是指物质由气态转变成液态的过程。任何气体在温度降到足够低时都可以液化；在一定温度下，压缩气体的体积也可以使某些气体液化。降低温度的方法是万能的，降到足够低时都可以液化。但压缩体积时，如果气体温度高于其临界温度，则无法压缩使其液化。

It refers to the process that substances change from gaseous state to liquid state. Any gas can be liquefied when the temperature drops sufficiently low; At a certain temperature, the volume of compressed gas can also make some gases liquefied. The method of lowering the temperature is universal. When it is low enough, it can be liquefied. However, when compressing the volume, if the gas temperature is higher than its critical temperature, it cannot be compressed to make it liquefied.

是指物质由气态转变成液态的过程。

It refers to the process that substances change from gaseous state to liquid state.

液化会对外界放热，反之，汽化是吸热过程。实现液化有两种手段，一是降低温度，二是压缩体积。临界温度是气体能液化的最高温度。由于通常气体液化后体积会变成原来的几千分之一，便于贮藏和运输，所以现实中通常对一些气体（如氨气、天然气）进行液化处理，由于这两种气体临界点较高，所以在常温下加压就可以变成液体，而另外一些气体如氢、氮的临界点很低，在加压的同时必须进行深度冷却，就叫液化。

Liquefaction will release heat to the outside, whereas vaporization is an endothermic process. There are two ways to realize liquefaction, one is to reduce the temperature, and the other is to compress the volume. The critical temperature is the maximum temperature at which a gas can be liquefied. Due to the fact that the volume of liquefied gas will become one thousandth of the original volume, which is convenient for storage and transportation, in reality, some gases (such as ammonia and natural gas) are usually liquefied. Because of the high critical points of these two gases, they can be turned into liquid under pressure at normal temperature, while other gases such as hydrogen and nitrogen have very low critical points, and must be cooled deeply while pressurized, which is called liquefaction.

任何气体在温度降到足够低时都可以液化；在一定温度下，压缩气体的体积也可以使某些气体液化。降低温度的方法是万能的，降到足够低时都可以液化。但压缩体积时，如果气体温度高于其临界温度，则无法压缩使其液化。

Any gas can be liquefied when the temperature drops sufficiently low; At a certain temperature, the volume of compressed gas can also make some gases liquefied. The method of lowering the temperature is universal. When it is low enough, it can be liquefied. However, when compressing the volume, if the gas temperature is higher than its critical temperature, it cannot be compressed to make it liquefied.