The reason why steam or water is widely used as a heat carrier for heating equipment is because of their very good physical and chemical properties and their economy.

Physical properties of steam:

(1) Liquid at room temperature (water is easy to turn into gas (steam) when heated)

(2) The specific heat capacity is large, and the heat of evaporation (latent heat) is also large.

(3) The heat transfer characteristics are good, and the volume after condensation (after the transformation of steam into condensate) is significantly reduced.

(4) As the pressure increases, the temperature also increases.

Chemical properties of steam:

(1) Non-corrosive and harmless to the human body.

(2) The chemical properties are stable and there is no danger of fire.

Other properties of steam:

After the heat energy of the steam is converted into power, the discharged steam can still be used as a heating source; The steam can be used in multiple cascades from relatively high to relatively low temperatures.

There are two main ways to heat the equipment used by steam as a heat carrier:

(1) Direct heating method

The direct heating method conducts all the heat of the steam, including sensible heat and latent heat, to the heated object (see Fig. 4), so it can be used regardless of whether it is superheated steam or saturated steam, and the steam pressure is not the main problem, so it is impossible for the direct heating method to save energy by reducing the steam pressure.

(2) Indirect heating method

Steam is introduced into the heating pipes (i.e., heat exchangers), and the heated object comes into contact with the surface of these pipes, and the latent heat released by the steam is absorbed by the heated object, so that the heating is realized. The steam emits latent heat and condenses into condensate. This condensate is then discharged into the atmosphere by a steam trap (see Figure 5). The so-called indirect heating is to use only the latent heat of steam. As mentioned earlier, the higher the vapor pressure, the less latent heat, while the sensible heat of saturated water increases; In other words, the supply of saturated steam at the right pressure for the heat exchanger used is the key to energy savings.