Will sealed water boil when heated?
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There is a container filled with half water, which is then sealed, assuming the container will not explode. So, with continuous external heat input, will the water in the container boil? I don’t think it will boil. Because the liquid surface can never reach the saturated vapor pressure (as there is no way for air to escape), if boiling occurs, the vapor pressure rises immediately, and boiling stops again. For example, if a sealed container is evacuated to a certain degree, the water inside will start to boil; however, continuous evacuation is necessary to maintain this boiling state. Just like the principle of a boiler, it is necessary to continuously release steam. Take popcorn for example; it doesn’t explode until the container is sealed, and it is only when pressure is released that the water inside the corn vaporizes and causes it to explode. And some people use pressure cookers to pop corn, as the pressure cooker remains connected to the outside world, which prevents the pressure from rising indefinitely; continued heating then allows…
Am I right? When searching on Baidu, everyone assumes that it will boil. Because heat is continuously supplied, eventually all the water turns into steam. Won’t this heat keep the water from rising in temperature? But at the critical point, namely 374°C, does it necessarily vaporize?
As long as the temperature reaches the boiling point of water, vaporization occurs. In a sealed container, the pressure increases, and thus the boiling point rises as well. If heating continues, the water temperature keeps rising. This is the principle behind pressure cookers; if there is no boiling, how can the pressure increase?
Can’t it be the high pressure resulting from evaporation? Must it be boiling inside a pressure cooker before the safety valve opens? Additionally, once the pressure cooker is opened, the pressure inside should be higher than one atmosphere; the boiling point remains unchanged. Shouldn’t the cooking time be the same whether using low heat or high heat?
This post was last edited by zjq1962 on 2018-12-16 at 16:23. Since heating takes place in a sealed container, the temperature keeps rising until vapor equilibrium is reached. If it is open, it can only reach the standard boiling point.
The following content is from Baidu: When pressure is applied to water in a sealed container, its boiling point increases. When the pressure reaches 220 atmospheres and the temperature reaches 374°C, the density of water expanded by the high temperature is exactly the same as the density of water vapor compressed by the high pressure. At this point, there is no distinction between the liquid and gas forms of water; they merge completely to form a new type of gas in a state of high pressure and high temperature. At this point, the water changes from its normal state to \"supercritical water\". The pressure and temperature at which water vapor and liquid water merge are known as the \"critical point\". Water that is above the “critical point” state is supercritical water.
The boiling point of the pressure cooker’s safety valve should be higher than 100°C, as there is still a lot of steam inside that needs to be released after the stove is turned off
Continuously heating the water will cause it to evaporate, until all the water turns into steam. But will boiling occur in a sealed environment? For example, in a boiler, if there were no steam outlet, would it still boil?
If no steam is produced, then how does the pressure increase?
Evaporation can occur at any temperature; it happens even without heating the water.