Boiler drum
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"To prevent a vacuum from forming inside the drum due to a temperature drop of 100°C, aeration is provided in the drum. This sentence comes from the documentation; why does a vacuum form inside when the temperature drops by 100 degrees?
Below 100 degrees, steam condenses, its volume decreases, creating a vacuum
At atmospheric pressure, the saturated steam is at a temperature below 100°C; it condenses into water. As the amount of steam decreases, the pressure in the vapor space drops gradually, eventually resulting in a vacuum
In power plants, this issue of installing vacuum valves on the drum does not arise; cooling at room temperature takes a long time, and the pressure remains above atmospheric pressure throughout, with steam partial pressure always present. For a simple large-diameter, thin-walled low-pressure steam pipe, this approach can be considered to avoid an increase in wall thickness or the need for reinforcing ribs.