Although the environmental temperature suitable for human existence has a certain range, too high or too low temperature will affect the quality of human life. Nowadays, people can use appliances such as air conditioners to enjoy a cool indoor environment in the hot summer.
The ancients dug an ice cellar to save ice
Before the advent of air conditioners and refrigerators, it was very difficult for people to drink iced drinks and eat cold products in the summer. Especially for the ancients who lived near the tropics, it became a luxury to get ice cubes in summer.
The wisdom of the ancients cannot be ignored. People have discovered long ago that the temperature in the deeper underground is lower. The low temperature environment can keep the ice cubes intact, so some people excavate ice cellars to preserve the ice cubes.
In winter, a large number of ice cubes are stored in the ice cellar, and some ice cubes can be left in the summer. However, this method of preserving ice cubes is more capable of high-ranking officials. It is difficult for ordinary people to enjoy the conditions for obtaining ice cubes in summer. However, the working people have summed up a lot of experience in long-term practice, and the ancients have indeed discovered a way to make ice in summer.
Is the method of making ice with hot water feasible?
2000 years ago, the Western Han Dynasty book " Huainanzi" recorded a method of ice making. The sink (well) becomes ice on the third day.” Put boiling water in an urn, seal it with cloth, and sink it into the well. In three days, ice cubes can be made.
Hot water ice making sounds incredible. Although the temperature of the well water in is very low, it has not reached the freezing point. Using hot water to cool down is indeed faster than using cold water, but it is obviously contrary to common sense to achieve a temperature lower than the surrounding environment.
For the ice making method described in "Huainanzi",Many people are skeptical. However, some scholars think that it may contain certain physical principles, but it is not easy to show them under normal circumstances. The air pressure at the bottom of the well is lower. In a low-pressure environment, the freezing point of water will rise. Does this mean that hot water can be used to make ice? There are many modern refrigeration methods, and the refrigeration of appliances such as refrigerators and air conditioners is generally based on the "scorching soup effect."
That is, the gas undergoes adiabatic expansion, and the temperature will decrease. If this effect can be continued, the temperature can be continuously reduced and the air can be liquefied. However, this process requires additional power supply. Obviously, the urn in the well water has only one adiabatic expansion process, and it is difficult to reduce the hot water in the urn to the freezing point. Someone tried to reproduce this method of making ice with hot water, and found that the temperature drop was indeed significant at the beginning.
However, as the temperature difference between the water in the container and the surrounding environment becomes smaller and smaller, the temperature drops more slowly, and finally reaches the equilibrium of heat exchange , the water in the container still does not freeze. Some people may think that the ancients drilled deep wells, and the temperature of the well water could reach near freezing point.
Hot water ice making is also feasible
But under the ancient conditions, it is very difficult to drill a deep well of several hundred meters, so the temperature of the well water will not be much lower than the temperature in the air. This has to make people wonder whether the ancients really made ice cubes.
Some people think that the literati who compiled this book did not personally verify the feasibility of the method, but just heard about this method of making ice with hot water and wrote it into the book. The specific operation is not explained clearly. Although the ancients used hot water to make ice with a small possibility of success, in addition to this method, the ancients can also use saltpeter to make ice.
Saltpeter will absorb heat after it is dissolved. Perhaps a large amount of saltpeter is mixed in the urn of boiling water to make ice, so it is not impossible for the hot water in the urn to drop to the freezing point. As for how the ancients did it, there is no way to verify it.
Only judging from the retained data, it is difficult to restore the actual operation process of the ancients. However, it is impossible to violate the basic physical principles. The method of making ice by the ancients will not violate the physical principles that have been discovered.
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