Principle of steam liquefaction

Principle of water vapor liquefaction: the process of changing a substance from a gaseous state to a liquid state. Liquefaction is the reverse process of vaporization. Gas molecules attract each other and condense into liquid. This substance gives off heat after liquefaction. Gases below the critical temperature can be liquefied. Liquefaction can be achieved by pressurizing or cooling, or by pressurizing and cooling together.

Gases with critical temperature higher than or close to room temperature, such as ether, chlorine, ammonia, sulfur dioxide, carbon dioxide and some hydrocarbons, can be compressed and liquefied at room temperature. Gases with very low critical temperature, such as oxygen, nitrogen, hydrogen and helium, must be cooled below the critical temperature before liquefaction by isothermal compression.

Because the volume of liquefied gas is usually one thousandth of the original volume, which is convenient for storage and transportation, some gases (such as ammonia and natural gas) are usually liquefied. Because the critical points of these two gases are very high, the pressure can be converted into liquid at room temperature, while the critical points of other gases such as hydrogen and nitrogen are very low, and they must be pressurized while cryogenic, which is called liquefaction.

Extended data:

There are two ways to liquefy: lowering the temperature (all gases are at all temperatures) and compressing the volume (some gases are at a certain temperature).

When the temperature is low enough, any gas can be liquefied; At a certain temperature, the volume of compressed gas can also liquefy part of the gas (or both). The method of cooling is omnipotent. When it is low enough, it will liquefy. But when the volume is compressed, if the gas temperature is higher than its critical temperature, it cannot be compressed and liquefied.

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