Saturated steam

Saturated steam refers to the steam in a saturated state, which is caused by the thermal motion between gas molecules
When liquid evaporates in a limited confined space, liquid molecules enter the upper space through the liquid surface and become vapor molecules. Due to the chaotic thermal motion of steam molecules, they collide with each other and collide with the container wall and liquid surface. When colliding with the liquid surface, some molecules are attracted by the liquid molecules and return to the liquid to become liquid molecules. At the beginning of evaporation, the number of molecules entering the space is greater than the number of molecules returning to the liquid. As evaporation continues, the density of space vapor molecules continues to increase, resulting in an increase in the number of molecules returning to the liquid. When the number of molecules entering space per unit time is equal to the number of molecules returning to the liquid, evaporation and condensation are in a dynamic equilibrium state. Although evaporation and condensation are still ongoing, the density of vapor molecules in space no longer increases, and this state is called saturation. A liquid in a saturated state is called a saturated liquid, and its corresponding steam is saturated steam. However, initially it is only wet saturated steam, and it becomes dry saturated steam after the water in the steam has completely evaporated. The process of steam from unsaturated to wet saturated and then to dry saturated does not increase in temperature. Continuing heating after dry saturated will increase in temperature and become superheated steam.
To check the enthalpy value of saturated steam, it is necessary to use an entropy enthalpy table. But the temperature and pressure of saturated steam are corresponding, so it is only necessary to monitor either data, and then find the corresponding enthalpy value based on the entropy enthalpy table. Multiplying it by the amount of steam, the heat of saturated steam can be calculated. The temperature and pressure relationship of superheated steam does not correspond. To calculate the heat of superheated steam, it is necessary to monitor the temperature and pressure of the superheated steam, and based on these two data, the corresponding enthalpy value can be found.
Saturation temperature
English name: saturation temperature.
Saturation temperature refers to the temperature ts at which liquid and vapor are in a dynamic equilibrium state, that is, saturated state. When in a saturated state, the temperature of the liquid and vapor is equal. When the saturation temperature is constant, the saturation pressure is also constant; On the contrary, when the saturation pressure is constant, the saturation temperature is also constant. As the temperature increases, a new dynamic equilibrium state will be formed at the new temperature. A certain saturation temperature of a substance must correspond to a certain saturation pressure.
Specific Interpretation
If a closed container is not filled with liquid, some liquid molecules will enter the upper space, known as "evaporation". As the number of vapor molecules in space increases, the vapor pressure it generates also increases. At a certain point, the number of vapor molecules in space no longer increases. At this point, the number of molecules leaving the liquid and the number of molecules returning from space reach a dynamic equilibrium, also known as reaching a "saturation state". At this point, the pressure generated by the steam is called "saturation pressure". For the same substance, the level of saturation pressure is related to temperature. The higher the temperature, the greater the energy possessed by the molecule, the easier it is to separate from the liquid and vaporize, and the corresponding saturation pressure is also higher. A certain temperature corresponds to a certain saturation pressure, and the two are not independent. Therefore, in a saturated state, the temperature corresponding to the saturation pressure is also known as the "saturation temperature".
Relationship with boiling point
During the gasification phase, the gas and liquid in the container have the same temperature. The relationship between boiling point and pressure is the same as the relationship between saturation temperature and saturation pressure. Therefore, the boiling point is equal to the saturation temperature at the same pressure. Although the values of the two are equal, their meanings are different. The saturation temperature is for the evaporation process, while the boiling point is for the boiling process. Evaporation occurs on the surface of gas-liquid interaction, while boiling occurs in the interior of the liquid where there is a gasification core. So the difference between the two must be grasped clearly. The state where gas and liquid coexist is called saturation. Further heating of saturated steam causes the temperature of the steam to rise, exceeding the saturation temperature, which is called superheated steam.
Relationship with condensation temperature
The condensation process is the reverse of evaporation. For pure substances, the condensation temperature is also called the liquefaction temperature, which is equal to the evaporation temperature under the same pressure. The saturation temperature can unify the two.
Condensation temperature
The condensation temperature refers to the critical temperature at which a substance transitions from a gaseous state to a liquid state. Different substances have different condensation temperatures. For the same substance, changes in external pressure can also lead to changes in condensation temperature. Generally speaking, as the external pressure increases, the condensation temperature will also increase, and vice versa, it will decrease.