Discovery and application of siphon principle
Siphon is an ancient invention of mankind. As early as BC 1 century, a strange siphon was created. In fact, siphon phenomenon is not entirely caused by atmospheric pressure, and siphon phenomenon can also occur in vacuum. The force that makes a liquid rise is the cohesion of molecules between liquids. When siphon happens, because there is more liquid flowing out of the pipeline than into the pipeline, the gravity on both sides is unbalanced. So the liquid will continue to flow in one direction. When the liquid flows into the pipeline, the pressure will decrease as it rises. If the pipeline where the liquid rises is very high, the pressure will decrease and bubbles (composed of air or other gases) will be generated in the pipeline. The working height of the siphon is determined by the formation of bubbles. Because the bubble will break the liquid, the force between gas molecules at both ends of the bubble will be reduced to zero, thus destroying the siphon effect, so the pipeline must be filled with water. At normal atmospheric pressure, the siphon must be filled with water.
Imagine that the solar collector is filled with cold water. When the solar collector absorbs solar energy, the water inside expands when heated, and the density becomes smaller, so it rises to the heat exchanger above. Dense cold water flows back to the bottom of the collector and continues to expand and rise after absorbing heat energy.
The thermal cycling movement is called thermosiphon effect. The greater the temperature difference between the heat collector and the heat exchanger, the faster the water circulates between them.
People in China have long known how to apply the siphon principle. In ancient China, siphons made according to siphonage principle were called "shooting", "leaning", "thirsty for black" or "crossing mountains and leaping dragons". At the end of the Eastern Han Dynasty, thirsty Wu appeared irrigation. It is also a physical phenomenon that ethnic minorities in southwest China drink with a long bamboo tube with a curved joint. In the Song Dynasty, Ceng Gongliang recorded in Wu Jing Zong Yao that a siphon made of bamboo tube led the spring water blocked by the mountain down. In ancient China, the siphon principle was also used to make water pumps. The water pump is a necessary fire extinguisher for guarding the city in wartime. In the fourth volume of Zhi Lin on Dongpo written by Su Shi in Song Dynasty, a salt well in Sichuan pumped salt water underground with a water pump. His book contains: bamboo is the tube, "I am obsessed with it because it is bottomless, hanging ripe skin for several inches, going in and out of water, breathing and opening and closing, and one tube leads to several barrels of water." "The tree planting book of the Ming Dynasty also talked about the method of pumping and watering saplings, and the siphon principle was also discussed in ancient China. The book "The Essentials of Guanyinzi Liquor", which was written in the Northern and Southern Dynasties, said: "There are two orifices in the bottle, which are filled with water and diarrhea; When the water is closed, it will not fall, and the cover (gas) will not rise. Although the well is thousands of miles away, it is on the water; If the cover (gas) does not fall, (water) will not rise. "A bottle with two holes can pour out water. If one hole is closed, the air pressure outside the other hole will be greater than the water pressure in the bottle, and water will not flow out. In Bing Wang's notes on Su Wen in Tang Dynasty, the physical phenomenon of atmospheric pressure was clearly described. Bing Wang said: "When the empty pipe is full, it will be suspended, and the water will not sink, so it can't come down, because there is no gas rising; An empty bottle with a small mouth can't be poured in, because the gas can't go out and neither can you. "It has been pointed out that an empty bottle with a small mouth can't hold water because the gas in the bottle can't get out. In Song Dynasty, Yu Yan supplemented the previous findings in Tan Tan on the Seats, saying, "When I was young, a Taoist saw me, burned a piece of paper, and put it in an empty bottle, covered with a silver basin of water. Water poured into the bottle, and the silver bottle clanged and covered with anger. It is also placed on the strong man's stomach according to law and will not fall off. "When burning paper in an empty bottle, part of the air in the bottle is driven out of the bottle by fire. After the fire is extinguished, a negative pressure is formed in the bottle, resulting in a certain vacuum. The air pressure outside the bottle presses the bottle tightly against the human abdomen. If you put the bottle in water, the water will immediately pour into the bottle. Zhuang in the Ming Dynasty also pointed out that when the gourd spoon was poured into the water, the water did not enter the gourd because there was air in the gourd.
Principle summary: Because the pressure difference is at work. When the pressure of the same level on both sides of the elbow is different, the water (or other liquid) in the pipeline will flow to the side with less pressure.
Three conditions must be met when using siphon principle:
1. Fill the pipe with liquid first.
2. The water level of the upper container from the highest point of the pipeline shall not be higher than the water column supported by atmospheric pressure.
3. The water outlet must be lower than the water surface of the upper container. In this way, the downward pressure of the effluent liquid sheet (the pressure of adding water at atmospheric pressure) is greater than the upward atmospheric pressure. Ensure the outflow of water.