Guide: 什么是蒸汽？亦称“水蒸气”。根据压力和温度对各种蒸汽的分类为：饱和蒸汽，过热蒸汽。

What is steam?

　　Also known as "water vapor". According to the pressure and temperature, the classification of various steams is: saturated steam, superheated steam.

What is saturated steam?

　　When the liquid evaporates in a limited enclosed space, the liquid molecules enter the upper space through the liquid surface and become vapor molecules. Because the vapor molecules are in turbulent thermal motion, they collide with each other and collide with the container wall and the liquid surface. When they collide with the liquid surface, some molecules are attracted by the liquid molecules and return to the liquid to become liquid molecules. .

　　"When evaporation begins, the number of molecules entering the space is more than the number of molecules in the returning liquid. As the evaporation continues, the density of space vapor molecules increases, so the number of molecules returning to the liquid also increases. When the number of molecules entering the space per unit time is equal to the number of molecules in the returning liquid, evaporation and condensation are in a dynamic equilibrium state. At this time, although evaporation and condensation are still going on, the density of vapor molecules in the space no longer increases. The state at this time is called the saturated state.

　　"The liquid in the saturated state is called saturated liquid, and its steam is called dry saturated steam (also called saturated steam).

What is superheated steam?

　　If the saturated steam is heated continuously, its temperature will rise and exceed the saturation temperature under this pressure. This kind of steam above the saturation temperature is called superheated steam. The superheated steam has its own application fields, such as the turbine used in the generator set, which passes through the nozzle to the motor, and drives the motor to rotate.

　　However, superheated steam is rarely used in the heat transfer process of industrial processes. This is because the superheated steam must be cooled to the saturation temperature before it is condensed to release the enthalpy of evaporation. Obviously, compared with the enthalpy of evaporation of saturated steam, the superheated steam is cooled to the saturation temperature. The heat released is very small, which will reduce the performance of the process equipment.

What is the use of steam?

The main uses of steam are: heating/humidifying; generating power; as a drive.

　　Steam is widely used as one of the heating media in industrial production. The reason why we choose steam as the heating medium is that saturated steam has a series of advantages such as high heat per unit mass, fast heat transfer, pressure and temperature correspondence, and easy control.

Advantages of industrial saturated steam heating:

　　①Intrinsically safe

　　②Steam contains a lot of latent heat of vaporization

　　③ Both heat and mass transfer

　　④The temperature is constant during the exothermic process

　　⑤High heat transfer coefficient

　　⑥One-to-one correspondence between pressure and temperature, easy to control

Among the advantages of saturated steam, what we care most about is the high heat and fast heat transfer rate. These two advantages can significantly improve our production efficiency.