Steam is also called “water vapor”. According to the pressure and temperature, all kinds of steam are classified as saturated steam and superheated steam. The main uses of steam are heating / humidification; It can also generate power; As a machine drive or the like.
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The main uses of steam are: heating / humidification; Generating power; As a drive.
Steam for heating or humidification
【Steam use】1. Positive pressure steam
Positive pressure steam refers to the steam with a pressure of 0.1-5 MPa and a temperature of 110-250 ℃. This is the most representative use of steam in industry. It is widely used in heat exchangers and steam boxes for heating and humidification.
In most cases, the steam used is saturated, that is, saturated steam. Because the corresponding relationship between pressure and temperature is fixed, the latent heat of steam can be used for rapid heating. In the food processing industry, superheated steam is sometimes used for cooking, drying and dehydration. Superheated steam is very easy to control after being heated to 200-800 ℃ under normal pressure, so it is used in today’s domestic steam oven market.
2. Negative pressure steam
Negative pressure steam refers to steam with pressure less than atmospheric pressure and temperature less than 100 ℃. The application of this kind of steam has developed rapidly.
When the negative pressure saturated steam is used like the positive pressure steam, the temperature of the steam can be quickly changed by adjusting the air pressure, which makes it possible to accurately control the temperature, while the hot water cannot. However, the negative pressure steam equipment must be equipped with a vacuum pump, because only lowering the air pressure will not make it lower than the atmospheric pressure.
Steam for power or drive
Steam can also be used to do work (for example, as power) and for steam turbines. An example that most people are familiar with is the steam locomotive and steam train [3] many years ago, and the application of steam as driving power is quite rare. However, the technology of using steam as driving power is still developing and improving.
Steam turbine is an indispensable equipment for thermal power plant. In order to improve efficiency, the technology of using high temperature and high pressure steam has been developed. Some thermal power plants use supercritical pressure steam of 25 MPa (ABS) and 610 ℃ in their turbines. In order to prevent turbine equipment from being damaged by condensed water, saturated steam should be avoided, so superheated steam is used in most cases. On the contrary, it is forbidden to use high-temperature steam in the field of nuclear power plants, because it can cause problems in the materials of turbine equipment, so high-pressure saturated steam is often used.
In the age of steam trains, passengers were amazed at the larger and more powerful engines. With the development of the times and the progress of technology, scientists are still developing steam engines. However, modern steam engines are not the bigger the better, but the more microscopic the better. German scientists have recently developed a micro steam engine. By measurement, it is only three thousandths of a millimeter.
Steam for cooling
Water vapor is the gas phase substance with the largest heat capacity among gas substances. It has a wide range of applications in cooling high-temperature objects, such as medium speed cooling of metal materials during quenching, and cooling of metal surfaces and tools during metal material processing. It has the advantages of visibility, prolonging tool life, reducing oxidation and reducing chemical emissions. It is an ideal material for cooling in metal cutting process.
In the process of metal stretching, it also has the advantages of lubrication, reduction of metal surface oxidation, and rapid cooling.
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