What is the magical “chimney effect”, in which a cylinder can raise a flame?

2022-07-23 0 By

When a tall building caught fire, the fire went from the second floor to the 17th floor in two minutes. Why did the fire move so fast?On the evening of March 14, 2019, a fire broke out in a high-rise residential building in Yuanhong Jinjiang Residential area, Binhe Road, Yuwangtai District, Kaifeng city, Henan Province. The fire may have been caused by electric vehicle charging in the corridor, and it burned to the roof in a few minutes.It was a very rapid spread of fire up the outer wall of the building, along some sort of pipe structure, and it was a very dramatic fire, and it was not an isolated incident, it’s a very common occurrence in a high-rise building.Why does a tall building fire spread so fast?In fact, this phenomenon is called the “chimney effect”, the chimney effect refers to the indoor air along the vertical slope of the space to rise or fall, resulting in the phenomenon of increased convection of air, it is one of the reasons that aggravate high-rise building fires.Inside the high-rise building, there are a large number of pipes, shafts, stairwells, exhaust channels and other horizontal and vertical channels, from the ground to the highest point.In the event of a fire, these areas become a ventilated “chimney”, accelerating the spread of the fire, and the more pipes there are, the faster the fire spreads, so the higher the building, the greater the “chimney effect”.How does the “chimney effect” work?The hot air from the low-rise fire flows up through the shaft, causing hot gas to accumulate at the top of the passageway, which leads to the fire accumulation at the top of the building, causing survivors to escape to the roof of the fire threat.According to the test data, a 100-meter high building (about 30 stories) without obstruction, it only takes 30 seconds for the smoke to spread down the vertical tube well to the top floor, and instantly the whole building can form a “three-dimensional fire field”.It can be said that once a high-rise building is on fire, evacuation and rescue are difficult, often difficult to control, the consequences are very serious.Are there any advantages to the chimney effect?Of course there is.The chimney effect can also be used to generate electricity.For example, Australia’s 1,000-meter “solar tower” project will have a capacity of 200 megawatts, enough to power 200,000 homes.Once in operation, it could reduce the production of greenhouse gas CO2 by at least 900,000 tons per year.The principle of the “solar tower” project is that the sun heats the air in the disc-shaped collector at the bottom of the “solar tower”. Due to the “chimney effect”, the air in the heat collecting area is heated by the solar radiation and then flows to the bottom of the tower, concentrating in the tower and forming a strong upward flow of air.The thermals continue their ascent up the solar tower’s “chimney”, powering a specially designed set of 32 turbines with a capacity of 6.25MW each.The air temperature at the bottom entrance of the tower is 70℃, the air flow rate is 15m/s, and the air outlet temperature at the top is 20℃. At night, the heat energy accumulated in the heat storage unit during the day is released to continue to drive the turbine, so the “solar tower” can work 24 hours a day, 365 days a year.I have to say, every coin has two sides, it depends on how people deal with it.