled water mixed with coffee bubbled out like a shaken Coke. Because the reporter was prepared in advance, it was relatively far away, and there was not much pure water, so it was not scalded.

Experiment 2:

The reporter also picked up a glass of cold water in the drinking fountain and heated it in the microwave oven for three and a half minutes.

When the heating time was up, the reporter took the glass out of the microwave oven and put it on the ground, then took a spoon and stirred it several times. At this time, the boiled water in the cup suddenly bubbled and boiled.

Experiment 3:

The reporter also picked up a glass of cold water in the drinking fountain and heated it in the microwave oven for three and a half minutes.

When the heating time was up, the reporter was not in a hurry to take out the glass, but left it in the microwave oven for a minute, then took it out and put it on the ground. Wait for the reporter to pour the coffee into the boiling water, the water surface is calm, there is no boiling phenomenon.

That's boiling water.

The results of the three groups of experiments are different. The reporter consulted Huang Leyang, a senior physics teacher at the Zhuzhou affiliated School of Beijing normal University.

Teacher Huang said that the reporter's experiment 1 and experiment 2 actually had a "sudden boiling" phenomenon. Microwave heating is used to drive water molecules to vibrate, which is a forced vibration, and the violent vibration of the molecules (2.45 billion vibrations per second) leads to a sudden rise in the temperature of the body.

The microwave oven heats water from all directions, which is different from convective heat transfer-we usually boil water in a kettle, the water below is heated first, and the temperature of the water above is relatively low, and there is a process of convection between the two. Therefore, using microwave to heat hot water, even if it reaches the boiling point, the tumbling phenomenon of convection is not seen, and it is still in a calm state. When we add something to the water, this balance is broken (the vibration of 2.45 billion times per second does not stop suddenly, and the vibration law is broken after encountering spoons, coffee, etc.), the water is likely to "boil" and the heat explodes in an instant. The liquid jumps up.

When brewing coffee, the acid and a little lime in the coffee will decompose carbon dioxide and heat when it comes to boiling water at 100 degrees Celsius. In this way, the effect of sudden boiling of water is more obvious.

And put the boiling water in the microwave oven for a period of time, the water temperature drops, the movement of molecules inside the liquid slows down, and then put something inside, the "sudden boiling" situation will not occur.

China Coffee Trading Network: www.gafei.com